Symposium Organizers
Alberto Vomiero University of Brescia
Sanjay Mathur University of Cologne
Zhong Lin Wang Georgia Institute of Technology
Eric Wei-Guang Diau National Chiao Tung University
Z5: Poster Session: Synthesis/ZnO/Gas Sensing
Session Chairs
Tuesday AM, November 29, 2011
Exhibition Hall C (Hynes)
Z1: Synthesis of Nano-Oxides
Session Chairs
Monday PM, November 28, 2011
Room 210 (Hynes)
9:00 AM - **Z1.1
Teaching ``Old'' Materials ``New'' Tricks: Site- and Shape-Specific Nanopatterning of Multifunctional Oxides.
Vinayak Dravid 1
1 Materials Science and Engineering,Internation Institute for Nanotechnology, Northwestern University, Evanston, Illinois, United States
Show AbstractThe natural evolution of functional materials architecture calls for their confinement in spatial and dimensional modes. Dimensional constraint arises from the emerging need for materials to be confined to 0- (i.e., nanocrystals), 1- (nanolines) and 2- (i.e., films/membranes) dimensions. The spatial confinement refers to inevitable attachment of materials to a substrate or an overlayer, for example. Further, by juxtaposing two or more functional materials in close proximity, there are exciting new opportunities for synergistic coupling of disparate phenomena in hybrid confined oxide systems. In this context, surface patterned nanoscale architecture for oxides offer unprecedented opportunities to revisit fundamental materials science phenomena; which flirt with thermodynamics of constrained systems on one hand and dynamics of nanoscale processes on the other. We have shown that nanopatterning of functional oxides via molecular precursors (or sol-gel) is not only possible, but that the internal microstructure can be readily controlled by post-patterning treatment. Such “directed assembly”, utilizing soft-electron beam and scanning probe lithography, allows for nanoscale patterning of highly porous, beaded/bamboo-like microstructure or single crystal epitaxial conversion of oxides (semiconducting, ferroelectric, ferromagnetic etc.) with appropriate single crystal substrate and thermal treatment(s).The presentation will cover synthesis and patterning of materials down to nanoscale, with an emphasis on multifunctional phenomena. Advanced scanning probe, in-situ and ex-situ electron, ion and photon microscopy, spectroscopy and synchrotron x-ray scattering approaches are being employed to fathom the most intricate details of the internal “microstructure” of nanostructures, coupled with innovative tools to validate their functional identity and localized properties. The presentation topics will range from nanopatterned oxides for investigating solid-state phenomena to magneto-ferroelectric coupling in heterostructure nanopatterns.It will be argued that multifunctional nanostructures and nanopatterns go beyond the “hype”, and present challenging yet exciting opportunities for synthesis-structure-architecture-form-function-performance relationships in complex oxide nanopatterns.
9:30 AM - **Z1.2
Tomography and 3D Analysis of Microstructures and Nanowire Arrays.
Frank Muecklich 1 , Frederico Miguel 1 , Flavio Soldera 1
1 Materials Science and Engineering, Institute Functional Materials, Saarbruecken, Saarland, Germany
Show AbstractMaterials microstructure is the unique and authentic monitor and the “memory” of all materials processing as well as operational load effects. Additionally, materials properties are strongly influenced by their microstructure. Three dimensional microstructure characterizations at different scale play the key role for understanding the relationship between processing, microstructure and properties. However, it could not be fully exploited so far due to the lack of adequate 3D characterization techniques in different scale. The microstructure tomography may solve this problem. For the nano scale it is based on serial sectioning of the volume of interest by the focused ion beam (FIB) and offers a nano scale resolution and at the same time a statistically relevant field of view size of cubes up to 100μm edge length. For the imaging procedure the well established SEM contrasts (namely SE contrast for morphology, EDS contrast for chemistry, EBSD contrast for phase composition, grain shape, size and orientation and more qualitatively, even stress and strain) is available. Consequently, Microstructure Tomography also includes the ultimate resolution of Atom Probe Tomography with “serial extraction” of individual atoms and their quantitative spatial and chemical analysis. After imaging and 3D reconstruction procedures, a detailed 3D image analysis enables the comprehensive quantitative evaluation of local microstructure evolution as well as degradation effects in different scale. Once the microstructure is quantitatively known, also the detailed volume simulation of local effective properties becomes possible. For the example of ordered SnO2 NWs arrays the potential of Microstructure Tomography will be shown. Through coating the array with silver, a metal matrix composite reinforced with SnO2 NWs was produced. FIB nanotomography was used to quantify the characteristics of NWs arrays, (which were grown in Sanjay Mathurs group, Chair Inorganic and Materials Chemistry, University of Cologne, Germany) with defined orientation on single TiO2(001) and TiO2(101) substrates through a CVD-VLS growth process. In comparison to conventional electron microscopy techniques, the achieved 3D analysis allows to extract detailed information such as: (i) the spatial distribution and orientation of ordered SnO2 NWs can be obtained in one-shot experiments; (ii) the bivariate length and diameter distribution of a large amount of NWs could be determined from the tomographic data set, allowing for detailed statistical analysis; (iii) in the case of composites, the uniformity and thickness of coatings could be evaluated and the local porosity and its characteristics of embedded NWs.
10:00 AM - Z1.3
Specifying the Aspect Ratio of Anatase from Nanorod to Nanoplatelet.
Robert Menzel 1 , Andre Duerrbeck 1 2 , Benjamin Cottam 1 , Sabina Ziemian 1 , Alexander Bismarck 3 , Milo Shaffer 1
1 Chemistry, Imperial College London, London United Kingdom, 2 Chemistry, University of Wuerzburg, Wuerzburg Germany, 3 Chemical Engineering, Imperial College London, London United Kingdom
Show AbstractAnisotropic TiO2 nanostructures, such as nanotubes, nanorods and nanoplatelets, are of particular interest in many fields, including photovoltaics, photocatalysis and sensors, as they can provide significant benefits compared to equiaxed nanoparticles. However, for the exploitation of their exceptional properties, full control over the morphology, size distribution, and surface chemistry of the nanostructures is required. Previously, we have explored various synthetic strategies to produce nanostructures with a wide range of morphologies, including high-aspect ratio titanate nanoribbons [1] and TiO2 nanotubes [2].This paper focuses on the controlled synthesis of monodisperse one- and two-dimensional anatase nanostructures in the presence of structure directing agents (SDA). High quality anatase nanorods with high aspect ratio were synthesised via a classical non-hydrolytic elimination reaction in the presence of carboxylic acids as SDA. The reaction was carried out in two stages in order to separate TiOx seed nucleation at lower temperatures from nanorod growth at higher temperatures. This separation enabled considerably improved control of titania nanorod formation in terms of product morphology, dimensions, crystallinity and uniformity [3]. The underlying nanorod formation mechanism was analysed in terms of classical, preferential crystal growth and oriented attachment of primary particles. Thin anatase nanoplatelets were synthesised by hydrothermal treatment of organic titanium precursors in the presence of fluoride as SDA. The impact of physical reaction parameters and reactant stoichiometry was studied in order to control size and thickness of the nanoplatelets.The morphology and crystal structure of these anisotropic nanostructures have been characterised via XRD, Raman spectroscopy and high resolution TEM. The surface chemistry of the nanostructures was modified through additives during synthesis, through post-synthetic ligand exchange, and via UV-irradiation treatments [4]. Various separation techniques, such as density gradient ultracentrifugation, were explored as means to obtain TiO2 nanorods and nanoplatelets with narrower size distributions. Inverse gas chromatography was utilised to quantify the impact of surface chemistry and predominant crystal facet on the surface energetics of the various anisotropic nanostructures.[1] R. Menzel, A.M. Peiro, J.R. Durrant, M.S.P. Shaffer, Chem. Mater., 2006, 18, 6059-6068.[2] B.F. Cottam, M.S.P. Shaffer, Chem. Comm., 2007, 4378-80.[3] R. Menzel, B.F. Cottam, S.C. Ziemian, A. Bismarck, M.S.P. Shaffer, subm.[4] U. Vukičević, S.C. Ziemian, A. Bismarck, M.S.P. Shaffer, J. Mater. Chem. 2008, 18, 3448-3453.
10:15 AM - Z1.4
Nanostructured Metal/Metal Oxide Nanowire Arrays by Self-Assembly and Replication.
Martin Bakker 1 , Amy Grano 1 , Katrina Staggemeier 1 , Franchessa Sayler 1 , Jan-Henrik Smatt 2
1 Department of Chemistry, The University of Alabama, Tuscaloosa, Alabama, United States, 2 Physical Chemistry, Abo Akademi University, Turku Finland
Show AbstractDirect synthesis of metal and metal oxide nanowires is often highly metal specific and generally allows poor control of nanowire diameter and aspect ratio. The use of a hard template such as anodic aluminum oxide (AAO), allows the diameter to be readily controlled. However, using AAO it is difficult to reliably obtain diameters less than about 8 nm. Further, the two dimensional nature of the synthesis makes scale up very difficult. Using sol-gel synthesis it is simple to produce highly ordered mesoporous silica consisting of arrays of pores with diameter controllable between 4 and 7 nm. The silica can be generated as particles, thin films or as large (>1 cm) monoliths. Using a variety of techniques grouped under the term "nanocasting", metal oxides can be readily grown into the pores in the silica. Removal of the template can be accomplished in one of a number of ways leaving the intact nanowires. The narrow pore size distribution of the mesoporous silica generates a similarly narrow distribution of diameters in the metal oxide nanowires produced. A further potential advantage of nanocasting into a monolith is that a series of partial replications can be envisaged that would leave the metal oxide nanowire attached to e.g. a conducting skeleton.We report here on our recent work using SBA-15 mesoporous silica particles and monoliths as templates for the formation of arrays of cobalt, nickel and cobalt, nickel and zinc oxide nanowires, the removal of the nanowires from the host template, and the TEM and SEM characterization of these nanowire arrays.
10:30 AM - Z1.5
Chemical Vapor Synthesis of Surface Doped Alkaline Earth Oxide Nanostructures.
Oliver Diwald 1 , Slavica Stankic 2 , Andreas Sternig 1
1 Chemical and Bioengineering, University of Erlangen-Nuremberg, Erlangen Germany, 2 Institut des Nanosciences de Paris, CNRS and Universite Paris, Paris France
Show AbstractChemical vapor synthesis (CVS) allows for the generation of metal oxide nanoparticle systems in form of non-equilibrium solids. After combustion of metal vapor mixtures and immediate quenching at room temperature the resulting nanocrystals can be characterized by a statistical distribution of the components inside the nanocrystal’s volume. Differences in ionic radius and/ or charge have been found to drive the annealing induced segregation of admixed cations to the particle surface. As demonstrated for CaxMg1-xO [1], BaxMg1-xO [2] and ZnxMg1-xO [3] nanoparticle powders, these effects can be utilized to generate composite surface structures and – consequently - to produce functional particle systems with dramatically altered chemical and optical surface properties which in turn can be tuned by synthesis and annealing parameters.[1]S. Stankic et al. Nano Letters, 2005, 5, 1889.[2]A. Sternig et al. Small 2010, 6, 582.[3]S. Stankic et al. Nanotechnology 2010, 21, 355603.
10:45 AM - Z1.6
Exploring the Phase Stabilities and Metal-Insulator Transitions of Binary and Ternary Vanadium Oxide Nanowires.
Luisa Whittaker 1 , Christopher Patridge 1 , Jesus Velazquez 1 , Tai-lung Wu 2 , G. Sambandamurthy 2 , Sarbajit Banerjee 1
1 Department of Chemistry, University at Buffalo, Buffalo, New York, United States, 2 Department of Physics, University at Buffalo, Buffalo, New York, United States
Show AbstractFinite size effects and substitutional/intercalative doping play a major role in altering the electronic phase diagrams of early transition metal oxides. A specific focus of our research have been vanadium oxides, which have a rich and complex phase diagram originating from the facile accessibility of different vanadium oxidation states and the various structural distortions adopted to accommodate non-stoichiometry and point defects. A major focus of our research program is to probe the strong modifications to the properties of VO2, V2O5, and metal vanadate phases upon scaling to the nanometer size regime. In particular, VO2 is a textbook example of a material exhibiting a metal—insulator phase transition with characteristic sharp changes in electrical conductivity and optical transmittance that can range up to five orders of magnitude. We have found that scaling to nanoscale dimensions and substitutional doping with tungsten/molybdenum strongly modifies the metal—insulator phase transition temperature and hysteresis for stoichiometric VO2 nanostructures. We have achieved the unprecedented depression of the metal—insulator transition to -50°C by a combination of finite size and substituional doping. The use of soft X-ray absorption spectroscopy in conjunction with single-nanowire Raman spectroscopy and electrical transport measurements to examine changes in the electronic structure of VO2 that underlie the sharp modifications of phase stabilities will be discussed. The precise role of dopant atoms in depressing the phase transition is also explored through hard X-ray XANES and EXAFS experiments. Scaling a related class of compounds, non-stoichiometric vanadium oxide bronzes to nanoscale dimensions also unravels intrinsic phase instabilities that do not have parallels in the bulk. We have observed a hitherto unreported up to six orders of magnitude charge-ordering-induced metal—insulator phase transition in nanostructures of novel β'-CuxV2O5 and δ-KxV4O10 phases (related to the Wadsley bronzes) with remarkable stochastic switching between the phases near the phase transition. The metal-insulator transition in these nanowires can further be induced via application of a voltage or through the flow of current.
Z2: Nano-Oxides for Photocatalysis and Water Splitting I
Session Chairs
Monday PM, November 28, 2011
Room 210 (Hynes)
11:30 AM - **Z2.1
Quantum-Confined Metal Oxide Hetero-Nanostructures for Solar Hydrogen Generation.
Lionel Vayssieres 1
1 MANA, NIMS, Tsukuba Japan
Show AbstractThe fabrication, electronic structure and photoelectrochemical characterization of novel quantum-confined metal oxide hetero-nanostructures will be presented along with new concepts to address the challenging problems of finding stable and cost-effective photo-catalysts for water splitting.
12:00 PM - Z2.2
Metal Oxide Hetero-Nanostructure Arrays for Solar Water Oxidation.
Coleman Kronawitter 1 2 , Lionel Vayssieres 4 , Bonnie Antoun 3 , Samuel Mao 2 1
1 Department of Mechanical Engineering, University of California at Berkeley, Berkeley, California, United States, 2 Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 4 International Center for Materials NanoArchitectonics, National Institute for Materials Science, Tsukuba Japan, 3 , Sandia National Laboratories, Livermore, California, United States
Show AbstractThe interfaces of transition metal oxide heterostructures provide a diverse platform for the discovery and study of unique interfacial electronic phenomena, which enables development of new artificial multifunctional materials for several proposed oxide-based electronic device technologies. In this context we explore the use of arrayed oxide heterostructures with nanoscale dimensionality as photoactive components of electrodes whose function is to oxidize water, a critical step in the clean and efficient production of solar fuels such as hydrogen. Oxide hetero-nanostructure arrays, assembled through combinations of chemical and vapor-phase fabrication techniques, are physically characterized and implemented as photoanodes in photoelectrochemical cells. In addition we demonstrate experimentally that the nanoscale organization of oxide phases results in new electronic characteristics, including a change in the occupancy and hybridization of d orbitals in the interfacial region of 3d transition metal oxide hetero-nanostructures.
12:15 PM - Z2.3
Self-Assembled TiO2 Nanowire/Graphene Hybrid Structure for Photoelectrochemical Applications.
Xuan Pan 1 , Changhong Chen 1 , Zhaoyang Fan 1
1 Department of Electrical and Computer Engineering, Texas Tech University, Lubbock, Texas, United States
Show AbstractTiO2/graphene hybrid material is a promising photocatalyst, and it may also be used for dye sensitized solar cells (DSSCs). Graphene, with its unique electronic properties, large specific surface area and high transparency, contributes to facile charge separation, adsorptivity and light absorption range in this hybrid structure. In our work, hydrothermal method was utilized to synthesize the graphene-TiO2 nanowire hybrid structures. The characteristics of the hybrid structure were evaluated based on photodegradation of methylene blue under visible light and as photoanode for DSSCs. Graphene sheets were gained by sonicating the expanded graphite in aqueous solution, which also contains surfactant for stable dispersions of graphene sheets. This suspension was placed into a Teflon-lined autoclave, together with TiO2 nanoparticles (NPs). The autoclave was maintained at 200°C for 24 hours and then cooled down to room temperature naturally. The obtained products were successively washed with dilute hydrochloric acid, deionized water and absolute methanol for several times until the pH value equals to 7. After recovered by filtration, the products were dried at 70°C for 6 hours, and eventually, the gray powder was attained. The hybrid structure is characterized by scanning electron microscopy and transmission electron microscopy. The graphene sheets were observed to be densely wrapped around by TiO2 nanowires (NWs) with a width of about 30 nm, which was self-assembled from the TiO2 NPs during the hydrothermal process. Unlike most reported hybrid synthesis methods, which usually simply mix materials with different kinds of nanostructures, in our process the TiO2 NPs transform into NWs, which proceeded simultaneously when the hybrid structures were synthesized. The reason is that graphene provides the nucleation sites for NW growth. An obvious advantage of our method is the firm and dense connection between graphene sheets and TiO2 NWs, providing strong mechanical supporting and superior electric connection. Comparing the photo degradation rates of methylene blue under visible light between the hybrid composites and pure TiO2 NWs, the hybrid structure showed an attractive advancement in photocatalysis. Thin film of such hybrid material was also applied into fabrication of solar cells to study the functions of graphene in enhancing charge transport.
12:30 PM - Z2.4
Experimental and Theoretical Study of TiO2 Anatase Nanoparticles Surfaces Properties for Photocatalytic Applications.
Olivier Durupthy 1 2 3 , Fabien Dufour 1 2 3 , Asmae Bouzoubaa 1 2 3 , Yuheng Wang 1 2 3 , Sophie Cassaignon 1 2 3 , Corinne Chaneac 1 2 3
1 , Université Pierre et Marie Curie Paris6, Paris France, 2 , CNRS, Paris France, 3 , Collège de France, Paris France
Show AbstractIn addition to their intrinsic physical properties due to their electronic band structure, photocatalytic materials must display a relatively high specific surface tailored to efficiently interact with the pollutant. Moreover, a good stacking of atoms constituting the cristaline structure is mandatory to display high activity since defects may act as recombination center between photogenerated electrons and holes [1]Thanks to the size of its band gap and its relative position toward HO-/HO. and O2/O2.- redox couples potential, TiO2 is one of the most efficient photocatalyst under UV irradiation and anatase is the active polymorph.[2] Recent works on that phase demonstrated in addition to an influence of the nanoparticles size and effect related to the nature of the exposed surfaces.[3]Organic additives as well as new activation methods such as microwave heating were efficiently used to obtain pure phase anatase nanoparticles with different shapes and consequently different exposed surfaces i.e. (100), (101) and (001).[4] The photocatalytic efficiency of each morphology was probed by the degradation of Rhodamine B in aqueous solution and the activity was correlated to the surface composition.In order to explain more thoroughly the observed differences the three anatase surfaces were also modeled using DFT implemented in the VASP code [5] coulped with the MUSIC model [6] in order extract data about their respective acidity. Moreover defects on the surface that may give rise to an increased activity were taken into account. The combination of experimental and theoretical approaches presented here may be extended to other application in which the the nature of the material surface is a key parameter.1. G. Benko, B. Skarman, R. Wallenberg, A. Hagfeldt, V. Sundstrom, and A.P. Yartsev, J. Phys. Chem. B 107, 1370 (2003),2. C. J. Barbé, F. Arendse, P Comte, M. Jirousek, F. Lenzmann, V. Shklover and M. Grätzel, J. Am. Ceram. Soc. 80, 3157. (1997)3. D. Q. Zhang, G. S. Li, H. B. Wang, K. M. Chan and J. C. Yu, Cryst. Growth Des. 10, 1130 (2010)4. O. Durupthy, J. Bill and F. Aldinger, Cryst. Growth Des. 7, 2696 (2007)5. J. Hafner,. J. Comput. Chem. 29, 2044 (2008)6. T. Hiemstra, P. Venema and W. H. V. Riemsdijk, J. Colloid Interface Sci. 184, 680 (1996)
Z3: Electrical Properties I
Session Chairs
Monday PM, November 28, 2011
Room 210 (Hynes)
2:30 PM - **Z3.1
Highly Thermally Stable Transparent Conducting Ga Doped ZnO Thin Film by Metal Organic Chemical Vapor Deposition.
Junliang Zhao 1 , Xiaowei Sun 1 2
1 , Tianjin University, Tianjin China, 2 , Nanyang Technological University, Singapore Singapore
Show Abstract Transparent conducting oxide (TCO) thin films have a large variety of applications in optoelectronic industry, such as transparent electrodes for light-emitting diodes (LEDs), liquid crystal displays (LCDs), photodetectors and solar cells. Currently the most developed TCO technology for practical applications is based on indium-tin-oxide (ITO). However, ITO will be difficult to meet the fast growing demand in the optoelectronics industry due to the scarcity of indium. Doped ZnO is one of the most promising indium-free candidates for replacing ITO due to the abundance of Zn element and the lower cost. In our study, highly transparent conductive Ga doped ZnO (GZO) thin films have been prepared on large-area (200mm×200mm) glass substrates by metal organic chemical vapor deposition. The effect of Ga doping on the structural, electrical and optical properties of GZO films has been systematically investigated. Under the optimum Ga doping concentration (~ 4.9 at.%), c-axis textured GZO film with the lowest resistivity of 3.6×10-4 Ω.cm and high visible transmittance of 90% has been achieved. Furthermore, our developed GZO thin film can well retain the highly transparent conductive performance in oxidation ambient at elevated temperature (up to 500OC). Such a highly thermally stable GZO film is promising to be used as transparent electrode for LEDs and solar cells. We prepared a GaInN based high brightness blue LED chip using GZO as top electrode, which shows an output power of 18.5mW at 20mA and an external quantum efficiency of ~27.5%. The performance is approaching that of the LED using ITO electrode. The GZO film also exhibits low transmittance (< 1% at 2500 nm) and high reflectance (> 70% at 2500 nm) to the infrared radiation, which enables potential applications in the energy-saving windows.
3:00 PM - Z3.2
Electronic Properties of Isosymmetric Phase Boundaries in Ca-Doped BiFeO3.
Jan Seidel 1 , Morgan Trassin 1 , Siriyara Jagannatha Suresha 1 , Ying-Hao Chu 1 , Ramamoorthy Ramesh 1
1 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractThe transition between crystallographically equivalent (isosymmetric) structures due to strain offers a new landscape in which to tailor highly anisotropic electronic responses in complex oxides. We present recent results on anisotropic electronic conductivity at isosymmetric phase boundaries in Ca-doped BiFeO3. The origin and nature of the observed conductivity is probed using a combination of temperature dependent conductive atomic force microscopy, high resolution transmission electron microscopy and X-ray diffraction.
3:15 PM - Z3.3
Nonvolatile Resistive Switching in Au/BiFeO3 Rectifying Junction.
Yao Shuai 1 2 , Chuangui Wu 2 , Wanli Zhang 2 , Shengqiang Zhou 1 , Danilo Buerger 1 , Stefan Slesazeck 3 , Thomas Mikolajick 3 , Manfred Helm 1 , Heidemarie Schmidt 1
1 Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, Dresden Germany, 2 State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu China, 3 , Namlab gGmbH, Dresden Germany
Show AbstractResistive switching in oxides has attracted increasing attention due to the potential application for nonvolatile memory devices [1,2]. Resistive switching has been observed usually in a metal-insulator-metal (MIM) capacitor-like structure, which can be set and reset to low resistance state and high resistance state by applying external voltages with opposite polarities. In an asymmetric MIM structure where a Schottky contact and an Ohmic contact are formed at the two interfaces, respectively, it is generally believed that the Schottky interface dominates the bipolar resistive switching behavior. BiFeO3 thin films have been grown on Pt/Ti/SiO2/Si substrates with pulsed laser deposition. RF sputtered Au has been used for the top electrode. The transport properties of the BiFeO3 thin films have been previously demonstrated to be sensitive to the interface [3]. In the present work, an interface-related resistive switching behavior with large switching ratio of ~300 has been observed in the Au/BiFeO3/Pt structure [4]. The different polarities of the external voltage induce an electron trapping or detrapping process, and consequently change the depletion layer width below the Au Schottky contact, which is revealed by capacitance-voltage measurements and by long-term low/high resistance state capacitance transient measurements at zero bias. The resistive switching shows a long term retention and non-destructive read-out character, which is proved by pulsed voltage measurements. A dynamic equilibrium process involving the extension of the depletion region can be used to explain the good retention in the Au/BiFeO3/Pt structure. The present work can help to further understand the physical origin of bipolar switching in BiFeO3 and in other thin film oxides with electron trapping centers.[1] K. Terabe et al., Nature 433, 47 (2005).[2] R. Waser and M. Aono, Nature Mater. 6, 833 (2007).[3] Y. Shuai et al., J. Appl. Phys., in press.[4] Y. Shuai et al., Appl. Phys. Lett. 98, 232901 (2011).
3:30 PM - Z3.4
Fabrication of Single Crystal TiO2 Nanowalls and High Temperature Electrical Conductivity Studies.
Maryam Abazari 1 , Shriram Ramanathan 1
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractFunctional oxide materials with dimensions approaching nanoscale are of interest in emerging energy technologies and further enable fundamental studies on dimensionality effects on carrier transport. Utilizing ion beam milling, we have developed single crystal ultra-thin free standing walls of TiO2 with various thicknesses ranging from few hundred nanometers to few microns. Electrodes have been patterned by lithography onto such structures. We have studied the temperature dependence of the electrical conductivity behavior in such ultra-thin walls in the temperature range upto 900K and compared with measurements on bulk single crystals. We will then compare their sensor response to oxygen pressure changes to evaluate how proximity to surfaces influence the conductivity response and associated transients. These preliminary results suggest a pathway to fabricate free-standing quasi-two dimensional oxide structures for probing mesoscopic conduction phenomena.
Z4: ZnO Functional Nanostructures I
Session Chairs
Monday PM, November 28, 2011
Room 210 (Hynes)
4:45 PM - Z4.2
Organometallic Routes to Zinc Oxide Nanoparticles: Applications in One-Pot, In Situ Synthesis of Hierarchical and Hybrid Polymer Systems.
Milo Shaffer 1 , Katherine Orchard 1 , Charlotte Williams 1
1 Department of Chemistry, Imperial College London, London United Kingdom
Show AbstractWell-defined, organically-modified ZnO nanoparticles were prepared via an efficient hydrolysis route, without the need for surfactant co-ligands, washing or size-selection steps. The products have a narrow size distribution and are soluble in organic solvents. The synthesis involves reacting a mixture of alkylzinc carboxylate complex and excess diethylzinc with water to yield carboxylate-capped ZnO nanoparticles. Varying the ratio of the different organometallic species enables control of either size or degree of surface modification. The method is conveniently compatible with cross-linking resin chemistries, and is applied for the in situ preparation of organically-modified ZnO polymer nanocomposites.A variety of hierarchical composites have been synthesised by combining carbon nanotubes or pre-prepared, sub-micron ZnO particles with ZnO nanoparticles, grown in situ. The mechanical and functional properties of these materials have been tested in order to assess the improvements in physical properties that arise from synergy between fillers of different length-scales.
5:00 PM - Z4.3
New Insights on the Role of Defects in Reactivity of ZnO Based Materials.
Marta Maria Natile 1 2 3 , Laura Bovo 1 2 3 , Lidia Armelao 1 2 3 , Eugenio Tondello 1 2 3 , Lorenzo Sorace 4 5 , Dante Gatteschi 4 5 , Michael Murphy 6 , Tsun-Kong Sham 6
1 ISTM, CNR, Padova, PD, Italy, 2 , INSTM, Padova, PD, Italy, 3 Dipartimento di Scienze Chimiche , Università di Padova, Padova, PD, Italy, 4 Dipartimento di Chimica, Università di Firenze, Sesto Fiorentino, FI, Italy, 5 , INSTM, Firenze, FI, Italy, 6 Department of Chemistry, University of Western Ontario, London, Ontario, Canada
Show AbstractZnO is one of the most versatile functional materials. Due to its unique and useful properties it has been extensively investigated for many applications ranging from catalysis to ferromagnetism, from luminescence to gas sensing. The properties of ZnO closely depend on the material microstructure, including crystal size and morphology. Moreover, doping with transition metal ions also offers an effective method to adjust the catalytic, optical and magnetic properties of ZnO. In this context the ability to produce ZnO with well-defined properties under soft and sustainable processing conditions is highly desirable. In recent years ZnO doped with different amount of transition metal cations (Mn, Co, Cu) are attracting the attention of our research group for their potential applications in the fields of spintronics and energetics.Herein, undoped and Cu-doped ZnO nanostructured samples were prepared by an innovative sol-gel method and annealed at different temperatures. This wet chemical method allows a careful tailoring of material characteristics: composition (dopant nature and amount), morphology, structure, crystallite size, as well as the defect structure; all of them, in fact, strictly influence the functional properties of interest. All the samples were characterized by the joint use of different techniques in order to clarify the structure-property relationships. XPS reveals the presence of copper in different oxidation states, while XANES and EXAFS spectra evidence that the diffusion of copper in ZnO matrix is favored by the increase of the annealing temperature. The catalytic activity of all the as prepared powders towards steam reforming of methanol was tested. This reaction, in fact, is considered one of the most technically feasible and convenient ways for production of hydrogen, the more efficient and sustainable energy carrier for the future. Both undoped and Cu-doped ZnO treated at low temperature show a significant activity in steam reforming of methanol with a good selectivity towards hydrogen and carbon dioxide. Besides copper, the remarkable defect structure of ZnO heated at lower temperature, as evidenced by EPR, seems to play a key role in the catalytic activity.
5:15 PM - Z4.4
Hydrothermal Growth of ZnO Nanorods: The Role of KCl for Tailoring Aligned Morphologies.
Jonathan Downing 1 , Mary Ryan 1 , Martyn McLachlan 1
1 Department of Materials Science and Engineering , Imperial College London, London United Kingdom
Show AbstractArrays of nanorods are of increasing use in a variety of applications, including solar cells, light emitting diode and piezoelectric generators. Low temperature processing of controlled nanorod morphologies has the potential to increase the functionality of devices through aiding infiltration, tailoring termination or increasing areal density, while also allowing for deposition of large area arrays at low cost.In this study we present recent results detailing the role of ionic additives, specifically KCl, to control ZnO nanorod length, width and areal density. Law et al. [1] and Zhou et al. [2] previously reported on the addition of the surfactant polyethylienamine (PEI) to hinder nanorod growth in the lateral direction, by contrast it is observed that KCl can alter growth in the dominant <002> direction; resulting in a facile methodology for preparation of various nanorod morphologies.Growth over a large concentration range is observed, leading to a correlation between rod length, width and density and KCl additive. Our hypothesis is that KCl controls growth through adsorption to the polar (002) face, primarily effecting nucleation and surface termination. Of particular interest is the ability of ionic species to promote homogeneous nucleation on the surface, leading to increased uniformity of nanorods lengths. It is seen that surface termination control is also possible owing to the ability of ionic species to stabilise the (002) face. XRD data are presented and when compared with morphology from SEM data gives a qualitative measurement of rod alignment of these films. Briefly device performance of hybrid photovoltaics devices constructed with these films will be presented in order to show the benefit of tailoring rod morphologies for this application. [1] Law, M. et al. Nat. Mater. 4, 455 (2005)[2] Zhou, Y. et al. Mater. Res. Bull. 43, 2113 (2008)
5:30 PM - Z4.5
Facile Synthesis of ZnO Superstructures Assisted by One-Dimensional Catalysts.
Xiaobin Xu 1 , Min Wu 2 , Michael Asoro 1 , Chao Liu 2 , Haiping He 2 , Paulo Ferreira 1 , Donglei Fan 1
1 Materials Science ant Engineering, Texas Materials Institute, Mechanical Engineering, Univerisity of Texas at Austin, Austin, Texas, United States, 2 Materials Science and Engineering, Zhejiang University, Hangzhou China
Show AbstractZnO superstructures have attracted great interest due to unique properties. In this work, We report a highly original approach to synthesize ZnO superstructures assisted by Au nanowires using hydrothermal method. The ZnO nanosuperstructures exhibit top surface of {1-20} and branches growth directions in [101] and [10-4], which are unique in all the reported ZnO structures. In addition, the superstructures can be readily grown on both rigid substrate, such as Si and glass, and flexible substrates such as kapton tapes, which enable them to find applications in electronics, solar cells, and piezoelectric devices.
Z5: Poster Session: Synthesis/ZnO/Gas Sensing
Session Chairs
Tuesday AM, November 29, 2011
Exhibition Hall C (Hynes)
9:00 PM - Z5.1
Identifying Valence Band Structure of M2 Phase from Mixed Phases in VO2 Thin Film.
Teruo Kanki 1 , Hidefumi Takami 1 , Shigenori Ueda 2 , Azusa Hattori 1 , Ken Hattori 3 , Hiroshi Daimon 3 , Keisuke Kobayashi 2 , Hidekazu Tanaka 1
1 ISIR, Osaka Univ., Ibaraki, Osaka, Japan, 2 , NIMS/SPring-8, Sayo-cho, Hyogo, Japan, 3 , NAIST, Ikoma, Nara, Japan
Show AbstractVanadium dioxide (VO2) shows orders-of-magnitude changes in resistance around 340 K, accompanied by structural deformation between the tetragonal rutile phase (R phase) with a metallic state at high temperature and the monoclinic phase (the so-called M1 phase) with an insulating state at low temperature. In the 70’s, Pouget et al. experimentally found a second monoclinic phase (M2 phase), suggested as a Mott-insulator, induced from small amounts of Cr substitution and uniaxial stress applied to VO2 [1,2]. Recently, the M2 phase has been a focus of attention not only to understand the transition mechanism between R and M1, but also to utilize “true” Mott metal-insulator transition that does not undergo the structural phase transition. However, experimental information regarding M2 electronic structure is still unknown, and it is difficult to obtain the experimental M2 electronic structure because this structure partially exists with M1 and /or R structures consisting of sub-micrometer scaled domains and is a transient phase around MIT. In this research, we have tried to obtain this missing M2 electronic structure by evaluating the mixed valence band spectra of R, M1 and M2 phases in the vicinity of MIT using bulk-sensitive hard x-ray photoemission spectroscopy (HX-PES). VO2 thin films were deposited on Al2O3(0001) substrates using a pulsed laser deposition technique. To confirm details of crystal structures of in-plane orientation and obtain evidence of mixed phases of the VO2 thin films, the RHEED measurements were performed at various temperatures. HX-PES experiments (hν = 5.95 keV) were performed in a vacuum chamber equipped with a temperature-controllable stage at the undulator beamline BL15XU of SPring-8. The identified spectrum of the M2 phase from the mixed phases has an energy gap at the Fermi level. The origin of the gap is thought to be due to the Coulomb reputation energy of the 3d states in equally-spaced vanadium atoms in the M2 phase. In this meeting, we will report the detail experimental results and their analysis. [1] J. P. Pouget et al, Phys. Rev. B 10, 1801 (1974) [2] J. P. Pouget et al, Phys. Rev. Lett. 35, 873 (1975)
9:00 PM - Z5.11
Remarkable Design and Synthesis of Novelty Functionalized Nanoparticles for Biological Testing and Further Technological Applications.
Aurelien Auger 1 , Peter Cherns 3 , Olivier Poncelet 1 , Chloé Schubert 1 , Wai-Li Ling 2
1 LITEN-LCSN, CEA, Grenoble France, 3 Grenoble Electron Microscopy@Minatec, CEA, Grenoble France, 2 IBS, Institute of Structural Biology, Grenoble France
Show AbstractRecently the impact of commercialized nanoparticles upon the environment and various biological systems has been identified as an essential issue of discussion. Therefore it is of the utmost importance for toxicologists to possess the tools to follow the behaviour and response of novel colloids and other nano-objetcs in biological systems. In our laboratory of the CEA-Liten in Grenoble (France), we have acquired the technology and the knowledge to detect a wide range of micro and nano-ojects. Initially developed to elaborate diverse industrial applications, those techniques allowed the production and the detection of numerous and exotic nanoparticles, either by fluorescence or by radioactivity.We have designed feasible synthetic strategies in order to produce nanoparticles composed of biological, metallic, fluorescent or radioactive cores, and further encapsulation within the desired material presenting similar characteristic to those usually used in Industry. The optimised processes involved in the different preparations of the nanomaterials have allowed us to accurately adjust their size, shapes and morphology. Hence diverse species such as DNA, silica, cerium oxide, silver and fluorescent dyes have been targeted and subjected to core functionalization of nanoparticles. Different reproducible synthesis of nanoparticles will be presented as well as their respective characterisations by microscopy (confocal, TEM and MEB), dynamic light scattering, fluorescent measurements and tomography.
9:00 PM - Z5.12
Surface Physical Property of the CrO2 Thin Films Prepared Using a Closed Chemical Vapor Deposition Method.
Yuji Muraoka 1 , Sho Yoshida 1 , Takanori Wakita 1 , Masaaki Hirai 1 , Takayoshi Yokoya 1
1 , Okayama Univ., Okayama Japan
Show AbstractChromium dioxide (CrO2) has attracted considerable attention because it is ferromagnetic at room temperature (TC = 393 K) and a half-metallic band structure fully spin-polarized at the Fermi level. Several classes of materials are predicted to have this half-metallic ferromagnetic property, including the Heusler alloys, magnetites, Fe3O4, CrO2 is presently the only material with experimentally proven spin polarization close to 100 % as measured Andreev reflection and Meservey-Tedrow tunneling. These results are motivation to use this material in spintronics devices such as magnetic field sensing and information storage.It is known that CrO2 can be produced in the form of thin film by thermal decomposition of CrO3 using chemical vapor deposition (CVD). High quality CrO2 films have been deposited on single-crystal rutile (TiO2) and sapphire (Al2O3) substrates. However, there are several problems for the CrO2 thin films prepared from a CrO3 precursor. An example is that CrO3 is extremely hygroscopic and toxic, and is very hard to handle. Another problem is that insulating layer like Cr2O3, which is most stable phase in Chromium oxide binary system, is easily formed on a surface of CrO2 thin film. This insulating layer prevents us to fabricate spintronics devices for applications. Thus it is strongly required to find an alternative precursor which is available to prepare CrO2 thin films without any insulating layer up to the surface of films.Recently, Ivanov et al. reported that epitaxial CrO2 thin films are successfully prepared from Cr8O21 precursor [1]. Since Cr8O21 is less hygroscopic and less toxic compared with CrO3, it would be a more appropriate precursor. In addition, they found from low-energy electron diffraction (LEED) observations that epitxial growth of rutile-phase CrO2 occurs to the top monolayer of the film [2]. Very recently, we have successfully prepared an epitaxial CrO2 thin film on a TiO2 (100) substrate by using a closed CVD method [3]. We found from soft x-ray photoemission measurements that the surface of the film is metallic. This result motivates us to study the physical nature of near topmost layer of CrO2 thin film. In this work, we prepare CrO2 thin films from Cr8O21 precursor using a closed CVD method and study the surface physical property by means of an x-ray photoemission spectroscopy with surface sensitive photon energy. The detailed results are given in a presentation.References[1] Ivanov et al., J. Appl. Phys. 89, 1035 (2001). [2] Ivanov et al., J. Appl. Phys. 105, 07B107 (2009).[3] K. Iwai et al., J. Appl. Phys. 108, 043916 (2010).
9:00 PM - Z5.13
Fabrication of out-of-Plane Composition-Graded Perovskite Oxide Films.
Joe Sakai 1 , Cécile Autret-Lambert 1 , Thierry Sauvage 2 , Jérôme Wolfman 1 , François Gervais 1
1 LEMA - UMR 6157, CNRS/CEA, University of Tours, Tours France, 2 CEMHTI - UPR 3079, CNRS, Orleans France
Show AbstractIn heteroepitaxially-grown films on single crystal substrates with a certain lattice mismatch, there exists a critical thickness at where dislocations appear and the lattice status changes from coherently-strained to relaxed. It has been pointed out that insertion of an out-of-plane composition-graded (CG) buffer layer is effective in reducing dislocation densities.[1] This structure is expected to enhance the critical thickness of the film, opening up the practical application of strongly correlated electron material films with physical properties controlled by strain, multilayered structure consisting of materials with various functions, or a film-substrate system with a large mismatch but free from the peeling off. So far, some CG oxide films have been deposited by means of multiple-target single-beam pulsed laser deposition (PLD) technique, in which the number of composition step was determined by the number of targets.[2] In the present study, we introduce a dual-target dual-beam PLD method for preparation of CG perovskite oxide films that would enable one to make the composition profile completely free from discontinuity.SrTiO3 (STO; 001) was used as substrates, and a combination of STO and BaxSr1-xTiO3 (BST; x = 0.6) was adopted as two target materials. During deposition, the intensity ratio of two laser beams for STO and BST targets was gradually changed from 100 : 0 to 0 : 100, expecting x variation of the film from 0 (at the interface) to 0.6 (at the surface). Actually, a 280 nm – thick CG film deposited at 600 degC under oxygen pressure of 1 x 10-5 mbar was confirmed by a reciprocal space mapping observation to be coherently strained, having an in-plane lattice perfectly pinned to that of STO (a = 0.3905 nm) and the final c-axis length of 0.409 nm that is consistent with the unit cell volume of BST (x = 0.6). Transmission electron microscopy (TEM) and Rutherford backscattering (RBS) were attempted to examine the composition and lattice gradient of films.This work was performed within the project of Pôle de compétitivité S2E2 through the Grant SESAME-CAPI. Access to the facilities of the CERTeM consortium located at Tours is gratefully acknowledged.[1] J. Tersoff, Appl. Phys. Lett. 62 (1993) 693.[2] X. Zhu et al., Appl. Phys. Lett. 80 (2002) 3376.
9:00 PM - Z5.14
Low Temperature, Microwave-Assisted Deposition of Nanostructured Titanium Dioxide Networks for Flexible Thin Film Devices.
B. Reeja Jayan 1 , Katharine Harrison 2 , Arumugam Manthiram 1 2
1 Materials Science and Engineering, The University of Texas at Austin, Austin, Texas, United States, 2 Mechanical Engineering, The University of Texas at Austin, Austin, Texas, United States
Show AbstractMetal oxides like TiO2 have been successfully employed for several applications. Traditionally, sintering at high temperatures (450 - 600 oC) is needed to synthesize the requisite phase of metal oxides such as the anatase phase of TiO2. This hampers the use of these oxides in devices made on flexible (plastic) substrates, which cannot withstand processing temperatures above 200 oC. We present here a novel sol-gel based microwave assisted solvothermal process for growing nanostructured films of crystalline (anatase) TiO2 at temperatures as low as 150 oC. Although, common wisdom advises against using metals or electrical conductors inside a microwave, we find that a conducting (ITO or metal) layer serves as a catalyst to deposit crystalline TiO2 thin films, which typically require temperatures above 450 oC. Strong interaction between the microwaves and the conductive layer results in localized heating of the conductive surface, causing the TiO2 film to nucleate, grow, and sinter in a single step inside the microwave reactor. Photovoltaic properties of hybrid polymer solar cells, incorporating these microwave-deposited nanostructured TiO2 networks in direct contact with organic light harvesting polymers (P3HT) will be presented. The phase and morphology characterizations of the TiO2 films by Glancing Incidence X-ray Diffraction (GIXRD), Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM) are complemented by photovoltaic device evaluation. The integration of these microwave grown films into devices is further aided by the ability to deposit patterned TiO2 films, simply by patterning the conductive substrate. The pattern scale can range from nanometers to several centimeters, thereby enabling our process to be adapted to a variety of devices like photodetectors and gas sensors, which require crystalline layers of various metal-oxide thin films.
9:00 PM - Z5.15
Atomic Layer Deposited Highly Conformal HfO2 Layers on Colloidal TiO2 Nanoparticles.
Mariyappan Shanmugam 1 , Mahdi Farrokh Baroughi 1
1 Electrical Engineering and Computer Science, South Dakota State University, Brookings, South Dakota, United States
Show AbstractAtomic layer deposition (ALD) is widely used to grow variety of metal oxides which have shown potential applications in various research areas such as photovoltaics and CMOS technologies. ALD method has salient features which include wide range of process temperature, ultra fine control over thickness, low defect density materials, conformal surface coverage on flat, inside of porous material network and on the surface of nanoparticles. Recently, a wide range of ALD grown metal oxides such as Al2O3, ZnO, TiO2 and HfO2 have attracted much of scientific attention for various applications. Since ALD provides metal oxides with low defect density, it is favored in memory applications and suitable for energy harvesting materials to passivate defective surfaces of semiconductors. This paper presents conformal growth of HfO2 on the surface of nanoporous TiO2. Nanoporous TiO2 colloidal paste, with average particle size of 25 nm, (Solaronix product) was deposited onto indium tin oxide coated glass substrates and sintered at 450°C for 30 minutes. HfO2 ultra thin layers of 1, 2, 5 and 10 cycles were deposited on nanoporous TiO2 by ALD method (Savannah 100, Cambridge NanoTech); Hafnium tetra chloride gas and water vapor were used sequentially as hafnium and oxygen precursors respectively, They were introduced to the chamber by short pulses of about 200 ms duration (purge process) to grow HfO2 on the surface of TiO2 at 200°C. The overall reaction that leads to the layer by layer growth of HfO2 thin film can be expressed by a complete reaction, HfCl4 + 2H2O→HfO2 + 4HClThis reaction can be written in forms of two half-reactions as below: yHf OH* + Hf Cl4→(HfO)y Hf Cl*(4-y) + yH Cl Hf Cl* + H2O→Hf OH* + 4HClwhere * represent the surface species. Atomic force microscopy confirmed that the porosity of the TiO2 was not blocked by the growth of HfO2 which asserted that HfO2 layer on TiO2 nanoparticles was very thin and conformal throughout the surface. High resolution transmission electron microscopy studies showed that 5 cycles of HfO2 on nanoporous TiO2 was about 2 nm thick and the growth was extremely conformal on the surface of TiO2 nanoparticles. XPS survey spectrum showed major Hf, Ti and O peaks which confirmed the growth of ultra thin HfO2 on the surface of nanoporous TiO2. Further, shift in binding energy observed from the XPS spectra obtained from 1, 2, 5 and 10 cycles of HfO2 grown TiO2 suggested that the first few atomic layers of HfO2 react with the TiO2 surface stronger than the 5, 10 cycles. References[1] J. Mater. Chem., 19, 2999 (2009)[2] J. Phys. Chem. C, 112, 10303(2008)[3] Appl. Surf. Sci. 244, 511 (2005)[4] Chem. Rev., 110, 111 (2010)
9:00 PM - Z5.16
Study on Impurities in HfO2 Contact with TaN Using APM and DFT Calculation.
Mino Yang 1 2 , Hionsuck Baik 3 , Anass Benayad 1 , Cheol-Woong Yang 2
1 AE group, Samsung Advanced Institute of Technology, Youngin, Gyeonggi, Korea (the Republic of), 2 School of Advanced Materials Science & Engineering, Sungkyunkwan University, Suwon, Gyeonggi, Korea (the Republic of), 3 , Korea Basic Science Institute, Seoul Korea (the Republic of)
Show AbstractTaN/HfO2 gate stack is a strong candidate for the alternative material to replace poly-Si/SiO2 in advanced metal-oxide-semiconductor field-effect transistors. From the Atom Probe Microscope (APM) experiment, a small number of Ta and N atoms diffused to HfO2 layer after annealing was verified. Also the evaporation of TaO molecules were detected at the TaN/HfO interface both before and after annealing the TaN/HfO2 thin film. The incorporation of Ta and N atoms can introduce structural changes in the host lattice and impurity levels in the HfO2’s band gap modifying the electronic and the related intrinsic properties. To understand their nature, the atomic and electronic configurations were simulated by the method of calculation based on Density Functional Theory known to give reliable energy values for point defect existing in crystal. We set up simple types of defect model (Ta and N) and expanded them to the combination with oxygen vacancy, the dominant point defect in HfO2. Then stable types of defect will be suggested with their electronic structure within bandgap, which might explain the evaporation of TaO and N atoms in APM.
9:00 PM - Z5.17
Role of Epoxides and Oxetanes in the Sol-Gel Synthesis of Metallic Oxide Aerogels.
Michael Lemoine 1
1 , CEA, Monts France
Show AbstractTantal oxide porous solids are prepared by a sol-gel process using metallic salt, TaCl5 as precursor in ethanol. The addition of epoxides or oxetanes, such as trimethylene oxide or 2,2-dimethyloxetane, as gelation agent results the formation of monolithic gels and gives an alternative route to the chemistry of alcoxydes to obtained metal oxide gels. The obtained gels are converted to aerogels by supercritical extraction with CO2(l). In the reaction mechanism, the oxetane acts as a gel promoter. Thus the nucleophilic counter-ion of the metallic cation attacks the oxetane cycle and gives the corresponding alcohol. The reaction is accompagnied by a protonation of the oxetane and so causes the pH increase in the reaction medium and generates the polycondensation. In order to control the ring-opening reaction of oxetane by counter-ion, the synthesis is conduced at 40°C. The influence of ratio oxetane /precursor and H2O/precursor on the gelation time and the texture of aerogels are studied. After supercritical drying, thermal treatments are practised on tantal aerogels. The tantal aerogels present shrinkage and different textures according to the used oxetane. A reaction occurs between the precursor, TaCl5 and ethanol. Therefore, TaCl2(OEt)3 is obtained and become the intermediate precursor. It generated covalent organic bounds in the resulted network and so the tantale aerogels are hybrid materials. Dried aerogels of metal oxides are characterized by nitrogen adsorption/desorption analysis. This approach produces monolithic mesoporous materials with high surface areas. Chemical analysis before and after thermal treatment can allows quantifying chemical elements (C, H, O) which are present in the materials. Moreover TGA/DTA/mass spectrometry before thermal treatment is practiced to identify the organic part of the aerogels due to their hybrid character. This characterization can show if the thermal treatment is efficient or not.
9:00 PM - Z5.18
Unusual Thermal Stability of a Gold-Titania Catalyst System.
Dean Barrett 1 , Paul Franklyn 1 , M. Scurrell 1
1 Chemistry, University of the Witwatersrand, Johannesburg, Gauteng, South Africa
Show AbstractAs research has progressed over the last decades since Haruta first discovered the amazing ability of nano scale gold to catalyse the CO oxidation reaction at low temperature much research has been done on attempting to stabilize gold nanoparticles for higher temperature applications such as automotive catalysts. The stabilization of the gold nanoparticles on the support is extremely important as catalytic activity is directly related to particle size 1-6. We have previously shown that the addition of Pt to Au enhances the thermal stability of the Au nanoparticles7.In the keynote lecture he delivered to the international conference on “New Industrial Applications for Gold”(2003), Dr. Haruta spoke on the future of R&D efforts on nanogold catalysts. The first involves the discovery of new capabilities for Au particles larger than 2 nm that are stable up to 673K.For catalysts containing nano gold for potential use in the automotive industry the ability of the catalysts to be able to withstand higher temperatures (above 773K) from exhaust gases is crucial in order to stop sintering of the catalysts and ultimately complete loss of activity.There are only three current examples of Au based of catalysts existing in the world today that are able to withstand temperatures of 773K or higher. Two of these catalysts show deactivation with time as well as a massive loss of surface area as well as encapsulation of the Au due to the loss of surface area. Further, neither of these two catalysts were exposed to temperatures over 773K 8,9.A patent from the Toyota motor company is the most significant development which describes a catalyst containing complex gold oxides of the form Au2Sr5O8. Here the gold is entirely ionic and is trapped in the oxide lattice. The Toyota catalyst is claimed to be able to withstand temperatures of up to 1073K.10.The catalyst that we have designed is a thermodynamically stable nano-structure of rutile phase titania. The morphology of the nano support structure results in very high surface area while remaining thermally stable and is not susceptible to phase changes resulting in a high degree of stability.The catalyst has been tested at temperatures exceeding 773K, even after exposure to a temperature of 873K for over 200 hours the catalyst still showed good catalytic activity with only a small drop in CO conversion. Finally the catalyst was tested at 1073K, again with only a small loss in activity. Industrial Au based catalysts were exposed to the same temperatures and in all cases showed complete deactivation.The deposition of Au onto the support in done using a method that provides strong interaction between the Au nanoparticles and the substrate, this together with the peculiar structure of our support are believed to be responsible for the high thermal stability of our system, a result which could have implications for supported-metal catalysis in general. The catalyst has been characterised using variable temperture in-situ X-ray diffraction, electron diffraction and TEM. Further the catalyst has been characterised using 3-Dimensional tomography which has revealed many of the reasons for the catalysts remarkable stability. All catalysts were tested on catalytic rigs in order to test activity towards the CO oxidation reaction.References1) M. Haruta, Catal. Today 36 (1997) 153.2) S.D. Lin, M. Bollinger and M.A. Vannice, Catal. Lett. 17 (1993) 2453) M. Okumura, S. Nakamura, S. Tsubota, T. Nakamura, M. Azuma and M. Haruta, Catal. Lett. 51 (1998) 53.4) Y. Yuan, K. Asakura, H. Wan, K. Tsai and Y. Iwasawa, Catal. Lett. 42 (1996) 155) M.M. Schubert, S. Hackenberg, A.C.v. Veen, M. Muhler, V. Plzak and R.J. Behm, J. Catal. 197 (2001) 113.6) M. Haruta, N. Yamada, T. Kobayashi and S. Iijima, J. Catal. 115 (1989) 301.7) D. Barrett, P. Franklyn and M. Scurrell (2010). Variable Temperature Study of Au and Au-Pt Nanoparticles on Selected Oxide Supports. MRS Proceedings, 1279, 40 8) Mellor JR, Palazov AN, Grigorova BS, Greyling JF, Reddy K, Letsoalo MP, Marsh JH (2002) Catal. Today 72, 145.9) Seker E, Gulari E (2002) Appl. Catal. A 232, 203.10) Pattrick G, van der Lingen E, Corti CW, Holliday RJ, Thompson DT (2003), Proc. 6th International Congress on Catalysis and Automotive Pollution Control (CAPOC 6)
9:00 PM - Z5.19
Investigation of Nanostructures in Pb-O System by Solution and Vapor Growth Techniques.
Davide Calestani 1 , Giacomo Benassi 1 , Marco Villani 1 , Laura Lazzarini 1 , Andrea Zappettini 1
1 , IMEM-CNR, Parma Italy
Show AbstractMetal-oxides and their nanostructures are today widely investigated because of their multiple functional properties and possible application in different fields. In this context, lead oxides remain a not completely explored case and their nanostructures are not frequently reported in literature. Lead and oxygen forms several compounds, differing in stoichiometric ratio and crystalline structures. This aspect makes the study of these oxides even more complicate.Aim of this work is the investigation of synthesis approaches to the growth of lead oxide nanostructures, and in particular of lead monoxide (PbO), which is a promising high-Z material for radiation detection. In particular the availability of single-crystal nanostructures could allow better investigations of transport properties, which is a fundamental parameter for detectors realization but not well defined for this material.Both solution and vapor based synthesis methods have been explored in order to obtain nanostructures with the desired crystalline structures. Different wet reactions starting from lead salt precursors have been tested as a function of the synthesis parameters (pH, temperature, concentration,…). Vapor phase growth has been instead based on the thermal evaporation and controlled oxidation of metallic lead, in order to promote the formation of the oxides with the lowest oxidation state. Structural and optical properties of the obtained nanostructures have been characterized and the different results have been compared.
9:00 PM - Z5.2
Effect of Growth Time on the Properties of Ga2O3 Nanowires Grown by CVD Technique.
Rajendra Singh 1 , Vipin Kumar 1 , Trilok Singh 1 , Vikram Kumar 1
1 Physics, Indian Institute of Technology Delhi, New Delhi India
Show AbstractMonoclinic gallium oxide (β-Ga2O3) is a transparent conducting oxides and is intrinsically an insulator with a wide band gap of 4.9 eV. It becomes an n-type semiconductor when synthesized under reducing conditions. Due to its large bandgap, it exhibits transparency from the visible into the UV region with a cutoff wavelength of about 260 nm. Ga2O3 may, therefore, be an attracting material for future generations of optoelectronic devices operating at shorter wavelengths. Moreover, nanoscale gallium oxide with a large ratio of surface area to volume is expected to have special conduction and semiconductor properties, which may find applications in nano-optoelectronic devices. In this report we have carried out growth of β-Ga2O3 nanowires on Si(100) substrates using tubular furnace based chemical vapor deposition technique. Au was used as nanocatalyst for the growth of β-Ga2O3 nanowires via vapor-liquid-solid (VLS) growth mechanism. Ga metal was used as the precursor and argon as the carrier gas. The temperature and pressure during the growth were 900oC and 100 torr, respectively. The growth time was 1 hr, 2 hr and 4 hr, respectively. The grown nanowire samples were characterized using various techniques such as scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence. The average diameter of the nanowires was about 40 nm and their length increased up to 5-10 microns as the deposition time varied from 1 to 4 hrs. The EDS analysis indicated that the nanoparticle present on the tip consisted mainly of Au, Ga and O, but the nanowire was composed of Ga and O elements only. The XRD spectra showed many peaks that matched well with the values for monoclinic Ga2O3. TEM images clearly showed the presence of gold nanoparticle on the tip of the nanowire, which is a characteristic of the VLS mechanism. The PL spectra of the nanowires grown for different times showed two UV peaks present quite closely at 363 and 385 nm, respectively. Moreover, broad band centered at about 715 nm was also visible in the PL spectra. The positions of the peaks/band did not change with time but their intensities varied as function of growth time. The potential recombination processes responsible for the PL emission will be discussed in more detail.
9:00 PM - Z5.20
Titania Condensation Using a Silicatein Inspired Block Copolymer Mimic.
Chetan Hire 1 , Homer Genuino 2 , Douglas Adamson 1 2
1 Institute of Materials Science, University of Connecticut, Storrs Mansfield, Connecticut, United States, 2 Chemistry Department, University of Connecticut, Storrs Mansfield, Connecticut, United States
Show AbstractBiosilicification, the biological formation of amorphous hydrated silica, occurs globally on a very large scale in a wide variety of organisms, e.g. diatoms, sponges, mollusks. Depending on the type of species, silica architectures thus formed can range from nanoscale to macroscopic dimensions. Silica spicules of Tethya aurantia, a marine sponge, were found to contain protein filaments. These filaments were dissociated into 3 subunits viz. Silicatein α, β and γ. Later Cha et. al. discovered that silicatein-α catalyses the condensation of silica from the corresponding silicon alkoxide. They also proposed a reaction mechanism based on catalysis by serine/histidine active site proteases in silicatein-α. Adamson et. al. have synthesized a non-peptide block copolymer mimicking the functional groups on Silicatein α. They have also shown that this polymer mimic of silicatein-α i.e. poly(hydroxylated butadiene-b-2-vinylpyridine) catalyses the condensation of silica from tetraethylorthosilicate (TEOS). This process does not require high temperatures or low or high pH. Later, it was also observed that the same polymer also acts as a template for condensed silica. It forms spheres of diameter 30 to 40 microns, which were found to be made up of much smaller spheres of size approximately 40nm in diameter. In this report, we are using the same block copolymer chemistry and architecture to condense titania. In order to achieve that, titanium isopropoxide (TIP) was added to polymer mimic solution in tetrahydrofuran (THF). After about 1 week, the reaction mixture formed a gel, which was allowed to dry. Titanium(IV) oxide (TiO) was also made by adding TIP to THF+water mixture and just water. Adding TIP to just THF did not yield any precipitate or gel. Comparing scanning electron microscope images of these samples showed that small particles were completely absent in mimic TiO samples suggesting the presence of high degree of condensation. To prove that the mimic polymer catalyses hydrolysis and condensation of TIP, we added TIP to the THF solutions of Pluronics F127, hydroxylated polyisoprene, polyisoprene and poly(2-vinyl pyridine). These solutions stayed clear for long time showing no signs of any condensation. Sol-gel TiO, made by conventional sol-gel method, crystallized at 350°C in DSC-TGA study. DSC-TGA of mimic TiO showed two decomposition temperatures which corresponds to the decomposition of mimic polymer. It didn’t show any crystallization. However, temperature XRD of Mimic TiO showed that as the temperature was increased the crystalline character of the sample increased. This can be explained only if mimic TiO was crystalline before heating and was well mixed with mimic polymer, so that it won’t show the crystalline character. But as the polymer burns off, the nanocrystalline TiO is separated. We are currently examining this hypothesis. In addition, application of mimic TiO for photodegradation of N-nitrosodimethylamine is being investigated.
9:00 PM - Z5.21
Fabrication of Scalable Nanoporous Anodized Aluminum Oxide Templates and Applications to Patterning of Nanoscale Materials.
Si-Hoon Lyu 1 , Myoung-Geun Choi 1 , Ji-Min Song 1 , Jang-Sik Lee 1
1 School of Advanced Materials Engineering, Kookmin University, Seoul Korea (the Republic of)
Show AbstractTypically, various lithographic techniques have been used to fabricate regular arrays of nanostructures, but these methods involve a high production cost and a long processing time. To solve these problems, several techniques have been introduced to synthesize nanoscale materials/devices in a controlled manner. In particular, nanoporous templates have been widely used because nanoscale materials/devices can be easily synthesized through electrodeposition or physical vapor deposition using nanoporous templates as a mask layer. Among the various nanoporous templates, self-organized nanoporous anodized aluminum oxide (AAO) is widely used as the mask for the fabrication of uniform nanoscale patterns. The use of nanoporous templates for the fabrication of high-density nanostructured materials via various deposition methods presents advantages over conventional semiconductor processes, including large-scale, low-cost fabrication, and a rapid processing speed. In this study, ultrathin AAO nanotemplates were fabricated with various pore sizes under 100-nm scale in a controlled manner. A regular array of HfO2 nanodots with controlled sizes was prepared on conductive substrates using the sputtering method at room temperature by utilizing the above mentioned AAO nanotemplates as the mask layer. The nanoscale HfO2 dots were synthesized with an accurate diameter according to the pore size of the masks. The HfO2 dot size increased almost linearly with the mask pore size. Thus, nanoscale device elements with controlled device sizes could be synthesized based on the process presented in this research. The AAO masks and the HfO2 nanodots were observed using field emission scanning electron microscopy (FE-SEM), and the nanodot structures were analyzed using high-resolution transmission electron microscopy (TEM). The topography and the electrical properties of the HfO2 nanodot devices were investigated using atomic force microscopy (AFM). Detailed template synthesis, structural and electrical characterization of metal-oxide nanodots will be presented and discussed.
9:00 PM - Z5.22
Expanding the Shape Diversity of Hollow Silica Nanoparticles via Structurally Complex Semiconductor Nanoparticles as Templates.
Yang Xu 1 , Yin Thai Chan 1
1 Department of Chemistry, National University of Singapore, Singapore Singapore
Show AbstractShape control of silica at the nanometer scale has been challenging due to its amorphous nature, rendering strategies involving facet-specific binding surfactants as used in the fabrication of crystalline nanoparticles of various shape anisotropies non-applicable. As a result, silica nanoparticles produced to-date have thus mostly been confined to spherical geometries, limiting their use in shape-specific applications. On the other hand, semiconductor nanostructures synthesized via a core-seeded approach can result in very uniform particles of various complex geometries. In this work, we introduce a facile method for the fabrication of monodisperse hollow silica nanostructures of different sizes and shapes by utilizing semiconductor nanostructures of various morphologies as the template. By appropriately varying the relative ratios of concentrations of precursors used for silica encapsulation, exquisite control over the silica shell growth was achieved, faithfully reproducing the shape complexity of the substrate semiconductor nanostructure. Selective etching of the semiconductor without any observable exacerbation of the silica shell morphology resulted in uniform hollow silica nanostructures of various complex shapes such as rods, pyramids, tetrapods and so on. Such structures expand on the range of shape complexity in hollow silica nanoparticles, which may enable newfound applications in drug delivery and chromatography.
9:00 PM - Z5.23
Improvement of Room Temperature Processed High Quality TCO Thin Film Using the DC/RF Superimposed Magnetic Field Shielded Sputtering (MFSS) Process.
JunYoung Lee 1 , YouJong Lee 1 , YunSung Jang 1 , MunPyo Hong 1 2
1 Display and Semiconductor Physics, Korea University, Chungnam Korea (the Republic of), 2 Center for Advanced Photovoltaic Materials (ITRC), Korea University, Chungnam Korea (the Republic of)
Show AbstractRecently, there have been commercial demands for room temperature processed Transparent Conducting Oxide (TCO) film, for applying to various flexible electronics devices based on a plastic substrate. But, in the room temperature TCO sputtering process, the electro-optical properties of the TCO thin film are degraded by high energy negative oxygen ions. The high energy negative oxygen ions can do critical physical bombardment damage to the forming TCO thin film and this effect does not allow recovery in the room temperature process not using thermal annealing. To solve these limitations, we have developed the Magnetic Field Shielded Sputtering (MFSS) system as a high quality TCO thin film deposition process at room temperature. The MFSS system is effectively suppressing the bombardment damage of the negative oxygen ions by a plasma limiter which composes of a permanent magnet array. Therefore, the MFSS processed ITO thin film had lower resistivity of 3.9Χ10-4 Ω cm than the normal DC Magnetron Sputtering ITO thin film (9.8Χ10-4 Ω cm) under the same sputtering conditions. In addition to these MFSS effect, we developed a DC/RF superimposed MFSS system for enhancement of the MFSS effect. The DC/RF superimposed MFSS system can lead to further improvements of the TCO thin film properties through the control of the energy of the reflected neutral Ar, based on the MFSS effect. As a result, the superimposed RF/DC MFSS processed ITO thin film showed significantly lower resistivity (3.0Χ10-4 Ω cm) for room temperature processes. Also, The MFSS ITO shows the nano-crystalline structure.
9:00 PM - Z5.24
Indium Tin Oxide Nanowhisker Morphology Control by Glancing Angle Deposition.
Allan Beaudry 1 , Ryan Tucker 1 , Joshua LaForge 1 , Michael Taschuk 1 , Michael Brett 1 2
1 Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada, 2 , NRC National Institute for Nanotechnology, Edmonton, Alberta, Canada
Show AbstractIndium tin oxide (ITO) undergoes self-catalyzed vapour-liquid-solid (VLS) growth under certain physical vapour deposition conditions.
1,2 In kinetic growth, ITO exhibits a distinctive orthogonal branch formation, reflecting indium oxide’s crystal structure.
2 Such branched structures can provide better electrical access to organic photovoltaic (OPV) device active layers, motivating efforts to control ITO nanowhisker morphology. ITO nanowhisker growth has been reported at a range of substrate temperatures, deposition rates, vapour incidence angles and deposition techniques. However, a systematic study of the deposition conditions resulting in ITO nanowhiskers has not yet been completed. In this study, VLS growth was coupled with glancing-angle deposition (GLAD) to allow for the effects of various deposition parameters on ITO nanowhisker morphology to be systematically determined. GLAD is a physical vapour deposition technique capable of producing a variety of nanostructures by controlling geometric shadowing of a collimated flux through substrate motion.
3 Nanostructured GLAD ITO films have been grown at room
4, 5 and elevated
6 substrate temperatures. GLAD nanopillar ITO films have resulted in improved OPV device performance
7, and ITO nanowhisker films may allow further improvements. We have recently demonstrated advanced control over ITO nanowhisker morphological properties using GLAD. Modulation of deposition parameters during deposition allows fabrication of unique and layered ITO nanowhisker structures with control over branching. In this paper, the effects of vapour flux angle, vapour flux rate, substrate temperature, and substrate rotation on ITO nanowhisker morphology, transmittance, reflectivity, and conductivity will be presented.
1 S. I. Castañeda et al. J. Appl. Phys., 83 (1998) pp. 1995 - 2002
2 S. Takaki et al. Jpn. J. Appl. Phys., 46 (2007) pp. 3537 – 3544
3 M. Brett and M. Hawkeye. Science, 319 (2008) pp. 1192-1193
4 Y. Zhong et al. J. Mater. Res., 23 (2008) pp. 2500 – 2505
5 K.D. Harris et al. Advanced Functional Materials, 18 (2008) pp. 2147-2153
6 C.-H. Chang et al. Nanotechnology, 22 (2011) p. 095201
7 D. Rider et al. Nanotechnology, 22 (2011) p. 085706
9:00 PM - Z5.25
Phase Segregation of Polymethylsilsesquioxane in Antireflection Coatings.
Wen Pin Chuang 1
1 , Industrial Technology Research Institute, Hsinchu Taiwan
Show AbstractWe herein describe the preparation and characterization of a phase separated fluorinated polymethylsilsesquioxane (PMSQ), which may be used as an antireflective coating. The results of FTIR analysis showed that when PMSQ is synthesized from methyltrimethoxysilane (MTMS), it exists mostly in the form of a cage structure. Its reflectivity of normally incident light (R) may be reduced from 3.9 to 0.9% by grafting 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FTES) by means of a sol gel process. In the study described herein, the minimum reflectivity of PMSQ was lowered to less than 1 % by coating it with a single layer of fluorinated polymethylsilsesquioxane, through phase segregation of PMSQ and FTES that took place during film formation. The RI of PMSQ at 550 nm was also reduced from 1.51 to 1.42 by heating at 80 °C for 30 minutes, a temperature suitable for substrates, such as plastics, that have low heat resistance. Wetting and adhesion to substrates were both improved by the additional grafting of tetraethoxysilane (TEOS), again by means of a sol gel process. Results of solid state 29Si NMR showed increases in T3, Q3, and Q4, which signal the effective grafting of both the TEOS and the FTES on the PMSQ. Results from Energy-dispersive X-ray spectroscopy (EDX) show that the quantity of fluorine atoms at the surface of the PMSQ film increased from 0 to 22 % providing the evidence of the phase segregation within the PMSQ film. When FTES is used, we found an increase in the water contact angle from 92° to 108°, which indicated that the hydrophobicity at the PMSQ film surface increased by increasing the FTES content from 0 to 100 wt%, using the weight of MTMS as 100%.
9:00 PM - Z5.26
Reproducible Nanowire Alignment in between Prepatterned Electrodes.
A. Wouter Maijenburg 1 , Michiel Maas 1 , Eddy J.B. Rodijk 1 , Waqqar Ahmed 2 , E. Stefan Kooij 2 , Edwin Carlen 3 , Dave H.A. Blank 1 , Johan ten Elshof 1
1 Inorganic Materials Science, University of Twente, Enschede Netherlands, 2 Physics of Interfaces and Nanomaterials, University of Twente, Enschede Netherlands, 3 BIOS Lab-on-a-Chip Group, University of Twente, Enschede Netherlands
Show AbstractTemplate-directed electrodeposition is an appropriate technique for the synthesis of photocatalytic nanomaterials in any desired shape. We have created nanowires with an arbitrary composition like ZnO and Ag, and nanotubes of Fe2O3. Using these nanowires and nanotubes, the synthesis of segmented or coaxial nanowires is very straightforward. After dissolving the membrane, a solution with well dispersed nanowires is obtained.One of the challenges for the realization of devices based on these nanowires and nanotubes concerns their connection to the macroscopic world via electrodes. Dielectrophoresis is the best option for reproducible nanowire alignment and we recently obtained a single set of parameters that could be used for the alignment of all different kinds of nanowire materials, ranging from metals to metal oxides.After alignment, electrical contact to the nanowires could be obtained with a low contact resistance, which opens up possibilities for the use of these nanowires in small sensors. Besides using these aligned nanowires for sensor applications, it is also possible to study their electrical characteristics. In this way we investigated the Schottky-barrier created in segmented ZnO|Ag nanowires, which is responsible for the good photocatalytic properties of these nanowires.
9:00 PM - Z5.27
Ellipsometric and X-Ray Photoelectron Spectroscopy Characterization of Titanium Dioxide Thin Films Created by Oxygen Plasma.
Gabriel Droulers 1 , Sonia Blais 2 , Jean-Francois Morissette 1 , Arnaud Beaumont 1 , Michel Pioro-Ladriere 3 , Dominique Drouin 1
1 Electrical and Computer Engineering, Université de Sherbrooke, Sherbrooke, Quebec, Canada, 2 Centre for Characterization of Materials, Université de Sherbrooke, Sherbrooke, Quebec, Canada, 3 Physics, Université de Sherbrooke, Sherbrooke, Quebec, Canada
Show AbstractIn recent years, a process to fabricate single electron transistors operating at room temperature has been developed [1]. In this process a titanium oxide is created by plasma oxidation of a titanium thin film and used as the dielectric for tunnel junctions. Two main factors change the junction’s characteristics: oxide thickness, which was measured with a specifically developed ellipsometric model; and quality of the oxide, which was measured using X-ray Photoelectron Spectroscopy (XPS).As demonstrated in a recently published article [2], we have developed an ellipsometric model to accurately measure the thickness of a titanium thin film whether it has intentionally been oxidized by plasma or not. Oxide thicknesses varying from 1.3 ± 0.4 nm for native oxides to 7.6 ± 0.4 nm for plasma oxidized samples were measured. Also, a saturation of the thickness was observed with increasing plasma duration and power. Indeed, at some point, the oxygen cannot penetrate deeper in the sample to oxidize the titanium layer.The quality of the oxide is also crucial for the electrical characteristics of fabricated devices. Impurities can result in defaults and traps in the tunnel barrier. We therefore measured the stoichiometry and composition of the oxide using XPS. The first conclusion is that a significant part of the native oxide is composed of sub oxides (TiO and Ti2O3). However, once oxidized in O2 plasma, the oxide rapidly becomes stoichiometric TiO2. Concerning the composition of oxides, a clear silicon contamination was noticed and tests using different carriers in the plasma reactor were carried out to establish its origin. This contamination was attributed to the silicon carrier used in the plasma system. The use of silicon, aluminum and anodized aluminum carriers showed that none of these materials was stable enough to limit its etching and prevent the re-deposition of the contaminants on the TiO2 surface. As a result, with the silicon and aluminum carriers, an 11 at.% impurity level was observed. In the case of anodized aluminum, the impurity level was increased to 19 at.%.In conclusion, these experiments have revealed potential optimization avenues. The ellipsometric model enables parametric testing of different plasma conditions to optimize the electrical characteristics of tunnel junction based devices. The quality of the oxide is the other avenue of improvement on the device fabrication process since a more stable or less contaminating support wafer could lead to better dielectric properties of the titanium oxide tunnel junctions.[1] C. Dubuc et al., IEEE TRANS. NANOTECHNOL. (2008), 68.[2] G. Droulers et al., J VAC SCI TECHNOL B (2011), 021010-1.
9:00 PM - Z5.28
Deposition of Indium Tin Oxide Nanoparticles Synthesized in Organic Phase.
Jonghun Lee 1 , Vismadeb Mazumder 1 , Shouheng Sun 1
1 Chemistry, Brown University, Providence, Rhode Island, United States
Show AbstractIndium tin oxide (ITO) nanoparticles are possible building blocks for ITO film fabrication. However, synthesis of monodispersed ITO nanoparticles has not been reported much. We report a novel synthetic method for ITO nanoparticles with size tunability from 10 to 16 nm. In addition, ITO thin film was fabricated on a glass substrate. The thickness of the film was controlled by varying the concentration of ITO solution. These films were annealed under Ar or forming gas in order to remove surface ligands and to enhance conductivity. We found that the transparency of the ITO films was dependent on its thickness. In addition, annealing atmosphere largely affected the conductivity of the films.
9:00 PM - Z5.29
Initial Reaction of Dimethylaluminum Isopropoxide with Hydrogen-Terminated Si (001) Surface.
Dae-Hee Kim 1 , Yeong-Cheol Kim 1
1 School of Energy, Materials & Chemical Engineering, Korea University of Technology and Education, Cheonan, Chungnam, Korea (the Republic of)
Show AbstractAlumina thin-film has recently been actively studied in solar cell industry to utilize its negative fixed charge to suppress the recombination rate of minority charge carriers as passivation layers. Dimethylaluminum isopropoxide (Al(CH3)2OC3H7, DMAI) is an aluminum precursor to deposit alumina thin-films for the atomic layer deposition process. In the present study, a relation between bond strength and energy barrier for DMAI reaction with a hydrogen-terminated Si (001) surface was investigated using density functional theory. There are three possible bond dissociations in DMAI for the surface reaction: Al-CH3, O-C3H7, and Al-O bonds with increasing bond strength order. When DMAI was adsorbed on the surface, the Al atom of DMAI was attracted to a H atom on the surface. Due to the attractive interaction between the Al and H atom, the Al-O and Al-CH3 bonds in the adsorbed DMAI were weakened, while the O-C3H7 bond remained unchanged. Therefore, the bond strength order was changed to the Al-CH3, Al-O, and O-C3H7 bonds after the molecule was adsorbed on the surface. The bond strengths of the adsorbed DMAI were well related to the energy barriers for DMAI reaction, because the bonds should be broken during the reaction.
9:00 PM - Z5.3
Improvement of Surface Morphology and Grain Boundaries of YBCO Superconducting Thin Films with Oxide Nanoparticle Additions.
Yijie Li 1 , Linfei Liu 1 , Da Xu 1 , Ying Wang 1 , Shengping Zhu 1 , Peng Zhu 1
1 Department of Physics, Shanghai Jiao Tong University, Shanghai, Shanghai, China
Show AbstractYBCO superconducting thin films with different oxide nanoparticle additions have been fabricated on NiW tapes by pulsed laser deposition process. For stoichiometric (123) YBCO films, it was found that when YBCO thickness was smaller than 0.8 micrometer, YBCO superconducting films had a high critical current density Jc of 4.0x106 A/cm2 (at 77 K, self magnetic field) . As YBCO film thickness increased over 1.0 micrometer, the Jc values of YBCO films decreased with increasing of YBCO film thickness. SEM and AFM observations showed that thick YBCO films had micrometer-scale grains and relatively broad grain boundaries which blocked superconducting current paths. In order to control the grain size and grain boundary width of YBCO films, Y2O3 and ZrO2 doping effects were investigated. AFM and SEM images showed the presence of nano-scale Y2O3, YSZ, BaZrO3 oxide particles on YBCO superconducting film surface. These nanoparticles on YBCO film surface changed YBCO epitaxial growth process and acted as new crystal nucleus. YBCO superconducting thin films with oxide nanoparticle additions showed smooth surface and higher superconducting critical current density.
9:00 PM - Z5.30
TiO2 Nanostructured Films by Direct Flame Deposition on Polymeric Microchip Chromatographic Columns for Phosphopeptide Enrichment.
Thomas Rudin 1 , Katerina Tsougeni 2 , Evangelos Gogolides 2 , Sotiris Pratsinis 1
1 Department of Mechanical and Process Engineering, ETH Zürich, Zürich Switzerland, 2 Institute of Microelectronics, NCSR “Demokritos”, Athens Greece
Show AbstractAssembling of devices with nanoparticles is a new frontier for integration of nanomaterials into products [1]. Microfluidic chromatographic columns are created by deposition of flame-made aerosol films on polymer-coated microchannel layouts. Uniform TiO2 films were obtained by direct deposition of freshly-made TiO2 nanoparticles on cooled Polymethyl methacrylate (PMMA) or Polyether ether ketone (PEEK) substrates. These crystalline nanoparticles were made by combustion of titanium-tetra-isopropoxide (TTIP) – xylene solution sprays [2]. The mechanical stability of such films was achieved by in-situ annealing them with a particle-free, xylene spray flame [3]. The whole process has a record low fabrication time of a few tens of seconds compared to several tens of hours for liquid chemistry methods. The annealed films were tested for stability by exposure to a fluid flow and were characterized by scanning electron microscopy (SEM) and atomic force microscopy before and after fluid exposure. Flame annealed films were stable to withstand a liquid flow across the substrate. So microfluidic devices containing microchannels 4 – 10 μm wide and 10 μm deep were coated with such nanoparticle films without any deformation of the microchannels and were successfully used in immobilized metal-oxide affinity chromatography (MOAC) to selectively trap phosphopeptides on these high surface-area nanostructured films. A new extremely fast method thus is proven for MOAC microchip stationary phase fabrication with applications in proteomics helping to understand the biological function of phosphorylated proteins at a molecular level.1. S.E. Pratsinis: Aerosol-based technologies in nanoscale manufacturing: from functional materials to devices through core chemical engineering. AlChE J. 56, 3028 (2010). 2. A. Teleki, S.E. Pratsinis, K. Kalyanasundaram, and P.I. Gouma: Sensing of organic vapors by flame-made TiO2 nanoparticles. Sensor Actuat. B-Chem. 119, 683 (2006). 3. A. Tricoli, M. Graf, F. Mayer, S. Kuhne, A. Hierlemann, and S.E. Pratsinis: Micropatterning layers by flame aerosol deposition-annealing. Adv. Mater. 20, 3005 (2008).
9:00 PM - Z5.31
Initial Reaction of Diisopropylaminosilane with Hydroxylized Si (001) Surface for Silica Thin-Film Growth.
Ji-Su Kim 1 , Dae-Hee Kim 1 , Seung-Bin Baek 1 , Yeong-Cheol Kim 1
1 School of Energy, Materials & Chemical Engineering, Korea University of Technology and Education, Cheonan, Chungnam, Korea (the Republic of)
Show AbstractThe initial reaction of diisopropylaminosilane (SiH3[N(C3H7)2], DIPAS), as an atomic layer deposition (ALD) Si precursor, with a fully hydroxyl (OH)-terminated Si (001) surface was investigated using density functional theory. When DIPAS was adsorbed on the surface, the N atom of DIPAS was located on the H atom of –OH with an adsorption energy of 0.56 eV. The N atom of N(C3H7)2 was bonded to the H atom of –OH to produce diisopropylamine (NH(C3H7)2, DIPA) as a byproduct, and the exposed O atom of –OH was bonded to the Si atom of the remaining silane (–SiH3) group. An energy barrier of 0.45 was required for DIPAS reaction. Since the reaction energy barrier is less than the adsorption energy, DIPAS would remain absorbed during the reaction, and, therefore, is an appropriate ALD Si precursor. The produced DIPA as a by-product was desorbed from the surface with an energy barrier of 0.33 eV, indicating that an extra energy was needed to remove it from the surface. Since a high energy barrier of 1.34eV was required for –SiH3 group reaction with a neighboring H atom, the further reaction would be suppressed and, therefore, the –SiH3 group would be the major groups on the surface during DIPAS reaction.
9:00 PM - Z5.32
Fabrication of Highly-Ordered Nanocrystalline Films through Rearrangement during Solvent Annealing.
Daisuke Hojo 1 , Takanari Togashi 1 , Tadafumi Adschiri 1
1 Advanced Institute for Materials Research, Tohoku University, Sendai, Miyagi, Japan
Show AbstractRealizing the printed electronics where metal oxide nanocrystals are incorporated has attracted considerable attention recently. In order to apply nanocrystals to the surfaces, three things have to be considered at least. 1) Disperse nanocrystals in a solvent. 2) Self-assemble nanocrystals on the substrate with drying the solvent. 3) Fix nanocrystals on the substrate. Among these processes, necessary interaction between the metal oxide cores, modifiers, solvent and the substrate is totally different. This could then lead to a difficulty to apply nanocrystals to the surface.We previously reported cerium oxide nanocrystals which were modified with decanoic acid for high-dispersibility in cyclohexane.[1] We also presented self-assemble mono-layered nanocrystal system, where the nanocrystals were covalently adsorbed to the pretreated Si surface.[2] The chemical bonds are established between nanocrystals and the substrate by using local ligand exchange between them. However, due to low mobility of nanocrystals in a solvent, arrangement of nanocrystals during self-assembly with drying occurred insufficiently.In this study, we observed rearrangement of the cerium oxide nanocrystals chemically adsorbed on the Si substrate during solvent annealing. The solvent anneal was conducted in tetrahydrofuran (THF) at 40-60°C for 5-15h. To evaluate nanostructures dispersed two dimensionally on the surface, atomic force microscope (AFM) and grazing-incidence small-angle-X-ray scattering (GISAXS) were used.AFM revealed that after the solvent anneal in THF, nanocrystals adsorbed on the substrate were rearranged to be more highly-ordered structures presumably due to high-mobility of nanocrystals in sufficient solvent vapors at higher temperatures. The roughness of this structure obtained was reduced. The GISAXS image also turned spot to streak pattern corresponding to the diameter of nanocrystals, ~6 nm after annealing. However, when THF annealing applying to the self-assemble mono-layered nanocrystal system, which was obtained by washing the nanocrystals on nanocrystals leaving the nanocrystals on the substrate.[2] No rearrangement occurred during annealing. Interaction between nanocrystals and the substrate is too strong to rearrange the system. This rearrangement of nanocrystals will be a key technology for layer-by-layer assembly and precisely controlled colloidal superlattices.[1] Zhang et. al, Adv. Mater. 19, 203 (2007).[2] Hojo et. al, Chem. Mater. 22, 1862 (2010).
9:00 PM - Z5.33
Growth of Vanadium Oxides Nanowires Using Vanadyl Acetylacetonate.
Takafumi Ishibe 1 , Jun Kikkawa 1 , Yoshiaki Nakamura 1 , Akira Sakai 1
1 Engineering Science, Osaka university, Toyonaka Japan
Show AbstractOne-dimensional nanostructures of vanadium oxides are currently the subject of intense research for discovering fundamental science at the nanoscale as well as for their potential applications such as sensors, switching devices, lithium ion batteries and catalysis. Vanadium oxides have many different chemical compounds and crystal structures, exhibiting a great variety of interesting characteristics. In particular, vanadium dioxide (VO2) draws much attention due to the high-speed metal(M)-insulator(I) transition (MIT) near room temperature, ~68 degree C and the spontaneous formation of periodic M and I domains in one dimensional structures. Nevertheless, the MIT mechanism in VO2 is still under discussion even for the bulk and the MIT behaviors in nanostructures are not understood. In this context, fabricating thin nanowires of vanadium dioxide is scientifically and technologically important. In this study, we found a low-temperature growth condition of vanadium oxides nanowires in metal-organic chemical vapor deposition processes. Vanadium oxides products were grown on SiO2/Si(001) substrates by using vanadyl acetylacetonate as a source material and argon or oxygen as a carrier gas. The source powder and the substrates were heated at about 90 and 360 degree C, respectively. The flow rate of the carrier gas was set at 20 ml/min and the pressure was ~1 torr, and the growth time was 6 h. Products on the substrates were characterized by scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). SEM images and XPS spectra showed that high-density vanadium oxides nanowires were grown on the substrates under the oxygen flow, while vanadium oxides films were formed under the argon flow. TEM observations revealed that most of the nanowires have the width of less than 50 nm and the length of ~1 μm. The vanadium oxidation states were characterized by the binding energy difference between V2p3/2 and O1s XPS peaks, and the nanowires and the films were attributed to VO2 and V2O3, respectively. We discuss chemical reactions on the formation process of the VO2 and V2O3 products from the original acetylactonate. We also present details of the structural properties of the nonowires by electron diffraction and TEM. [This work was partly supported by KAKENHI(22760513).]
9:00 PM - Z5.34
Solvothermal Synthesis of Shape Controlled of Titanium Oxide Nanocrystals.
Cleocir Dalmaschio 1 , Edson Leite 1
1 Lab LIEC, Deparatmento de Química, Universidade Federal de São Carlos, Sao Carlos, São Paulo, Brazil
Show AbstractDesign and morphological control of crystal facets is a commonly employed strategy to optimize the performance of various crystalline materials. The conventional understanding of the atomic surface structure of a crystal is that facets with a higher percentage of uncoordinated atoms are usually more reactivate. In TiO2 anatase crystal the surface is usually dominated by {101} facets, which present the lowest surface energy, as demonstrated by theoretical studies the follow sequence for surface relative energy: {101}<{100}<{001}. Using solvothermal microwave process, this study describes a synthesis route to control of the shape of TiO2 nanocrystals by adjust the reaction solvent system. Two organic solvents with identical chain but different terminal functional group were used with different molar fractions to synthesis titania nanocrystals with controlled morphological design. As know that the face {001} is the higher surface energy and more oxidative face than other faces. Then, organic molecules with oxidative character capping the faces {001} will be easily removed leading to a growth process that result in nanorods crystals in this type of solvent. On the other side, in less oxidative solvent attach on the surface sites lead a regular shaped nanocrystal, resulting in spherical nanoparticles. Mixture of solvents lead to thermodynamically stable shape by the control of preferential sites to attachment the organic molecules. In this case the nanocystals shows a morphological shape of slightly truncated tetragonal bypiramidal, that is a predicted shape for anatase crystal under equilibrium conditions. The attachment of different functional groups presented in the solvent shows an easily and simple way to control the growth and shape of TiO2 nanocrystals that have been successfully synthesized through easily adjusting the reaction solvent system.
9:00 PM - Z5.35
A Phase-Field Model for the Structural Transition of Vanadium Dioxide Single Crystals.
Yijia Gu 1 , Jinbo Cao 2 3 , Junqiao Wu 2 3 , Long-Qing Chen 1
1 , The Pennsylvania State University, University Park, Pennsylvania, United States, 2 , University of California, Berkeley, Berkeley, California, United States, 3 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractVanadium dioxide (VO2) is a strongly correlated material. It undergoes a metal-insulator transition accompanied by structural changes. In addition, the VO2 single crystals with reduced dimensions, including nanobeams, nanopatelets and so on, exhibits unique self-assembly domain patterns. In this study, we used a unified thermodynamic potential to describe all the structural transformations of VO2, including R, M1, M2 and T phases. A phase field model was employed to investigate the effect of external constrictions on the structural transitions. A strong dependence on spatial dimensions and applied strain conditions of equilibrium domain structures was revealed and discussed. Our result may be used to guide experiments to obtain desired microstructures and further electric properties.
9:00 PM - Z5.36
Direct Synthesis of Pure Radiative VO2 (M) Plate like Structures via Hydrothermolysis at Low Temperature.
Aline Simo 2 3 , Lawrence Edomwonyi-Otu 1 2 , Malik Maaza 2 , Reginald Madjoe 3
2 Materials Research Department, Ithemba Labs - National Research Foundation, Somerset West, Cape Town, Western Cape, South Africa, 3 Physics Department, University of Western Cape, Bellville, Cape Town, Western Cape, South Africa, 1 Chemical Engineering Department, Ahmadu Bello University, Zaria, Kaduna, Nigeria
Show AbstractFacile and direct synthesis of radiative VO2 (M) plate-like is reported. The snowflake material presents superstructures plate-like aggregate with an anisotropic orientation in shape governed by V2O5 and NaOH concentration giving high surface energy liable for chemical reactions with the medium. Pure crystalline VO2 (M) has been obtained with a complete hydrothermolysis of the precursor. The morphological, structural, elemental composition, crystallinity and vibrational bands of the powders were characterized by Powder X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Selected Area Electron Diffraction (SAED) and Fourier Transform-Attenuated Total Reflection (FTIR-ATR) infrared spectroscopy.
9:00 PM - Z5.37
Engineering the Structure of Gold Nanoparticle Loaded Boehmite Nanorods towards Materials with Novel and Controllable Plasmonic and Catalytic Properties.
Priyank Mohan 1 , Tran Thu 1 , Pham Thanh 1 , Yasushi Enomoto 2 , Yasufumi Matsumura 2 , Hiroaki Takahashi 1 , Derrick Mott 1 , Goro Mizutani 1 , Shinya Maenosono 1
1 MATERIAL SCIENCE, JAIST, Nomi City, Ishikawa, Japan, 2 New Business Development and Promotion Department, New Business Development Bureau, Nippon Steel Chemical Co.,Ltd., Kisarazu, Chiba, Japan
Show AbstractNanoparticle (NP) loaded metal oxides (nanocomposites) have been attracting the interest of scientists from all disciplines due to the novel properties induced by the nanoscale structures. These materials hold great promise with opportunities for a new generation of functional materials with improved and tailorable properties for applications in optical devices, chemical and biological sensors, active catalysts, separation, biotechnology etc. Au NP loaded Boehmite is one excellent example of a metal oxide nanocomposite that has been demonstrated to possess enhanced optical and catalytic properties. While much research has been conducted on Au NP loaded Boehmite materials, few studies could demonstrate control over both the Au NP and Boehmite characteristics in terms of size, shape, and final composite structure. While most attempts focus on thermal induced reduction of the gold in a Boehmite matrix, we have independently synthesized Boehmite nanorods with an average length of 149 nm and width of 21 nm as well as monodispersed Au NPs with a size of 13 nm. We then independently loaded these Boehmite NRs with Au NPs to create a remarkably uniform nanocomposite in terms of the structural components. By using this approach, the nanocomposites resulting optical and catalytic properties can be tuned by finely controlling the Au NP size, shape, or degree of loading. This allows a great advantage in controlling the nanocomposite properties as compared to the traditional approaches towards this class of nanocomposite material. This presentation focuses on the synthesis and formation of the Au/Boehmite nanocomposite structure with highly uniform properties. The resulting materials provided an ideal platform for studying the origin of the enhanced optical and catalytic properties displayed by these materials which includes the electron transfer that occurs between gold and the Boehmite support. The results are discussed in terms of characterization of the materials using techniques such as XPS, STEM-HAADF, HR-TEM, UV-Vis, as well as others.
9:00 PM - Z5.38
Synthesis of Oxidized Fe Nanowires by Annealing.
Seonggi Min 1 , Jin-Hee Lim 2 , Leszek Malkinski 1 , John Wiley 2
1 Advanced Materials Research Insitute(AMRI), The University of New Orleans, New Orleans, Louisiana, United States, 2 Chemistry, University of New Orleans, New Orleans, Louisiana, United States
Show AbstractTechnology of elongated magnetically hard nanoparticles is far less developed than that of spherical magnetic nanoparticles. This work reports on new fabrication method and properties of magnetically hard magnetite nanowires in anodized alumina membrane (AAM). First, Fe nanowires with 60 nm diameter and 100 nm interpore distances have been synthesized by electrodeposition using AAM template. A two-step annealing process was used to transform Fe nanowires into Fe3O4 nanowires. Fe nanowires were annealed at 500 oC for 2 hours in pure oxygen flow. This oxidation led to the formation of nanowires with mixed composition of Fe3O4 and Fe2O3. A subsequent 2 hour annealing in pure flowing hydrogen at the temperature of 350 oC reduced the oxygen content and transformed the nanowires into Fe3O4. The crystalline structures of iron and iron oxide nanowires after heat treatments were studied with XRD. The evolution of XRD patterns after subsequent annealing treatments is presented in Figure, as compared to XRD profile of polycrystalline Fe nanowires. After 2 h annealing at 500 oC in the presence of oxygen flow nanowires were transformed to nanowires of mixed Fe2O3 and Fe3O4 phases. The presence of these two phases was confirmed by XRD studies of Fe particles. After 2 h annealing at 325 oC for 2 h in pure hydrogen gas flow, XRD spectra were in agreement with the Fe3O4 pattern. TEM images show that the polycrystalline nanowires are compact and uniform. Field cooled (FC) and zero-field cooled temperature dependent magnetization curves for Fe3O4 nanowires indicate the Verwey transition at 130 K. Hysteresis loop measurements revealed strongly anisotropic magnetization characteristics. Room temperature coercivity of Fe3O4 nanowires was 732 Oe for the magnetic field parallel to nanowire axis and 310 Oe for the perpendicular field; the saturation fields were 2910 Oe and 8290 Oe, respectively.
9:00 PM - Z5.39
Ga2O3/(La,Sr)CoO3 (LSCO) Core-Shell Nanorod Arrays for High Temperature Gas Sensing.
Hui-Jan Lin 1 , Haiyong Gao 1 , Puxian Gao 1
1 Materials Science and Engineering, University of Connecticut, Storrs, Connecticut, United States
Show AbstractGa2O3 nanorod arrays have been successfully fabricated on silicon substrates. Using hydrothermal method, well-aligned GaOOH nanorod arrays with certain preferential orientations and surface planes can be obtained. After annealing, GaOOH could fully transform to beta-Ga2O3 porous nanorod arrays. Sputtered (La,Sr)CoO3 (LSCO) LSCO porous material nanofilm could further increase surface area which helps its high temperature gas sensing performance. X-ray diffraction analysis and electron microscopy were systematically conducted to identify the nanorod phases and, growth directions and, surfaces and interfaces. Its gas sensing performance over various gases such as CO and O2 has been tested using both electrical and electrochemical characterization methods at high temperatures up to 800 oC. These well-aligned porous Ga2O3/LSCO co-shell nanorod arrays could provide new impact candidates forin high temperature catalysis, electronics, and chemical sensing applications.
9:00 PM - Z5.40
Simultaneous NH3 and Humidity Sensing Using Individual SnO2 Nanowires: Study and Quantification of the Interfering Effects.
Feng Shao 1 , Nuria Lopez 4 , Francisco Hernandez-Ramirez 1 2 , Juan Daniel Prades 2 , Thomas Fischer 3 , Sanjay Mathur 3 , Joan Ramon Morante 1 2
1 , Catalonia Institute for Energy Research (IREC), Sant Adrià del Besos Spain, 4 , ICIQ, Tarragona Spain, 2 , University of Barcelona, Barcelona Spain, 3 , University of Cologne, Cologne Germany
Show AbstractNH3 is a toxic, odorous and flammable gas that forms explosive mixtures with air. Being widely used in manifold industrial processes, the needs for detecting this pollutant and quantify its concentration are tremendous. Metal oxide nanowires have emerged as promising building-blocks of a new generation of gas sensors due to their intrinsic properties [1,2]. In this work, we show the feasibility of using individual SnO2 nanowires as gas sensors for the quantitative detection of ammonia, paying a special attention on how their responses are strongly affected by moisture. Actually, it is well-known that a competition between these two species takes place onto SnO2 surface when they are put together, leading to a complex adsorption process that involve many derivative species. This lack of selectivity is a major drawback for the development of a new and better generation of metal oxide-based nanosensors. For this reason, new strategies to discriminate gas blends become necessary. In this contribution and with the aiming at revealing the kinetics of SnO2 (110) surface interacting with NH3 and moisture, we applied first principle DFT calculation techniques. This work was performed with the simulation code package VASP [3], employing the generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (RPBE) method to describe the exchange and correlation energy. The optimized structure of stoichiometric SnO2(110) surface slab that we used herein was constructed in a previous work [4]. The modeling of a series of possible reaction products of NH3 on SnO2 (110) in atmosphere condition will be presented and discussed; and these theoretical results will be compared to experimental measurements obtained with gas sensors made up of individual SnO2 nanowires. These sensors do not have grain boundaries and do not undergo diffusion drifts due to their small dimensions and good crystallinity. For this reason, they are considered excellent test platforms to validate theoretical value.[1] S. Barth et al., Progress in Materials Science 55 (2010) 563-627[2] F. Hernandez-Ramirez et al., Phys. Chem. Chem. Phys. 11 (2009) 7105[3] G. Kresse et al., Physics review B, 47 (1993) 558.[4] N. Lopez et al, Phys. Chem. Chem. Phys., 12 (2010) 2401-2406.
9:00 PM - Z5.41
Development of a High Quality Nanolaminate Single Gas Barrier Layer by Neutral Beam Assisted Sputtering (NBAS) Process.
YunSung Jang 1 , YouJong Lee 1 , JunYoung Lee 1 , MunPyo Hong 1 2
1 Display and Semiconductor Physics, Korea University, Chungnam Korea (the Republic of), 2 Center for Advanced Photovoltaic Materials (ITRC), Korea University, Chungnam Korea (the Republic of)
Show AbstractRecently, the growing interest in organic microelectronic devices including OLEDs has led to an increasing amount of research into their many potential applications in the area of flexible electronic devices based on plastic substrates. However, these organic devices require a gas barrier coating to prevent the permeation of water and oxygen because organic materials are highly susceptible to water and oxygen. In particular, high efficiency OLEDs require an extremely low Water Vapor Transition Rate (WVTR) of 1Χ10-6gm-2day-1. The Key factor in high quality inorganic gas barrier formation for achieving the very low WVTR required (1Χ10-6gm-2day-1) is the suppression of defect sites and gas diffusion pathways between grain boundaries. In this study, we developed an Al2O3 nanolaminated single gas barrier layer using a Neutral Beam Assisted Sputtering (NBAS) process. The NBAS system is based on the conventional RF magnetron sputtering and it has an electron cyclotron resonance (ECR) plasma source and metal reflector. Plasma gas ions in the ECR plasma can be accelerated into the plasma sheath between the plasma and metal reflector, which are then neutralized mainly by Auger neutralization. The neutral beam energy is controlled by the metal reflector bias. The controllable neutral beam energy can continuously change crystalline structures from an amorphous phase to nanocrystal phase of various grain sizes. Therefore, the Al2O3 films can be nanolaminate structure by controlling the Auger neutral beam energy. The formation of a nanolaminated structure can lead to effectively limits gas diffusion through the pathways between grain boundaries. Our results verify the nanolaminated structure of the NBAS processed Al2O3 single gas barrier layer through dielectric constant measurement, break down field measurement, Raman spectroscopy, and Transmission electron microscopy (TEM) analysis. As a result, the WVTR of Al2O3 nanolaminated single gas barrier layer was measured to be under 1Χ10-6gm-2day-1 therefore we can confirm that NBAS processed Al2O3 nanolaminated single gas barrier layer is suitable for OLED applications.
9:00 PM - Z5.45
Gas Sensor Based on Nanostructured CaCu3Ti4O12 Thin Film.
Anderson Felix 1 , Marcelo Orlandi 1 , Jose Varela 1
1 Physical-Chemistry Department, São Paulo State University, Araraquara, São Paulo, Brazil
Show AbstractChemical sensors based on semiconducting metal oxides (MOX gas sensors) have attracted significant attention due to its simplicity, low cost, small size and its integration in electronic devices. Such devices can be applied in different areas - industry, environment, health, biomedical, automotive, security, etc. Researches aimed at discovering new materials and/or growth of nanoscale materials such as thin films, nanoparticles, nanobelts, etc., has favored the development of sensors with high sensitivity and selectivity combined with low energy consumption. In recent years, CaCu3Ti4O12 (CCTO) has attracted considerable attention due to your electric properties which indicate its possible application in electronic devices. This material exhibits a dual behavior of the conductivity, i.e., this material has characteristics of n-type or p-type semiconductor depending on the growth process. In this context, we prepared gas sensors based on CaCu3Ti4O12 thin film by polymeric precursor method. These materials were characterized by structural (X-ray diffraction) and morphological (SEM-FEG) techniques. Sensor measurements were realized using Al2O3 substrates at different temperatures using oxidizing and reducing atmospheres. We have also performed d.c. electrical measurements in order to determine the activation energy in different atmospheres, and impedance measurements to study the different contributions of bulk and the surface in the sample’s conductivity. Such measurements showed that the CCTO have n-type conductivity and can detect small amounts of gases in the environment, and have high sensitivity and response time of few minutes.
9:00 PM - Z5.46
Sensing Properties of 1D Vanadium Pentoxide Nanostructures.
Nirton Vieira 1 , Waldir Avansi 1 2 , Alessandra Figueiredo 1 , Caue Ribeiro 2 , Valmor Mastelaro 1 , Francisco Guimaraes 1
1 , Universidade de São Paulo - USP, São Carlos, São Paulo, Brazil, 2 , Empresa Brasileira de Pesquisas Agropecuárias - Embrapa, São Carlos, São Paulo, Brazil
Show AbstractThe application of one dimensional (1D) V2O5.nH2O nanostructures as pH sensing material was evaluated. 1D V2O5.nH2O nanostructures were obtained in hydrothermal conditions with systematic control of morphology forming different nanostructures: nanoribbons, nanowires and nanorods. Deposited onto Au-coated substrates, 1D V2O5.nH2O nanostructures were employed as gate material in pH sensors based on separative extended gate FET (SEGFET) as an alternative to FET isolation from the chemical environment. 1D V2O5.nH2O nanostructures showed pH sensitivity around the expected theoretical value. Despite the structural changes due to the hydrothermal synthesis conditions, similar results were observed for V2O5.nH2O synthetized at 160 °C (in nanorribon form with monoclinic phase), 180 °C (in nanowires form with orthorhombic phase) and 200 °C nanowire (form with orthorhombic phase). Within the limits of experimental error, the sensitivity does not change for any nanoforms of V2O5.nH2O, indicating that the pH sensitivity is not dependent on the phase or nanostructure. Due to high pH sensing properties, flexibility and low cost, further applications of 1D V2O5.nH2O nanostructures comprise enzyme-FET-based biosensors using immobilized enzymes.
9:00 PM - Z5.47
Influence of Crystal Morphology in Nanostructured CuO-Based Gas Sensors.
Diogo Volanti 1 , Anderson Felix 1 , Marcelo Orlandi 1 , Jose Varela 1
1 , Sao Paulo State University, Araraquara, São Paulo, Brazil
Show AbstractChemical sensors based on a metal oxide semiconductor (MOS gas sensor) have attracted significant attention due to their simplicity, low cost, small size and integration into electronic devices for applications such as industry, environment, health, biomedical, automotive, security, etc. Research to discover new materials and/or the growth of nanoscale materials (nanoparticles, nanobelts, etc.) has favored the development of sensors with high sensitivity and selectivity combined with low energy consumption. In this work, we have studied the influence of morphology on the sensing gas response of nanostructured copper (II) oxide materials. These materials were previously characterized by structural (X-ray diffraction) and morphological (SEM-FEG and TEM) techniques. CuO crystals are produced in the tenorite phase and have three different morphologies: urchin-like, fiber-like and nanorods. Sensing gas tests were performed using interdigital substrates at different temperatures (200 - 300 Celsius degrees) in an oxygen atmosphere. These measurements demonstrated that all morphologies have p-type conductivity and can detect small amounts of gases (500 ppm) in the environment. However, the sensitivity and response time are directly related to the kind of morphology and vary exponentially with oxygen concentration and temperature. Results confirm that urchin-type morphology has a higher sensitivity (Rgas/Ro = 10) while nanorods have a better response time (16 seconds). These differences may be related to different crystal planes exposed on the surface of structures. In summary, the manufacture of gas sensors based on CuO by controlling the morphology favors this type of application.
9:00 PM - Z5.48
Nanoneedles of Aluminum Oxide (Al2O3) Doped with Tungsten Trioxide (WO3) and Their Application in NO2 Sensor.
Dachi Yang 1 , Jennifer Carpena 1 , Luis Valentin 1 , Oscar Resto 1 , Luis Fonseca 1
1 , University of Puerto Rico. Río Piedras, San Juan United States
Show AbstractWe demonstrate that one-dimensional (1D) nanoneedles of aluminum oxide doped with tungsten oxide (Al2O3@WO3) have been synthesized onto the surface side of aluminum foil with evaporating tungsten oxide source in the opposite. The morphologies of Al2O3@WO3 nanoneedles have been modulated via tuning the oven temperatures and growth duration. The as-grown Al2O3@WO3 nanoneedles show high response to the gas of NO2. Individual and multiple sensor prototypes of Al2O3@WO3 nanoneedles have been developed by integrating nanoneedles with four-point-probe electrodes and inter-digitated electrodes. Our investigation on Al2O3@WO3 nanoneedles provided experimental base both on practical applications of this new material on NO2 sensor prototypes and future nanotechnology.
9:00 PM - Z5.49
Nanowire Based Gas Sensors in Wireless and Power-Autonomous Detector Systems.
Jordi Llosa 1 2 , Mikel Martinez de Marigorta 2 , Jordi Becares 2 , Oriol Monereo 1 , J. Daniel Prades 1 , Francisco Hernandez-Ramirez 1 3 , Ignasi Vilajosana 2 , Sanjay Mathur 4 , Albert Cirera 1
1 Departament d'Electronica, Universitat de Barcelona, Barcelona, Barcelona, Spain, 2 , WorldSensing, S.L.N.E., Barcelona Spain, 3 , Institut de Recerca en Energia de Catalunya (IREC), Barcelona Spain, 4 Department of Inorganic Chemistry, University of Cologne, Cologne Germany
Show AbstractFor years the need of heating the sensing materials has kept the power needed to operate conductometric gas sensors, such as the ones based on metal oxides, above the mW range. Today, the self-heating effect in nanowires allows us to reduce such value to a few μW. This minute power requirements makes possible considering, for the first time, energy harvesting techniques as a suitable power sources for such applications. After the first proof-of-concept devices [4], we present now the fully functional prototypes that integrate individual nanowires, wireless communications and energy harvesting and accumulation systems that features fully autonomous operation.To fabricate the sensors, individual SnO2 nanowires [5] were electrically accessed with the help of a FIB equipment [6]. The signal conditioning and measurement subsystem is based on our previous findings reported elsewhere [7]. The control and communication functionalities are based on the Atmel ZigBit module with integrated 10-bit ADCs, 128KB of data memory and low power wireless communications based in the 812.15.4 protocol and working in the 868MHz frequency. All these components rendered power consumption values lower than 30uW using duty cycling techniques. The power processing subsystem relays on a Si-based photovoltaic panel that stores its energy in a rechargeable battery using a supercapacitor to improve the battery life and the number of charging cycles.The system displays an autonomous response to gases such as CO, NO2, NH3, temperature and humidity that can be recorded remotely with the help of a small embedded computer or a common PC. Stress test showed that the system can keep operating in real Sun illumination conditions continuously without component failure or power drain.This finding, which represents a breakthrough enabled by the use of nanotechnology in sensing applications, paves the way to yet unexplored possibilities in the field of chemical sensing such as multi-spot hazard detection, embedded systems and global awareness applications.References[1] F. Hernandez-Ramirez et al., Physical Chemistry Chemical Physics 11 (2009) 7105-7110[2] E. Strelcov et al., Nanotechnology, 19 (2008) 355502[3] J. D. Prades et al., Applied Physics Letters, 93 (2008) 123110[4] J. D. Prades et al., Sensors and Actuators B-Chemical, 144 (2010) 1 [5] S. Mathur et al., Small, 1 (2005) 713 [6] F. Hernandez-Ramirez et al., Nanotechnology, 17 (2006) 5577[7] F. Hernandez-Ramirez et al., Nanotechnology, 18 (2007) 495501
9:00 PM - Z5.5
Control of the Oxidation at Nickel Surfaces via Surface Alloying.
Badri Narayanan 1 , Ivar Reimanis 1 , Hanchen Huang 2 , Cristian Ciobanu 3
1 Department of Metallurgical and Materials Engineering, Colorado School of Mines, Golden , Colorado, United States, 2 Department of Mechanical Engineering, University of Connecticut, Storrs, Connecticut, United States, 3 Division of Engineering, Colorado School of Mines, Golden, Colorado, United States
Show AbstractControlling the corrosion in materials relevant for aeronautics applications require fundamental understanding of the initial oxidation stages in these materials. While the knowledge accumulated in corrosion control is vast, little of it tackles the initial oxidation stages, especially in materials with fast oxidation kinetics such as nickel or iron. Here we present density functional theory calculations and molecular dynamics simulations of the initial oxidation stages of crystalline nickel surfaces. We study the process of oxygen dissociation at the metal surface, in particular the effect of crystalline surface orientation, of the presence of other metallic species with which Ni forms alloys, and of applied strain. The diffusion of atomic oxygen below the first atomic layer is responsible for the thickening of the oxide layer, and can be controlled by strain. The source of applied strain is the formation of the oxide interface on the metal surface which usually has different lattice constant and surface orientation than the oxide formed on it. We will show that for certain surface orientations, this strain is accommodated by a gradual decay of the concentration of atomic oxygen over several atomic layers into the surface, and also how the oxidation processes can be hampered by the presence of other metallic species (in particular aluminum).
9:00 PM - Z5.51
Microstructure Dependence of Hydrogen Sensing Properties of Palladium Functionalized Tungsten Oxide Films.
Meng Zhao 1 , JianXing Huang 1 , ChungWo Ong 1
1 Applied Physics, The Hong Kong Polytechnic University, Hong Kong China
Show AbstractPalladium (Pd) catalyzed tungsten oxide (WO3) is effective in sensing hydrogen (H2). Further improvements are achieved recently by using nanostructured WO3. In literature, detection sensitivity S (defined as the ratio of the sensor’s resistance in air to that in H2-containing gas), response time tres and recovery time trec vary broadly. We conjecture that the discrepancy of these gas sensing parameters could originate from the variation of their microstructures, which can be specified by grain size D; porosity θ and surface roughness zRMS. In this study, we investigated these dependences, by measuring and comparing S, tres and trec of WO3 films of different D, θ, zRMS produced by using magnetron sputtering performed at various substrate temperatures Ts and pressures P; and supersonic cluster beam deposition (SCBD) technique.For magnetron sputtered films (named as SP1-3), increase of Ts (50 ~ 550°C) mainly results in an increase of D and drop of θ (from 17 – 4%), and increase in zRMS. Crystallization occurred at Ts = 350°C, where D was measured to be ≈ 5 nm. On the other hand, the rise of P (3 ~ 60 mTorr) can greatly enlarge zRMS, but also can increase θ slightly. An SCBD film is an assembly of about 3 ~ 5 nm nanoclusters, such that it has extremely high θ > 40% and the roughest surface of zRMS ≈ 12 nm.Results measured by exposing the samples to 4% H2-argon mixture and air in a test cycle at 60°C are summarized in the Table. (i) SP1 has the highest S, because it contains crystallites of moderate sizes, which should have fairly good H2-induced resistive response. Moreover, the structure is dense enough for the crystallites to contact intimately, facilitating reduction of resistance during hydrogenation. In addition, its surface is relatively rough and can accommodate more catalytic Pd atoms without causing short circuit. The short tres is associated with the high S value, because a substantial fractional change in resistance occurs in a short period of time. Its drawback is the long trec due to the low mobility of reactant species in the dense material structure. (ii) S of SP2 is 100 times lower than that of SP1, because its crystallites are larger, such that the nano-sensing effect is weakened. Its structure is the densest among all samples, explaining why trec is as long as 3000 min. (iii) S of SP3 is the weakest because its highly disordered structure degrades the H2 sensing properties, but its trec is very short due to the large θ. (iv) SCBD film combines the merits of small D, large θ and zRMS. Hence, Pd coated SCBD WO3 film possesses the best compromise of these factors and is supposed to be the best candidate for the use in H2 detection.
9:00 PM - Z5.53
Low Power Consumption Single Nanowire Gas Sensing Devices.
Roman Jimenez-Diaz 1 , Jordi Sama 1 , J. Daniel Prades 1 , Albert Romano-Rodriguez 1 , Francisco Hernandez-Ramirez 2 , Joaquin Santander 3 , Carlos Calaza 3 , Luis Fonseca 3 , Carles Cane 3
1 , University of Barcelona, Barcelona Spain, 2 , IREC, Catalonia Institute for Energy Research, Barcelona Spain, 3 , Instituto de Microelectronica de Barcelona, IMB-CNM-CSIC, Bellaterra Spain
Show AbstractNanowires have emerged as potential building blocks for future electronic devices [1]. However, significant requirements arise from the use of elements with dimensions in the nanometer scale: large scale synthesis of structures with homogeneous properties and reliable, affordable and fast contact fabrication, among others. In this work, a methodology for the fabrication of gas sensors by integrating individual metal oxide nanowires (NWs) as sensing elements and microhotplates for low power consumption and fast operation is presented. SnO2 nanowires with radii in the range 20–200 nm were synthesized by chemical vapor deposition (CVD) of a molecular precursor [Sn(OtBu)4] as described elsewhere [2]. High resolution TEM images of several nanowires showed them to be dislocation free bodies displaying interplanar spacings corresponding to the rutile structure of SnO2; no amorphous shell was observed. Some of these nanowires were dispersed in propylene glycol and, afterwards, a droplet of this solution was spread onto suspended MEMS hotplates which contained integrated microheaters. To guarantee the formation of good electrical contacts between pre-patterned microelectrodes and nanowires, Electron Beam Assisted Deposition and Ion Beam Assisted Deposition processes were performed. These nanowires were electrically contacted using a FEI Strata 235 dual beam instrument equipped with an injector to deposit Pt. The details of this fabrication method were explained in detail elsewhere [3]. Finally, dc electrical measurements were done using a Keithley 2602 Source Measure Unit, enabling the estimation of the key-parameters of these nanowires. The devices were tested using well-controlled environmental conditions of gas and temperature. Metal oxide materials exhibit a temperature dependent response to different gas species when used as chemiresistors [1]. The integration of microheaters in the measuring platform enabled an optimal control of the working temperature, allowing fast and reproducible modulation of the temperature up to 600 K with reduced power consumptions due to the thermal isolation and reduced dimensions of these microhotplates, thus enhancing the mechanism of adsorption and desorption of gas species in metal oxides materials and expediting the use of these nanowires as gas sensors. The obtained results demonstrated that working with microhotplates simplifies the experimental setup and also decreases the power consumption of the devices. Moreover, the huge potential of nanowires as building-blocks of a new generation of devices with improved performances has been exposed. For this reason microhotplate-based technologies are a promising approach for the fabrication of nanosensors in a scalable process.References:[1] E. Comini, Anal. Chim. Acta 568 (2006) 28-40.[2] S. Mathur et al, Small 1 (2005) 713.[3] F. Hernandez-Ramirez et al, Nanotechnology 17 (2006) 5577-5583.
9:00 PM - Z5.55
Harsh Environment Plasmonic Sensing Using an Array of Gold-Metal Oxide Nanocomposite Films.
Nicholas Joy 1 , Manjula Nandasiri 2 , Tamas Varga 3 , Vaithiyalingam Shutthanandan 3 , Weilin Jiang 3 , Ponnusamy Nachimuthu 3 , Satyanarayana Kuchibhatla 3 , Suntharampillai Thevuthasan 3 , Michael Carpenter 1
1 College of Nanoscale Science and Engineering, SUNY Albany, Albany, New York, United States, 2 , Western Michigan University, Kalamazoo, Michigan, United States, 3 , Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractHigh temperature chemical sensing has been demonstrated using an array of thin metal oxide films with embedded gold nanoparticles. The optical technique of plasmonic sensing was used to monitor changes in the absorption spectrum which are the result of changes in the surface plasmon resonant (SPR) frequency on the gold nanoparticles during gas exposures. For the first film, ~270nm CeO2 was grown using molecular beam epitaxy (MBE) and gold was implanted followed by annealing to form nanoparticles. For the second and third films, 30 to 50nm of TiO2 and yttria stabilized zirconia (YSZ) were separately co-sputtered with gold by physical vapor deposition (PVD) and then annealed to form a polycrystalline metal oxide matrix with gold nanoparticles throughout the films. Films were simultaneously exposed to ppm levels of the analytes; H2, NO2, and CO at 5%, 10%, and 21% oxygen background levels at a temperature of 500°C. In order to gauge the potential for gas-selective response, the multivariate method of principal component analysis (PCA) was used for the separate gas exposures. By using changes in absorption intensity at various wavelengths as the input, the results show separate clusters of points in PCA space that correspond to separate analyte gases. This separation means that the sensing response from different analytes can be distinguished, and is a first step towards selective sensing in gas mixtures. While the PCA analysis points to the functionality of the Au-metal oxide nanoscale films and thereby their promise for sensing applications, the sensing mechanism providing the response across the sensing elements will also by highlighted.
9:00 PM - Z5.56
Gas Sensing Properties of SrTi1-xFexO3 Thin Films.
Valmor Mastelaro 1 , Maria Ines Bernardi 1 , Pedro Pellisiari 1 , Luis da Silva 1 , Sergio Zilio 1 , Khalifa Aguir 2 , François Flory 2 , Jacques Guerin 2
1 Physics and Materials Science Department, IFSC - Universidade de São Paulo, Sao Carlos, Sao Paulo, Brazil, 2 CNRS, IM2NP (UMR 6242), Aix-Marseille Université, , Marseille France
Show AbstractDue to the introduction of more stringent regulations governing air-pollution, it becomes important to focus research on the development of low-cost gas sensors in order to access applications where the use of conventional analytical systems is prohibitively expensive [1]. Perovskite based materials has been extensively studied as gas sensors because its structure forms a wide variety of oxides compositions from simple to complexes ones [2]. Moreover, the perovskite oxide is particularly attractive for high-temperature applications because its chemical and physical stability improves the reliability and long-term sensor performance [2]. This work presents preliminary results concerning the gas sensor behavior of SrTi1-xFexO3 thin films around 70 nm of thickness with 0.0 ≤ x ≤ 0.25 obtained by using an electron beam evaporation technique. X-ray diffraction technique showed that all compositions present only a single cubic phase similar to the SrTiO3 compound. The analysis by AFM of the surface morphology of thin films before and after annealing at 500 oC showed that the surface roughness is very small. A decrease in the band gap value was observed as the amount of iron increases. The electrical characteristics of the thin films as a function of sample composition and temperature were evaluated regarding the response to different gases. The better performance concerning gas sensibility was observed when thin films were exposed to O3 gas at 260 oC. Work supported by FAPESP and CAPES (Brazil) and COFECUB (France) [1] K. Sahner, R. Moos, M. Matam, J.J. Tunney, M. Post, Sensors and Actuators B 108, 102 (2005).[2] J. W. Fergus, Sensors and Actuators B 123, 1169 (2007).
9:00 PM - Z5.57
Controllable Synthesis of Zinc Oxide (ZnO) Nanoparticles via Precipitation Method at Low Temperature.
Ozlem Yildirim 1 , Caner Durucan 2
1 Metallurgical and Materials Engineering, Orta Dogu Teknik Universitesi, Ankara Turkey, 2 Metallurgical and Materials Engineering, Middle East Technical University, Ankara Turkey
Show AbstractZinc oxide (ZnO) has attracted considerable attention over the last few decades due to its attractive properties such as wide direct band gap (3.37 eV) and large exciton binding energy (60 meV). With reduction in size to nano scale, novel electrical, mechanical and optical properties can be attained for ZnO nanoparticles due to surface and quantum confinement effects. These unique properties of ZnO provide several advantages in electronic and optoelectronic devices. Meanwhile, due to the special needs in these diverse applications, there has been a strong interest in synthesis of ZnO nanostructures with well-controlled size and morphology. Aqueous precipitation method is especially attractive since it provides possibilities in controlling the size and morphology of the oxide nanoparticles at low processing temperature. In this study, phase pure ZnO nanoparticles with different size and morphology were synthesized by using zinc acetate dihydrate and polyvinyl pyrrolidon (PVP) as zinc source and chelating agent, respectively. Ethylene glycol (EG) or DI-water was used as solvents. The effects of precipitation temperature, chelating agent concentration and solvent type on size and morphology of ZnO nanoparticles have been reported. Analytical characterization of precipitation products was performed by using XRD, SEM, TEM, FTIR, UV and PL-spectroscopy. Phase pure spherical ZnO nanoparticles with average particle sizes changed from 13.0 ± 1.9 nm to 9.0 ± 1.3 nm were synthesized in different precipitation temperature ranging from 25 to 80 °C. Particle morphology of spherical ZnO nanoparticles did not change but particle size decreased from 13.0 ± 1.9 nm to 5.3 ± 0.3 nm with increasing PVP amount. A morphology change from spherical to isosceles triangular shape was observed when DI-water was employed as solvent instead of EG. The results of this study illustrate that highly crystalline ZnO nanoparticles can be directly synthesized at the relatively low temperature (< 80 °C) without any need for subsequent calcination step and size and morphology of nanoparticles can be controlled by precipitation temperature, chelating agent concentration and solvent type. At the end, precipitation mechanism(s) for achieving such physical changes for ZnO nanoparticles has been proposed and discussed in detail.
9:00 PM - Z5.58
Giant Efficiency Enhancement of Solar Cells with Graded Antireflection Layers Based on Syringe-like and Tower-like ZnO Nanorod Arrays.
Liko Yeh 1 , Kun-Yu Lai 1
1 photonics and Optoelectronics, National Taiwan University, Taipei Taiwan
Show AbstractIn this letter, syringe-like and tower-like ZnO NRAs synthesized by the hydrothermal method is demonstrated as an effective AR coating for tandem solar cells. Taking advantage of the nanostructures with favorable tip geometry, the abrupt interface between air and surface layer can be replaced with the engineered AR layers containing the smooth refractive index transition, significantly suppressing the surface reflection on the device over a wide range of wavelengths. This leads to the noticeable improvement of the external quantum efficiencies (EQE). The simulations based on rigorous coupled-wave analysis (RCWA) and finite-difference time-domain (FDTD) analysis show the dependence of the optical power transmitted to the solar cells on the geometry of ZnO nanostructures, further confirming that the improved flatness of the refractive index profile near the air-nanostructure interface is the key to excellent AR performance. Under AM 1.5G illumination, energy conversion efficiency of single junction device is significantly enhanced by up to 32%.
9:00 PM - Z5.6
Characterization of Un-Stabilized Orthorhombic Zirconia Synthesized at Ambient Temperature and Pressure.
Miriam Trubelja 1 , Donald Potter 1 , Karren More 1 , Claudia Rawn 1 , Joseph Helble 1
1 Chemical Engineering, University of Connecticut, Storrs, Connecticut, United States
Show AbstractBulk structures of un-stabilized ZrO2-x with x in the 0 < x < 0.44 range under ambient pressure exist in three different structures (monoclinic, tetragonal and cubic). At ambient temperature and elevated pressures above 3.5 GPa, zirconia, at these compositions, a fourth phase is found, the orthorhombic structure. Work done in this project demonstrates that nanoscale zirconia particles containing the unstabilized orthorhombic cotunnite structure can be produced through a dilute sol-gel method. Extensive characterization of this material including 1) high temperature x-ray diffraction work under four different environments , Differential Scanning Calorimeter, 3) FTIR, etc., indicates that the structure synthesized is linked to the amount and placement of the oxygen vacancy population in the material. The critical factor in determining the structure synthesized appears to be the amount of water (i.e. oxygen) present during the processing. These results also indicate that surface energy alone is not the controlling factor in determining the crystal structure synthesized.
9:00 PM - Z5.60
Post-Growth Fluorine Annealing of ZnO Nanowires.
Abhishek Prasad 1 , Archana Pandey 1 , Yoke Khin Yap 1
1 Physics, Michigan Technological University, Houghton, Michigan, United States
Show AbstractZnO nanostructures are especially promising for applications at the nanoscale. As- grown ZnO nanostructures have native which make it challenging to dope it p-type. Theoretical calculations show interstitial fluorine can generate p-type character in ZnO. To test the hypothesis, here we report on the controlled annealing of ZnO nanostructures in diluted fluorine gas. Zinc oxide nanowires/ nanorods are obtained using Chemical Vapor Deposition. Annealing results show that low temperature and low gas flow rate is best for suppressing the native defects in Zinc Oxide nanowires. As grown and annealed ZnO nanostrucutres were characterized by PL, raman and STM-TEM. Interesting results on role of fluorine in suppressing defects will be presented.
9:00 PM - Z5.61
Physical Properties of Hydrothermally Grown ZnO Nanowires on Seeding Layer Produced by the Atomic Layer Deposition.
Mikhail Ladanov 1 2 3 , Paula Algarin Amaris 1 , Pedro Villalba 4 , Garrett Matthews 5 , Manoj Ram 2 3 , Ashok Kumar 2 3
1 Department of Electrical Engineering, University of South Florida, Tampa, Florida, United States, 2 Department of Mechanical Engineering, University of South Florida, Tampa, Florida, United States, 3 Nanotechnology Research and Education Center, University of South Florida, Tampa, Florida, United States, 4 Department of Chemical and Biomedical Engineering, University of South Florida, Tampa, Florida, United States, 5 Department of Physics, University of South Florida, Tampa, Florida, United States
Show AbstractCurrently, ZnO nanostructures are studied extensively for their applications in a wide variety of devices, such as solar cells, nanogenerators, photovoltaic devices, sensors, and supercapacitors. Such devices require control over the properties of ZnO nanostructures, including, in case of nanowires, their size, shape and density. While there are many ways to grow ZnO nanowires, the most simple, cost-effective and suitable for large scale production is the hydrothermal route. In this process, for ZnO nanowires to grow, the substrate requires a seeding layer, for instance, in a form of thin film of ZnO. Quality of this film directly influences the morphological properties of the resulting ZnO nanowires. Such a film could be grown by several different techniques, including thermal decomposition of zinc acetate, sputtering of ZnO or any other growth technique that provides a polycrystalline ZnO thin film. In this work we have used the atomic layer deposition (ALD) technique to grow the seeding layer of ZnO, and studied how the properties of ZnO thin films grown by ALD affect properties of ZnO nanowires grown on this film using the hydrothermal method. ALD thin films were used both as-grown and annealed in argon and oxygen atmospheres. We have characterized the ZnO thin films by means of atomic force microscopy and grazing incidence X-ray diffraction (XRD), while ZnO nanowires were characterized by means of XRD and scanning electron microscopy.
9:00 PM - Z5.62
Controlled Growth, Characterization and Device Application of ZnO Nanotubes and Nanowires.
Wenjie Mai 1 , Zhiwen Liang 1 , Long Zhang 1 , Kun Wang 1 , Peihua Yang 1
1 Physics, Jinan University, Guangzhou China
Show AbstractControlled growth of nanostructures has long been regarded as one of the biggest obstacles to their commercial applications. Pure ZnO nanotubes and pure nanowires have been respectively achieved by a simply solution method. Concentrations of precursors are found to play a crucial role in determining the morphology of one dimensional ZnO nanostructures. The influences of initial concentration and synthesis time have been systematically investigated. The growth of these slim nanotubes is more likely driven by screw dislocations instead of self-etching. Two different scenarios are proposed to explain the distinct growth of nanotubes and nanowires at different concentrations. Our new findings provide a new perspective on controlled growth of nanotubes and nanowires, and even more complex nanostructures. The large scale of arrays with different one-dimensional ZnO nanostructures should be very useful in fabricating novel devices, such as field emitters and dye-sensitized solar cells.ZnO nanotubes and nanowires fabricated by the above method have been applied as UV-sensitive wettability switches, which changes from superhydrophobicity to superhydrophilicity under UV illumination. Interesting, our ZnO nanotubes and nanowires show different responses to different wavelength of UV lights and this phenomenon has not been reported before. A possible explanation involving their morphology and size is proposed.These n-type ZnO nanostructures have also been grown on p-silicon substrate, with and without graphene sheets in between, forming two kinds of electrical devices. They display different rectifying electrical behaviors, which are potentially useful in semiconductor device applications.
9:00 PM - Z5.64
Highly Efficient and Durable Quantum Dot Sensitized ZnO Nanowire Solar Cell with Noble Metal-Free Counter Electrode.
Minsu Seol 1 , Easwaramoorthi Ramasamy 1 , Jinwoo Lee 1 , Kijung Yong 1
1 , POSTECH, Pohang, Gyungbuk, Korea (the Republic of)
Show AbstractA highly efficient quantum dot sensitized solar cell has been fabricated using CdSe/CdS co-sensitized ZnO nanowire array as a photoelectrode, ordered mesocellular carbon foam (MSU-F-C) as a counter electrode (CE), and a polysulfide electrolyte as a hole transporter. The 1-dimensional nanowire structure grown by facile ammonia solution method provides efficient photoelectron collection and light harvesting, and the CdSe/CdS co-sensitization allows utilization of the whole visible wavelength region of the incident solar spectrum. The ordered mesocellular carbon form used here provides extremely high surface area and the ordered large size mesopores with an interconnected pore structure, which offers more active sites to reduce the redox species and facilitates the diffusion of redox relay in the electrolyte. As a result, it exhibits lower charge transfer resistance (Rct) between the counter electrode/electrolyte interface, and thus presents highly efficient photovoltaic performance, compared to conventional noble metal-based counter electrodes. The cell with MSU-F-C CE yields the highest efficiency of 3.60 %, with open-circuit voltage, short-circuit current density, and fill factor of 685 mV, 12.6 mA/cm2, and 0.42, respectively. Furthermore, it exhibits high durability in the polysulfide electrolyte with remarkable stability irrespective of the solvent used in the electrolyte solution.
9:00 PM - Z5.65
Synthesis and Applications of ZnO/WOx Hierarchical Hetero-Nanowires.
Heejin Kim 1 , Seongho Jeon 1 , Mikyung Lee 1 , Junghan Lee 1 , Kijung Yong 1
1 , POSTECH, Pohang Korea (the Republic of)
Show AbstractOne-dimensional nanostructures have been investigated recently due to their potential applications as building blocks in multiple nano-devices. Especially, the development of hierarchical nanostructure is an increasing research area due to its unique and useful properties. In this research, a novel hierarchical heteronanostructures were fabricated using a simple two step process. The hetero-nanostructure consists of ZnO nanowires as branches and WOx nanowhisker as backbone. Firstly, WOx nanowhiskers were grown on W substrate using a thermal evaporation at 1050°C. Subsequently, ZnO nanowires were grown on the WOx nanowhisker surface via a hydrothermal method at 95 oC. The density and morphology of ZnO nanowires could be controlled with various reaction parameters such as reaction time, growth temperature, and solution compositions. The morphology and crystalline was observed using SEM, TEM, and XRD analysis. Results of nano-structual analysis by SEM, and TEM showed that ZnO nanowires were uniformly deposited on the WOx nanowhisker surface with a diameter 30~50 nm , and a length 1~1.5 μm. In addition, they showed single crystallinity with sharp interfaces between ZnO/WOx NWs. Furthermore, our hierarchical ZnO/WOx heteronanostructures showed enhanced field electron emission properties compared to WOx nanowhiskers. These results indicate that our novel heteronanostructures will be promising electron emitters in future field emission devices.
9:00 PM - Z5.66
Resistive Switching Characteristics of ZnO Thin Film with Multifunctionality.
Seunghyup Lee 1 , Kijung Yong 1
1 Chemical Engineering, POSTECH, Pohang Korea (the Republic of)
Show AbstractResistive switching of materials are widely studied for its potential application to emerging memory device; resistive random access memory (ReRAM). In this study, resistive switching characteristics of simple ZnO thin film device were investigated. The ZnO films were grown on Pt/Ti/SiO2/Si substrate by radio frequency sputtering deposition. With top electrode deposition on the films, metal-insulator-metal (MIM) structures were fabricated and current-voltage (I-V) characteristics of the structures were measured. The structure shows reproducible and stable unipolar resistive switching after electroforming with compliance current. The switching was performed regardless of the applied voltage polarity which suggests the switching can be explained by the formation and rupture of conductive pathways inside the film, which are referred to as the filaments. For emerging application, the structure was fabricated on transparent conducting oxide coated polymer substrate, which is transparent and flexible. The device revealed stable and reproducible resistive switching characteristics while maintaining its transparency and flexibility. Moreover, with the application of hydrophobic ZnO nanorods array over the surface of device, the device revealed water resistant characteristics. That is, the resistive switching characteristics were not degraded even with the certain amount of water pouring all over the device when its electrical characteristics were measured. In summary, multifunctional resistive switching devices with water resistance, flexibility and transparency is studied for its emerging applications.
9:00 PM - Z5.67
Synthesis of ZnO Nanowires by Hydrothermal Technique for Integration into Chalcopyrite Thin Films.
Hakan Karaagac 1 , Saif Islam 1
1 , University of California, Davis, Davis, California, United States
Show AbstractThe effect of substrate on quality of fabricated ZnO nanowires (NWs) was studied by growing on different substrates using hydrothermal growth technique. ZnO seed layer with different thicknesses (varied between 10-750 nm) was deposited onto ITO/soda-lime glass and n- Si wafer (with (100) orientation and 1-10 (Ω.cm) resistivity) substrates. The ZnO seed layer was deposited using radio-frequency (RF) magnetron sputtering. Following the deposition, hydrothermal growth process was applied to ZnO/ ITO/soda-lime glass substrates. The ZnO NWs/ITO/soda-lime substrates were subsequently coated with 2-2.2 μm thick AGIS thin film by electron-beam (e-beam) technique for the construction of the p-n junction. The investigation of the surface morphology of the synthesized nanowires (NWs) has been carried out using scanning electron microscopy (SEM) measurements. It was observed that there are high dense, nearly uniformly distributed and vertically oriented ZnO nanowires (NWs) grown on Si wafer and soda-lime glass substrates. The diameter of the ZnO NWs was ranging from 70 – 125 nm and their lengths were varied between the 0.6-1.1 μm, although some deviations were observed. In addition, we have observed that the thickness of ZnO seed layer has an important effect on the quality of grown ZnO NWs. Moreover, the production of ZnO NWs has been tested using different growth times by keeping the rest of other growth parameters constant, which has shown that the optimum growth time is 2 h. The production of ZnO NWs was followed by deposition of AGIS thin film by electron beam deposition so as to construct the nanowires embedded in a thin film model based p-n junction. It has been shown that the I-V curve exhibits the typical characteristic of a p-n junction, which shows diode behavior with rectification factor around 103 at 1 V.
9:00 PM - Z5.68
Preparation and Photocatalytic Properties of Hybride Core-Shell Reusable CoFe2O4-ZnO Nanospheres.
Armstrong Wilson 1 , Sanjay Mishra 1 , Ram Gupta 2 , Kartik Ghosh 2
1 Department of Physics, Univ Memphis, Memphis, Tennessee, United States, 2 Physics, Astronomy, and Materials Science, Missouri State University, Springfield, Missouri, United States
Show AbstractThe aim of this study is to obtain a magnetically separable photocatalyst, which is stable, reusable, and easy to prepare. In this study the synthesis of core-shell CoFe2O4-ZnO composite hollow nanospheres and its efficacy as photocatalyst is presented. Magnetic material CoFe2O4, also a p-type semiconductor, is used as a catalyst support because of its high magnetic anisotropy, moderate Ms, and high Hc. ZnO an n-type semiconductor is also a suitable alternative to TiO2 due to their similar bandgap energy (3.2 eV) and its lower cost. Magnetic CoFe2O4 and ZnO shell of different thicknesses was deposited onto glucose derived carbon nanospheres using wet-chemical technique to form carbon-CoFe2O4-ZnO hierarchal structure. The photocatalytic efficacy of CoFe2O4-ZnO hollow spheres was assessed by the photocatalytic degradation of methylene blue (MB)300 nm absorption peak, in the presence of UV light. In this paper we discuss the effect of increasing ZnO shell thickness (sample A, B, and C) and efficacy of recycled nanospheres in MB degradation. The XRD pattern of the composite shows the presence of CoFe2O4 and ZnO. The particle size, as assessed by TEM and SEM, was calculated to be 662 nm (A), 722nm (B) and, 786 nm (C), respectively. Increase in the particle size and ZnO XRD peak intensity indicate ZnO shell thickening. Ms of composites decreases with ZnO shell thickening, from value 59.16 (sample A) to 51 emu/g (sample C). The photocatalysis of MB was carried out for 300 min at RT and samples were recovered using external magnet, dried at 100oC for 2 hours, and were reused for photocatalytic study. Surprisingly, there is no perceptible change in the photocatalytic efficacy of samples upon repeated runs, indicating that the magnetically separable photocatalyst is stable and effective for the removal of organic pollutants in water. The degradation rate constant after the first run for samples, A, B, and C was 0.0307, 0.0329, and 0.0374 min-1, respectively. The rate of photodegradation is greater in CoFe2O4-ZnO (C) sample than others. This indicates that the ZnO shell thickness obviously is a photocatalytic activity factor. The observed photocatalysis rate in CoFe2O4-ZnO samples is higher than that observed for pure ZnO NPs. This is probably due to the fact that the hollow spheres with ZnO shell possess an unusual hierarchically nanoporous structure which allows more efficient transport for the reactant molecules to get to the active sites on the framework walls, hence enhancing the efficiency of photocatalysis. The BET surface area of the three samples is 40.2, 42.6 and 44.3 m2/g further supports the above fact. Furthermore, the p-n junction field between CoFe2O4-ZnO also increases the rate of charge separation leading to higher photodegradation efficacy of the composite. The hybrid structure exhibited a good photocatalytic activity in cyclic use, suggesting it’s one of the promising candidates for photocatalytic treatment of the wastewater.
9:00 PM - Z5.69
Crystallization Study of Titania Nanotubes Free Standing Arrays Synthesized by Anodization.
Eugen Panaitescu 1 2 , Pegah Hosseinpour 2 , Joshua Morris 1 , Laura Lewis 2 , Latika Menon 1
1 Physics, Northeastern University, Boston, Massachusetts, United States, 2 Chemical Engineering, Northeastern University, Boston, Massachusetts, United States
Show AbstractTitania nanotubes recently emerged as promising alternatives for applications in solar energy harvesting. They combine the wide gap semiconductor properties of anatase with the high surface area per unit volume and intrinsic carrier paths offered by their nanostructural nature. Titanium oxide nanotubes arrays obtained by anodization of titanium foil are amorphous, and crystallization is usually achieved by annealing at temperatures up to 450°C. Our studies revealed that free standing arrays flaked off the original samples cannot withstand such temperatures, as the nanotubular morphology is collapsing, thus there is a link between nanotubes attachment to the original substrate and structural resistance to high temperature annealing. Differential scanning calorimetry proved that the phase transition to anatase occurs between 270 and 285°C, and low rates, below 1°C/min are required in order to preserve the original morphology at the nanoscale for the free standing arrays. Coupling of differential scanning calorimetry with spectroscopy and imaging techniques allowed us to investigate the role of various annealing parameters in the final properties of the material such as the degree of crystallinity and grain size for better photovoltaic and photocatalytic properties.
9:00 PM - Z5.7
Effect of Chain Length and Solution Composition on Dispersion Interactions within Mixed Monolayers on Nanocrystalline TiO2.
Meghan Kern 1 , David Watson 1
1 Chemistry, University at Buffalo, Buffalo, New York, United States
Show AbstractMetal oxides are a class of materials that exhibit physical stability and many useful optical, chemical, and electronic properties. Titanium dioxide is a wide band-gap semiconductor known for its photovoltaic and photocatalytic activities, as well as its low cost. The properties and reactivity exhibited by the surface can be tailored through functionalization of the TiO2 surface; making it widely used as a platform for applications ranging from chemical sensing to molecular electronics. The fundamental aspects controlling the formation and composition within mixed monolayers (MM) can be influenced by the structure, functionalization, relative abundance, and spatial distribution of the surfactants. Intermolecular interactions between adsorbates, such as disulfide formation, have also been reported to influence the composition of MM.1 This presentation will focus on the effect of dispersion interactions on the composition of MM on nanocrystalline TiO2 films. In this study, MMs formed from coadsorption solutions of equal parts of bromo-terminated (Br) and methyl-terminated (Me) carboxylic acids on nanocrystalline TiO2 were investigated. MMs of BHA and Me, where the number of CH2 groups, n, is 19, underwent dispersion-induced compositional changes. The mole fraction of Me on the surface (χMe,surf) increased on time scales of several hours, well after the establishment of saturation surface coverages. The compositions of MMs equilibrated to equal the compositions of mixed coadsorption solutions. Equilibration was attributed to an increase of dispersion forces between alkyl chains of adsorbed Me, causing these adsorbates to be bound more strongly than BHA to TiO2. The compositional changes were correlated with a red shift of the asymmetric CH2 stretching (νa(CH2)) band in the IR spectra of MMs to lower frequency over time. The magnitude of the spectral shift increased as the alkyl chain length (n) of Me increased. These findings were consistent with an increase of ordering within the monolayer over time and as a function of n.A threshold mole fraction of Me in solution (χMe,soln) was necessary to induce compositional changes. The threshold χMe,soln increased with n, and the rate of compositional changes increased with χMe,soln and n. However, no compositional changes were observed for MMs containing Me with n<14, irregardless of solution composition. A thermodynamic model, derived assuming thermodynamic equilibrium and independent adsorption, accounts for the compositional changes observed within these systems. Our findings illustrate that dispersion forces between adsorbates can influence the extent of ordering and the composition of MMs of alkylcarboxylates on TiO2. 1.Mann, J. R., et al., Influence of Solvation and the Structure of Adsorbates on the Kinetics and Mechanism of Dimerization-Induced Compositional Changes of Mixed Monolayers on TiO2. Langmuir 2009, 25 (20), 12217.
9:00 PM - Z5.70
Investigation on the in-Flame Growth Process of Metal Oxide Semiconductors.
Alessandro Faccinetto 1 , Hans Orthner 1 , Hartmut Wiggers 1 2 , Christof Schulz 1 2
1 IVG, Institute for Combustion and Gasdynamics, University of Duisburg-Essen, Duisburg Germany, 2 CeNIDE, Center for Nanointegration Duisburg-Essen, University of Duisburg-Essen, Duisburg Germany
Show AbstractGas-phase growth processes such as flame synthesis are particularly attractive as a way to produce oxidic semiconductor nanoparticles because of their overall versatility, and in the ideal situation the quality and properties of the synthesized nanoparticles would be directly controlled by selecting the appropriate flame conditions. Among these tunable properties, of utmost importance are the particle size, composition and morphology that play a fundamental role in determining the electrical and optical properties of the synthesized materials. In particular, the nanoparticle stoichiometry and crystal structure can be modified by changing flame parameters like equivalence ratio and temperature.A novel experimental facility has been set up that combines a flame reactor with molecular-beam sampling, in-line particle-mass spectrometry, and in-line time-of-flight mass spectrometry. While the particle-mass spectrometer provides particle size distributions at a given point in the reactive gas mixture, the time-of-flight mass spectrometer simultaneously gives information about the gas-phase composition at the same location. The measurements are further supported by molecular-beam-assisted particle deposition with subsequent ex-situ investigation by transmission electron microscopy and X-ray diffraction for the characterization of size, morphology, stoichiometry, and phase composition, and impedance spectroscopy for electrical characterization. Our interest on this approach is twofold. On the one hand, it provides quantitative information on fundamental processes responsible for the nanoparticles growth in the gas phase. On the other hand, it allows producing high-purity nanoparticles with specific particle-size distributions and stoichiometries directly by controlling the flame conditions.This work focuses on the flame synthesis of metal-oxide nanoparticles such as tungsten, molybdenum, tin and iron oxides in laminar, premixed, low-pressure H2/O2 flames doped with suitable gaseous precursors (halides or carbonyls). Metal-oxide nanoparticles are increasingly demanded for high-tech applications since they offer a wide spectrum of unique properties including structural flexibility, switchable optical properties, and catalytic behavior. We investigate the nanoparticle size distribution and the reaction intermediate concentrations as a function of several parameters, like precursor concentration, particle residence time, equivalence ratio, and fresh-gas velocity. Emphasis is put on the characterization of the synthesized materials as a function of the flame conditions, in order to complete the chemical characterization of the processes taking place during the nanoparticle growth. It is shown that especially tuning and control of the MexOy stoichiometry during particle synthesis plays an important role with respect to electrical and sensing properties, and that these properties are directly related to the reaction conditions during the synthesis.
9:00 PM - Z5.73
Decoration of Metallic Nanoparticles (Au, Pt, and Pd) on Flower-like In2O3 Nanobundles for CO Sensing Applications.
Hsiang-Yu Lai 1 , Chun-Hua Chen 1
1 Materials Science and Engineering, National Chiao Tung University, HsinChu Taiwan
Show AbstractFlower-like In2O3 nanobundles assembled by nanoparticles which couple advantages of the zero- and one-dimensional nanostructures can excellently fit the structural needs for sensor relative applications. Flower-like nanobundles were fabricated by calcination of intermediate compounds, In(OH)3, synthesized by a facile solution route without assistance of any surfactant and template. The decoration of Au, Pt, and Pd nanoparticles on flower-like In2O3 nanobundles were newly designed and fabricated through a chemical reduction approach mainly for purpose of enhancement of CO sensing performance. To our knowledge, the present novel assembles as well as their applications in CO sensing is the first to be reported. The prepared metal nanoparticles functionalized flower-like In2O3 nanobundles exhibit significantly enhanced electrical response and sensitivity on monoxide gas sensing. Metal nanoparticles here have been experimentally proven to act as catalysts to promote the ionosorption of oxygen species and thus greatly improve the CO sensing properties. The further fine structure of the formed nanoparticle assembles as well as its effects on the CO sensing properties will also be qualitatively and quantitatively addressed.
9:00 PM - Z5.74
The Catalyst Effects for Growing Well-Aligned ZnO Nanowire Arrays.
Jinhyun Cho 1 , Sungwoo Yang 2 , Jungsang Kim 1 , Jie Liu 2
1 Electrical and Computer Engineering, Duke University, Durham, North Carolina, United States, 2 Chemistry, Duke University, Durham, North Carolina, United States
Show AbstractIn early 2000, well-aligned vertical ZnO nanowires were achieved using sapphire (Al2O3) or gallium-nitride (GaN) substrates via a gold (Au)-catalyzed vapor-liquid-solid (VLS) method. Although this heteroepitaxy brought some progress in the alignment of ZnO nanowires, the expensive and insulating substrates are incompatible with the fabrication and the commercialization of nano-scaled devices. In addition, the presence of gold catalysts in nanowires potentially decreases optimal performance. Consequently, homoepitaxy using ZnO nanocrystal seeds coated on the surface of silicon (Si) substrates is a more favorable approach in terms of cost and versatility. Although previous reports suggested synthetic methodologies to generate ZnO nanocrystal seeds derived from either zinc acetate combined with sodium hydroxide (NaOH) (or potassium hydroxide (KOH)) or solely zinc acetate, neither of the ZnO nanocrystal seeds obtained using these synthetic methods yield well-aligned vertical nanowires on the amorphous substrate in the VLS process. In this study, we present a novel ZnO catalyst synthesized using ammonium hydroxide (NH4OH) precursor combined with zinc acetate to grow well-aligned vertical nanowire arrays on the amorphous oxide substrate via the VLS method. Unlike zinc acetate-derived seeds, we discovered that hydroxide ion (OH-) from NH4OH were directly used to form zinc acetate, which in turn was the starting material for ZnO seeds. Regardless of the concentration, NH4OH-derived seeds produce well-aligned vertical nanowire arrays. We also demonstrated that sodium ions in NaOH-derived seeds caused the misalignment of nanowires in control experiments. In order to elucidate the catalyst effects on the alignment during nanowire growth, seed orientation was examined using transmission electron microscopy (TEM). Statistical collection of seed orientations evidently exhibited that NH4OH-derived seeds lead to the c-axis alignment of nanocrystal seeds normal to the substrate.
9:00 PM - Z5.75
Nanostructural Crystal Growth and Nanocrystalline Porous Material Fabrication through Low-Temperature E-Field Induced Kinetic Demixing.
Mahmut Aksit 1 , David Toledo 1 , Richard Robinson 1
1 MSE, Cornell University, Ithaca, New York, United States
Show AbstractMetal oxide nanostructures have gained much attention due to their use in field effect transistors, solar cells, display panels, energy storage and thermoelectrics. Here we report a novel method for low cost and large scalable fabrication of nano-structured metal oxides. Electric field induced kinetic demixing was performed at low temperatures on oxides of M1-M2-O, where M1 is one or more of Li, Na, Ca, K, Mg, Sr, and M2 is one or more of Cu, Co, Ni, Fe, Mn, Cr, V. The synthetic procedure involves a) sol-gel coordination of metal ions, b) pyrolysis into oxide flakes, c) pressurized pellet formation, d) electric-field induced kinetic demixing, and e) calcination. The kinetic demixing experiments were performed at much lower temperatures (300 °C or room temperature) compared to previous kinetic demixing techniques in literature (> 1100 °C). Our results show a unique phenomenon not previously reported in literature: an abrupt transition in the concentration of the species is observed after e-field induced kinetic demixing. After the kinetic demixing the material clearly separates into two regions. One of the regions is alkali rich and dense and the other one is alkali deficient and porous. The calcination of the alkali rich part results in extremely large crystals (up to 4 mm) of complex metal oxides with nanosize features (stacked nanosheets). The calcination of the porous part results in very homogonous and porous network of transition metal oxide nano-crystals with micrometer range pore sizes. Preliminary results are shown for electrochemical and thermoelectric measurements using these novel materials.
9:00 PM - Z5.76
On the Correlation of Crystal Defects and Band Gap Properties of ZnO Nanobelts.
Anjana Asthana 1 2 , Kasra Momeni 2 , Abhishek Prasad 3 , Yoke Khin Yap 3 , Reza Shahbazian Yassar 2
1 Material Science & Engg., Michigan Technological U., Houghton, Michigan, United States, 2 Mechanical Engg. & Engg. Mechanics, Michigan Technological University, Houghton, Michigan, United States, 3 Physics, Michigan Technological University, Houghton, Michigan, United States
Show AbstractOne-dimensional (1D) ZnO nanostructures including nanowires and nanobelts are of great interests for field emission applications particularly for flat panel displays, as they can be synthesized in a well-aligned densely packed arrays. With a large exciton binding energy, thermal stability, oxidation resistant and favorable aspect ratio, ZnO nanowires and nanobelts are considered to be an effective field emission source . The field emission properties of the nanostructured materials can be strongly influenced by the presence of localized resonant states . Therefore, it is imperative to estimate the band gap of ZnO nanobelts used as field emission emitters. We report here, the investigations of crystal and electronic structure of the as-synthesized and annealed ZnO nanobelts by in situ high-resolution transmission electron microscope equipped with a scanning tunneling microscopy probe. The in-situ band gap measurements of individual ZnO nanobelts were carried out in scanning tunneling spectroscopy mode using the differential conductance dI/dV – V data. The band gap value of the as-synthesized ZnO nanobelts was calculated to be ~ 2.98 eV, while this property for the annealed nanobelts (~ 3.21 eV) was close to the band gap value for bulk ZnO materials (~ 3.37 eV). The difference in the band gap value of the as-synthesized ZnO nanobelts and annealed ones was attributed to the planar defects (e.g. stacking faults and twins). These defects can alter the electronic structure by producing the localized resonant states that result in band gap reduction.
9:00 PM - Z5.78
Solution Processable Metal Oxide Core-Shell Nanoparticles towards Interparticle Coupling Improvement.
Olivier Margeat 1 , Christine Videlot-Ackermann 1 , Jorg Ackermann 1
1 , CINAM - CNRS, Marseille France
Show AbstractChemical synthesis of nanoparticles (NPs) provides a rich choice of materials (metal or oxide) with precise control on their size, morphology and even atomic structure leading to useful physical and chemical properties. Such colloidal solutions are then processable to form large assemblies of NPs in order to create solid-state devices such as field-effect transistors or solar cells. The main limitation at this point concerns the insulating barrier around each single NP, coming from the use of surface ligands to stabilize the NPs during synthesis.1 The post-synthesis improving of interparticle coupling remains a challenge to fully take the benefit of all the published chemical synthesis of NPs. Few examples deal with post-synthesis complete ligand exchange, usually using small linking organic species showing degradation of the properties with time. Recent results using metal chalcogenide complexes (MCCs) have drawn attention as they could quantitatively replace the organic ligands of NPs, leading to stable colloidal solutions in polar solvents.2-4 The reduced interparticle spacing obtained in that case enables strong electronic coupling between neighboring NPs, yielding films with high mobilities. This approach was successfully applied to various metal and semiconductor NPs, however extension to metal oxide has not yet been reported.In this work, we describe the use of a peculiar MCC (a tin sulfide complex namely SnS44-) as ligand removal agent applied to various semiconductor metal oxide NPs (such as copper oxides, CuO or Cu2O, both p-type semiconductor). This ligand exchange occurs through a phase transfer technique, using hydrazine free (i.e. non-toxic) MCC, and leading to stable colloidal solutions of all-inorganic materials in polar solvents. The quantitative ligand removal has been studied as well as the changes in NPs solubilities. Thin films made by spin-coating of these all-inorganic NPs were realized and studied for photovoltaic properties and transistor applications. In both cases, improvement of the properties highlights better coupling between metal oxide NPs.[1] Law M.; Luther J.M.; Song Q.: Hughes B.K.; Perkins C.L.; Nozik A.J.; J.Am.Chem.Soc. 2008, 130, 5974.[2] Kovalenko M.V.; Scheele M.; Talapin D.V.; Science 2009, 324, 1417.[3] Kovalenko M.V.; Bodnarchuk M.I.; Zaumseil J.; Lee J.S.; Talapin D.V.; J.Am.Chem.Soc. 2010, 132, 10085.[4] Tangirala R.; Baker J.L.; Alivisatos A.P.; Milliron D.J.; Angew. Chem. Int. Ed. 2010, 49, 2878.
9:00 PM - Z5.8
Spontaneous Oxide Nanowire Formation during the Thermal Oxidation of Metals.
Lu Yuan 1 , Yiqian Wang 2 , Rediola Mema 1 , Qingtian Du 2 , Rongsheng Cai 2 , Qike Jiang 3 , Jianbo Wang 3 , Boquan Li 4 , Guangwen Zhou 1
1 Department of Mechanical Engineering & Multidisciplinary Program in Materials Science and Engineering, State University of New York, Binghamton, New York, United States, 2 The Cultivation Base for State Key Laboratory, Qingdao University, Qingdao China, 3 School of Physics, Center for Electron Microscopy and MOE Key Laboratory of Artificial Micro- and Nano-Structures, Wuhan University, Wuhan China, 4 Department of Mechanical Engineering, Worcester Polytechnic Institute, Worcester, Massachusetts, United States
Show AbstractFormation of one-dimensional metal oxide nanowires (NWs) or whiskers has been intensively investigated because of wide technological applications including superconductivity, electronic devices, gas sensing, and heterogeneous catalysis as well as the intrinsic interest in structures with reduced dimensions. More recently, considerable attention has been directed to oxide NW formation by thermal oxidation of metals in oxygen atmosphere, largely due to its technical simplicity and large-scale growth capability. Oxide whisker growth from the oxidation of metals has long been observed; however, a satisfactory growth mechanism for the spontaneous formation of these one-dimensional oxide structures has not yet been established. In this work we present a detailed study of CuO and α-Fe2O3 NWs formation during the oxidation of copper and iron as model systems to understand the mechanism of oxidation-induced oxide NWs growth. Meanwhile, our interest in this system also stems from the prospective broad applications of nanostructured CuO and α-Fe2O3. Our results show that the CuO and α-Fe2O3 NW formation follows the same growth mechanism: For Cu system, there are two oxide layers formed after oxidation; and for the Fe system, there are two or three oxide layers formed depending on the oxidation temperature. Irrespective of their difference in the number of oxide layers formed, the top layer on which oxide NW growth occurs has a limited thickness up to 1 µm and fine grain sizes compared to the inner thick oxide layers which are composed of coarse columnar grains. It is shown that the driving force for NW formation is related to the compressive stresses generated by the CuO/Cu2O interfacial reaction for CuO NW growth and Fe2O3/Fe3O4 interfacial reaction for Fe2O3 NW growth.Cations diffuse along grain boundaries from the region in compression to the outer surface of the oxide layer, which is stress free, and then deposit on the top of oxide grains which serve as the structure template for the NW growth. A kinetic model based on the stress-driven grain boundary diffusion followed by rapid surface diffusion of cations on the sidewall of nanowires is developed to account for the oxide NW growth. The mechanism proposed explains our observations on CuO and Fe2O3 NW formation and other past observations as well as demonstrates a greater universality of the principle of stress-driven NW formation in layered systems, where the stress gradient in thin layers can be introduced via solid-state interfacial reaction or other means.
9:00 PM - Z5.9
Structural/Spectroscopic Study on NiFe2O4 Films Grown on MgAl2O4 and SrTiO3 Single Crystalline Substrates.
Jose Manuel Rebled 1 2 , Sonia Estrade 1 , Michael Foerster 2 , Franco Rigato 2 , Florencio Sanchez 2 , Francesca Peiro 1 , Josep Fontcuberta 2
1 LENS-MIND Electronics, Universitat de Barcelona, Barcelona, Barcelona, Spain, 2 Magnetic Materials and Functional Oxides, ICMAB-CSIC, Barcelona, Barcelona, Spain
Show AbstractFerrimagnetic materials based on spinel structures, such as NiFe2O4, are at the centre of intensive investigations due to their potential applications in spintronic devices, magnetic storage systems, etc. However, when the size is reduced from bulk to nanometre scale, the functionalities (i.e. saturation magnetization) are strongly depending of the growth conditions. Then, a deep understanding of the behaviour of such materials at the nanometre scale, especially in the case of ultra-thin films, has to be achieved.Here we report structural (Transmission Electron Microscopy) and spectroscopic (Electron Energy Loss) analysis on NFO thin films in a thickness range from 3nm to 30nm, grown on top of (001) oriented MgAl2O4 substrate (spinel) and (001) SrTiO3 substrate (perovskite) and using two different processes, i.e., rf-sputtering (RF) and pulsed laser deposition (PLD). Previous reports on the subject attributed the detrimental properties of NFO thin-films on STO substrates to structural reasons, such as antiphase boundaries (APBs), because of the difference in symmetry and the mismatch between the unit cell of both materials. This is in agreement with the more favourable magnetic results when working with spinel substrates, where structural defects are not so abundant. However, our findings indicate that, at least in the case of STO substrate, Ti diffusion through the layer due to interstitial voids in NFO structure can also account, at least partially, for these detrimental magnetic results. Although RF and PLD processes seem to introduce some differences on the grown mechanism (Stranski-Krastanov growth in RF and Volmer-Weber 3D growth in PLD), the Ti diffusion is observed in all the films. Nonetheless, going further on the study, we observe a different behaviour if the STO substrate orientation is changed to (111), where no Ti diffusion is detected and, consequently, better magnetic results are obtained.
Symposium Organizers
Alberto Vomiero University of Brescia
Sanjay Mathur University of Cologne
Zhong Lin Wang Georgia Institute of Technology
Eric Wei-Guang Diau National Chiao Tung University
Z6: Electrical Properties II
Session Chairs
Tuesday AM, November 29, 2011
Room 210 (Hynes)
9:15 AM - **Z6.1
III-V Semiconductor Nanowires Coated with Functional Oxides.
Chennupati Jagadish 1
1 Department of Electronic Materials Engineering , The Australian National University, Canberra, Australian Capital Territory, Australia
Show AbstractNanowires are considered as building blocks for the next generation electronics and photonics. Significant progress has been made in growing nanowires of various materials including elemental and compound semiconductors and functional oxides. III-V composund semiconductors are particularly suitable for high performance electronics and optoelectronic applications. In this talk, I will review our research on III-V compound semiconductor nanowire growth and controlling the size, shape and composition and crystal structure. I will discuss implications of changes in crystal structure on band structure and optical properties. Results on axial and radial heterostructures will be discussed including the growth of III-V nanowires are silicon. I will present our recent work on integrating III-V nanowires with functional oxides by coating these nanowires by using Atomic Layer Deposition and effect of this on optical properties of III-V nanowires. Possible applications of these combined structures will be discussed.
9:45 AM - Z6.2
Fiber-Based Hybrid Nanogenerators for/as Self-Powered Systems in Bio-Liquid.
Caofeng Pan 1 2 , Zetang Li 1 , Wenxi Guo 1 , Jing Zhu 2 , Zhonglin Wang 1
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Materials Science and Engineering, Tsinghua University, Beijing China
Show AbstractHarvesting energy from multiple sources available in environment is highly desirable for building self-powered nanosystems for in-vivo medical applications. Here we present a flexible hybrid nanogenerator, consisting of a fiber nanogenerator (FNG) and a fiber-based biofuel cell (FBFC), which are entirely integrated on a single carbon fiber for simultaneously or independently harvesting mechanical and biochemical energy. The FBFC generates a DC output voltage of 100 mV and current of 100 nA, while the FNG generates an AC output with a peak value of 3 V and peak current of 200 nA. Thus, such a hybrid NG can produce a peak output voltage of 3.1 V and peak current close to 300 nA to function as a power source. Alternatively, the FNG can also serve as a proactive sensor that is powered by the FBFC for quantifying pressure variation in bio-liquid. As the pressure applied on the nanosystem increases from ambient atmosphere P0 to 1.35 P0, the response current of the nanosystem increases nearly 7%. Our hybrid NG provides a new approach for energy harvesting from the environment wherever is a fluctuation in pressure, such as in blood vessel and gas/oil/water pipe, for potential applications in biomedical devices, wireless sensors and environmental/infrastructure monitoring.
10:00 AM - Z6.3
Strain-Gated Piezotronic Logic Nanodevices.
Wenzhuo Wu 1 , Zhong Lin Wang 1
1 School of Material Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractConventional CMOS based logic units are electronically triggered and driven by externally applied gate voltages, which are considered as “static” and are separated from the dynamic mechanical actuation units in nano-electromechanical systems (NEMS). We present the first piezoelectric trigged mechanical-electronic logic operation using the piezotronic effect, through which the integrated mechanical actuation and electronic logic computation are achieved using only ZnO nanowires (NWs). By utilizing the piezoelectric potential created in a ZnO NW under externally applied deformation, strain-gated transistors (SGTs) have been fabricated. Using the SGTs as building blocks, universal logic components such as inverters, NAND, NOR and XOR gates have been demonstrated for performing piezotronic logic calculations. In contrast to the conventional CMOS logic units, the SGT based logic units are driven by mechanical agitation and relies only on n-type ZnO NWs without the presence of p-type semiconductor components. The mechanical-electronic logic units can be integrated with NEMS technology to achieve advanced and complex functionalities in nanorobotics, microfluidics and micro/nano-systems.
10:15 AM - Z6.4
Nano-Scale Template Deposition for Preparation of Functional Oxide Nano-Wire, Nano-Box, and Nano-Dot Materials.
Hidekazu Tanaka 1 , Takayoshi Kusizaki 1 , Atsushi Ono 1 , Azusa N. Hattori 1
1 The Institute of Scientific and Industrial Research, Osaka University, Osaka Japan
Show AbstractA facile process to fabricate integrated functional oxide nano-box arrays, nano-wire and nano-dot is developed. This method can fabricate highly integrated 3D nanostructures with sub-10-nm resolution and high aspect ratio and have a great tuneability in feature shapes, sizes and materials through different combination of imprint molds and target materials of physical vapor deposition. Sidewall deposition using pulsed laser deposition or sputtering onto nano-scale integrated resist templates prepared by nano-imprint lithography enables us to prepare Au1, Mo2, ZnO, (Fe,Zn)3O4 hollow nano box and/or nano-wire arrays whose wall thickness size can be systematically controlled from 100nm down to several ten nm. The ZnO oxide semiconductor nano-box with 30nm wall thickness and nano-wire with 20 nm wire width, have c-axis oriented structures and show intense luminescence peak around 400nm at room temperature. The (Fe,Mn)3O4 ferromagnetic semiconductor nano-wire with 30nm wall thickness also have c-axis oriented structures and exhibited magnetoresistive properties at room temperature. Moreover, using the Mo nano box mask as template for oxide deposition, extremely small epitaxial ferromagnetic semiconductor oxide of (Fe,Mn)3O4 nano-dot structures can be directly grown on sapphire substrates at the deposition temperature of 350C in a pulsed laser deposition process. We also report construction of multi-dimensional oxide nano spintronic device with large magnetoresistance, enhanced spin polarization and so on3-5. This nano-fabrication technique allows us to construct novel functional oxide spintronic/optic devices with well-defined multi-dimensionality.References) H. Tanaka et al., 1 Nanotechnology, 20 (2009) 395301, 2 Nanotechnology 22 (2011)185306, 3 Nano Lett., 9 (2009) 1962-1966, 4 Nano Lett. 10 (2010) 2772-2776, 5 Nano Lett. 11 (2011) 343-347,
10:30 AM - Z6.5
Nanoscale Imaging of the Electronic Conductivity of the Native Oxide Film on Metals Using Conductive Atomic Force Micrscopy.
Tewfik Souier 1 2 , Guang Li 1 , Karim GadElrab 1 , Sergio Santos 1 , Matteo Chiesa 1
1 LENS : Material Science and Engineering, Masdar institue of Science and Technology, Abu Dhabi United Arab Emirates, 2 Service de Physique et Chimie des Surfaces et Interfaces, CEA Saclay, Gif-sur-Yvette France
Show AbstractThe stability of many metals in ambient environments results from the presence of a thin surface oxide layer that acts as kinetic barrier to the transport of ions, molecules, and electrons. For instance, Mo, Ti, Al and FeCr alloys owe their technological usefulness largely to the spontaneous formation of 2-3 nm thick surface film of metal oxide. Although the oxide layer on these metals is chemically stable in most oxidizing conditions, recent reports using scanning electrochemical microscopy (SECM) and scanning Kelvin microscopy (SKPM) demonstrate that microscopic defects sites within the passive film can act as efficient shunt pathway for electron transport. In theory, these defects should be in the sub-micron or nanoscale range as demonstrated in the Point Defects Model. The experimental prove of the existence of such nano-scale defects have been obtained using scanning tunneling microscopy (STM) but only in single crystals. We report in this paper, the electrochemical atomic force microscopy as well as current sensing atomic force microscopy techniques to characterize the native oxide layer on different industrial stainless steels. By means of C-AFM, the obtained current maps reveal that the passive layer of different stainless steels (ferritic, austenitic and Duplex) exhibit a different semiconducting properties. Moreover, highly conductive nanometric spots are observed both inside the grains and at the grain boundaries. The density of these defects is found to depend on the phase content, annealing and strain hardening. Finally, I-V spectra, obtained at nanosclae, offer the possibility to quantify both the band gap and energetic surface states which play important roles in local electrochemical stability. Finally, similar observations have been obtained and discussed both on titanium and aluminum thin films.
Z7: Chemical Sensors I
Session Chairs
Tuesday PM, November 29, 2011
Room 210 (Hynes)
11:15 AM - **Z7.1
Metal Oxide Nanowires as N- and P-Type Semiconductor Chemical Sensors.
Elisabetta Comini 1 , Guido Faglia 1 , Matteo Ferroni 1 , Andrea Ponzoni 1 , Dario Zappa 1 , Giorgio Sberveglieri 1
1 SENSOR, Brescia University and CNR-IDASC, Brescia Italy
Show AbstractNowadays the increasing concerns on the effects of pollution on health and of safety stress the need of real-time monitoring of the environment, therefore there is a remarkable effort in terms of research for the development of sensors devoted to several applications[1,2]. Metal oxide chemical sensors are investigated from more than five decades, their electrical conductivity varies with the composition of the surrounding gas atmosphere. In 1991 Yamazoe showed that reduction of crystallite size went along with a significant increase in gas sensing performances[3] . Therefore the interesting challenge became the fabrication of materials with small crystallize size which keep their stability over long-term operation at high temperature. In traditional polycrystalline gas sensors, the high temperature required for the surface reactions to take place induces a grain growth by coalescence and prevents the achievement of very stable materials. Quasi one-dimensional metal oxide nanostructures have several advantages with respect to their traditional thin- and thick film counterpart such as very large surface-to-volume ratio, dimensions comparable to the extension of surface charge region, superior stability owing to the high crystallinity[4], relatively simple preparation methods, possible functionalization of their surface with a target-specific receptor species[5], modulation of their operating temperature to select the proper gas semiconductor reactions, catalyst deposition over the surface for promotion or inhibition of specific reactions and finally the possibility of field-effect transistors (FET) configuration that allows the use of gate potential to customize sensitivity and selectivity[6].In 2002, the field of semiconductor nanowires underwent a significant expansion and became one of the most active research areas within the nanoscience community[7]. Stimulating advances have been made at an extraordinarily fast rate in different laboratories all over the world following curiosity, discovery or hypothesis driven research. Nowadays it is almost a decade from the first presentation of metal oxide nanowires as chemical sensors. Significant advances have been made both in terms of preparation procedures and their integration into functional sensing devices, while progress in fundamental understanding of their functional properties is slow-moving. In fact, the full integration still remains a challenge that has been wisely approached in different ways. In this presentation we will review the most recent developments in bottom up and top down approaches for chemical sensors application. 1 Samuelson, L. et al. Mater. Today (2003) 6, 22 2 Duan, X.F. et al. Nature (2001) 409, 66 3 Yamazoe, N. Sensors and Actuators B (1991) 5, 7 4 Wang, Z.L. Adv. Mater. (2000) 12, 1295 5 Kolmakov A. Proceedings of SPIE (2006) 6370, 63700X1-8 6 Law, M., et al. Angewandte Chemie Int. Ed. (2002) 41, 2405 7 Xia, Y. N. et al. Adv. Mater. (2003) 15, 353
11:45 AM - Z7.2
Parallel Nanowire Gas Sensors with Combined Resistive-Surface Ionisation Readout.
Francisco Hernandez-Ramirez 1 2 , Juan Daniel Prades 2 , Angelika Hackner 4 , Thomas Fischer 3 , Gerhard Mueller 4 , Sanjay Mathur 3 , Joan Ramon Morante 1 2
1 , Catalonia Institute for Energy Research (IREC), Sant Adrià del Besos Spain, 2 , University of Barcelona, Barcelona Spain, 4 , EADS, Munich Germany, 3 , University of Cologne, Cologne Germany
Show AbstractOne of the main limitations of conductometric gas sensors based on metal oxides is the poor selectivity and important cross sensitivity to common interfering gases such as humidity [1]. In this contribution, gas detection experiments were performed with individual tin dioxide (SnO2) nanowires specifically configured to observe surface ion (SI) emission response towards representative analyte species. The high selectivity of these SI sensors emerges from the dissimilar sensing mechanisms of those typical of standard resistive-type sensors (RES). Therefore, by employing this detection principle (SI) together with RES measurements, better selectivity than that observed in standard metal oxide sensors could be demonstrated [2]. Herein, parallel nanowire device (PND) configurations were used. PNDs consist of a pair of nanowires running parallel to each other while being separated by a small air gap of less than 1 micron width. The first nanowire is a CVD-deposited SnO2 nanowire, contacted to allow conventional resistive (RES) response gas tests. The second nanowire consists of a thin strip of focused ion beam (FIB) deposited platinum, which can be negatively biased with regard the SnO2 and thus, extract positive ions from its surface as the PND is exposed to easily ionisable analyte gases. We present an equivalent circuit model of a PND and show how its observable output parameters can be related to the two orthogonal SI and RES responses. This model was successfully tested by comparison to experimental data obtained on a real prototype PND. Simplicity and specificity of the gas detection as well as low-power consumption make these single nanowire devices promising technological alternatives to overcome the major drawbacks of solid-state sensor technologies, providing extremely useful information.[1] F. Hernandez-Ramirez et al. Phys. Chem. Chem. Phys. (2009) 33, 7105-7110[2] F. Hernandez-Ramirez et al. Nanoscale (2010) 3, 630-634
12:00 PM - Z7.3
Tin Oxide Nanowire Sensor with Integrated Temperature and Gate Control for Multi-Gas Recognition.
Eric Dattoli 1 , Kurt Benkstein 1
1 Biochemical Sciences, NIST, Gaithersburg, Maryland, United States
Show AbstractThe selectivity of a chemiresistive gas sensor comprising an aligned array of single-crystalline tin oxide nanowires is shown to be greatly enhanced by combined temperature and gate voltage modulation. The dual modulation was effected by utilization of a novel microsensor platform that consists of a suspended nitride membrane embedded with individually addressable platinum-heater and back-gate structures. Rapid cycling of temperature and gate modulation was shown to significantly improve analyte recognition accuracy in a volatile organic compound (VOC) discrimination task (μmol/mol levels of ketones and alcohols) as compared to the modulation of one of these parameters alone. Specifically by employing thermal and gate bias cycling in an optimally programmed fashion, a single nanowire sensor was shown to be over 97% effective in achieving correct recognition among three separate VOCs. The good selectivity shown in the results to be presented here demonstrate that the potential exists for nanowire sensors to tackle real-world, multi-chemical detection problems. Moreover to address stability concerns, a practical approach was utilized for obtaining repeatable sensor behavior. Large numbers of single-crystalline nanowires in an array configuration were used as the sensing material in the examined sensor device. By configuring these uniformly structured nanowires in a parallel configuration, repeatable measurements were ensured as wire-to-wire variability would be averaged out across the many nanowires in the array.
12:15 PM - Z7.4
CdS Quatum Dots Sensitized WO3 Thin Film as Chemical Gas Senors.
Isabella Concina 1 , Elisabetta Comini 1 , Saulius Kaciulis 2 , Giorgio Sberveglieri 1
1 Dept. Chemistry and Physics, Brescia University, CNR-IDASC SENSOR Lab, Brescia Italy, 2 , Institute of Nanostructured Materials, CNR-ISMN, Roma Italy
Show AbstractSemiconductor quantum dots (QDs) are attracting a widespread attention due to their outstanding opto-electronic features, making them appealing to be exploited in a variety of domains [1]-[5]. SILAR (successive ionic layer absorption and reaction) is a simple and versatile approach envisaging the in situ generation of naked QDs by means of successive impregnations of a metal oxide (MOX) structure host in solutions containing ionic precursors of the desired semiconductor [6][7][8]. MOX porous structure is believed to provide for both stabilization of QDs and size limitation. This configuration allows an intimate contact between QDs and MOX, thus favoring electron transfers. Since gas sensing working principle relies on interaction between gases and surface atoms of an active layer, semiconductor QDs could be optimal candidates for sensing, due to both high surface-to-volume ratio and the presence of dangling bonds on their surface. Nonetheless, they have been rarely studied since the stabilizers usually employed impair an effective interaction with the environment.In this work we explored the properties of WO3 thin film sensitized with CdS QDs as sensing material. The absence of any capping ligand should preserve the permeability toward gases of the active composite layer and allow QDs to mediate the interaction between the analytes and the MOX surface. CdS QDs were generated on a WO3 thin film surface using both different precursor concentrations (modulation of MOX surface coverage) and number of SILAR cyles (tuning of QDs sizes). Response of the CdS sensitized-WO3 toward several gases has been evaluated at both different temperatures (100, 200 and 300°C) and light conditions (dark, under UV and visible illumination).Growth of CdS QDs is limited, due to the poorly porous structure of WO3, and nanocrystals preserved small size even at high SILAR cycle number (less than 4 nm for 20 cycles at 0.05 M) [9].Composite materials were found to be Cd-enriched in all cases, thus indicating the presence of Cd2+ ions free on the nanocrystal surface with an incomplete coordination sphere capable to interact with external chemicals.An optimal equilibrium between precursors' concentration and number of SILAR cycles allowed for a significant increase in the conductivity of WO3 (up to two orders of magnitude). The features of composite material, as well as performances as gas sensors, will be discussed.[1]M. Bruchez Jr, et al, Science 1998, 281, 2013-2016[2]X. Michalet, et al., Science 2005, 28, 538-544[3]L. Medintz, et al., Nat. Mater. 2005, 4, 435-446.[4]R. C. Somers, et al., Chem. Soc. Rev. 2007, 36, 579-591.[5]J. H. Bang and P. V. Kamat, ACS Nano 2009, 3, 1467-1476.[6]S. Ruhle, et al., Chem. Phys. Chem. 2010, 11, 2290-2304.[7]Y-L. Lee and Y.-S. Lo, Adv. Func. Mat. 2009, 19, 604-609.[8]H.-J. Lee, et al., Nano Lett. 2009, 9, 4221-4227.[9]W. Yu and X. Peng, Chem. Mat. 2003, 15, 2854-2860.
12:30 PM - Z7.5
Analyzing Gaseous Blends with Self-Heated Nanowires in Pulsed-Operation.
J. Daniel Prades 1 , Francisco Hernandez-Ramirez 1 2 , Thomas Fischer 3 , Martin Hoffmann 3 , Ralf Mueller 3 , Nuria Lopez 4 , Sanjay Mathur 3 , Joan Ramon Morante 1 2
1 Departament d'Electronica, Universitat de Barcelona, Barcelona, Barcelona, Spain, 2 , Institut de Recerca en Energia de Catalunya (IREC), Barcelona, Barcelona, Spain, 3 Institute of Inorganic Chemistry, Universität zu Köln, Cologne Germany, 4 , Institut Català d’Investigació Química (ICIQ), Tarragona Spain
Show AbstractOne of the main limitations of conductometric gas sensors based on metal oxides is the poor selectivity and important cross sensitivity to common interfering gases such as humidity. Any of the several solutions proposed so far (i.e. (1) selective absorbing filters, (2) catalytic additives (3) sensor arrays and pattern recognition algorithms or (4) working temperature modulation) yield to a partial solution to the problem.It has recently been reported that self-heating effect in individual metal oxide nanowires [1], can also be used to modulate the sensors’ temperature profile at higher pulsing frequencies, making available the direct observation of the kinetics associated with the chemical interactions between the metal oxide and the gases of interest [2]. These features pave the way to employ the self-heating effect in pulsed operation mode to improve the selectivity and analytical capabilities of metal oxide-based sensors, keeping moderate power requirements.In this contribution we will demonstrate the feasibility of using this approach in individual SnO2 nanowires for the quantitative analysis of carbon monoxide (CO) and humidity (H2O) gas blends [3]. Data revealed that the modulation of the electrical resistance by the effect of CO and H2O increase monotonously with the concentration of both gases but it is not additive, which is a first evidence of the competitive behavior of these two species. Concerning the sensor’s dynamic response, there is also a crossed-influence: for low CO concentrations, the presence of water makes the response time decrease remarkably, even reaching saturation, hinting again to the existence of competitive processes. This surprising acceleration, which was unnoticed before due to the slower dynamic response of common micro-macro sensors, can give way to methods for the quantitative analysis of CO-humidity mixtures by means of one single low power consumption sensor. We will show that, using a simple algorism based on double entry calibration tables of the magnitude of the response and the response time of the sensors to different CO-humidity blends it was possible to discriminate up to 20 different gas mixtures.Finally, experimental response and recovery times of individual SnO2 nanowires toward oxidizing and reducing gases obtained with the here-proposed methodology were related to the reaction barriers redicted by theoretical models and other experimental techniques.References[1] J. D. Prades, et al., Appl. Phys. Lett. 93 (2008) 123110. [2] J. D. Prades, et al., Appl. Phys. Lett. 95 (2009) 053101. [3] J. D. Prades, et al., Appl. Phys. Lett. 97 (2010) 243105.
12:45 PM - Z7.6
Catalysts Modified Indium Oxide Nanoparticle Film Sensor Arrays for Sensing Application.
Kun Yao 1 , Daniela Caruntu 1 , Charles O’Connor 1 , Weilie Zhou 1
1 AMRI/Chemistry, Advanced Materials Research Institute/UNO, New Orleans, Louisiana, United States
Show AbstractHomogenous In2O3 nanoparticles (NPs) with diameters in a range of 7~10 nm were synthesized via a chemical solution method and well assembled on both Si and flexible substrate for gas detections. Based on our previous work on tuning different parameters of NP based sensors, surface modification was found to play the most crucial role in improving the sensitivity. In this presentation, the NP sensor arrays were assembled and modified with different noble metals of Au, Pd and Pt, respectively, showing clearly responses when exposed to several target gases. Besides the highly enhanced sensitivity, such sensor arrays demonstrated a good selectivity like one key to one lock for the targeted gases, which implied that ideal selectivity was possibly to be realized in a certain condition. The particle size dependence of the metal modifiers to the sensitivity was further investigated by tuning the sputtering parameters, and three different trends of sensitivities were observed in different metal modified sensors. Then a sensor fabricated on a flexible substrate was also tested at different bending angles for sensing performance, showing great potential for future application.
Z8: Photoelectrochemical Systems I
Session Chairs
Tuesday PM, November 29, 2011
Room 210 (Hynes)
2:30 PM - **Z8.1
Heterojunction Nanowire Array Films for Solar Energy Conversion.
Craig Grimes 1 , Ningzhong Bao 1
1 State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology, Nanjing, Jiangsu China
Show AbstractWe consider the synthesis of several heterojunction nanowire film architectures and their photovoltaic - photofuel application. The high surface area heterojunction nanowire film topology offers the exciting potential of successfully combining the best attributes of different materials into a low cost, readily synthesized device platform. For example, we consider a novel photocorrosion stable heterojunction WO3/BiVO4 photoanode for photoelectrochemical water splitting. The heterojunction films are prepared by solvothermal deposition of a WO3 nanorod-array film onto fluorine-doped tin oxide (FTO) coated glass, with subsequent deposition of a low bandgap, 2.4 eV, visible light responding BiVO4 layer by spin-coating. The heterojunction structure offers enhanced photoconversion efficiency and increased photocorrosion stability. Compared to planar WO3/BiVO4 heterojunction films, the nanorod-array films show significantly improved photoelectrochemical properties due, we believe, to the high surface area and improved separation of the photogenerated charge at the WO3/BiVO4 interface. Photovoltaic heterojunction nanowire films are made by coating TiO2 nanowire array films by Sb2S3 (stibnite) using a chemical bath deposition technique, with inorganic-organic heterojunction solar cells constructed by depositing poly(3-hexylthiophene, P3HT) on the Sb2S3 surface. Under front-side AM 1.5G illumination typical devices of optimal design show a short-circuit current density of approximately 17 mA cm-2, an open circuit potential of 0.5 V, and fill factors of ≈ 0.6 for power conversion efficiencies of 4.5%. Devices tested over a period of six months showed no degradation in performance. Given the encouraging photoconversion efficiencies of Sb2S3 -based photovoltaics and the abundance of antimony in the earth’s crust relative to that- for example, of Cd or Te, it appears antimony sulfide may offer an exciting opportunity for achieving high efficiency low cost solar cells.
3:00 PM - Z8.2
Alternative Oxides for Quantum Dot and Dye Sensitized Solar Cells.
Arie Zaban 1 , Shay Yahav 1 , Menny Shalom 1 , Shlomit Greenwald 1 , Zion Tachan 1 , Sven Ruehle 1
1 Chemistry, Bar Ilan University, Ramat Gan Israel
Show AbstractQuantum dots (QDs) have recently attracted considerable attention as light absorbers for solar cell applications due to their tuneable size dependent absorption properties. Deposited onto a nano-structured, wide bandgap semiconductor, light to electric power conversion efficiencies (η) up to 4-5% have been achieved. The working principle of QDSCs is similar to dye-sensitized solar cells (DSC) with respect to the photovoltage that is determined by the energy difference between the electron quasi Fermi level (EFn) in the oxide semiconductor and the redox potential (Eredox) of the liquid electrolyte. The photovoltage is, therefore, limited by the energy difference between the conduction band edge (ECB) of the nano-structured film and Eredox. For DSCs with high light to electric power conversion efficiencies the variety of photovoltage determining materials is quite limited, using a mesoporous TiO2 film as the wide bandgap semiconductor in conjunction with an organic I-/I3- redox electrolyte. Recently new electrolytes have shown better photovoltages, however a replacement of the wide bandgap oxide to achieve higher ECB failed to exceed the performance of TiO2. QDSCs are typically sensitized with CdS, CdSe, PbS, or Ag2S QDs in conjunction with an aqueous polysulfide redox electrolyte. In the following we show that QDSCs may benefit from the use of oxides other than TiO2. Recently we showed that QDSCs cannot be simply understood as analogues to DSC with an inorganic sensitizer. The polysulfide electrolyte significantly changes the energy levels of the nano-structured oxide and the QDs. Consequently a number of oxides which show little or no photovoltaic performance in DSCs work rather good in conjunction with QDs and polysulfide. For example, we find efficient electron injection from excited CdSe QD into ZrO2 while electron injection from excited dye states has never been observed. Further differences between DSCs and QDSCs relate to the thickness of the absorber layer which can be increased in QDSCs beyond a QD monolayer. Subsequently the film thickness of the oxide nano-structure can be reduced and new electrode geometries are desired. New results, materials and design concepts for high efficiency QDSCs will be discussed.
3:15 PM - Z8.3
Highly Efficient CdS/CdSe Quantum-Dot Sensitized Solar Cell with Hierarchically Organized TiO2 Nanostructured Films.
Jong Hoon Park 1 , Jun Hong Noh 1 , Dong Hoe Kim 1 , Kug Sun Hong 1
1 Department of Material and Science, Seoul National University, Seoul Korea (the Republic of)
Show AbstractQuantum dot sensitized solar cells (QDSSCs) have attracted much attention recently because of high extinction coefficient and quantum yield of QD sensitizers. However, the reported efficiencies of QDSSCs are low because the conventional mesoporous TiO2 photoelectrode is unsuitable for QDSSCs in terms of assembling QDs on surface of TiO2. Here, we introduce suitable photoelectrode architecture for the QDSSCs synthesized by pulsed laser deposition (PLD) method. Hierarchically organized TiO2 nanostructures composed of 20 nm size anatase nanocrystals were obtained by controlling deposition parameters and the architecture showed unique channel-shaped structure with high porosity. To fabricate QDSSC, CdS and CdSe quantum dots were assembled onto the prepared TiO2 nanostructured film and then ZnS was deposited on QDs as a passivation layer using chemical bath deposition (CBD). The photovoltaic characteristics of the prepared QDSSCs were investigated under 100 mWcm-2 illuminations. The PLD-QDSSC showed remarkably higher fill factor of 64% compared to the reported QDSSCs. In this presentation, we will discuss the improved cell performance for the PLD-QDSSC in terms of unique channel-shaped photoelectrode. This study will offer a clue to prepare suitable photoelectrode for efficient QDSSCs.
3:30 PM - Z8.4
Heterostructured Photoanodes Based on Calcogenides over TiO2 Nanorods Arrays.
Cristian Fabrega 1 , Andres Parra 1 , Teresa Andreu 1 , Joan Ramon Morante 1 2
1 , Catalonia Institute for Energy Research (IREC), Sant Adrià del Besòs, Barcelona, Spain, 2 Electronics, University of Barcelona, Barcelona Spain
Show AbstractTraditionally, metal oxides have attracted the interest of the community as photoanode material because of their good optical, electrical properties and stability to photocorrosion. However, its practical applications are limited by its low efficiency due to the wide band gap, characteristic from metal oxides. Many attempts have been made with the aim of extend the light absorption to the visible region of the solar spectrum (cation and anion doping, noble metals nanoparticles…). The use of other semiconductors with lower band gap as a light absorbers with an appropriate energy band alignment with respect to the metal oxide, have demonstrated to be potentially successful. Among the possible absorbers, calcogenide materials have displayed the best results in terms of efficiency.One of the key parameters that determine the effectiveness of the absorption layer formation is the deposition technique (CBD, SILAR, electrodeposition…).In this work, different deposition techniques of calcogenide materials (CdS, PbS, CuInS2…) over TiO2 nanorods arrays to form heterostructured photoanodes are presented and evaluated from the point of view of hydrogen production efficiency. For each one of the proposed calcogenides, different conditions (pH, precursor concentration, solvent…) have been systematically controlled to determine its influence on the deposited layer and their consequences on the hydrogen production will be discussed.
3:45 PM - Z8.5
Improving the Performance of ZnO-Based Excitonic Solar Cells through Careful Engineering of the Photoanode.
James Bendall 1 , Lioz Etgar 2 , Michael Graetzel 2 , Mark Welland 1
1 Nanoscience Centre, University of Cambridge, Cambridge United Kingdom, 2 Laboratory for Photonics and Interfaces, EPFL, Lausanne Switzerland
Show AbstractZinc oxide (ZnO) nanowires, with their high surface-to-volume ratio and important inherent physical properties, are finding use in a variety of technologically important applications including photovoltaic cells and non-volatile memory devices [1][2]. They can be grown under hydrothermal synthetic conditions to produce highly reproducible structures over large-scale areas at low cost [3][4]. Here we present our latest work on the synthesis, characterisation and usage of advanced zinc oxide nanostructures within photovoltaic devices. Complete optical and morphological characterisation of these structures has been carried out, revealing careful engineering of the morphology, dimensions and surface chemistry. We have developed a number of methods for producing nanowire core-shell structures that show a marked improvement when used in excitonic solar cells (XSCs) [5]. The use of such structures have allowed us to report on one of the highest PV efficiencies for zinc oxide nanowire-based XSCs using a liquid electrolyte and a newly developed organic dye. [1] Efficient ZnO Nanowire Solid-State Dye-Sensitized Solar Cells Using Organic Dyes and Core−shell Nanostructures. N O. V. Plank, I. Howard, A. Rao, M. W. B. Wilson, C. Ducati, R. Sakharam Mane, J. S. Bendall, R. R. M. Louca, N. C. Greenham, H. Miura, R. H. Friend, H. J. Snaith and M. E. Welland J Phys Chem C 113 43 18515 – 18522.[2] Novel nonvolatile memory with multibit storage based on a ZnO nanowire transistor. J.I. Sohn, S.S. Choi, S.M. Morris, J.S. Bendall, H.J. Coles, W-K. Hong, G. Jo, T. Lee & M.E. Welland. Nano Letters (2010) 10 (11) 4316 – 4320.[3] An investigation into the growth conditions and defect states of laminar ZnO nanostructures. J. S. Bendall, G. Visimberga, M. Szachowicz, N. O. V. Plank, S. Romanov, C. M. Sotomayor-Torres and M. E. Welland., J. Mater. Chem., 2008, 18, 5259 – 5266.[4] Investigating the Hydrothermal Growth of Zinc Oxide Nanostructures Through Seed Layer Control. J.S. Bendall & S.C. Tan Zeitschrift für Physikalische Chemie 2011 225(3), 341-350.[5] An efficient DSSC based on ZnO nanowire photo-anodes and a new D-π-A organic dye. J.S. Bendall, L. Etgar, S.C. Tan, N. Cai, P. Wang, S.M. Zakeeruddin, M. Grätzel & M.E. Welland Energy and Environmental Science 2011 (accepted).
Z9: Synthesis of Nanostructured Oxides
Session Chairs
Tuesday PM, November 29, 2011
Room 210 (Hynes)
4:30 PM - **Z9.1
Strategies for Controlled Assembly at the Nanoscale.
Federico Rosei 1
1 EMT, INRS, Varennes, Quebec, Canada
Show AbstractThe bottom–up approach is an alternative for low cost manufacturing of nanostructured materials [1]. It is based on the concept of self–assembly of nanostructures on a substrate. We demonstrate various strategies to control nanostructure assembly (both organic and inorganic) at the nanoscale. We developed various approaches, which include, in particular: (i) deposition on naturally patterned substrates, which exploit long–range reconstructions that can be used to control the adsorption of organic molecules [2]; (ii) we can control the size and luminescence properties of semiconductor nanostructures, synthesized by reactive laser ablation [3]; (iii) we developed new tools to gain atomic scale insight into the surface processes that govern nucleation, growth and assembly [4-8]; (iv) by controlling inter-molecular interactions, we create specific nanoscale patterns including guest/host architectures [9-13]; (v) we developed a simple surface modification strategy for biomaterials which enhances biocompatibility [14-18]; (vi) we devised new strategies for synthesizing multifunctional nanoscale materials to be used for electronics, photovoltaics and catalysis [19-22].We demonstrated the formation of long range ordered patterns in a variety of nanoscale systems, which are potentially interesting for a variety of applications in electronics, biomedicine and energy.References[1] F. Rosei, J. Phys. Cond. Matt. 16, S1373 (2004); [2] F. Cicoira, J.A. Miwa, D.F. Perepichka, F. Rosei, J. Phys. Chem. A 111, 12674 (2007); [3] D. Riabinina, C. Durand, J. Margot, M. Chaker, G.A. Botton, F. Rosei, Phys. Rev. B 74, 075334 (2006); [4] F. Ratto, A. Locatelli, S. Fontana, S. Kharrazi, S. Ashtaputre, S.K. Kulkarni, S. Heun, F. Rosei, Small 2, 401 (2006); [5] F. Ratto, A. Locatelli, S. Fontana, S. Kharrazi, S. Ashtaputre, S.K. Kulkarni, S. Heun, F. Rosei, Phys. Rev. Lett. 96, 096193 (2006); [6] F. Ratto, S. Heun, O. Moutanabbir, F. Rosei, Nanotechnology 19, 265703 (2008); [7] F. Ratto, T.W. Johnston, S. Heun, F. Rosei, Surf. Sci., 602, 249 (2008); [8] F. Ratto, F. Rosei, Mater. Sci. Eng. R 70, 243 (2010); [9] K.G. Nath et al., J. Am. Chem. Soc. 128, 4212 (2006); [10] J. MacLeod, O. Ivasenko, D.F. Perepichka, F. Rosei, Nanotechnology 18, 424031 (2007); [11] K.G. Nath et al., J. Phys. Chem. C 111, 16996 (2007); [12] O. Ivasenko et al., Chem. Comm. 10, 1192 (2009); [13] J. MacLeod et al., J. Am. Chem. Soc. 131, 16844 (2009); [14] L. Richert et al., Adv. Mater. 20, 1488 (2008); [15] S. Clair et al., J. Chem. Phys. 128, 144795 (2008); [16] F. Variola et al., Biomaterials 29, 1285–1298 (2008); [17] F. Vetrone et al., Nanoletters 9, 659 (2009); [18] L. Richert et al., Surf. Sci. 604, 1445 (2010); [19] C. Yan et al., Adv. Mater. 22, 1741 (2010); [20] C. Yan et al., J. Am. Chem. Soc. 132, 8868 (2010); [21] R. Nechache et al., Adv. Mater. 23, 1724–1729 (2011); [22] G. Chen et al., D. Ma, Chem. Commun., in press (2011).
5:00 PM - Z9.2
Rapid Synthesis of Nanocrystalline ZnGa2O4 Phosphor at Low Temperature.
Suresh Kulkarni 1 2 , Srinivasrao Shivashankar 1 2
1 Materials Research Centre, Indian Institute of Science, Bangalore, Karnataka, India, 2 Centre for Nano Science and Engineering, Indian Institute of Science, Bangalore, Karnataka, India
Show AbstractZnGa2O4, an important fluorescent compound semiconducting oxide with a wideband gap, has been recognized as an attractive candidate for phosphor host material for flat panel displays due to its excellent thermal and chemical stabilities. Energy-efficient synthesis of high quality ceramic material such as ZnGa2O4 is still a challenge. The present work reports a novel microwave assisted soft-chemical synthesis technique for the rapid synthesis of phase-pure unsubstituted and substituted ZnGa2O4 nanoparticles and the study of their optical properties. Environment-friendly solvents and non-hazardous metalorganic complexes, namely metal acetylacetonates, were employed as precursors. The reaction mixture is a solution of acetylacetonates of Zn and Ga in 1:2 molar proportion dissolved in a suitable combination of solvents (such as alcohols), together with a surfactant. Under single mode microwave irradiation (2.45 GHz) in a closed chamber, operating pressure can be raised at no extra power consumption, leading to high rate of nucleation forming nanocrystalline, phase-pure ZnGa2O4 of the cubic spinel structure, as verified by XRD and electron microscopy (EDAX). The as prepared ZnGa2O4 are highly crystalline with a crystallite size of ~5nm as calculated by Debye-Scherrer equation. The crystalline spinel oxide is formed at temperatures as low as 170±4oC within two minutes, and at a high yield of 96%, requiring no post-synthesis annealing. Polycrystalline ZnGa2O4 doped with Mn2+, Cr3+, Cu2+, and Co2+ were also prepared using same procedure. The effect of time and temperature on the yield and rate of reaction are studied. ZnGa2O4 can also be synthesized at lower temperature, but longer reaction times are needed, e.g., at 100oC, 15 min of irradiation is required for undoped ZnGa2O4 to have quantitative yield. The ZnGa2O4 nanocrystals without further surface modification can be readily dispersed in chloroform to form a fully transparent colloidal solution using which the bandgap ZnGa2O4 was determined by UV–visible spectrophotometry to be ~4.5 eV. Upon excitation of the ZnGa2O4 powder by UV light (360 nm), intense blue emission was observed, which is surmised to be due to the defect structure in the oxide produced by the synthesis procedure adopted. Entire synthesis procedure, including solution preparation, microwave irradiation, and centrifugation takes about 30 minutes, which is faster than any procedure reported for a complex oxide like ZnGa2O4, as well as one with a small thermal budget. Results of the detailed investigation of the structure, morphology, and optical properties of doped and undoped nanocrystalline ZnGa2O4 will be presented.
5:15 PM - Z9.3
Selective Phase Engineering of Insulator and Metal Phase in Single-Crystal Vanadium Dioxide Nanowires.
Won-Kyung Seong 1 , Ji-Yeong Lee 1 , In-Suk Choi 1 , Kwang-Ryeol Lee 1 , Dae-Joon Kang 2 , Myoung-Woon Moon 1
1 Convergence Technology Laboratory, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 BK21 Physics Research Division, Sungkyunkwan University , Suwon Korea (the Republic of)
Show AbstractStrongly correlated electron materials exhibit many fascinating phenomena, such as ferroelectric materials, high-temperature superconductivity, and metal-insulator transition (MIT). In these materials, competing states can often coexist and form nano- or micro-scale domains of different phase. Vanadium dioxide (VO2) is a strongly correlated material, which undergoes a MIT with a conductivity change of several orders at the critical temperature about 68°C in the unconstrained bulk. Ion beams have been widely used to modify nano-scale structure morphology. In addition to the physical machining, its complicated ion-solid interaction induces bending structure on the nano-scale by extrinsic stresses. Using these stresses, one dimensional nanostructures were showed bending phenomena in the direction of beam incidence. We have fabricated epitaxial VO2 nanowires by using a vapor-phase transport process. Electron microscopy results reveal that single-crystal VO2 nanowires having a [010] growth direction grow on out of the basal r planes of sapphire. We conducted nanowire permanent-bending experiment by using Ar ion beam irradiation to generate precise position and angle-controlled shape. We also describe the influence of permanent bending on the monoclininc to rutile structural phase transition in free standing single-crystal VO2 nanowire by using temperature dependent in-situ transmission electron microscopy, Raman spectroscopy, and focused ion beam (FIB) to permit the systematic electrical transport. In a free-standing VO2 nanowire, the effect of strains as a driving force of bending under reducing condition stabilizes the rutile phase, which in single-crystal nanowires produces the coexisting domain structures. Surprisingly, coexisting rutile and monoclinic domains are observed in free-standing VO2 nanowires at room temperature. We can manipulate ordered arrays of metallic and insulating domains along single-crystal nanowire of VO2 by continuously tuning the bending over a wide range of value. These insights open the door toward more systematic approaches to synthesis for VO2 nanostructures in desired phase and to use for application including ultrafast optical switching, smart window, meta-material, resistance random access memory (RAM) and synapse devices.
5:30 PM - Z9.4
Synthesis, Structural and Luminescence Properties of Rare-Earth Doped Titanate Nanoribbons.
Carlos Diaz-Guerra 1 , Polona Umek 2 , Javier Piqueras 1
1 Facultad de Físicas. Depto. Física de Materiales, Universidad Complutense de Madrid, Madrid, Madrid, Spain, 2 , Jozef Stefan Institute, Ljubljana Slovenia
Show AbstractControlled synthesis and doping is required for device integration of metal-oxide nanostructures. In particular, titania (TiO2) and titania - based nanostructures are interesting materials for potential applications in optoelectronics, ion-exchange processes, photocatalysis, gas sensors and fuel-cell electrolytes [1]. Doping of titanate nanostructures with optically active ions, such as rare earth (RE) ions, opens the possibility of integration of these materials as emitters in a wide interval of wavelengths covering the ultraviolet, visible and near infrared spectral ranges. However, due to the large radius mismatch between RE3+ and Ti4+ ions and their charge imbalance, it is difficult to incorporate RE dopants into the titanate lattice through diffusion processes or chemical methods [2]. In this work, protonated titanate nanoribbons were grown by a hydrothermal method [3] and were ex-situ doped with Eu3+ and Er3+ ions and thermally treated at 100 an 400 oC for 10 h. The morphology, composition and structural properties of the samples were investigated by scanning electron microscopy, energy-dispersive X-ray microanalysis, Raman spectroscopy, X-ray diffraction and transmission electron microscopy. The luminescence properties of the nanostructures were assessed by photoluminescence (PL) in a confocal microscope, photoluminescence excitation (PLE), and cathodoluminescence (CL) spectroscopies.The obtained results demonstrate the effective incorporation of both Er and Eu in the titanate nanostructures. Er3+ intraionic transitions give rise to two groups of emission lines in the green (520 – 570) nm and red (645 – 690) nm spectral ranges, while emission related to Eu3+ intraionic transitions, detected in the (540 - 710) nm range, appears peaked at 614.4 nm. Measurements carried out at different excitation conditions, reveal that effective luminescence emission from the RE3+ ions is achieved through the band absorption of the titanate host matrix rather than trough the intrinsic transitions between RE3+ ion levels. Moreover, our PL and PLE measurements suggest that Er3+ ions may occupy two different sites in the crystal structure of the doped nanoribbons and that Eu3+ takes a low symmetry site without an inversion center in the host lattice.[1] A. Hagfeldt and M. Grätzel, Chem. Rev. 95 (1995) 49.[2] Wenqin Luo, Renfu Li,Guokui Liu, Mark R. Antonio, and Xueyuan Chen, J. Phys. Chem. C 112, 10370 (2008).[3] P. Umek, P. Cevc, A. Jesih, A. Gloter, C.P. Ewels, and D. Arcon, Chem. Mater. 17, 5945 (2005).
Symposium Organizers
Alberto Vomiero University of Brescia
Sanjay Mathur University of Cologne
Zhong Lin Wang Georgia Institute of Technology
Eric Wei-Guang Diau National Chiao Tung University
Z10: Nano-Oxides for Energy Storage I
Session Chairs
Wednesday AM, November 30, 2011
Room 210 (Hynes)
9:15 AM - **Z10.1
Engineering Nanostructured Electrodes Away from Equilibrium for Lithium-Ion Batteries.
Guozhong Cao 1
1 Department of Materials Science and Engineering, University of Washington, Seattle, Washington, United States
Show AbstractThe development of nanostructured electrode material is regarded as one of the key potentials for the further advancement in lithium-ion batteries. This presentation summarizes our recent efforts in the synthesis and characterization of nanostructured metal oxide electrode materials for high-performance Li-ion batteries, and electrode materials include manganese oxide nanowall arrays, vanadium oxide nanofibers, vanadium oxide - carbon nanocomposites, and titanium oxide nanotube arrays. Enhanced Li+ intercalation capacities, improved rate capabilities and better cyclic stability were achieved by architecting micro- or nanostructure, controlling materials crystallinity and introducing desired defects on surface and/or in bulk. The fabrication of binderless and additive-free nanostructured electrodes for Li-ion batteries via sol-gel processing is also high-lighted.
9:45 AM - Z10.2
Non-Aqueous Sol-Gel Routes to Metal Oxide Nanostructures for Li-Ion Batteries.
Andrea Pucci 1 , Seunghwan Baek 2 , Seung-Ho Yu 2 , Marc-Georg Willinger 3 , Dong-Chan Lee 2 , Yung-Eun Sung 2 , Nicola Pinna 1 2
1 Chemistry and CICECO, University of Aveiro, Aveiro Portugal, 2 School of Chemical and Biological Engineering, Seoul National University, Seoul Korea (the Republic of), 3 Department of Inorganic Chemistry, Fritz Haber Institute of the Max Planck Society, Berlin Germany
Show AbstractNon-aqueous sol-gel routes are elegant approaches for the synthesis of nanomaterials such as, metal oxide nanocrystals [1] and ordered organic-inorganic hybrid materials [2]. These routes involving the reaction of metal oxide precursors in organic solvents (e.g. benzyl alcohol) at moderate temperature and pressure, offer advantages such as high crystallinity of the as synthesized oxides, high purity, high reproducibility and the ability to control the crystal growth without the need of additional ligands. Moreover, non-aqueous sol-gel is particularly suitable for one-pot synthesis of multi-metal oxide and doped materials [3].In this communication, after an introduction to non-aqueous sol-gel routes to inorganic nanocrystals, we will present our recent work on the synthesis of nanostructured oxide materials for Li-ion battery targeting high power applications. We will especially focus on:i) A simple surfactant and template-free synthesis of crystalline Li4Ti5O12 nanostructures based on the “benzyl alcohol route”. The solvothermal treatment of lithium and titanium alkoxide in benzyl alcohol leads to 1-2 µm sized hierarchically structured spherical particles which are constituted of platelet-like nanocrystallites in the size range of a few nm. This is the first report showing that crystalline Li4Ti5O12 can be directly obtained by soft chemistry solution routes. The as synthesized crystalline nanostructures show good lithium intercalation/deintercalation performances even at high rate (up to 30C) and good cycling stability. Thermal treatment of the nanostructures at 750 °C improves the performances, approaching the theoretical capacity of Li4Ti5O12 with no noticeably (less than 5%) capacity loss after 200 cycles [4].ii) Metal oxides/carbon nanostructured composites. Here, the “benzyl alcohol route” is used for the one-pot fabrication of composite nanostructures based on SnO2 and Fe3O4 nanoparticles leading to high capacity and high rate anode materials. In these works the synthesis and characterization of the oxide-based nanostructures will be presented together with their electrochemical properties.References[1]N. Pinna, M. Niederberger, Angew. Chem. Int. Ed., 2008, 47, 5292-5304. [2]N. Pinna, J. Mater. Chem., 2007, 7, 2769-2774.[3]N. Pinna, M. Karmaoui, M.-G. Willinger, J. Sol-Gel Sci. Technol., 2011, 57, 323.[4] S.-H. Yu, A. Pucci, T. Herntrich, M.-G. Willinger, S.-H. Baek, Y.-E. Sung, N. Pinna, J. Mater. Chem., 2011, 21, 806-810.
10:00 AM - Z10.3
Nano-Sized Thin and Highly-Conformal Oxide Coatings for Enhanced Cycleability of Li-Ion Battery Cathodes.
Dongsheng Guan 1 , Ying (Jane) Wang 1
1 Mechanical Engineering, Louisiana State University, Baton Rouge, Louisiana, United States
Show AbstractSpinel LiMn2O4 suffers from severe dissolution when used as a cathode material in rechargeable Li-ion batteries. Surface coatings of metal oxides can alleviate the dissolution and enhance the capacity retention of LiMn2O4. Currently these oxide coatings are usually non-uniform and incomplete, because most of them are achieved by wet chemistry methods which lack controllability. Herein we present a study about using the atomic layer deposition (ALD) method to deposit ultra-thin and highly-conformal Al2O3 coatings onto LiMn2O4 cathodes with precise thickness-control at atomic scale, for enhanced cycleability of the cathodes. In this study, XPS technique has been used to detect Al element on the surface of coated cathodes; SEM images show that coated particles preserve the original shape of bare particles, indicating that the ALD coating is highly conformal; high-resolution TEM images confirm the growth of uniform and nano-sized thin coatings around the LiMn2O4 particles. Both bare and ALD-coated cathodes have been assembled into CR2032 coin cells, which are cycled at a current density of 240 mA/g (2C) in a potential range of 3.4~4.5 V (vs. Li/Li+) for electrochemical measurements. The ALD-coated cathodes exhibit significantly improved cycleability compared to bare cathodes at both room temperature and 55 degreeC. For example, the cathode coated with 4 Al2O3 ALD layers (~0.8 nm thick) delivers an initial capacity of 73.8 mAh/g and a final capacity of 58.5 mAh/g after 50 electrochemical cycles, showing the capacity retention of 79.3% at room temperature, while bare cathode delivers an initial capacity of 85.1 mAh/g and a final capacity of 43.6 mAh/g, showing a capacity rention of only 51.2%. The ALD-coated cathodes also demonstrate improved cycleability when cycled at 55 degreeC. Such enhanced electrochemical performances of ALD-coated cathodes are ascribed to the high-quality ALD oxide coatings that are ultra-thin, highly-conformal, dense, complete, and thus protect active material from severe dissolution into electrolyte. In addition, cycling performances of coated cathodes can be optimized easily by manipulating coating thicknesses via varying ALD growth cycles. We have varied ALD growth of oxide coatings from 2 to 10 ALD layers (from 0.4 nm to 2 nm thick), and found that the cathode coated with 4 Al2O3 ALD layers (~0.8 nm thick) shows the best cycleability.
10:15 AM - Z10.4
Nanostructured Bilayered Vanadium Oxide Electrodes for Rechargeable Sodium-Ion Batteries.
Sanja Tepavcevic 1 , Vojislav Stamenkovic 2 , Christopher Johnson 3 , Tijana Rajh 1
1 CNM, Argonne National Laboratory, Argonne, Illinois, United States, 2 Materials Science Division, Argonne national Laboratory, Agronne, Illinois, United States, 3 Chemical Sciences and Engineering Division, Argone National Laboratory, Argonne, Illinois, United States
Show AbstractFabricating electrodes with high discharge/charge capacity, good stability and excellent coulombic efficiency is of great interest to the scientific community. Nanostructured thin films of layered vanadium oxide, prepared by electrochemical deposition on Ni substrate, have been used as a cathode for rechargeable Na-ion batteries. In order to understand role of initial crystal structure on electrode performance we investigated two nanostructured V2O5 electrodes: bilayer-V2O5 and orthorombic-V2O5. Ex-situ and in-situ synchrotron characterizations revealed presence of an electrochemically responsive bilayer structure with intralayer spacing that accommodates intercalation of Na+ ions. Sodium intake induces organization of overall layered structure with appearance of both long and short-range order, while deintercalation is accompanied with the loss of long-range order whereas short-range order is preserved. The bilayer-V2O5 electrodes exhibit higher electrochemical activity and higher stable reversible capacity on repeated cycling than its orthorhombic counterpart. In the 3.8 to 1.5 V range significantly large specific capacity of 250 mAh/g at C/8 was achieved with bilayer-V2O5 as compared to only 150 mAh/g with orthorhombic-V2O5 at 20 mA/g. The electrodes were stable to repeated cycling and during prolonged galvanostatic cycling (up to 350 cycles) the average capacity of bilayer-V2O5 electrodes remains at 85% of its initial value. The stability evaluation during charge-discharge cycles exhibited a highly efficient 3 V (versus Na/Na+) cathode material with excellent performance and high energy density of ~ 760 Wh/kg, which demonstrates that vanadium oxide based electrodes are highly capable for advanced energy storage applications.
10:30 AM - Z10.5
Charge-Storage Processes in Model MnO2-Li-HOPG Systems: UHV-STM Investigations.
Satyaveda Bharath 1 , Wentao Song 1 , Kevin Zavadil 2 , Janice Reutt-Robey 1
1 Chemistry and Biochemistry, University of Maryland, College Park, College Park, Maryland, United States, 2 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractNanostructured materials have the potential to substantially improve the speed, efficiency, and cyclic lifetime of energy storage systems such as the lithium-ion battery (LIB). Nanometer-scale oxide cathodes elements allow for greater extent of lithium incorporation due to improved strain accommodation relative to conventional cathode structures. Exposed surface facets in structures with high surface/volume ratio will act as gateways to lithium insertion, playing an important kinetic role in charge storage. However, detailed mechanisms of lithium insertion and their dependence on oxide facet orientation and grain size and shape are largely unknown. As a platform for fundamental investigations of charge-transfer processes in nanocrystalline materials, we have developed a MnO2-Li-HOPG model system. This system consists of low-dimensional β-MnO2 and cubic spinel Li1+xMn2-xO4 nanocrystallites, synthesized by the reactive co-deposition of elemental manganese (Mn) and molecular oxygen (O2) on native and modified graphite (C(0001)) supports under ultrahigh vacuum conditions. Nanocrystallite phase and composition has been confirmed using single particle electron diffraction, as well as TOF-SIMS and scanning AES. Morphology of individual nanocrystallites, and their registration to the C(0001) support, have been determined with ambient AFM and UHV STM methods. The morphological response of β-MnO2 nanocrystallites to Li+ insertion has been preliminarily explored under solid-state conditions with UHV-STM. The sensitivity of these methods are currently limited by low β-MnO2 – C(0001) electrical conductivity, and efforts to overcome this limitation will be described.Supported by the Science of Precision Multifunctional Nanostructures for Electrical Energy Storage (NEES), an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (BES) under award DESC0001160.
Z11: Photoelectrochemical Systems II
Session Chairs
Wednesday PM, November 30, 2011
Room 210 (Hynes)
11:15 AM - **Z11.1
Electron Transport and Recombination in Nanostructured Metal-Oxides.
Juan Bisquert 1
1 , Universitat jaume I, Castello Spain
Show AbstractThe use of metal-oxide nanostructures in energy harvesting systems such as dye-sensitized solar cells requires to determine a number of properties concerning the transport and loss of the harvested electrons that must reach a collecting substrate. A powerful method for the determination of such properties is impedance spectroscopy, that provides resistances and capacitances that when properly interpreted determine charge transfer and transport rate. However, it is very important to measure the properties at varying electrode potential, which causes a strong variation of electron density in the metal oxide. We show the application of these methods, how they provide fundamental insights to the basic electronic processes occurring in nanostructured metal oxides, and how the methods are applied to establish device properties.
11:45 AM - Z11.2
Effects of Interfacial Charge-Transport Behavior on the Performance of the TiO2 Nanotube-Based Dye-Sensitized Solar Cells.
Lu-Lin Li 1 , Eric Wei-Guang Diau 1
1 Department of Applied Chemistry, National Chiao Tung University, Hsinchu Taiwan
Show Abstract Self-organized anodic titania nanotube (TNT) arrays have a great potential as materials for photocatalysis, gas sensing, self-cleaning and lithium batteries, especially in dye-sensitized solar cells (DSSC). Electrochemical anodization is a facile and widely used technique for growing well-ordered TNT arrays on Ti foil directly. Although one-dimensional nanotube arrays feature excellent charge collection efficiency due to their rapid electron transport and slow charge recombination, the interfacial properties between TNT and substrate are important factors to be considered for affecting the electron transport properties of the TNT-DSSC devices. In this study, we demonstrate the enhancement of the charge-collection efficiency by decreasing the interfacial impedances for both the back- and the front-side illuminated TNT-DSSC devices.We report a method of detachment and transfer of TNT arrays inversely onto a transparent substrate of conducting oxide to fabricate dye-sensitized solar cells with illumination from the front side. The ordered TNT arrays were produced by first anodization at 60 V for 8 h. After annealed at 460oC for 1 h, the as-prepared TNT arrays were detached by the second anodization at 20 V for 4 h. The detached TNT arrays were then transferred and attached inversely onto a TCO substrate. Dry etching of the NT surface in a highly dense plasma reactor under BCl3/Cl2 for 90 s opened previously closed ends of the tubes. The inverted (bottom-up) TNT–TCO substrate was fabricated into a DSSC device that shows a cell performance (η = 6.24%) significantly improved over those of a front-illuminated counterpart with an upright (face-up) structure (η = 4.84%) due to the reduced interfacial impedance of the former device. Furthermore, we found that the performance of the back-side illuminated TNT-DSSC devices is hindered by a thin compact layer of rutile TiO2 underneath the nanotubes after annealed. Based on the synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy, a pure anatase TiO2 was found in the detached TNT arrays; whereas a mixture of rutile and anatase TiO2 was obtained in the TNT/Ti substrate due to the compact layer involving the rutile phase. Electrochemical impedance spectroscopy (EIS) measurements have also been carried out to understand the electron transport property of the interface.References: 1. C.-C. Chen, H.-W. Chung, C.-H. Chen, H.-P. Lu, C.-M. Lan, S.-F. Chen, L. Luo, C.-S. Hung and E. W.-G. Diau, J. Phys. Chem. C, 2008, 112, 19151.2. L.-L. Li, C.-Y. Tsai, H.-P. Wu, C.-C. Chen, E. W.-G. Diau, J. Mater. Chem., 2010, 20, 2753.3. L.-L. Li, Y.-J. Chen, H.-P. Wu, N. S. Wang, E. W.-G. Diau, Energy Environ. Sci., 2011 (DOI: 10.1039/c0ee00474j).
12:00 PM - Z11.3
Electron Transport and Recombination in Electrodeposited, Dye-Modified Nano-ZnO.
Melanie Rudolph 1 , Ushula Mengesha Tefashe 2 , Gunther Wittstock 2 , Derck Schlettwein 1
1 Institute of Applied Physics, Justus-Liebig-University Giessen, Giessen Germany, 2 Department of Pure and Applied Chemistry, Carl von Ossietzky University of Oldenburg, Oldenburg Germany
Show AbstractIn dye-sensitized solar cells (DSCs), electron transport and recombination reactions are strongly influenced by surface electronic states in the nanostructured, dye-modified metal oxide photoanode. One important aspect is the question of how the electronic structure at the surface and thereby charge transfer across the oxide/electrolyte interface is influenced by the presence of the surface-bound dye molecules. The aim of the present study was to clarify how modifications of the surface of electrodeposited zinc oxide by adsorption of indoline dye molecules like D149 affect recombination as well as charge transport within the nanostructured ZnO matrix. For this purpose, mesoporous zinc oxide films were prepared by electrochemical deposition in the presence of the template molecule eosinY, followed by removal of the template. The films were modified by adsorption of different amounts of the sensitizer molecule D149. Structural characteristics like porosity, film thickness and dye loading were determined. The photoelectrochemical properties of the samples were analyzed in contact with the iodide/triiodide redox couple. Charge transport and recombination were characterized based on determination of electron diffusion coefficients and electron lifetimes by means of time-resolved photocurrent and photovoltage measurements as well as intensity-modulated photovoltage and photocurrent spectroscopy (IMVS and IMPS). The kinetics of charge transfer between electrolyte and photooxidized sensitizer molecules at the ZnO surface were investigated as a function of dye coverage using scanning electrochemical microscopy (SECM) [1]. The applicability of the dye-modified zinc oxide films as photoanodes in DSCs was assessed based on photovoltaic properties determined by current-voltage characterization. The combined results of photoelectrochemical and SECM measurements suggest that the average distance between adsorbed dye molecules plays a critical role both for the rate of dye regeneration as well as for the overall photocurrent. Further correlations between structural and functional parameters of the dye-sensitized zinc oxide films will be discussed. [1]U. M. Tefashe, T. Loewenstein, H. Miura, D. Schlettwein, G. Wittstock, J. Electroanal. Chem. 2010, 650, 24.
12:15 PM - Z11.4
Fabrication of Hierarchically Structured ZnO Photoanodes for Highly Efficient Dye Sensitized Solar Cells.
Nafiseh Memarian 2 , Isabella Concina 1 , Antonio Braga 1 , Alberto Vomiero 1 , Seyed Mohammad Rozati 2 , Giorgio Sberveglieri 1
2 Physics Department, University of Guilan, Rasht Iran (the Islamic Republic of), 1 Dept. Chemistry and Physics, Brescia University, CNR-IDASC SENSOR Lab, Brescia Italy
Show AbstractZnO photoanodes are recently applied as promising alternatives to traditional TiO2 in dye sensitized solar cells. We report hierarchically structured ZnO films as the photoanodes in DSCs for the enhancement of photoconversion efficiency, based on three main concepts: (i) high optical density of the sensitized layer, allowing complete light absorption in the spectral range of the dye; (ii) high light scattering of the absorbing layer, in order to enhance the residence time of light inside the sensitized film and improve light absorption; (iii) inhibition of back reaction, which causes electron recombination between the conducting layer at the anode and the electrolyte. The films are prepared by the simple, cheap and large area scalable spray pyrolysis method. The films are composed of polydispersed ZnO aggregates consisting of nanosized crystallites. The aggregates are submicrometer-sized and, thus, can act as efficient light scattering centers, while the nanoparticles deliver the mesoporous structure and the high specific surface area needed for high dye loading. Additionally, a ZnO compact buffer layer is formed between the conducting substrate and the layer composed of polydispersed aggregates. Such a layer can efficiently act as a blocking layer for the back reaction between the conducting glass at the anode and the electrolyte, preventing electron recombination and improving the functional properties of the cells. Optimized structure led to high light absorption, efficient electron transport and collection, inhibition of back reaction electron recombination, and resulted in unprecedented overall photoconversion efficiency up to 7.4%, which is higher than 6.58% for ZnO nanoparticles [1] and 5.4% for hierarchically structured ZnO without blocking layer [2],[3].[1]M. Saito, S. Fujihara Energy Environ Sci 2008, 1, 280-283.[2]Q. Zhang, T. P. Chou, B. Russo, S. A. Jenekhe, G. Cao Angew Chem Int Ed 2008, 47, 2402-2406.[3]H.-M. Cheng, W.-F. Hsieh Energy Environ Sci 2010, 3, 442-447.
12:30 PM - Z11.5
Fabrication and Characterization of ZnO Microflowers as Highly Efficient Photoanodes for Quasi-Solid State Dye-Sensitized Solar Cells.
Chao Zhu 1 , Yan Tao Shi 1 , Chun Cheng 1 , Kwok Kwong Fung 1 , Ning Wang 1 , Lin Wang 1
1 Physics, Hong Kong University of Science and Technology, Hong Kong Hong Kong
Show AbstractDeveloping highly efficient ZnO hierarchically structured photoanodes, especially those with excellent electrical performances, is meaningful so as to realize further photovoltaic promotions for dye-sensitized solar cells (DSCs). Here, we report a simple method (direct precipitation from solution at room temperature) for mass production of ZnO microflowers (MFs) that are constructed by interlaced single crystalline and porous ZnO nanosheets with dominant surfaces of {11-20} planes as determined by transmission electron microscopy. Because the nanosheets formed a hierarchical structure in the MFs, the photoanodes made from the MFs showed excellent performance in quasi-solid (using PEO gel electrolyte) dye-sensitized solar cells (DSCs). Because of the novel ZnO hierarchical nanostructures, the MF photoanodes not only maintained the advantages of ZnO nanostructure such as in dye-loading and light-scattering, but also demonstrated excellent electrical properties. For example, their electron diffusion coefficient was nearly one order of magnitude higher than that in traditional nanoparticle (NP)-based photoanodes. The performance of the DSCs has been therefore largely improved. We demonstrate that the MF-based DSCs can have a conversion efficiency of 4.12% under 100mW cm-2 light illumination, much higher than 1.26% of normal ZnO NP-based DSCs. The morphologies (e.g., size, thickness and parking density of the nanosheets) of the hierarchical structure in the MFs can be tuned by changing the experimental conditions and the relationship between the MF structures and their performance as photoanodes have been investigated. By optimizing experimental parameters, the highest current density of 10.26 mA cm-2 and an efficiency of 4.93% have been obtained, indicating a great potential for the development of high-efficient quasi-solid DSCs.
12:45 PM - Z11.6
Functional Interfaces in Pure and Blended Metal Oxide Nanoparticle Networks.
Oliver Diwald 1 , Nicolas Siedl 1 , Michael Elser 1 , Stefan Baumann 1
1 Chemical and Bioengineering, University of Erlangen-Nuremberg, Erlangen Germany
Show AbstractThe exploration of interfacial phenomena in metal oxide nanoparticle networks as well as the identification of related synergistic effects is vital to the development of particle-based photovoltaic and photoelectrochemical devices. In this contribution, we present the generation and characterization of blended networks made of TiO2, ZrO2 and SnO2 nanoparticles by heteroaggregation in aqueous dispersion. Particles prepared by chemical vapor synthesis were transformed into colloidal dispersions and subsequently aggregated to yield mesoporous nanoparticle networks.[1] Under controlled experimental conditions in terms of temperature and pressure as well as energy and flux of photons, the activation of molecular oxygen at the surface of photoexcited nanocrystals was studied with electron paramagnetic resonance spectroscopy and used to compare the photoactivity of nanomaterials with different concentrations of solid-solid interfaces.[2] As a major result we found that networks of intermixed nano-particles exhibit substantially enhanced crossections for charge separation. The superior performance holds also in comparison to homogeneous metal oxide nano-particle networks that exhibit a higher charge recombination loss in comparison to powders of unconnected nanocrystals. Thus, the adjustment of the composition and concentration of solid-solid interfaces inside the nanoparticle network clearly determines the branching ratio between the separation and recombination of photogenerated charge carriers.[1] S. Baumann et al. Langmuir 2011, 27, 1946-1953.[2] N.Siedl et al. J. Phys. Chem. C, 2009, 113, 15792.
Z12: ZnO Functional Nanostructures II
Session Chairs
Wednesday PM, November 30, 2011
Room 210 (Hynes)
2:30 PM - **Z12.1
Ultrasound Assisted Synthesis of ZnO Nanowire and Devices at Room Ambient on Arbitrary Substrates.
M Saif Islam 1 , Avinash Nayak 1 , Hakan Karaagac 1 , Logeeswaran Vj 1 , Aaron Katzenmeyer 1
1 Department of Electrical Engineering, University of California, Davis, California, United States
Show AbstractZnO is an earth-abundant semiconductor and its nanostructures, with superbly rich physical shapes and material properties, have recently been used in the fabrication of a number of novel nanodevices. Although several techniques for synthesizing ZnO nanostructures were demonstrated, there are few reports on rapid and facile processes for uncatalyzed direct growth on untreated arbitrary substrates under mild conditions. In this talk, we will present a sonochemical method that meets these criteria. We will compare the electrical, optical and device properties of ZnO nanostructures grown under different physical conditions and will discuss their potential device applications.
3:00 PM - Z12.2
Functionalization of ZnO Nanostructures by CdS Nanoparticles: Effects on Functional Properties.
Davide Calestani 1 , Marco Villani 1 , Laura Lazzarini 1 , Roberto Mosca 1 , Andrea Zappettini 1
1 , IMEM-CNR, Parma Italy
Show AbstractZinc oxide (ZnO) nanostructures are today one of the most studied topic in materials science and the research about all the possible synthesis method for these unique and versatile nanocrystals is still growing exponentially. Indeed, ZnO is not only very important for its optical and semiconducting properties, but it has also a polar crystal structure and piezoelectric properties, it is a good transparent conducting oxide for photovoltaic applications and high temperature and radiation resistant circuits. Moreover it is a good n-type gas-sensing material and photocatalyst and, in addition, it is used for cantilevers production and for the preparation of diluted- and ferro-magnetic materials for semiconductor spintronics. But, above all, the enormous potentiality of this material rises from the possibility to combine all these application fields with the large variety of available ZnO nanostructures and the nearly infinite number of possible surface functionalizations by different materials.Authors previously reported about the vapor phase synthesis of different ZnO nanostructures. The growth of specific morphologies have been optimized, stabilized and then coupled with different vapor and solution based techniques for adding different functionalizing materials (metal colloidal nanoparticles, organic molecules and inorganic materials,…). Among them, a detailed study on cadmium sulphide (CdS) deposition over ZnO nanorods and tetrapods is here reported. At first, a focused optimization of CdS synthesis process have been faced in order to avoid the typical damaging of ZnO surfaces in alkaline solutions, that are generally used for the synthesis of calcogenide nanostructures.Then fundamental and functional characterizations, such as scanning and transmission electron microscopy, x-ray diffraction, photoluminescence, photo-induced currents, photocatalytic activity and gas sensing properties, have been performed in order to study the effects of materials coupling on ZnO chemical and physical properties. In particular, some evidence of excitonic charge transfer and a selective inversion of the response towards specific gases in the obtained CdS-functionalized ZnO nanostructures have been observed and discussed.
3:15 PM - Z12.3
ZnO Nanorod Decorated with RuOx Nanoparticles by Atomic Layer Deposition.
Seokhwan Bang 1 , Seungjun Lee 1 , Joohyun Park 1 , Youngbin Ko 1 , Seokyoon Shin 1 , Hagyoung Choi 1 , Kiyeol Ham 1 , Jihoon Kim 1 , Hyeongtag Jeon 1
1 , Hanyang University, Seoul Korea (the Republic of)
Show AbstractZinc oxide (ZnO) nanorod, with its excellent luminescent properties and the ease of growth of nanostructures, has a considerable attention for the next generation photonic devices such as solar cell, light emitting diode, and ultraviolet lasers. However, when ZnO nanorod is applied for these applications, a large number of carriers are trapped by intrinsic defects or inside luminescence centers, resulting in a low efficient ultraviolet emission. This is one of most important issues for photonic applications of ZnO. Solutions, which use the surface plasmon (SP) by using the various metal capping, have recently been introduced. Plasmons are created when incident light excites coherent oscillation of the free electrons in metal or metal nanoparticle. Unlike planar SPs on metal surfaces, SPs in metallic particles can be excited by incident light without any special condition. This phenomenon gives rise to unique properties, such as an intense absorption feature, enhanced electromagnetic, and charge transfer. In this study, as the methods to improve efficient ultraviolet emission from near band edge, we will introduce the ZnO nanorod decorated with ruthenium oxide (RuOx) nanoparticles. Atomic layer deposition (ALD) was used to deposit highly conformal RuOx nanoparticles in one-dimensional ZnO nanorod synthesized by hydrothermal method. As increasing in ALD cycle, the change in both density and size of RuOx nanoparicles were examined by Transmission electron microscopy (TEM). Chemical bonding between ruthenium and oxygen was analyzed by X-ray photoelectron spectroscopy (XPS). The enhancement in the ultraviolet emission through applying the RuOx nanoparicles was verified by the Photoluminescence (PL). This results can be explained by energy transfer mechanism between the defect related emissions and SP coupling emissions. The more detailed chemical/optical results will be discussed and presented.
3:30 PM - Z12.4
Hydrogen Co-Doping in Cu-Doped ZnO Grown by Solution Method.
Xiaohu Huang 1 2 , Chuan Beng Tay 1 2 , Thirumalai Venky Venkatesan 1 2 , Soo Jin Chua 1 2 3
1 Department of Electrical and Computer Engineering, National University of Singapore, Singapore Singapore, 2 NUSNNI-Nanocore Laboratory, E3-05-29, 2 Engineering Drive 3, National University of Singapore, Singapore Singapore, 3 , Singapore-MIT Alliance, E4-04-10, 4 Engineering Drive 3, Singapore Singapore
Show AbstractCu-doped ZnO, with its rich physical properties, has potential applications in photonics, electronics, and spintronics. Here we will show how co-doping with hydrogen, usually present in solution growth method but neglected before, influences the physical properties of Cu-doped ZnO. The samples are grown by a low temperature (~ 90
oC) solution method. In the as-grown samples, the photoluminescence (PL) is dominated by defects band due to the presence of various intrinsic defects. However, after annealing the samples to about 425
oC, the defects band is suppressed exponentially with annealing duration, and the near band edge emission is enhanced by a factor of ~ 30. The reason of this can be ascribed to annealing-activated hydrogen donor, which is identified to be H
O by both PL and Raman characterizations. After annealing the samples at higher temperatures, the near band edge emission drops due to dissociation of the hydrogen donor, while a structured green luminescence increases with increasing annealing temperature, and dominates the PL spectra after annealing above 700
oC. The nature of the green luminescence is further investigated by variable temperature PL measurements, which is related to Cu dopant occupying Zn site. Since hydrogen shallow donor contributes to electron carriers in ZnO, conductivity type and carrier concentration of Cu-doped ZnO can be tailored through activation and dissociation of hydrogen donor. Furthermore, it is found that the room temperature ferromagnetism of Cu-doped ZnO can be also tuned by hydrogen co-doping through hydrogen-mediated coupling. The results shed lights on how to tailor different physical properties of ZnO simultaneously by hydrogen co-doping, which could be adopted to fabricate multifunctional materials.Correspondence should be addressed to Prof. Soo Jin Chua. E-mail:
[email protected] 3:45 PM - Z12.5
Characterization of Piezoelectric Potential and Piezotronic Effect in ZnO Nanowires via 3DKPM.
Dylan Bayerl 1 , Matthew Starr 1 , Xudong Wang 1
1 , University of Wisconsin - Madison, Madison, Wisconsin, United States
Show AbstractZnO has become a widely studied material system due to its promising optoelectronic, photoelectrochemical and piezoelectric properties to name a few. More recently, it has become a model system for the emerging field of piezotronics which explores the coupling of piezoelectric and semiconducting properties. The piezotronic effect has many interesting and promising applications such as transistors, sensors, optoelectronics and nanogenerators. While the theory and application of piezotronic systems have progressed steadily, there exists an absence of well-defined experimental methods for quantifying the piezoelectric potential generated by individual nanowires (NWs) and the effect of free charge carriers on said potential. We present a 3-dimensional Kelvin probe microscopy (3DKPM) technique for characterization of true piezoelectric potential in individual ZnO NWs. By resolving a full 3-dimensional mapping of electrical potential distribution around the NW, this technique enables a quantification of in-plane piezoelectric potential difference free of the measurement errors due to ambiguous probe-sample separation distance and absolute reference potential to which the widely used Scanning Kelvin Probe Microscopy (SKPM) is subject. ZnO NWs under various static bending conditions were characterized. Direct evidence of intriguing piezoelectric-semiconductor coupling effects predicted for ZnO was obtained where native mobile charge carriers redistributed to compensate piezoelectric polarization inside strained NWs. By depleting strained NWs of mobile charge carriers, the uncompensated piezoelectric potential could be quantified directly and was found to be in agreement with theoretical predictions. With the advent of this quantitative method for characterizing piezoelectric potential in ZnO NWs, a new era of experimental study of the strain-size-potential and piezotronic relationships in piezoelectric NWs is anticipated.
Z13: Chemical Sensors II
Session Chairs
Wednesday PM, November 30, 2011
Room 210 (Hynes)
4:30 PM - **Z13.1
The Synthesis-Structure-Property Relationship in Metal-Oxide Nanocrystals Based Gas-Sensors.
Mauro Epifani 1
1 , CNR-IMM, Lecce Italy
Show AbstractThe use of semiconducting metal oxides (MOXs) nanocrystals was suggested in 1991 by Yamazoe and coworkers as a powerful way for improving the performances of chemoresistive gas-sensors. The high response of nanocrystal-based sensors was predicted and experimentally demonstrated by the same authors. They explained the sensitivity in terms of enhanced modulation of the charge depletion layer in the MOX nanocrystal due to the interaction with the surrounding gases. Since then, intensive efforts were devoted to the development of metal oxide nanostructures based gas-sensors, and an increasing number of papers appeared in the literature. On the other hand, when comparing the results of the literature reports, it is clear that the sensing properties span a very broad range, depending on the processing route, the thermal history, morphology of the material and so on. This spread of the results can not be fully explained by the dependence of the gas response on the particle size. For getting a deeper insight in the sensing properties of metal oxide nanocrystals, a careful analysis of the synthesis-structure-performance paradigm was carried out. Three case studies will be presented: i) the NO2 sensing properties of SnO2 nanocrystals; ii) the alkane sensing properties of SnO2 nanocrystals; iii) the ammonia sensing properties of Cr-doped WO3 nanocrystals. In the first two studies, a coupled theoretical/experimental approach was adopted. The reduced state of the SnO2 nanocrystal was evidenced and characterized by XPS, electrical measurements and cathodoluminescence spectroscopy. DFT modeling was first used to investigate the structure of the oxygen vacancies, then to demonstrate their role in enhancing the sensing properties, by locally modulating the charge distribution in the nanocrystals. In turn, the oxygen vacancies are generated by synthesis procedure, involving sol-gel colloidal processing in coordinating environment, followed by heat-treatment. The heat-treatment generates a reducing carbon layer around the nanocrystals. This finding finally matched the synthesis of the sensing material with the device performance. In the third case, the insertion of Cr ions in the WO3 structure was carried out by using a metalorganic precursor. The result was interstitial placement of Cr3+ ions in the WO3 structure. Cr concentration below 5% controls the concentration of oxygen vacancies, so enhancing the response to ammonia and annihilating the response to NO2. Above 5% Cr concentration, the WO3 lattice is no more capable of accommodating the Cr cations, which form the Cr2WO6 phase. After this point, the lattice parameters and the electrical conductivity reverse toward the values of pure WO3.While the relationship between the synthesis pathway and the materials properties is obvious, the emerging picture evidences the importance of elucidating how it is manifested in the surface chemistry, since it dominates the gas-sensor response.
5:00 PM - Z13.2
High Throughput Fabrication Method of Individual Metal Oxide Nanowires Based Devices.
Roman Jimenez-Diaz 1 , Jordi Sama 1 , J. Daniel Prades 1 , Albert Romano-Rodriguez 1 , Francisco Hernandez-Ramirez 2 , Joaquin Santander 3 , Carlos Calaza 3 , Luis Fonseca 3 , Carles Cane 3
1 , University of Barcelona, Barcelona Spain, 2 , IREC, Catalonia Institute for Energy Research, Barcelona Spain, 3 , Instituto de Microelectronica de Barcelona, IMB-CNM-CSIC, Bellaterra Spain
Show AbstractNanowires have emerged as potential blocks for future electronic devices; however, the requirements arisen from the use of elements with dimensions in the nanometer range slow down the development of novel devices [1]. In this work, a methodology for the high throughput production of gas sensors based on individual metal oxide nanowires (NWs) is presented. SnO2 nanowires with radii in the range 20–200 nm were synthesized by chemical vapor deposition (CVD) of a molecular precursor [Sn(OtBu)4] as described elsewhere [2]. Some of these nanowires were dispersed in ethanol creating solutions with different concentrations. Afterwards, their manipulation to achieve placement and alignment of the nanowires in predefined positions was carried out by spreading a droplet of the solution (~10 μl) onto a SiO2 / Si wafer with pre-patterned microelectrodes, while between these specially designed microelectrodes an AC voltage of controlled frequency and amplitude was applied. Dielectrophoretic (DEP) force tends to align the nanowires along the potential variation and positions them in the gap between the electrodes. Afterwards, SEM inspection was used to evaluate the efficiency of the process with different nanowire concentrations and frequency of the voltage applied. This step allowed determining the optimal experimental conditions to perform the DEP alignment process with SnO2 nanowires. Afterwards, the sample was introduced in a Focused Ion Beam system for the deposition of platinum, obtained from the decomposition of a metalorganic precursor by means of Electron Beam Induced Deposition. Electrical contacts from the nanowire to the microelectrodes were fabricated with electron beam scanning of the sample to prevent modification of the sample with ions [3]. After contacting the nanowires, DC electrical measurements were performed. Ohmic and rectifying responses were obtained as commonly found by the use of the FIB method [4]. Moreover, some of these nanowires were tested as gas using well controlled environmental conditions. The obtained results demonstrated the huge potential of nanowires as building blocks of a new generation of devices with improved performances. For this reason in this work, DEP based technologies are a promising approach for the fabrication of nanodevices in a scalable process will be discussed. [1] Satyanarayana V.N.T. et al., Progress in Materials Science 52 (2007) 699-913.[2] S. Mathur, et al., Small 1 (2005) 713.[3] F. Hernandez-Ramirez, et al., Nanotechnology 17 (2006) 5577-5583.[4] Z. Zhang, et al., Advanced Functional Materials 17 (2007) 2478-2489.
5:15 PM - Z13.3
Nanoscale Hollow Spheres and Its Use for Sensing as Well as for Gas Sorption and Gas Separation.
Claus Feldmann 1
1 Institut für Anorganische Chemie, Karlsruhe Institute of Technology (KIT), Karlsruhe Germany
Show AbstractNanoscale hollow spheres with a wide range of compositions can be prepared via a microemulsion-based synthesis. This includes oxides (e.g., AlO(OH), La(OH)3, ZnO, SnO2, TiO2), sulfides (e.g., CuS, Cu1.8S, Cu2S, Ag2S) and metals (e.g., Au, Ag) [1-3]. The hollow spheres exhibit outer diameters of 10–50 nm, a wall thickness of 2–10 nm and an inner cavity ranging from 5 to 30 nm in diameter. Outer diameter and inner cavity size of the hollow spheres can be selectively adjusted during synthesis via the size of the initial micelles [4].With specific surfaces of up to 600 m2/g nanoscale hollow spheres become relevant for sensor applications as well as for gas sorption and gas separation. To this concern, SnO2 hollow spheres deposited on common sensor substrates show a good response to reductive gases (e.g., CO, H2, ethanol) in a concentration range of 50 to 300 ppm [5]. The possibility to selectively modify the inner or outer surface of the hollow spheres – e.g., by metal nanoparticles for activation – allows to establish highly efficient and selective sensors. Moreover, the Plasmon resonance of metal hollow spheres (e.g., Ag, Au) gives access to a detection of various adsorbents [6].Aiming at gas sorption and gas separation, nanoscale AlO(OH) hollow spheres show a remarkable CO2 uptake (i.e. 200–300 mg/g). Suited temperature-pressure cycles, moreover, allow a reversible storage of CO2 as well as a separation from CO2–N2 mixtures while the CO2 uptake on the hollow spheres is 4-times as high as compared to N2.References[1] H. Goesmann, C. Feldmann, Angew. Chem. Int. Ed. 2010, 49, 1362 (Review).[2] H. Gröger, F. Gyger, P. Leidinger, C. Zurmühl, C. Feldmann, Adv. Mater. 2009, 21, 1586.[3] P. Leidinger, R. Popescu, D. Gerthsen, H. Lünsdorf, C. Feldmann, Nanoscale 2011, 3, 2544.[4] P. Leidinger, R. Popescu, D. Gerthsen, C. Feldmann, Small 2010, 6, 1886.[5] F. Gyger, M. Hübner, C. Feldmann, N. Barsan, U. Weimar, Chem. Mater. 2010, 22, 4821.[6] C. Kind, R. Popescu, E. Müller, D. Gerthsen, C. Feldmann, Nanoscale 2010, 2, 2223[7] S. Simonato, H. Gröger, J. Möllmer, R. Staudt, A. Puls, F. Dreisbach, C. Feldmann, 2011, submitted.
5:30 PM - Z13.4
Au/ZnO Nano-Composites Synthesized by Deposition-Precipitation with Urea (DPU) as Upstream Catalytic Filters for Gas Sensors.
Loic Joanny 1 2 , Pierre Fau 1 2 , Myrtil Kahn 1 2 , Bruno Chaudret 3 2 , Katia Fajerwerg 1 2
1 Laboratoire de Chimie de Coordination, CNRS, Toulouse France, 2 , PRES Université de Toulouse, Toulouse France, 3 LPCNO, INSA, Toulouse France
Show Abstract One of the major goals for sensors devices is their selectivity properties, i.e. their capability to isolate and recognize a specific gas from a mixture containing several gaseous components. For metal oxide gas sensors (MOS) one strategy to achieve this goal is to develop some complex metal oxide layers based on mixed compositions (CuO/SnO2/ZnO...) and/or on well controlled structures (wires, nano-wires, flakes…). Another strategy is to catalytically modify the gas mixtures before it reaches the sensitive layers. In that aspect, the catalytic properties of gold deposited on metal oxide powders have been highlighted by the seminal work of Haruta in the late 80’s. Gold nanoparticles (< 5 nm) supported on reducible metal oxide (TiO2, CeO2, MgO…) have been investigated in several oxidation reactions. These gold based catalysts have a very high catalytic activity for CO oxidation even at room temperature. The urea based deposition-precipitation (DPU) technique has been developed by C. Louis and co-workers and used to efficiently prepare oxide supported gold catalysts. However, to the best of our knowledge, no example has been reported yet on the use of this method for the preparation of Au/ZnO nano-composites.We present here the deposition-precipitation with urea of gold nanoparticles (1 wt %) supported on several commercial or home-made ZnO nanopowders. The influence of the textural properties (N2 physisorption measurements) of the different ZnO supports calcinated at 350 or 500°C on the dispersion of Au nanoparticles is presented. The gold nano-composites are characterized by X-ray diffraction, XPS, HR-TEM and UV-Vis spectroscopy. Comparison of the different nano-composites in term of their catalytic properties are evaluated as filters by measuring the response of commercial SnO2 gas sensors in humid air (50% relative humidity) to CO gas (from 100 ppm up to 500 ppm). It is noteworthy that this approach makes it possible to fully eliminate, at room temperature, the CO gas from the upstream of the gas sensor for CO level up to 500 ppm. This result opens the way of improved arrays of selective gas sensors with catalytically modified gas mixtures.a) Y. Zheng, J. Wang, and Pengjun Yao, Sens. and Act. B: 156, 2, (2011), 723.b) K.W. Kim, P.-S. Cho, S.-J. Kim, J.-H. Lee, C.-Y. Kang, J.-S.Kim and S.-J. Yoon, Sens. and Act. B, 123, 1, (2007), 318. M, Haruta, T. Kobayashi, H. Sano, N. Yamada, Chem. lett., 2 (1987) 405. L. Delannoy , K. Fajerwerg 1, P. Lakshmanan, C. Potvin, C. Methivier, C. Louis, App. Cat. B: 94 (2010), 117 C. Milone, M. Trapani, R. Zanella, E. Piperopolulos and S. Galvagno, Mat. Res. Bull. , 45, 12, (2010), 1925. R. Zanella, L. Delannoy and C. Louis, App. Cat.: A, 291, 1-2, (2005), 62.
5:45 PM - Z13.5
Synthesis-in-Place of Highly Ordered TiO2 Nanotube Thin Films on Various Substrates and Their Applications to Ultrasensitive Chemical Sensors.
Ho Won Jang 1 2 , Do Hong Kim 1 , Jin-Sang Kim 1 , Seok-Jin Yoon 1
1 Electronic Materials Research Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 Nano-Materials Science and Engineering, University of Science and Technology, Seoul Korea (the Republic of)
Show AbstractTiO2 is of great interest owing to its various applications such as dye-sensitized solar cells, photoelectrochemical water splitting, antireflection coatings, Li-ion batteries, and chemical sensors. For these applications, since the device performance largely depends on the surface-to-volume ratio of the TiO2 electrodes or catalysts, tremendous efforts have been devoted to synthesize TiO2 nanomaterials with large specific surface areas. Among them, TiO2 nanotubes have attracted great interest due to the facile synthesis of them using anodic oxidation processes. Many studies reported that highly ordered TiO2 nanotubes could be obtained from the anodization of Ti or Ti-alloy foils. However, the anodization of Ti films on Si or glass substrates failed to obtain high quality TiO2 nanotube thin films on the substrates, which are expected to be favorable for high-quality chemical sensors. Here we report direct synthesis of highly ordered TiO2 nanotube thin films onto patterned Si, glass, or sapphire substrates. By anodizing Ti films on patterned Si or glass substrates, we could obtain highly ordered TiO2 nanotube thin films on the substrates. The orderness of the TiO2 nanotubes is unparalleled with those of the previously reports. Furthermore, the directly synthesized TiO2 nanotubes on the Si or glass substrates could be used as chemical sensors without additional processes. The experimental results reveal that the chemical sensors based on the high-quality TiO2 nanotubes exhibits superior gas sensing properties to flat TiO2 thin films. It is shown that the TiO2 nanotube sensors can detect ppb levels of acetone, nitrogen oxides, and ammonia, which suggests promising applications of the TiO2 nanotube sensors for a non-invasive and painless method of diagnosing disease through the breath.
Symposium Organizers
Alberto Vomiero University of Brescia
Sanjay Mathur University of Cologne
Zhong Lin Wang Georgia Institute of Technology
Eric Wei-Guang Diau National Chiao Tung University
Z14: Synthesis of Nano-Oxides
Session Chairs
Thursday AM, December 01, 2011
Room 210 (Hynes)
9:30 AM - **Z14.1
Zinc Oxide and Copper Oxide Nanostructures: Fundamentals and Applications.
Magnus Willander 1
1 , Linköping university, Norrköping Sweden
Show Abstract Copper oxide (CuO) and zinc oxide (ZnO) nanostructures complement each other since CuO is unintentional p-type and ZnO unintentional n-type. In the first part of my talk I will show results from ZnO nanorods (NRs) /polymer p-n hybrid heterojunctions chemically grown on paper and using printing process on paper for LED applications as well as some large area light emitting diodes (LEDs). I will also show how ZnO NRs can be used for intracellular biosensors/chemical sensors for example to examine cell apoptosis. Then I will discuss some influence of ZnO on biological materials. In the second part of my talk I will discuss the growth of CuO nanostructures and how to combine them with ZnO nanowires to make p-n heterojunction diodes. The catalytic activity of CuO with other industrial dyes and the possible degradation is to be shown. Moreover the characteristics of ZnO NRs/CuO nanoflowers junctions are to be discussed in details. Finally, different applications ZnO NRs/CuO nanoflowers pn heterojunctions grown by the chemical approach are to be highlighted. Example of these applications is metallic ion sensing and other possible photonic devices.
10:00 AM - Z14.2
Hierarchically Branched TiO2 Nanotubes with Controlled Branch Numbers and Diameters.
Bo Chen 1 , Kathy Lu 1
1 Materials Science and Engineering, Virginia Tech, Blacksburg, Virginia, United States
Show AbstractOver the past decade, electrochemical anodization of self-organized TiO2 nanotubes has been studied intensively and mainly focused on uniform diameters throughout the TiO2 nanotubes depth direction. In the present study, we demonstrate a generic method to fabricate hierarchically branched TiO2 nanotubes by adjusting the anodization voltage. Initially ordered root TiO2 nanotubes are obtained by the typical two-step anodization. After the formation of root nanotubes during the second-step anodization, the applied voltage is decreased by a factor of sqrt(1/n) to generate n-branched nanotubes (1~n, “~” stands for the junction where the branching takes place, and n stands for the number of branches produced) from the root nanotube, and the diameter of the branched nanotubes is sqrt(1/n) of the root nanotube. The number of branches and the diameter of the branched nanotubes are dependent on the reduction of the applied voltage. If the applied voltage is further decreased by a factor of sqrt(1/m), each of the branched nanotubes further subdivides into m smaller nanotubes (1~n~m). Continuing this approach, four layers of branched TiO2 nanotubes with 1~n~m~k structures are obtained. As a result, hierarchically branched TiO2 nanotubes with controlled diameters are achieved. On the other hand, when the anodization voltage is increased by a factor of n, some nanotubes enlarge the diameter to n times of the root nanotubes, while other nanotubes terminate the growth. As a result, TiO2 nanotubes with n~1 structure are obtained. A combination of 1~n branched nanotubes with n~1 TiO2 nanotubes leads to anodized TiO2 nanotubes with 1~n~1 structure. This novel approach not only generates hierarchically branched TiO2 nanotube structures, but will also open up new opportunities for the applications in dye-sensitized solar cells and photocatalysts.
10:15 AM - Z14.3
Ferromagnetism in PrCoO3-δ through Heteroepitaxy.
Virat Mehta 1 2 , Elke Arenholz 3 , Shameek Bose 4 , Chris Leighton 4 , Yuri Suzuki 1 2
1 Materials Science and Engineering, UC Berkeley, Berkeley, California, United States, 2 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 4 Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractPerovskite cobaltites (ACoO3) exhibit spin state transitions at temperatures that vary with the A site cation radii and thus electronic bandwidth. The 3d6 Co3+ in this system has the ability to adopt spin configurations ranging from the low spin diamagnetic S=0, through intermediate spin paramagnetic S=1 to high spin paramagnetic S=2. With small amounts of thermal energy the system can alter its crystal field into a higher spin configuration and give rise to a spin state transition. In the bulk, LaCoO3 exhibits the lowest spin state transition temperature (TSST) of the cobaltites, requiring only ≈30 K before the onset of some high spin Co in the crystal is observed[1]. By substituting La with Pr, a smaller cation, the Co adopts a higher TSST≈200 K and a more stable low spin configuration due to the decreased bandwidth[1]. In order to probe the relative stability of the spin state in these different chemical compounds and to probe the limits of using heteroepitaxy to induce spin state functionality we studied the magnetic state of epitaxial cobaltite thin films. We and others have already demonstrated ferromagnetism in LaCoO3 films under tensile strain[2, 3]. In this work, we present the stabilization of a ferromagnetic ground state in epitaxial PrCoO3 films grown using pulsed laser deposition on SrTiO3, LSAT, and LaAlO3 substrates. On SrTiO3 and LSAT, PrCoO3 films exhibit ferromagnetism with Tc<50 K and Msaturation<1uB/f.u, compared to Tc<75K and Msaturation<1uB/f.u. for LaCoO3. Films on LaAlO3, however, show no obvious ferromagnetic hysteresis or Tc. Films were also grown as a function of O2 deposition pressures from 10–320 mTorr with higher O2 pressures necessary for the synthesis of stoichiometric PrCoO3 films. Together these results suggest that engineering magnetism via epitaxial strain is not unique to LaCoO3 and can be generalized to other perovskite cobaltite systems.[1] Tachibana, M. et al, Phys. Rev. B, 77, 094402 (2008).[2] Mehta, V.V. et al, Journal of Appl. Phys. 105, 07E503 (2009).[3] Park, S. et al, App. Phys. Lett. 95, 072508 (2009).
10:30 AM - Z14.4
Metal Oxide Nanowires as Protein Mimics.
Wolfgang Tremel 1 , Filipe Natalio 1 , Rute Andre 1 , Aloysius Hartog 2 , Ron Wever 2
1 Institut für Anorganische Chemie, Johannes Gutenberg-Universität, Mainz Germany, 2 Van't Hoff Institute for Molecular Sciences, Universiteit van Amsterdam, Amsterdam Netherlands
Show AbstractManufactured nanostructures that mimic enzymes are of great interest as they potentially have improved properties relative to native enzymes, such as greater resistance to extremes of pH and temperature and lower sensitivity to proteases. These enzymatic activities look like the intrinsic properties for some metal or metal oxide nanoparticles and nanowires and the antioxidative enzymatic activities of these nanomaterials have shown great potential in prevention of oxidative stress associated cell death and disease progression in various experimental models. We have studied the biomimetic properties of V2O5 nanowires. V2O5 nanowires catalyze peroxidative reactions in aqueous media and other solvents. The reactions catalyzed by the V2O5 nanowires follow a Michaelis-Menten behavior with an excellent catalytic activity superior in comparison to natural vanadium haloperoxidase (V-HPO) and horseradish peroxidases (HRP). The kinetic parameters were compared with those of peroxidase and haloperoxidase enzymes. The new nanostructured vanadium-based materials are re-usable and retain their catalytic activity in different organic solvents (up to 90% v/v), making them a promising catalyst mimic of peroxidases. The V2O5 nanowires display iodinating activity as confirmed by colorimetric assays using thymol blue (TB), UV/Vis spectrophotometry and mass spectrometry (FD-MS). In the presence of dopamine these nanowires catalyze the fast and efficient synthesis of melanin-like biopolymers under mild conditions (aqueous solution, neutral pH and room temperature). The synthetic biopolymers resemble their natural counterparts both in their chemical and morphological features. In addition, the synthetic biopolymer self-assemble into fibril-like structures by forming stacks due to π interactions between the aromatic rings.Finally, V2O5 nanowires also display an intrinsic biomimetic bromination activity, with an exceptional operational stability and superior catalytic activity compared to their natural V-HPO counterpart. We have demonstrated the ability of V2O5 nanoparticles to produce HOBr under seawater conditions. The resulting antibacterial, antifouling and disinfecting properties were demonstrated on surfaces for gram-positive and gram-negative bacteria, making V2O5 nanowires promising paint preservative components as a replacement for enzymes in antibacterial, antifouling and disinfection formulations in water-based paints.
10:45 AM - Z14.5
Reactive Nanolaminates with Tailored Energy Yield.
Edward Mily 1 , Hasan Akyildiz 3 , Yu Hong Jeon 2 , Jon Ihlefeld 2 , Carissa Goldstein 1 , Douglas Irving 1 , Donald Brenner 1 , Jon-Paul Maria 1
1 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States, 3 , Middle East Technical University, Ankara Turkey, 2 , Sandia National Labs, Albuquerque, New Mexico, United States
Show AbstractMulti-layer nano metal-oxide/metal thin films have the potential to augment and improve existing energetic materials used in the military and industry. Here we report on a series of reactive oxygen exchange nanolaminates between an oxygen source, CuO, and a reactive metal oxygen sink where the propensity for energy release is tailored by material selection and by multilayer geometry. These results suggest it is possible to create a class of energetic materials whose yield can be tailored for specific applications.In one set of experiments we demonstrate that by considering anion transport in the terminal oxide, we can produce multilayers that are unstable at room temperature, or those which require substantial thermal energy to ignite. We first explored this terminal phase hypothesis by comparing CuO-metal laminates with the reactive metals: Mg, Zr, and Al. The nanolaminates were exposed to rapid furnace anneals and subsequent x-ray diffraction to identify the onsets of oxygen exchange. Zr-CuO laminates were the least stable, owing to the fast oxygen transport through the ZrO2 terminal oxide, while CuO-Al laminates were the most stable, owing to the excellent diffusion barrier properties associated with Al2O3. CuO-Mg exhibited intermediate stability. A second demonstration is made for laminates of CuO and Al1-xTix where x is varied systematically between the pure end members. We identify a composition of ~ 35% Ti, above which the laminates react at RT, and below which temperatures of 300 °C and above are require to initiate oxygen exchange. We will present sets of x-ray diffraction, SEM, and TEM data that illustrate the evolution of phase and microstructure in these “rapid” and “slow” oxygen exchange multilayer systems.In a second set of experiments we explore how geometry can be used to regulate the exothermic exchange reactions. For the reactive laminate systems of CuO-Al, CuO-Zr, and CuO-Mg, we prepared sets of multilayers of constant total thickness, but where the individual layer thicknesses are varied such that the number of metal oxide interfaces range from1 to 7. Using ex-situ x-ray diffraction and rapid furnace anneals, we identify that the minimum temperature needed to initiate the reaction drops in all cases on the order of 200°C as the number of interfaces increases. Calorimetry data for these samples show multiple exotherms that exhibit thickness-dependent temperatures. The exotherms can be attributed to the oxygen exchange from CuO and Cu2O to the reactive metal. The magnitude of the Cu2O exotherm and its temperature are strongly dependent upon the number of interfaces.Finally, we demonstrate that an applied voltage can be used to joule heat the electrically conductive laminate constituent and initiate the exothermic oxygen exchange. In all cases, small applied voltages could initiate the reaction. X-ray diffraction and optical images reveal that such reactions occur homogeneously over sample areas greater than 20 cm2.
Z15: ZnO Functional Nanostructures III
Session Chairs
Thursday PM, December 01, 2011
Room 210 (Hynes)
11:45 AM - Z15.2
Hybrid ZnO-Au Nanoparticle Complexes from a Simple Dithiol Modification Process: Understanding and Tailoring of Electro-Optical Properties.
Diane Steeves 1 , Jason Soares 1 , Jisun Im 2 , Jagdeep Singh 2 , James Whitten 2
1 , US Army Natick Soldier RD&E Center, Natick, Massachusetts, United States, 2 Department of Chemistry and Centers for Advanced Materials and High-Rate Nanomanufacturing, University of Massachusetts Lowell, Lowell, Massachusetts, United States
Show AbstractMetal oxide nanoparticles are finding use in many applications ranging from catalysis to optoelectronics. In particular, nano-crystalline zinc oxide (nano-ZnO) is an important electro-optical material and is a promising semiconductor for hybrid devices due to its wide bandgap and bimodal photoluminescence (PL) spectrum. The focus herein has been on surface modification of nano-ZnO for the creation of metal:metal oxide hybrid complexes in order to tailor the inherent PL of nano-ZnO. ZnO hybrid complexes were created using a simple a thiol modification approach, wherein organothiol modifiers are covalently attached to the surface of ZnO nanoparticles. The degree of surface modification (e.g. monolayer vs. encapsulation) can be controlled; reaction under ambient conditions creates a thiol monolayer, while elevated temperatures result an encapsulation of the nano-ZnO. Using this thiol modification approach, a hybrid system of ZnO nanorods decorated with gold nanoparticles (AuNPs) has been synthesized using the monolayer conditions and dithiol linkers. Although ZnO:AuNP complexes have previously been created, this is the first successful attempt to covalently attach AuNPs to the surface of ZnO using dithiol chemistry and to understand the influence on electronic properties. This dithiol functionalization strategy allows one to control the metal:metal oxide spacing and Au packing density, thus facilitating tailoring of the optical properties. AuNPs functionalized with octanethiol were tethered to the nanorod surface using various dithiol linking agents. Attachment of the dithiol to the AuNPs and ZnO nanorods occurs via ligand exchange and Zn-S bond formation, respectively. Hybrid complexes of varying AuNP surface density were created by adjusting the AuNP:ZnO ratio and dithiol concentration. X-ray photoelectron spectroscopy and electron microscopy confirm attachment of AuNPs to the nanorod surface. The influence of the proximal metal on the PL of the ZnO was investigated. As the AuNP surface coverage increases, the visible and UV emission bands decrease. Furthermore, the UV emission band is increasingly blue shifted as the AuNP surface density increases. The PL spectrum can be tuned by varying the chain length of the dithiol linker and the AuNP:ZnO ratio. Raman spectroscopy was employed to investigate effects on nano-ZnO crystal lattice structure. Energy level diagrams were constructed to facilitate the understanding of the electronic processes that enable control of the nano-ZnO optical properties upon AuNP adsorption. The information derived from these studies facilitate the formation of ZnO:AuNP complexes with increasing control of the electro-optical properties, enabling design of a series of hybrid materials with specific optical responses. The creation of hybrid metal:metal oxide complexes through this simple thiol modification approach could have significant implications on the development of chemical sensors, as well as photovoltaic devices.
12:00 PM - Z15.3
Possible Applications of ZnO Nanorods for Pinning-Centers of Magnetic Vortices in High-Tc Superconductors.
Sang-Wook Han 1 , Zhenlan Jin 1 , Changin Park 1 , Kyu-Jeong Song 1 , Chan Park 2
1 Physics Education, Chonbuk National University, Jeonju Korea (the Republic of), 2 , Seoul National University, Seoul Korea (the Republic of)
Show AbstractWe examined the capability of ZnO nanorods as the pinning centers of magnetic vortices in YBa2Cu3O7 (YBCO) superconducting films. ZnO nanorods with a low density were synthesized on SrTiO3 (STO) substrates using MOCVD and, subsequently, YBCO films were deposited on the ZnO nanorods/STO templates. X-ray diffraction demonstrated that YBCO films were grown with a high quality aligned along their c-axes perpendicular to the substrate surface while ZnO nanorods underneath YBCO films remained constant. Transmission electron microscopy revealed that YBCO films were crystallized between and above ZnO nanorods. Extended x-ray absorption fine structure shows no extra disorder in the Cu-O planes of YBCO films on ZnO nanorods/STO templates. The mean distance between ZnO nanorods underneath YBCO films was 280 nm which might be the optimized pinning centers of magnetic vortices in YBCO films.
12:15 PM - Z15.4
Corrosion Protection of Alloy Coated Steel by Means of Modified Nanocrystalline Zinc Oxide Films.
Ozlem Ozcan 1 , Katharina Pohl 1 , Guido Grundmeier 1
1 Technical and Macromolecular Chemistry, University of Paderborn, Paderborn Germany
Show AbstractZnO nanocrystalline films have attracted great amount of scientific interest due to application possibilities in the fields of catalysis, optics and microelectronics. Our recent work has shown that ZnO nanorod films can also be utilized for corrosion protection of zinc [1]. The hydrothermal synthesis method offers a practical way for the deposition of nanocrystalline ZnO films which can be adapted to technical applications [2]. Moreover, their electrical properties can be tuned by means of plasma treatment, doping and morphology control.
In this paper we are presenting the hydrothermal synthesis of ZnO nanorod and nanocrystalline films on pure zinc and alloy coated steels and their modifications by means of low temperature plasma treatment and doping. The films were characterized for their morphology and crystalline structure by means of scanning electron microscopy (FE-SEM) and Raman spectroscopy, respectively. The unmodified ZnO films showed n-type semiconductivity and calculated donor densities were in the order of 5×1019 cm−3, which could be increased by hydrogen and decreased by oxygen plasma treatment.
Current density vs. potential curves collected between ± 0.2 V around the open circuit potential have shown that the umodified ZnO nanorod and nanocrystalline films resulted in a significant decrease of cathodic and anodic current densities in comparison to the bare passive film coated zinc surface. Oxygen plasma treatment resulted in a further suppression of the cathodic current densities while increasing the anodic current densities. Hydrogen plasma treatment resulted in a further suppression of the anodic current densities while increasing the cathodic current densities. Both effects can be explained based on the changes in the semiconducting properties and the degree of disorder as assessed by Mott-Schottky Analyis and Raman Spectroscopy, respectively.
In case of doping, the change in donor density and corrosion resistance was even more pronounced. Depending on the dopant concentration, ZnO nanorod and nanocrystalline films were able to suppress both anodic and cathodic corrosion reactions. In conclusion, the results have demonstrated that the ZnO nanocrystalline films are promising candidates to be used as thin corrosion protection layers e.g. for galvanized steel sheets.
[1] O. Ozcan, K. Pohl, P.Keil, G. Grundmeier, Electrochem. Commun. (2011), doi:10.1016/j.elecom.2011.05.016.
[2] L. Vayssieres, Adv. Mater. 15-5 (2003) 464-466.
12:30 PM - Z15.5
Multifunctional Coatings for Cotton Fabrics through Zinc Oxide Nanowires.
Elif Ates 1 , Husnu Unalan 1
1 Department of Metallurgical and Materials Engineering, Middle East Technical University, Ankara Turkey
Show AbstractTextile industry holds a great potential in commercialization of nanotechnological products. In the last few years, superhydrophobic surfaces have attracted much interest because of their important potential applications in protective coatings. In this work, we present the preparation of superhydrophobic textiles by zinc oxide (ZnO) nanowires. The fabrication of ZnO nanowires has been currently realized by various methods. Among them, microwave synthesis method was preferred due to fast, low cost, low temperature production under normal atmospheric conditions [1]. Following seeding, this method simply includes dipping the substrates in an equimolar mixture of zinc acetate dihydrate and hexamethylenetetramine solution in deionized water and heating with a commercially available microwave oven at atmospheric pressure for a few minutes. We have analyzed the morphology, distribution and structure of the as-grown nanowires on cotton with field-emission scanning electron microscope and x-ray diffraction. Following structural characterization, contact angle measurements of ZnO nanowire decorated cotton surfaces were made to determine their hydrophilic/hydrophobic properties and tuned by stearic acid functionalization. For the determination of ultraviolet protection properties of the ZnO nanowire decorated cotton samples, UVVIS spectral measurements were conducted. Finally, methylene blue test was used to determine the photocatalytic activity of the ZnO nanowires on cotton. Results obtained in here reveal an ideal multipurpose coating that can be simply applied onto textile surfaces. [1] H.E. Unalan, P. Hiralal, N. Rupesinghe, S. Dalal, W.I. Milne, G.A.J. Amaratunga, Nanotechnology 19 (2008) 255608.
Z16: Photoelectrochemical Systems III
Session Chairs
Thursday PM, December 01, 2011
Room 210 (Hynes)
2:30 PM - **Z16.1
Piezoelectric Semiconducting Metal Oxide Nanostructure-Based Energy Scavenging: Fundamentals and Applications.
Sang-Woo Kim 1
1 School of Advanced Materials Science & Engineering,, Sungkyunkwan University, Suwon, Suwon, Gyeonggi-do, Korea (the Republic of)
Show AbstractMechanical energy scavengers utilizing piezoelectricity have attracted great attention because they are suitable for a variety of applications ranging from electronic systems to molecular sensors. Intensive studies regarding piezoelectric nanogenerators have been explored, demonstrating new implications such as fiber-type energy scavengers, piezotronic strain sensors, and Schottky contact-based nano/biosensors in a self-powered mode. In the meeting, I will present the fabrication and characterization of graphene electrode-based large-scale nanogenerators that are operated by flexing the device itself, showing direct-current (DC)-type charge generation. Such nanogenerators lead to new types of embeddable energy harvesting technologies and new implications such as deformable mobile electronics or tactile skin sensors. Additionally, we will present the mode transition of charge generation between DC and alternating-current (AC) from piezoelectric nanogenerators according to the morphology of the ZnO nanorods. Tilted ZnO nanorods grown on a relatively low seed density generate DC-type piezoelectric charges under a pushing load, whereas vertically-aligned ZnO nanorods on a relatively high seed density create AC-type charge generation. The mechanism for the geometry-induced mode transition will be proposed and characterized. In addition, the output potentials generated by vertical pushing and lateral bending to vertically aligned nanorods will be compared using numerical and analytical calculations.
3:00 PM - Z16.2
Nanocrystalline Dicadmium Stannate (Cd2SnO4) for Solar Energy Harvesting Applications.
Sarika Kelkar 1 , Parvez Shaikh 1 , Satishchandra Ogale 1
1 Physical and Materials Chemistry, National Chemical Laboratory, Pune, Maharashtra, India
Show AbstractBinary and multinary metal oxide nanomaterials have a great potential for optoelectronic applications as they provide more leverage to tune the desired optical and electronic properties by changing their stoichiometry and chemical structure. In this context, the Cadmium Tin Oxide system is very interesting as it has high electron carrier density, high mobility and optical bandgap in the range of 2.1 to 2.7 eV. This ternary system shows two polymorphs namely monocadmuim stannate (CdSnO3) and dicadmium stannate (Cd2SnO4). Amongst the two the CdSnO3 polymorph, being more conveniently achievable as pure phase, has been studied in more detail for applications such as gas sensing, energy storage and dye sensitized solar cells. However Cd2SnO4 polymorph has been studied only in the form of thin films for application as transparent conducting substrates. The formation of single phase Cd2SnO4 nanoparticles is primarily hampered by the formation of more stable phases such as SnO2, CdO and CdSnO3. There is a very small window of temperature and composition where Cd2SnO4 phase is stable.Here we report the synthesis of single phase Cd2SnO4 nanoparticles using combustion synthesis method. Both cubic as well as orthorhombic pure phases were obtained by tuning the post heat treatment procedure for the same precursor conditions.Due to the volatile nature of Cadmium, the fine tuning of the ratio of Cd to Sn cations and fuel to total cations (Cd+Sn) was extremely crucial in order to obtain the pure phase nanoparticle (10-15 nm ) Cd2SnO4 system. An in-depth analysis of the phase formation has been performed by XRD, HRTEM and TGA. This is followed by the characterization of the optical and electronic properties by diffuse reflectance spectroscopy, photoluminescence measurements and cyclic voltammetry. The measurements show good potential for solar energy harvesting applications. Photoanodes with thick, mesoporous coatings of the nanoparticle Cd2SnO4 were prepared by doctor blade technique. The performance of Cd2SnO4 as a photoanode for dye sensitized solar cells and for photoelectrochemical hydrogen generation has been investigated using I-V characterization and impedance spectroscopy under 1 Sun air mass 1.5.
3:15 PM - Z16.3
Growth of Ultralong Zn2SnO4 Nanowires for Photovoltaic Applications.
Jiajun Chen 1 , Liyou Lu 1 , Wenyong Wang 1
1 Dept. Phys. Astronomy, University of Wyoming, Laramie, Wyoming, United States
Show AbstractAs one of the transparent conducting oxides (TCOs), Zn2SnO4 (ZTO) has attracted more and more interest due to its high electron mobility, high conductivity and low visible absorption. In this study, we present controlled growth of ultra-long ZTO nanowires by chemical vapor deposition. High purity ZTO nanowire networks were obtained after removal of ZnO nanowires by HCl etching. The ZTO nanowires are single-crystalline with inverted spinel structures, having diameters of 50~200 nm and lengths of several hundred microns. The nanowires have a chainlike morphology, which was formed by stacking rhombohedral crystals along the [1-11] growth direction. This unique structure made the surface facets of the nanowires are all {111} equivalent. The nanowires were transferred to TCO/glass substrates by printing method for photovoltaic applications. The large surface area and staggered surface structure of the nanowires may improve the adsorption of dye molecules or quantum dots in sensitized photovoltaic cells and the single-crystal nanowires can also work as boundary-free channels for carrier transport. All these properties of ZTO nanowires will benefit the performance of solar cells.
3:30 PM - Z16.4
Developing Solution and Vacuum Processing of ZnO for Hybrid Photovoltaic Applications.
Jonathan Downing 1 3 , Robert Hewlett 1 3 , Joseph Franklin 1 3 , Natalie Stingelin 1 3 , Thomas Anthopoulos 2 3 , Mary Ryan 1 , Martyn McLachlan 1 3
1 Materials, Imperial College London, London United Kingdom, 3 Centre for Plastic Electronics, Imperial College London, London United Kingdom, 2 Physics, Imperial College London, London United Kingdom
Show AbstractThe development of hybrid (oxide:organic) photovoltaic devices (h-PV) is an attractive prospect, owing to the suitability of such devices for high-throughput, low-cost solution processing. Despite their promise the development of such devices has been slow - the typical efficiencies (< 0.5%) are significantly lower than even modest organic photovoltaics (OPVs). Our efforts to overcome current performance limitations have been focused on two complementary approaches, i) preparation of highly crystalline planar heterojunctions and ii) preparation of controlled interdigitated architectures.i) Using pulsed laser deposition (PLD) we have been able to deposit highly crystalline ZnO on rigid and flexible substrates at temperatures as low as 50°C. The low temperature processing has allowed the preparation of normal and inverse device architectures based on ZnO and a range of polymers (P3HT, P3HS) and small molecules (pentacene). Additionally the planar devices have allowed charge transfer at the organic:oxide interface to be studied effectively for the different compositions, allowing correlation between device performance, composition and configuration to be made unambiguously.ii) Using a modified hydrothermal growth method we have successfully formed a range of ZnO nanorods in which the aspect ratio has been controllably varied. We report the preparation of highly interpenetrating networks using these rods and P3HT infiltrated using both conventional solution and novel solid state processing techniques. The role of rod length/spacing in addition to infiltration method on measured device performance will be discussed in addition to limitations of the processing encountered during our studies.For both families of structures we describe the changes in measured device performance observed as structure and composition are varied. We pay particular attention to the bulk and interfacial properties of the oxide:organic components. The measurements are supported by detailed structural (SEM, AFM, XRD) and electronic (mobility, resistivity) characterization of the individual layers and (where appropriate) the complete device structures
Z17: Nano-Oxides for Energy Storage II
Session Chairs
Thursday PM, December 01, 2011
Room 210 (Hynes)
4:15 PM - **Z17.1
Core-Shell Metal Oxide Nanostructures and Their Energy Applications.
Chih-Yen Chen 1 , Chia-Wei Hsu 1 , Li-Jen Chou 1
1 Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan China
Show AbstractThe hybrid nanostructures such as core–shell nanowires1 and nanopeapods2 haveattracted extensive attention due to their unique optical and electrical properties. But there are few reports on their energy applications. In this study, we report the metal-oxides hybrid nanostructures for their possible applications in Lithium Ion Battery and Microbial Fuel Cell(MFC) as the cathode or anode electrode materials.The nanostructures were mainly fabricated by vapor-liquid-solid (VLS) method and analyzed by field emission scanning (FESEM) and transmission electron microscopes (FETEM) - A MFC composed of bacteria and electrodes was fabricated and tested, the results indicate that metal oxides hybrid nanostructures as the electrodes can improve the open circuit voltage as well as the current density of the cell.[1] Chin-Hua Hsieh, Mu-Tung Chang, Yu-Jen Chien, Li-Jen Chou, Lih-Juann Chen, and Chii-Dong Chen “Coaxial Metal-Oxide-Semiconductor (MOS) Au/Ga2O3/GaN Nanowires”, Nano Letters, Vol. 8, No. 10, p 3288 - 3292.[2] Chin-Hua Hsieh, Li-Jen Chou, Gong-Ru Lin, Yoshio Bando, and Dimitri Golberg“Nanophotonic Switch: Gold-in-Ga2O3 Peapod Nanowires” Nano Letters, Vol. 8, No.10, p 3081 - 3085.
4:45 PM - Z17.2
High Power and High Capacity Anode for Lithium and Sodium Ion Batteries Based on Amorphous TiO2 Nanotubes.
Hui Xiong 1 , Handan Yildirim 1 , Michael Slater 2 , Subramanian Sankaranarayanan 1 , Jeffrey Greeley 1 , Christopher Johnson 2 , Tijana Rajh 1
1 Center for Nanoscale Materials , Argonne National Laboratory, Argonne, Illinois, United States, 2 Chemical Sciences and Engineering, Argonne National Laboratory, Argonne , Illinois, United States
Show AbstractRechargeable Li-ion batteries offer the highest energy density of any current battery technology, and are expected to provide a solution for our future energy-storage requirements. However, Li-ion batteries have a number of limitations[1], such as capacity loss during long-term cycling and safety issues due to dendritic Li plating on commercial graphite anodes at fast charging rates. Use of chemically inert anode materials such as metal oxides, with lithiation voltages positive of Li-deposition compared to graphite, can address these issues and improve the stability and safety of Li-ion batteries. In addition, we are studying new alternative battery approaches such as Na-ion batteries that utilize more abundant and affordable materials. Here we report self-organization of high capacity/high power TiO2 nanotube anodes driven by intercalation of transporting ions (Li+ and Na+). In our work, we start with amorphous TiO2 nanotubes that are electrically connected to the metallic collector. This geometry enables efficient potential distribution that provides the driving force necessary for intercalation of transporting ions. As a result, the self-organization of transporting ions and the TiO2 amorphous host matrix transforms into a crystalline material with the highest theoretical capacity that can possibly be achieved in a titania electrode. Molecular dynamics and DFT calculations show evolution of the disordered structure into an energetically favorable cubic structure. The theory predicts high Li diffusivity in this crystalline environment. We demonstrate near theoretical reversible capacity (310 mAh/g) of the amorphous-to-crytalline TiO2 nanotube anode in a full cell, the highest value observed experimentally with any form of TiO2 polymorphs. Materials synthesized using our approaches have unprecedented stability (>600 cycles) and exceptionally power capability. In addition, we achieved for the first time reversible intercalation of Na transporting ions into TiO2 electrodes using the same approach. The electrodes self-improve to reach the capacity of 150 mAh/g. [1]J. M. Tarascon, M. Armand, Nature 2001, 414, 359.
5:00 PM - Z17.3
High-Dielectric Constant Al2O3 / TiO2 Atomic Scale Multilayers for Energy Storage Capacitors and Logic Devices.
Geunhee Lee 1 4 , Wei Li 1 , Bernd Kabius 2 , Ram Katiyar 4 , Orlando Auciello 1 3
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 4 Department of Physics and Institute for Functional Nanomaterials, University of Puerto Rico, San Juan, Puerto Rico, United States, 2 Electron Microscopy Center, Argonne National Laboratory, Argonne, Illinois, United States, 3 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractHigh dielectric constant materials are investigated for applications in nanoscale microelectronics, and as capacitors for energy storage and logic memory devices. Al2O3 and TiO2 were investigated as high-K materials to replace SiO2 as gate and for high-capacitance capacitors for electronics. The dielectric constants of Al2O3 and TiO2 are approximately 7 and 80, respectively. Our previous studies showed that amorphous TixAl1-xOy films, exhibit dielectric constant of ~ 30, with 4.8 eV bandgap. We report now that giant dielectric constants (> 800) can be achieved with Al2O3/TiO2 nano-laminates, synthesized by atomic layer deposition (ALD), with sub-layer thickness ≤ 1 nm, for frequencies ≤ 104 Hz. A step-like decrease in dielectric constant to ~ 50 occurs between 104 – 105 Hz. The high dielectric constant is attributed to Maxwell-Wagner (M-W) relaxations, resulting from electrical heterogeneity of the multilayers. Al oxidation is favored over Ti-oxide since the Gibbs free energy for Al oxidation is more negative than for Ti. Therefore, O atoms diffuse preferentially to the Al2O3 sublayers, as shown by cross-section TEM and EELS analysis, resulting in oxygen depletion in the Ti-oxide sublayers, resulting in electrically conductive TiOx. The different electrical conductivities of the TiOx and Al2O3 layers results in surface charges accumulation at the interfaces. The surface charges relax with ac field and cause M-W relaxation. We used ALD to produce large area capacitors via conformal coating of large area ridge arrays fabricated on Si surfaces. These capacitors can yield ≥ 10 µF capacitance. The nano-laminates are explored for applications such as energy storage embedded capacitors in a Si microchip implantable in the human retina to restore sight to people blinded by genetically-induced degeneration of photoreceptors, for supercapacitors integrated with ferroelectric-based high-efficiency photovoltaic devices for energy generation/storage systems, and for high-K gate oxide with low leakage current for Si-base logic and memory devices.
5:30 PM - Z17.5
Metal-Metal Oxide Electrode, A Promising Energy Storage Candidate for Supercapacitor Applications.
Anirudha Jena 1 , N. Munichandraiah 2 , S. Shivashankar 1 3
1 Materials Research Centre, Indian Institute of Science, Bangalore, KARNATAKA, India, 2 Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore, KARNATAKA, India, 3 Centre for Nano Science and Engineering (CeNSE), Indian Institute of Science, Bangalore, KARNATAKA, India
Show AbstractElectrochemical capacitors (supercapacitors) represent an emerging energy storage technology that offers high power density, long cycle life, quick charging and safety. Metal oxides show pseudocapacitive behaviour (i.e., redox capacitors), representing a class of capacitors with potential for high energy densities resulting from the fast and reversible redox reactions at/near the interface of the active storage material and electrolyte. In the present effort, a composite of metallic nickel embedded in its own oxide matrix has been synthesized via a novel microwave-assisted chemical route. A metalorganic complex of nickel, Ni(II) tertiarybutyl-3-oxobutanoate, synthesized in house, was used as precursor. A domestic microwave oven (2.45 GHz) was used for synthesis of the Ni/NiO nanostructures by subjecting a solution of the nickel complex in chloroform to irradiation for a few minutes, in the presence of a suitable reducing agent. The resulting powder was characterized by XRD, SEM, TEM, Raman spectroscopy, X-ray photoelectron spectroscopy, revealing that it comprises nanometric crystalline material of intimately mixed Ni and NiO. The deconvoluted core level spectrum confirms the presence of both Ni0 and Ni2+.Electrochemical measurements of such material are significant because of the Ni0/Ni+2 redox couples present within, which can enhance capacitance of the nanomaterial by adding a pseudocapacitive component. The Ni/NiO powder electrode material was pasted onto a stainless steel plate, using PVDF as binder. Cyclic voltamograms were recorded in 0.1M Na2SO4 electrolyte at different scan rates, providing substantially rectangular plots, when the potential range was 0 to -0.8 V. A linear behavior of cathodic current vs sweep rates indicates a charge-transfer process rather than a diffusion-controlled one. The electrodes were subjected to charge–discharge cycling at different current densities within the above potential range. The specific capacitance of the Ni/NiO electrode material was calculated from charge-discharge data to be 125 F/g, with excellent cyclability. The stability of the electrode was confirmed by subjecting it 1000 charge-discharge cycles. The resistivity of the metal-metal oxide electrode material, the resistivity of the electrolyte within the porous layer of the electrode, and the contact resistance between the electrode and the current collector were studied using electrochemical impedance spectroscopy at open circuit potential. It was found that the charge transfer resistance (Rct) and the diffusive resistance (Warburg impendence, W) of the Ni/NiO material are small. The electrode characteristics were also studied by systematically varying the nature (basic and neutral) concentration of the electrolyte. Optimization of the Ni/NiO composite is expected to yield higher specific capacitance, thus making it a promising electrode material.
Z18: Poster Session: Photoelectrochemistry/Electrical and Magnetic Properties
Session Chairs
Friday AM, December 02, 2011
Exhibition Hall C (Hynes)
9:00 PM - Z18.10
Morphological Control of Co3O4 and Its Photocatalytic Properties.
Jiahui Kou 1 , Rajender S. Varma 1
1 , Sustainable Technology Division, National Risk Management Research Laboratory, U.S. Environmental Protection Agency, cincinnati, Ohio, United States
Show Abstract Cobaltosic oxide (Co3O4), a p-type semiconductor, belongs to the normal spinel crystal structure based on a cubic close packing array of oxide ions. The size, surface, geometry, and crystal phase of catalysts are important parameters for controlling their chemical, optical, and electrical properties. 3D hierarchical structure of Co3O4 was prepared using organics-free method. It was formed by hundreds of small nano platelets. Their diameters are about 100 nm, and the thicknesses are about 20 nm. They stacked to constitute the triangular prisms. To the best of our knowledge, the 3D triangular prism structure has not been described before. Co3O4 displayed high efficiency to catalyze isopropanol conversion even using common incandescent bulbs as light source. Exposed definite planes often affect the property of photocatalytic material. Co3O4 has two optical band gaps, 2.2 and 1.5 eV. The first band gap of Co3O4 can be associated to O2- →Co2+ charge-transfer process (basic optical band gap energy, or valence to conduction band excitation), while the second one to O2- → Co3+ charge transfer (Co3+ level is located below the conduction band). The (001) and (111) planes contain only Co2+ cations, while the (110) plane is composed mainly of Co3+ cations. Size-controlled 2D hexagonal Co3O4 was prepared to systemically investigate the effect of exposed planes (111) on photocatalytic property. We observe that (111) exposed plane displays high photocatalytic activity.
9:00 PM - Z18.11
Electromechanical Actuation in Suspended Single-Crystalline VO2 Nanoplatelets.
Alexander Tselev 1 , John Budai 1 , Evgheni Strelcov 2 , Jonathan Tischler 1 , Andrei Kolmakov 2 , Sergei Kalinin 1
1 , Oak Ridge National Laboratory, Knoxville, Tennessee, United States, 2 Physics Department, Southern Illinois University Carbondale, Carbondale, Illinois, United States
Show AbstractDevelopment and manufacture of functional nanoscale devices and systems ranging from smart dust sensors to nanoscale robots requires generating and controlling mechanical motion on the nanoscale. The existing approaches for electromechanical actuation include systems based on piezoelectric, electrostatic, magnetic, and electrothermal principles. Actuators based on piezoelectric phenomena possess fast response speeds and allow simple electrical control. However, devices of this type achieve only relatively small effective deformations and have large footprint. In turn, electrothermal bimorph and quasi-bimorph actuators utilizing differential thermal expansion have the smallest footprint among nanoactuator classes. However, the use of operational temperatures in excess of 600 °C is necessary for a large displacement range, which leads to undesirably large thermal gradients, power consumption, and thermal-cross talk. Here, we demonstrate current-induced electromechanical actuation enabled by the metal-insulator transition (MIT) in VO2 nanoplatelets grown by a vapor transport technique. The proposed concept ultimately employs coupling of both electronic and structural aspects of the MIT in VO2 to achieve actuator action. Vanadium dioxide VO2 is a strongly-correlated electron oxide, which exhibits an abrupt, first-order MIT on cooling at a temperature of about Tc = 68 °C in bulk, which can be reduced by doping, with a few orders of magnitude change of electrical conductivity. The MIT is accompanied by a change of the lattice structure from tetragonal in metallic phases to a monoclinic in semiconducting phases with about 1% change of the lattice parameter. This large ~1% difference in the lattice parameters can be employed to generate electrically controlled mechanical motion. Namely, we show that Joule heating leads to formation of metal-semiconductor domains in suspended VO2 nanoplatelets carrying an electrical current. The metal and semiconductor domains are self-organized in chains providing a path for the current flow. This results in nanoplatelet bending depending on the current strength, which can be used for electrically-controlled actuator action. We find that with similar device sizes, achievable displacements are comparable to those characteristic for the existing electrothermal actuator designs, while operational temperatures are well below 100 °C. The actuation action can be achieved in a wide temperature range, including room temperature. We numerically and analytically analyze the main prerequisites for the realization of a current-controlled actuator based on the proposed concept. Research at ORNL's CNMS was sponsored by the Division of Scientific User Facilities, BES, U.S. DOE. The research at SIUC was supported through NSF ECCS-0925837 and SISGR-DOE ERKCM67. JDB and JZT were supported by the Division of Materials Sciences and Engineering, BES, U.S. DOE.
9:00 PM - Z18.12
Photo-Induced Changes in Cs+ Langmuir Adsorption Constant in Metal Oxide Sensitised Piezoelectric Based Self-Cleaning Sensors.
Philip Foran 1 , Colin Boxall 1
1 Engineering Department, Lancaster University, Lancaster United Kingdom
Show AbstractFunctional metal oxides such as TiO2 find use as, amongst other things, anode materials in dye sensitised solar cells, self-cleaning glass coatings and photocatalysts for gas/liquid phase pollutant destruction. In particular, the latter two applications rely upon the photo-generation of energetic charge carriers within the TiO2 matrix to drive the oxidation of organic contaminants or surface reconstruction resulting in an increase in surface bound titanol groups. The latter may increase both surface wettability and the number of surface sites at which pollutant/substrate adsorption may occur prior to their destruction at that surface. Whether such photoinduced adsorption effects exist is one of the great unsolved questions of photocatalysis. 137Cs and 90Sr are radionuclides resulting from nuclear fission. Their level of radiotoxicity and half-life of ≈ 30 years each make them a substantial hazard should they be released into the environment, for example from stored spent nuclear fuel pins. Current detection systems for 137Cs and 90Sr include ICP-MS and scintillation detectors, neither of which are well suited to in-situ detection in aqueous streams.We have deposited and characterised TiO2 films onto Quartz Crystal Microbalances (QCMs) using a sol-gel method, to investigate potential applications as self-cleaning aqueous sensors. For the first time, we have used the QCM to measure microgravimetrically Cs+ by adsorption onto a TiO2 film in real time. In the simplest case, such experiments yield two parameters of interest: K, the Langmuir adsorption coefficient and ΔMmax, the maximum mass of substrate adsorbed at the TiO2-coated quartz crystal (microgravimetric transducer) surface. Importantly we have found that illumination of the TiO2 film results in a 100% increase in ΔMmax i.e. illumination allows for greater adsorption of substrate to occur than in the dark. Our studies also show that K increases approximately 200% indicating a higher affinity for surface adsorption under illumination. The photoinduced change in ΔMmax and K are thought to be due to the increase in surface bound titanol groups, thus increasing the number of available adsorption sites – and so confirming the existence of photoinduced adsorption processes in photocatalytic systems.Further, enhanced Cs+ detection (compared to TiO2) was achieved by application of a thin film of titanosilicate ETS-10, a zeolite analog whose ion exchange capacity, chemical stability, resistance to radiation and sub-nm pore size has been shown suitable for the retention of toxic and radioactive metal ions, such as Cs+ and Sr+, from wastewaters. ETS-10 films exhibited minimum detection limits of 10μM Cs+. The photoactive properties of ETS-10 can be exploited to both further improve detection limits/resolution and to self-clean the sensor of any organic contaminants, so prolonging device life and reducing the need for maintenance, both of which are especially desirable in a nuclear environment.
9:00 PM - Z18.13
Improved Synthesis and Catalytic Activity of Cobalt Oxide Nanowires by Copper Doping.
Yunzhe Feng 1 , Xiaolin Zheng 2
1 Materials Science and Engineering, Stanford University, Stanford, California, United States, 2 Mechanical Engineering, Stanford University, Stanford, California, United States
Show AbstractCobalt oxide (Co3O4) is the most active catalyst for oxidation reactions of hydrocarbons among the single phase metal oxides. Previously, Co3O4 catalysts have been extensively studied in the form of nanoparticles (NPs) supported on porous substrate (e.g., Al2O3, ZrO2 and SiO2). However, the aggregation of NPs at large loading, especially at high temperature, hinders the further enhancement of their catalytic activities. Recently, a new structure of Co3O4, i.e., one-dimensional (1-D) nanowires (NWs) supported on metal wire cloth meshes, was reported to be a simple and efficient way to apply Co3O4 as catalyst in practical reactors, for which NWs are less likely to agglomerate so that the catalyst loading can be increased. However, it remains a challenge to uniformly grow Co3O4 NWs on metal meshes with high coverage density. Here, we report an improved one-step ammonia-evaporation-induced synthesis method, which introduces Cu ions to facilitate the nucleation process of Co(OH)2. Hence, the morphology and coverage density of Co3O4 NWs on the stainless steel wire meshes can be controlled by varying the amount of Cu ions. Optimal amount of Cu doping exists to maximize the surface area of the as-grown NWs and the optimized cobalt to copper atomic ratio is about 8:2 in the initial solution. The XRD, EDX, ICP and XPS analysis shows that the main phase of the NWs is Co3O4, with some Cu doped in the core region. Furthermore, the catalytic activities of the Cu-doped Co3O4 NWs were tested for the methane oxidation. The methane conversion percentage over the optimized NWs is about 50% higher than that over the undoped Co3O4 NWs in a temperature range of 300 to 400oC. This significant improvement is attributed to the higher coverage density, smaller grain size and hence larger surface area of the Cu-doped Co3O4 NWs from the improved synthesis method. We believe that these results not only provide a new method to control the morphologies of 1-D metal oxide nanostructures synthesized in aqueous solution, but also present an economical, scalable and yet efficient catalyst of Cu-doped Co3O4 NWs for hydrocarbon oxidation reactions.
9:00 PM - Z18.14
Morphology Control of Mesoporous Spherical TiO2: Aggregation of Nano-Crystallites for Efficient Dye-Sensitized Solar Cells.
Yong-June Chang 1 , Yoon-Cheol Park 1 , Byung-Gon Kum 1 , Eui-Hyun Kong 1 , Hyun Myung Jang 1 2
1 Department of Materials Science and Engineering, and Division of Advanced Materials Science (AMS), Pohang University of Science and Technology (POSTECH), Pohang Korea (the Republic of), 2 Department of Physics, Pohang University of Science and Technology (POSTECH), Pohang Korea (the Republic of)
Show Abstract Dye-sensitized solar cells (DSCs) consisting of a wide band-gap semiconductor film, a dye and an electrolyte have been regarded as a promising alternative to silicon-based photovoltaic cells. Till now, extensive researches have been conducted to improve DSC performances in the field of materials chemistry. One of the research trends driving innovations in DSCs is the modification of oxide nanostrucutres. Since the rise of nanotechnologies in 2000s, various oxide systems have been proposed in order to provide an efficient light-to-electric conversion in DSCs. However, traditional anatase nanocrystalline TiO2 is considered to be still the most convincing material for the photoanode of DSCs. Here, we present hierarchically-structured mesoporous spherical TiO2 (MS TiO2) as a main layer for DSCs. This porous spherical structure is composed of nano-crystallites (~10 nm) that cluster together to form larger secondary particles, thereby functioning as light scatterers without sacrificing the internal surface area needed for effective dye-uptake. For this, we have developed a new synthetic route that can produce MS TiO2 having tunable secondary particle diameters (ranging from 587 to 1554 nm) together with controlled internal pore sizes (~10 nm for all samples) through the controlled-sol-gel and a subsequent solvo-thermal process. The degree of particle aggregation could be controlled simply by adding ammonia in the solvothermal reaction. The MS TiO2 were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and nitrogen sorption analysis. The morphology dependent photovoltaic efficiencies were also compared.
9:00 PM - Z18.15
Size Controlled Flame Synthesis of Copper Oxide Nanoparticles for Li-Ion Conversion Reaction Electrodes.
Oliver Waser 1 , Andreas Guentner 1 , Sotiris Pratsinis 1
1 Particle Technology Laboratory, Institute of Process Engineering, ETH Zurich, Zurich Switzerland
Show AbstractCopper oxide nanoparticles have high catalytic activity for reactions involving H2, p-type semiconducting behavior with a bandgap at approx. 1.5 eV and as conversion reaction electrode material for Li-ion batteries. The latter have a high active to passive mass ratio offering specific capacities up to 5 times larger than those of commercially used intercalation-based materials. Compared to other conversion reaction oxides, CuO exhibits the highest electrochemical potential (1.4 V vs. Li/Li+) and a large specific charge of about 670 mAh/g. Flame spray pyrolysis (FSP) is an effective, continuous and scalable route to manufacture high purity metal oxides. Furthermore, FSP has shown great capability to control particle characteristics such as crystal phase and size over a wide range. So cooper oxide nanoparticles were made by spraying 0.25 M Cu solution in 2-ethylhexanoic acid and xylene. Controlled increase in particle size was obtained by raising the ratio between precursor to dispersion flow rate, hence increasing the enthalpy density and Cu concentration within the flame. Doubling the precursor molarity to 0.5 M and shielding the flame by a tube further increased concentration and particle residence time at high temperature allowing further particle size enlargement. Particle characterization was done by BET, TEM, XRD and electrochemical performance analysis. Phase pure CuO particles were produced within a controlled crystal size ranging from 3 to 40 nm and specific surface area (SSA) from 164 to 19 m2/g corresponding to BET equivalent diameters of 5 to 50 nm. TEM analysis indicated a narrow particle size distribution and spherical to cubic particle morphology. The impact of CuO particle size on electrochemical performance was investigated in electrodes containing 70 wt% CuO, 20 wt% acetylene carbon black and 10 wt% PDVF binder at a constant current rate of C/5, where one C is defined as the charge/discharge of the theoretical capacity within 1 h.
9:00 PM - Z18.16
Hydrothermally Grown Nanostructured Tungsten Trioxide (Hydrate) Film and Its Photocatalytic Property.
Zhihui Jiao 1 , Xiaowei Sun 1 2
1 School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore Singapore, 2 Department of Applied Physics, Tianjin University, Tianjin China
Show AbstractWe report the growth of sheet-like nanostructured tungsten trioxide hydrate film on fluorine doped tin oxide (FTO) substrate via a facile crystal-seed-assisted hydrothermal method with CH3COONH4 as capping agent. While dense thin film composed of irregular particles with smaller surface area was obtained without CH3COONH4. X-ray diffraction (XRD) studies indicated that both films were of orthorhombic structure. The film grown with CH3COONH4 after dehydration showed obvious photocatalytic activities that could generate anodic photocurrents of 1.16 mA/cm2 for oxidization of methanol and 0.5 mA/cm2 for water splitting with the highest photoconversion efficiency of about 0.3% under simulated solar illumination.
9:00 PM - Z18.17
Amyloid-like Peptide Templated Anatase TiO2 for DSSCs.
Ruslan Garifullin 1 , Mustafa Guler 1
1 Materials Science and Nanotechnology, Bilkent University UNAM-Institute of Materials Science and Nanotechnology, Ankara Turkey
Show AbstractNanostructured anatase titania offers promising solution for charge transfer efficiency because most of the losses in DSSC's are due to conduction in the TiO2. Here, we demonstrate a new method to produce nanostructured TiO2 involving self-assembling amyliod-like peptides that can organize into three-dimensional fibrous network. This network plays a role of a template in the process of mineralization. In order to achieve efficient accumulation of titania precursor (titanium isopropoxide) on the nanofibers, peptides are functionalized with carboxylate groups that provide successive nucleation centers. Thermal treatment of mineralized nanostructures at elevated temperatures leads to thermal decomposition of organic template and conversion of precursor to anatase TiO2. Nanostructured titania obtained at the end of this process preserves original three dimensional structure of the self-assembled peptide nanofiber network. Due to geometry of the templated TiO2, fast and directional charge transfer to the surface of the conducting oxide layer becomes possible. This charge transfer enhancement should substantially decrease conduction losses in the electrode. Moreover, nanostructured titania possesses high surface area, which should increase interaction between TiO2 and sensitizer, and provide higher photon to electron conversion efficiency.
9:00 PM - Z18.18
The Effect of a Blocking Layer on the Photovoltaic Performance in CdS Quantum-Dot-Sensitized Solar Cells.
Jongmin Kim 1 , Hongsik Choi 1 , Changwoo Nahm 1 , Joonhee Moon 1 , Chohui Kim 1 , Seunghoon Nam 1 , Dae-Ryong Jung 1 , Byungwoo Park 1
1 WCU Hybrid Materials Program, Department of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Show AbstractIn order to reduce the surface recombination at the interface between the fluorine-doped tin oxide (FTO) substrate and polysulfide electrolyte in CdS quantum-dot-sensitized solar cells (QDSCs), compact TiO
2 was deposited on the FTO electrode by sputtering. The TiO
2-coated CdS-sensitized solar cell exhibited enhanced power-conversion efficiency (0.52%) compared with a bare CdS-sensitized solar cell (0.23%). Charge-transfer kinetics were analyzed by impedance spectroscopy, open-circuit decay, and cyclic voltammetry. The TiO
2 layer deposited on the FTO substrate acts as a blocking layer, which plays a significant role in reducing the electron back transfer from the FTO to the polysulfide electrolyte. Interestingly, with respect to the incident photon-to-current conversion efficiency (IPCE) data, asymmetric enhancement was observed from the sample with a thicker blocking layer. This is because CdS quantum dots absorb ultraviolet light completely with the TiO
2 layer because of the high extinction coefficient of the CdS quantum dots compared with dye molecules. [1] J. Kim, H. Choi, C. Nahm, J. Moon, C. Kim, S. Nam, D.-R. Jung, and B. Park,
submitted. [2] J. B. Sambur, T. Novet, and B. A. Parkinson,
Science 330, 63 (2010). Corresponding Author: Byungwoo Park:
[email protected]9:00 PM - Z18.19
The Effect of TiCl4-Treated TiO2 Compact Layer on the Performance of Dye-Sensitized Solar Cell.
Hongsik Choi 1 , Changwoo Nahm 1 , Jongmin Kim 1 , Joonhee Moon 1 , Seunghoon Nam 1 , Chohui Kim 1 , Dae-Ryong Jung 1 , Byungwoo Park 1
1 WCU Hybrid Materials Program, Department of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Show AbstractIn order to prevent the charge recombination at the interface between the transparent-conducting oxide (TCO) substrate and electrolyte, a TiO
2 compact layer was deposited on the substrate by hydrolysis of TiCl
4 aqueous solution. Optimum thickness of the compact layer was found to be ~25 nm, which showed ~24% increase in the power-conversion efficiency compared with the bare cell. Impedance spectra indicated that the interfacial charge-transfer resistance of TCO/electrolyte interface was increased by more than a factor of three with the TiO
2 compact layer at 0.4 V. Moreover, the electron-carrier lifetime of the 25 nm-deposited cell was improved by a factor of five compared with the bare cell. [1] H. Choi, C. Nahm, J. Kim, J. Moon, S. Nam, C. Kim, D.-R. Jung, and B. Park,
submitted. [2] A. Burke, S. Ito, H. Snaith, U. Bach, J. Kwiatkowski, and M. Grätzel,
Nano Lett. 8, 978 (2008). Corresponding Author: Byungwoo Park:
[email protected]9:00 PM - Z18.20
Suppression of Charge Recombination in Photoelectrodes of TiO2-Coated ZnO Aggregates Using Wet-Chemical Processing.
Chohui Kim 1 , Jomgmin Kim 1 , Hongsik Choi 1 , Changwoo Nahm 1 , Byungwoo Park 1
1 WCU Hybrid Materials Program, Department of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Show AbstractSubmicrometer-sized polydisperse ZnO aggregates consisting of 30 nm-sized nanoparticles are synthesized using a hydrolysis method for photoelectrodes in dye-sensitized solar cell. The hierarchical structure of ZnO-based photoelectrodes influences the scattering of visible light for the prolonged optical-path distance, while the nanocrystallites provide relatively high surface area. Chemically deposited TiO
2 layer on the ZnO surface improved open-circuit voltage (
Voc) as well as short-circuit current (
Jsc). Consequently, these enhancements gave rise to better power-conversion efficiency (PCE) resulting in ~20% increase. Electrochemical impedance spectroscopy (EIS) demonstrated that the TiO
2 coating increased charge transfer resistance at the ZnO/electrolyte interface. [1] Q. Zhang, T. P. Chou, B. Russo, S. A. Jenekhe, and G. Cao,
Angew. Chem. Int. Ed. 47, 2402-2406 (2008). Corresponding Author: Byungwoo Park:
[email protected]9:00 PM - Z18.22
Photothermal Laser Processing of TiO2 Nanoparticles Films.
Lina Schade 1 2 , Hartmut Wiggers 2 3 , Nils Hartmann 1 2
1 Physical Chemistry, University of Duisburg-Essen, Essen Germany, 2 NanoEnergieTechnikZentrum, University of Duisburg-Essen, Duisburg Germany, 3 Institut für Verbrennung und Gasdynamik, University of Duisburg-Essen, Duisburg Germany
Show AbstractSemiconductor nanoparticles (NPs) show great promise as nanoscopic building blocks in a variety of energy applications including thermoelectrics and photovoltaics. TiO2-NPs, as an example addressed here, are commonly used to fabricate electrodes for dye-sensitized solar cells. Annealing and sintering of the NPs film is a key step in this fabrication process in order to build up highly conductive nanoporous electrode structures. In our studies we compare electrode structures, which are prepared using TiO2-NPs charges having distinct average diameters of 25 nm and 90 nm, respectively. Dispersions of these TiO2-NPs are spin-coated on transparent electrically conducting substrates yielding thin films. Subsequently, these films are processed using conventional annealing/sintering methods. As an alternative, in this study, photothermal annealing with UV-Lasers is carried out. Photothermal laser processing allows for rapid local annealing of NPS film/ substrate interface. In addition, using a focused laser beam allows one to locally modify and finely tune the electrode micro-/nanostructure. The morphological and chemical structure is characterized using scanning electron and scanning Auger electron microscopy. In order to test the device performance, the electrode substrates are implemented in dye-sensitized solar cells and characterized following standard protocols.
9:00 PM - Z18.23
Synthesis of Nanocrystalline Zinc Antimonate (ZnSb2O6) for Dye-Sensitized Solar Cells.
Seong Sik Shin 1 , Dong Wook Kim 1 2 , In-Sun Cho 3 , Sangwook Lee 1 2 , Dong Hoe Kim 1 , Chan Woo Lee 1 , Kug Sun Hong 1 2
1 Department of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of), 2 Research Institute of Advanced Materials, Seoul National University, Seoul Korea (the Republic of), 3 Department of Mechanical Engineering, Stanford University, Stanford, California, United States
Show AbstractDye-sensitized solar cells have been extensively studied as a promising alternative for solar energy conversion devices due to their high efficiency and low production cost. In particular, various researches have been attempted in order to achieve the high efficiency cells. Among those efforts, the development of oxide semiconductor is considered to be a highly critical factor for further improving the cell performance. In this study, nano-sized zinc antimonate, ZnSb2O6, was synthesized by a facile hydrothermal method, and the optimized nanoparticles in size and morphology were obtained by controlling the reaction conditions such as pH value, reaction temperature and time. The crystal structure and morphology of the prepared nanoparticles were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). The optical properties were also evaluated using UV-vis spectroscopy and photoluminescence spectroscopy (PL). Moreover, dye-sensitized solar cells based on the synthesized ZnSb2O6 nanoparticles were fabricated and their performances were evaluated by the current-voltage (I-V) characteristics. Based on the additional electrochemical analysis such as open circuit voltage (VOC) decay, electrochemical impedance spectra (EIS), and Intensity-modulated photovoltage/photocurrent spectroscopy (IMVS/IMPS), the electron transport properties were investigated in detail. From these results, we demonstrated the potential of ZnSb2O6 as a photoelectrode material for dye-sensitized solar cells.
9:00 PM - Z18.24
Production of TiO2 Nanotubes and Nanowires Nanofoams with Controlled Alignment.
Marcio Dias Lima 1 , Monica Jung de Andrade 1 , Ray Baughman 1
1 , University of Texas at Dallas, Richardson, Texas, United States
Show AbstractTitanium oxide nanotubes and nanowires (TONTs and TONWs) arrays have attracted considerable attention due to its (bio-)chemical, optical and electronic properties. Titania have many applications like photocatalytic removal of organic pollutants, water splitting/photolysis, sensors, sensitized solar cells, electrochemical devices for energy storage and medical applications. For each application there is a preferred crystalline phase, as well a micro/nanostructure. For example, anatase is preferred for charge separation devices, while rutile is used predominantly in gas sensors and as dielectric layers.Carbon nanotubes (CNTs) have been produced in a large variety of morphologies and arrangements and their use as a template for synthesis of TiO2 nanostructures can increase the numbers of possible nanoarchitectures/nanoarrangements for TONTs and TONWs as well. Here we report a new approach for production of nanofoams constituted of aligned TONTs and TONWs. They were synthesized using CNTs either as free-standing horizontally aligned sheets, or as vertically aligned arrays, or both simultaneously, as templates. Metallic titanium was deposited over the CNTs by using e-beam PVD and after thermal treatment conformal composite of titanium over CNTs is obtained. By oxidation the CNTs are removed and TONTs or TONWs are obtained. By combining aligned sheets and vertical arrays is possible to obtain orientation of the TONTs or TONWs in all 3 axis. The oxidation temperature determines the phase of titanium oxide produced. The synthesis of NT or NW can be tuned by controlling the amount of titanium deposited. Since the process is completely liquid free the TONTs/TONWs are not agglomerated and the resulting nanofoam is highly porous. Nanowires with diameters as low as 10 nm and aspect ratios around 30 000 were produced, the highest so far reported in the literature. Large free-standing, optically transparent sheets or meshes of the arrays can be produced. By using capillary forces of a drying solvent the nanofoams can be firmly attached to a variety of substrates. The arrays can be easily handled in the free-standing form and the uni-axially oriented arrays can even be twisted into yarns of pure TONTs/TONWs.
9:00 PM - Z18.25
Scattering Analysis of the Indium-Tin-Oxide (ITO) Nanowhiskers on ITO Film Substrate for A-Si Solar Cell.
Hsiao-Wei Liu 1 , Chia-Hua Chang 2 , Cheng-Chung Lin 3 , Peichen Yu 2
1 Display Institute, National Chiao Tung University, Hsinchu City, Taiwan, Taiwan, 2 Electro-Optical Engineering, National Chiao Tung University, Hsinchu, Taiwan, Taiwan, 3 Institute of Photonic System, College of Photonics, National Chiao Tung University, Tainan, Taiwan, Taiwan
Show AbstractThe power conversion efficiency of thin film solar cell depends on the effective light absorption, which can be improved by a light trapping mechanism for broad spectral wavelengths. Light trapping techniques such as textured surfaces and highly reflective back contacts enhance the optical absorption in thin film solar cells by increasing the light absorption path due to scattering. Such a scattering capability at rough interfaces inside a solar cell is generally characterized by a haze ratio. In this work, we demonstrate the measured haze characteristics of novel indium tin oxide (ITO) nano-whiskers deposited on an ITO-coated glass substrate. The ITO nanowhiskers for scattering layer have shown superior properties for both antireflection and scattering efficiency. Moreover, as ITO is a widely used transparent conductive oxide material and the growth technique involves only deposition in low temperature, it is very appealing to employ nano-whiskers in thin-film solar cells as light trapping textures.Next, we construct two theoretical models to analyze the scattering capability, namely, the relationship between haze ratio and the distribution of the structure size and shape. First, an equivalent spheres model based on a classical Mie theory is developed. The radius of equivalent sphere and the space distribution of spheres are used for the curve-fitting of the measured haze ratio for various nanowhisker structures. The calculated result shows that the haze-ratio of an ITO whisker layer matches the measurement closely. However, there still exists slight discrepancy in the long wavelength regime as the arbitrarily-oriented nanowhisker structures do not resemble spheres but rather look like a collection of cylinders. Therefore, a scattering model based on cylinder particles is currently under development to investigate the scattering property of nano-whiskers in more detail. The studies are crucial to the development of novel light trapping structures for thin film solar cells.
9:00 PM - Z18.26
β-AgVO3/Polyaniline Nanocables with Enhanced Electrochemical Properties.
Yanzhu Luo 1 , Liqiang Mai 1 2 , Xu Xu 1 , Yuqiang Pi 1 , Lin Xu 1 2
1 State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, WUT-Harvard Joint Nano Key Laboratory, Wuhan University of Technology, Wuhan, Hubei, China, 2 Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States
Show AbstractSilver vanadium oxides and conductive polymers have attracted much attention in energy storage. Here, β-AgVO3/polyaniline nanocables were constructed by chemical oxidative polymerization based on nanowires. XRD and FTIR patterns showed that PANI coating was successfully formed without obvious influence on the structure of β-AgVO3. TEM images indicated an uniform of PANI layer on the surface of β-AgVO3 nanowires. Electrochemical measurements exhibited that polyaniline coating could significantly improve the electrochemical performances. The electrical conductivity increased with the amount of PANI, which was helpful for the electrochemical performance within a certain range. However, too much polymer would bring some adverse effects. AcknowledgementsThis work was supported by the National Nature Science Foundation of China (51072153, 50702039), Program for New Century Excellent Talents in University (NCET-10-0661) and the Fundamental Research Funds for the Central Universities (2010-II-016). Thanks to Prof. C.M. Lieber of Harvard University, Prof. Z. L.Wang of Georgia Institute of Technology and J. Liu of Pacific Northwest National Laboratory and G. Liu of Oak Ridge National Laboratory for strong support and stimulating discussion.
9:00 PM - Z18.27
Homogeneous Iron Phosphate Nanoparticles for Food Fortification and Lithium Battery Cathodes by Flame Assisted Spray Pyrolysis Synthesis.
Thomas Rudin 1 , Sotiris Pratsinis 1
1 Department of Mechanical and Process Engineering, ETH Zürich, Zürich Switzerland
Show AbstractLow-cost synthesis of nanoparticles with uniform characteristics was achieved by flame-assisted spray pyrolysis (FASP) of inexpensive precursors and solvents (e.g., ethanol) [1]. In FASP, cheap fuel gases (acetylene or methane) are used to promote the gas-to-particle conversion and prevent formation of inhomogeneous product by droplet-to-powder conversion. Typically low cost precursors for nanoparticle flame synthesis by lead to bimodal particle size distributions, with only a fraction of nanoparticles and the rest rather large droplet-derived or-precipitated submicron sized particles. Such a bimodal particle size distribution is usually undesired and as it may deteriorate performance of the final product. Careful design of the burner can facilitate the use of inexpensive gaseous fuels minimizing formation of the large particles [1]. Here such a FASP reactor design was used for production of iron phosphate particles that find application in food fortification [2] and as cathode materials in lithium batteries [3]. It is shown, that the FASP principle is not limited to single component oxides only, enabling the production of homogeneous, complex and functional nanopowders from inexpensive precursors. Furthermore, the scale-up of the FASP burner design is explored.1. T. Rudin, K. Wegner, and S.E. Pratsinis: Uniform nanoparticles by flame-assisted spray pyrolysis (FASP) of low cost precursors. J. Nanopart. Res. 13, 2715 (2011). 2. F. Rohner, F.O. Ernst, M. Arnold, M. Hibe, R. Biebinger, F. Ehrensperger, S.E. Pratsinis, W. Langhans, R.F. Hurrell, and M.B. Zimmermann: Synthesis, characterization, and bioavailability in rats of ferric phosphate nanoparticles. J. Nutr. 137, 614 (2007). 3. O. Waser, R. Büchel, A. Hintennach, P. Novak, and S.E. Pratsinis: Continuous flame aerosol synthesis of carbon-coated nano-LiFePO4 for Li-ion batteries. J. Aerosol Sci. in press (2011).
9:00 PM - Z18.28
Dealumination of H-ZSM-5 through Regeneration of Their Nanostructure to Promote Catalytic Activity.
Yuichiro Yamazaki 1 , Masafumi Nakaya 1 , Kohji Omata 2 , Muneyoshi Yamada 3 , Atsushi Muramatsu 1
1 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai Japan, 2 Department of Applied Chemistry , Tohoku University, Sendai Japan, 3 , Akita National College of Technology, Akita Japan
Show Abstract The synthesis of light olefin from dimethyl ether (DTO) reaction on H-ZSM-5 zeolite catalyst is feasible as an olefin synthesis process. In order to apply the catalyst to real use in DTO reaction, the catalyst life is required to be extended, because the catalyst life is short due to deposit of carbonaceous species on catalyst. Therefore, both high stability in catalytic activity and high activity after regeneration are desired. Catalyst regeneration often causes the decrease of initial activity and the contraction of the regeneration interval. Consequently, the inhibition and the clarification of irreversible deterioration on catalytic activity are essential to develop the catalysts with long catalyst life on DTO reaction. Here, we report the dealumination extended catalyst life of H-ZSM-5 on DTO reaction by measuring the acidities and crystal structure of that after regeneration. Catalytic activity tests were carried out at 723 K using a fixed bed flow reactor. After reaction, deactivated catalyst was regenerated in air flow at 923 K for 3 h. The reaction – regeneration cycle was repeated three times. The catalyst life of H-ZSM-5 (Si/Al molar ratio 45, supplied by Süd-Chemie corp.) was increased as increasing the number of this cycle (catalyst life of 1st, 2nd, and 3rd reaction was 110 h, 130 h, and 167 h, respectively). This improvement on catalytic activity might be caused by dealumination from zeolite framework, because the decrease of acid amount and surface area of micropore was observed after regeneration.In order to confirm this hypothesis, dealuminated H-ZSM-5 was consciously synthesized by steaming treatment at 723 K. The duration of this treatment is the same as catalyst life in 1st reaction. The catalyst life was 253 h and this life exceeded the one in 3rd reaction. This result strongly evidences that dealumination causes the improvement of catalyst life. In order to investigate when the dealumination was proceeded, 27Al MAS NMR spectra of fresh, reacted and regenerated catalysts with steam treated catalyst after reaction were obtained. The signal at 50-60 ppm on fresh catalyst was assigned only framework four-coordinated Al species. In addition to this signal, a signal on reacted catalyst was also observed at 30-40 ppm. In contrast, this signal on regenerated catalyst decreased whereas that at 0 ppm increased. The signal at 0 ppm was assigned to extra-framework six-coordinated Al species. These results indicate the formation of “unstable Al species” during reaction such as four-coordinated species and five-coordinated species. These “unstable Al species” would be changed to extra-framework six-coordinated species by regeneration. In conclusion, it was revealed that dealumination of H-ZSM-5 zeolite framework by produced steam during reaction causes the extension of catalyst life.
9:00 PM - Z18.3
Resistance Change Caused by Electrochemically Induced Carrier Injection in NiO Films.
Takatoshi Yoda 1 , Kentaro Kinoshita 1 2 , Takahiro Fukuhara 1 , Satoru Kishida 1 2 , Koichiro Honda 3 4 , Nobuhiro Sawai 3
1 engineering, Tottori University, Tottori, Tottori, Japan, 2 , Tottori University Electronic Display Research Center, Tottori, Tottori, Japan, 3 , FUJITSU LAB. LTD., Atsugi, Kanagawa, Japan, 4 , Tohoku University, Sendai, Miyagi, Japan
Show AbstractWe reported that we can overcome a limit of the analysis on physical properties of ReRAM filament because of its locality by writing a low and high resistance states directly on a wide area of a NiO film using conductive atomic force microscopy (C-AFM) [1]. The contrast of scanning electron microscope (SEM) image of the C-AFM writing area depends on the written resistance. The SEM contrast is bright for a low resistance area, whereas dark for a high resistance area. Based on the reports about the dopant-type dependence of SEM contrast in Si [2], it is suggested that high resistance area is i- or n-type Ni1-δO (δ≤ 0), and low resistance area is p-type Ni1-δO (δ> 0). To verify this, in this study, the effect of electron beam (EB) irradiation on the C-AFM writing area was investigated. Furthermore, scanning non-linear dielectric microscopy (SNDM) measurement, which sensitively detects carrier type of the specimen, was performed on the C-AFM writing area.A 60-nm NiO film was deposited on a Pt(100nm)/Ti(20nm)/SiO2(100nm)/Si(625μm) substrate by DC reactive magnetron sputtering. LRS and HRS were written to the NiO film by scanning the AFM-tip with the tip contacted to the NiO film. The AFM-tip was grounded, and bias voltage was applied to the Pt-BE, where BE is a bottom electrode. At the low acceleration voltage, Vaccel, of 0.8 kV, the contrast of LRS and HRS areas were bright and dark, respectively. On the other hand, at higher Vaccel of 3.0 kV, the contrast of both LRS and HRS areas became dark independent of the resistance. These results are consistent with those reported in ref. [1]. We calculated trajectories of the incident electrons in the NiO film by using Monte Carlo method. Depths from which secondary electrons are emitted were estimated to be 8 nm and 50 nm for Vaccel of 0.8 kV and 3.0 kV, respectively. Therefore, the resistance change occurs near the surface. LRS and HRS areas were then irradiated by EB. The contrast of the LRS area disappeared in 10 min for the irradiation voltage, Virrad, of 0.5 kV, whereas the contrast of HRS area remained for longer than 30 min. Considering that NiO is easy to be a Ni-deficient p-type semiconductor, this result suggests that LRS and HRS areas are p-type Ni1-δO (δ> 0) and i- or n-type Ni1-δO (δ≤ 0), respectively, which is consistent with the report by Kinoshita et al. [1]. Moreover, SNDM signal is positive in low resistance area, while negative in high resistance area. SNDM signal becomes positive if the capacitance increased due to narrowing of the depletion layer when positive electric field is biased from the substrate. Therefore, the result of SNDM measurement is consistent with the results of the EB irradiation measurement. Our result also suggests that artificial carrier injection is possible by utilizing C-AFM writing technique. [1] K. Kinoshita et al., Mater. Res. Soc. Symp. Proc. 2011 accepted, [2] P. Kazemian et al., J. Appl. Phys. 100, 054901, (2006).
9:00 PM - Z18.30
Mesoporous Spinel Li4Ti5O12 Nanocomposite with Thin Carbon Layer for Lithium Ion Battery.
Eunae Kang 1 , Jin Kon Kim 1 , Yoon Seok Jung 2 , Anne Dillon 2 , Jinwoo Lee 1
1 , pohang university of science and technology, Pohang Korea (the Republic of), 2 , National Renewable Energy Laboratory, golden, Colorado, United States
Show AbstractA spinel Li4Ti5O12 nanocomposite with thin carbon layers and large pores is simply fabricated via self-assembly of block copolymer and inorganic precursor. Polyisoprene-block-poly(ethylene oxide) (PI-b-PEO) containing a sp2 carbon is employed to induce the structure of mesoporous Li4Ti5O12. Then as-synthesized material is heat-treated up to 700 C to convert inorganic sources to the spinel Li4Ti5O12 sustaining mesoporous structure. Small portion of the PI in block copolymer is converted to carbon in confined space that coats the pores of mesoporous Li4Ti5O12. Carbon from part of PI preserved the porous mesostructure and improves the electronic conductivity. This mesoporous Li4Ti5O12 is used as anode for lithium ion battery compared with Bulk Li4Ti5O12 . When cycled at 10 C-rate, Mesoporous Li4Ti5O12 shows reversible capacity of 115 mA h g-1. However, a Bulk Li4Ti5O12 exhibits only 69 mA h g-1 at 10 C-rate. Excellent performance of mesoporous Li4Ti5O12 with carbon coating layer is attributed to short path way of electron and lithium ion and electrical conductivity.
9:00 PM - Z18.31
Binder-Free Cobalt Oxide Nanoparticle Films through Electrophoretic Deposition, for Li-Ion Batteries.
Don-Hyung Ha 1 , Mohammad Islam 1 , Richard Robinson 1
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Show AbstractThere has been increasing interest in the use of nanoscale materials for Li-ion battery electrodes due to their high surface-to-volume ratio and reduced Li-ion diffusion length which results in faster charge/discharge. Nanomaterials also show the ability to accommodate strain through volume expansion without pulverization or capacity fading. In particular, nanoscale transition metal oxides have been studied as alternative anode materials due to their high capacity. In this work we have developed a hollow cobalt oxide nanoparticle (NP) film for Li-ion battery electrodes that require no additional support materials such as carbon black or polymers to establish good electrical pathways. Due to the absence of binder materials, the NP films can reduce the extra weight of the binders and improve the battery capacity/weight ratio. The colloidal cobalt NPs are prepared by decomposition of organometallic precursors in non-aqueous conditions. The NP film is formed by using electrophoretic deposition (EPD). During EPD, a film is formed on both the positive and negative electrodes but the film on the positive electrode is slightly thicker than that of the negative electrode, which indicates that more particles are negatively charged. The EPD deposited films are calcined to form hollow cobalt oxide (Co3O4) NPs that act as the Li-ion battery anode. Battery charge/discharge cycling of these films show low degradation and are near the theoretical capacity limits for this material. In addition, these binderless films show good electrical contacts while the drop-casted films calcinated under identical conditions show poor contacts and poor battery performance. Interestingly, the film formed on the negative side during EPD shows better cycle performance than that on the positive electrode. In order to investigate the different chemistry of the NPs on the negative electrodes, positive electrodes, and drop-casted electrodes, we have performed X-ray absorption spectroscopy. Results from this study show that the film formed on the positive electrode has similar features to drop-casted film.
9:00 PM - Z18.32
An In Situ Method of Creating Metal Oxide-Carbon Nanocomposite and Their Application in Lithium-Ion Batteries.
Zichao Yang 1 , Jingguo Shen 1 , Lynden Archer 1
1 Chemical and Biomolecular Engineering, Cornell Univ, Ithaca, New York, United States
Show AbstractTransition metal oxides are attractive as anode materials for lithium-ion batteries (LIBs) due to their high lithium intercalation capacity and generally high natural abundances and their use on the nanoscale is being actively pursued. However, there are still challenges associated with the use of these metal oxides, including the pulverization problem and limited electrical conductivity of many metal oxides. It has been shown that these problems may be alleviated by creating metal oxide-carbon composites, which improve upon the mechanical flexibility and the electrical conductivity of the material.There are different approaches for creating the carbon composites such as carbon nanopainting and attaching the metal oxide nanoparticles to carbon substrates. The current work describes an alternative method of creating metal oxide-carbon nanocomposites, in which the metal oxide nanoparticles are created in situ and embedded in a porous carbon matrix, which is made through calcination of a polyacrylonitrile-based polymer. Fe3O4 is used as a model compound.Characterization techniques such as X-Ray diffraction, transmission electron microscopy and Raman spectroscopy were used to investigate the physical and chemical properties of the composite. Cyclic voltammetry of the composite shows lithium intercalation at 1.2V and 0.8V, which may be attributed to the reduction of Fe3+ to Fe2+ and Fe2+ to Fe0, respectively. Very stable capacity is observed over >110 cycles at charging rate of 1C. Performance at other charging rates up to 5C is also shown and is seen to be stable. The contribution of factors including electrical conductivity, mechanical properties and porous nature of the carbon matrix in enhancing the electrochemical performance is investigated. The application of the method to other related materials such as MnO, Sn and Si is discussed.
9:00 PM - Z18.33
Nanostructure of Magnetic Layers in Perpendicular Magnetic Recording Media
Faraz Hossein-Babaei 1 , Robert Sinclair 1 , Kumar Srinivasan 2 , Gerardo Bertero 2
1 Materials science and engineering, Stanford University, Stanford, California, United States, 2 Research and development, Western Digital Media Corp., San Jose, California, United States
Show AbstractIn perpendicular magnetic recording (PMR) media, each bit of data is written in physically distinct magnetic grains with magnetizations perpendicular to the film surface. At the present state of the art, pushing the technology toward higher data storage densities, nearing 1 Tb in-2, requires the dimensions of one bit to approach a few tens of nanometers [1], and many magnetic grains per bit are needed considering the signal-to-noise ratios for the writing and reading processes. Here, we examine perpendicular magnetic recording media comprising Co-rich grains of such small dimensions manufactured by sputter deposition of the magnetic layer (ML) on a Ru seed layer [2]. The ML nanostructure, composed of about 10 nm grains [3], is believed to be controlled by this seed layer [4,5]. The magnetic grains in the ML are ideally separated by one nanometer wide amorphous intergranular phase (IP) of a metal oxide serving to magnetically separate the crystalline grains [1].Owing to the nanometric feature scales involved, the transmission electron microscope (TEM) is the most suitable tool for characterization. However, discriminating the ML and Ru layer from one another using the broad beam TEM imaging modes is impeded by the overlapping of the structural features of both layers in the images. We report a novel use of scanning transmission electron microscope-energy dispersive spectrometry (STEM-EDS) to simultaneously observe the nanostructures of the ML and Ru layer. Distinct chemical maps with nanometeric resolutions were obtained from the two layers based on their unique compositions. In each layer, the grain and IP regions can be distinguished owing to the differences between compositions of the columnar grains and the IP in either layer evident in the maps. Presence of Moiré fringes due to interference of the crystals of the two layers imaged in diffraction contrast TEM images ensured both the ML and Ru layer were present in the regions examined. The results show a strong grain-to-grain agreement between the two layer structures.References:[1] Piramanayagam, S. N., J. Appl. Phys. 2007, 102, No. 011301.[2] Bertero, G. A.; Wachenschwanz, D.; Malhotra, S.; Velu, S.; Bian, B.; Stafford, D.; Wu, Y.; Yamashita, T.; Wang, S. X. IEEE Trans. Magn., 2002, 38, 1627–1631.[3] Kwon, U.; Sinclair, R., Velu, E. M. T.; Malhotra, S.; Bertero, G. IEEE Trans. Magn., 2005, 41, 3193–3195.[4] Weller, D.; McDaniel, T. Media for Extremely High Density Recording. In Advanced Magnetic Nanostructures; Sellmyer, D. J., Skomski, R., Eds.; Springer: US, 2006; pp 295–324.[5] Judy, J. H. J. Magn. Magn. Mater., 2005, 287, 16–26.
9:00 PM - Z18.34
Magnetic Reversal of Flame-Synthesized Single Crystal γ-Fe2O3 Nanowires.
Pratap Rao 1 , Xiaolin Zheng 1
1 Mechanical Engineering, Stanford University, Stanford, California, United States
Show AbstractSingle crystal γ-Fe2O3 nanowires (NWs) with 40-60 nm diameters and <110> growth directions were grown for the first time by single-step, atmospheric, catalyst-free flame vapor deposition (FVD) with rapid axial growth rates up to 5 μm/minute, on iron and silicon substrates. To the best of our knowledge, this FVD synthesis is the first demonstration of the direct growth of γ-Fe2O3 NWs from vapor, and produces NWs of superior crystallinity. As a result of the improved crystallinity, these FVD γ-Fe2O3 NWs exhibit enhanced magnetic properties compared to γ-Fe2O3 NWs synthesized by other methods. Specifically, these FVD γ-Fe2O3 NWs are single magnetic domains with saturation magnetizations of 68 emu/g and room temperature coercivities of 200 Oe compared to the zero or small room temperature coercivities previously reported for γ-Fe2O3 NWs, nanotubes or NW-like structures synthesized by other methods. These NWs likely reverse their magnetization by the incoherent process of curling.
9:00 PM - Z18.35
Intercluster Interaction and Magnetic Interaction between Iron Core and Iron Oxide Shell in Nanocluster.
Maninder Kaur Tarsem Singh 1 , Qi Yao 1 , You Qiang 1
1 Department of Physics, University of Idaho, Moscow, Idaho, United States
Show AbstractThe cluster – cluster interactions and magnetic interactions between the iron core (ferromagnetic) and iron oxide (ferrimagnetic) shell in iron/iron oxide nanoclusters have been investigated by field dependent isothermal remanent magnetization (IRM) and dc demagnetization (DCD) measurements at room temperature. In this study the surface/boundary spins of clusters were not frozen and were thermally activated during the measurements. This helps the exchange interaction to transmit through the interface. A cluster deposition system which combines magnetron sputtering with gas aggregation technique is used to prepare iron/iron oxide core shell nanoclusters of different size (10-25 nm) by varying the ratio of argon and helium gas [1]. The tools such as transmission electron microscopy, x-ray diffraction and energy dispersive microscopy have been used for physical characterization, and vibrating sample magnetometer and magnetic force microscopy for magnetic characterization. The two remanence curves measured for different size of nanoclusters provide the information on the energy barrier distribution [2-3]. The nature of the intercluster interactions varies with the size of the nanoclusters. The exchange interactions between surface atoms can be significant for the clusters that are in close proximity. To overcome the magnetocryatlline energy barrier, smaller clusters require less field and time compared to bigger size clusters. Henkel plot shows more negative deviation from non-interacting case that reveals the strong exchange interaction which increases with the growth size of the cluster. The intercluster interactions were also evaluated using delta M plot. All nanoclusters represent the negative peaks of demagnetizing interactions (magnetostatic) at low field followed by the positive peaks of magnetizing interactions (exchange). [1] Y. Qiang, J. Antony, A. Sharma, J. Nutting, D. Sikes, and D. Meyer, “Iron/iron oxide core-shell nanoclusters for biomedical applications,” J. of Nanoparticle Research, vol. 8, no. 3-4, pp. 489-496, Oct. 2005.[2] S. Laureti et al., “Magnetic interactions in silica coated nanoporous assemblies of CoFe2 O4 nanoparticles with cubic magnetic anisotropy,” Nanotechnology, vol. 21, no. 31, p. 315701, Aug. 2010.[3] T. Thomson, K. O’Grady, and G. Bayreuther, “Magnetization reversal mechanisms and time-dependent processes in thin Tb/Fe multilayer films,” J. of Physics D: Applied Physics, vol. 30, no. 11, pp. 1577-1587, Jun. 1997.
9:00 PM - Z18.36
Doped Magnetic Core Shell Nanoparticles for Highly Efficient Intracellular Delivery of Biomolecules.
Shraboni Ghoshal 1 , Birju Shah 1 , KiBum Lee 1
1 Chemistry and Chemical biology, Rutgers, The State University of New Jersey, PISCATAWAY, New Jersey, United States
Show AbstractCore shell nanoparticles are a class of multicomposite nanoparticles where the core nanoparticle is generally coated by a layer of polymer, metal or nonmetal. Core shell structures are of special interest because of the fact that they contain the properties of the various components in a very condensed manner. We here demonstrate the use of a novel core@shell nanoparticle with a magnetic core and a thin outer shell of gold. The advantage of having a gold outer shell is the magnetic property of the core is restored while gold provides easier surface modification. Also, the gold shell can be used for other applications such as photothermal therapy or Raman imaging.Previous studies have shown that doped magnetic nanoparticles greatly increase the magnetization of the nanoparticle. ZnFe2O4 nanoparticle is an example of such doped magnetic nanoparticle. This system has a new and different lattice arrangement compared to more common Fe2O3 and Fe3O4 nanoparticles and hence having a uniform coating of gold was challenging. We have successfully made ZnFe2O4@Au core shell nanoparticles for which we have the advantage of having the properties of two different nanoparticles, a strong magnetic nanoparticle and a gold nanoparticle- into a single system. As an application of our system, we wanted to see the cellular uptake of siRNA GFP into cells using our ZnFe2O4@Au nanoparticles using magnetofection. Once the core@shell nanoparticles were synthesized and made biocompatible, we conjugated it with siRNA GFP and observed the cellular uptake of siRNA GFP by the cells under the influence of a magnetic plate. We coated our core shell nanoparticles with a polyamine dendrimer to conjugate the siRNA. Our ZnFe2O4@Au nanoparticles were found to be highly effective in translocation of the siRNA inside the cells and 50% knockdown of GFP in cells in a small time frame of 15 minutes was observed.The gold outer shell provided an easy chemical surface to functionalize with polyamine dendrimer and siRNA. We are currently extending the application of our ZnFe2O4@Au nanoparticles for Raman imaging of cells. This talk will mainly focus on the properties of doped magnetic nanoparticles, preparation of core shell structure and the utilities of such multimodal nanoparticle system in intracellular delivery of various biomolecules.
9:00 PM - Z18.37
Magnetic Multi-Granule Nanocluster Ranging from Tens of Nanometer to Hundreds of Nanometer: Solid-State Phase Transformation, Magnetic Property, and Magnetic Resonance Effect.
Jinmyung Cha 1 , Ji Sung Lee 2 , Young Keun Kim 2 , Jin-Kyu Lee 1
1 Chemistry, Seoul National Univ., Seoul Korea (the Republic of), 2 Materials Science and Engineering, Korea University, Seoul Korea (the Republic of)
Show AbstractThe development of magnetic nanoparticles with high magnetic response is of great importance for several applications. Recently, the convenient synthesis of magnetic multi-ganule nanoclusters (MGNCs) was reported by the reaction of FeCl3 in ethylene glycol as solvent as well as reductant in the present of sodium acetate. However, the precise formation mechanism and magnetic property of MGNC is not clear. Formation of magnetic MGNCs by simple refluxing method systematically studied to suggest a new mechanism of the solid-state phase transformation after the hydrolysis/condensation of FeCl3 along with the partial reduction of Fe3+ to Fe2+ by ethylene glycol. Based on the proposed mechanism, the size of MGNCs could be precisely and reproducibly controlled from tens of nanometer to hundreds of nanometer by varying initial reaction conditions and the synthetic scale could be easily increased up to gram-scales. The magnetism and magnetic properties in magnetic MGNC system as the size changes have been investigated. We were able to monitor, for the first time, the entire spectrum of coercivity behaviors including the domain state change as well as the superparamagnetic transition associated with size variation in a wide range, up to hundreds of nanometer, of nanostructured magnetic particles prepared by a single synthesis method. Moreover, we have studied to understand the size effect that as-prepared MGNCs with a wide range of sizes have on the transverse relaxation time (T2) of water proton. Through understanding of magnetic properties and magnetic resonance effect as the size changes, magnetic MGNC with optimum sizes were developed to maximize the magnetic resonance sensing. More detailed results of the investigation of synthetic mechanism, magnetic properties, and magnetic resonance effect of the MMGNs will be discussed.
9:00 PM - Z18.39
Defect Mediated Room Temperature Ferromagnetism and Its Control in VO2 Films Grown on c-Sapphire Substrates.
Sudhakar Nori 1 , Tsung-Han Yang 1 , Jagdish Narayan 1
1 Department of Materials Science & Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractThe room temperature ferromagnetic (RTFM) properties in vanadium-based oxide system driven by the stoichiometric defects are complex yet very interesting. Vanadium oxide (VO2) is an interesting material exhibiting ultra-fast and a very sharp low temperature semiconductor to above room temperature metallic transition at ~340 K. The vanadium oxide (VO2) thin films were grown on c-plane sapphire substrates by pulsed laser deposition technique (PLD) under different ambient conditions. The ferromagnetism of the epitaxial VO2 films can be switched “on/off” by altering the ambient cooling parameters. In addition, the saturated magnetic moments and coercivity of VO2 films are found to be a function of oxygen partial pressure of the growth process. The RTFM properties of VO2 films have been correlated with the nature of microstructure and growth parameters. The motivation behind the present work is to investigate if there is any direct evidence between the native stoichiometric defects and magnetic properties leading to the ferromagnetic coupling. It turns out that the post growth; cooling-cycle ambient parameters have a direct bearing on the physical properties. In this presentation, we report the interesting magnetic studies on as–grown and undoped epitaxial thin films of VO2 on c-plane sapphire substrates by altering the cooling-cycles and other ambient parameters. In addition, the RTFM is also found to vary with the oxygen partial pressure during the growth and post-growth stages. The origin of the induced magnetic properties can be qualitatively understood to stem out of intrinsic structural and stoichiometric defects. The observed magnetic properties are discussed and correlated with structural characteristics and defects in the absence of impurity content as determined by high resolution transmission microscopy (TEM) analysis and X-Ray Photoelectron Spectroscopy (XPS).1. T. Yang, S. Nori, H. Zhou, J. Narayan, Appl. Phys. Lett. 95, 102506 (2009)2. T. Yang, C. Jin, R. Aggarwal, R.J. Narayan, and J. Narayan, J. Mater. Res. 25, 422 (2010)
9:00 PM - Z18.4
Photodecomposition of 4-Chlorophenol over Micro Arc Oxidized Ag-Doped TiO2 Nanocrystalline Porous Layers.
Negin Salami 2 , Mohammad Reza Bayati 1 , Farhad Golestani-fard 1 , Hamid Reza Zargar 3
2 Metallurgy and Materials Engineering, Iran University of Science and Technology, Tehran Iran (the Islamic Republic of), 1 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States, 3 Metals and Materials Engineering, University of British Columbia, Vancouver, British Columbia, Canada
Show AbstractIn this research, micro arc oxidation technique was employed to grow Ag-doped TiO2 porous layers. A porous morphology with a rough surface was revealed by the SEM and AFM results. Compositional studies, conducted by XRD and XPS methods, showed that the fabricated layers mainly consisted of the anatase phases. A small amount of rutile phase was also detected at high voltages, e.g. 500 V. Considering the XRD patterns, the anatase average crystalline size was determined as 67.8 and 21.5 nm for the pure TiO2 and silver doped TiO2 layers, respectively. A red-shift was observed in the absorbance edge of the layers when Ag was introduced into the titania lattice giving rise to a visible-light response. Photocatalytic efficiency of the layers was studied through decomposition of 4-chlorophenol solution on their surface under visible and ultraviolet irradiations. The doped layers exhibited more favorable potential to decompose the pollutants either in aqueous phase or gaseous phase under ultraviolet and visible lights.
9:00 PM - Z18.40
Novel Core-Shell Structured Magnetic Ternary Oxide Nanocubes.
Lingyan Wang 1 , Jin Luo 1 , Bridgid Wanjala 1 , Natasha Chernova 1 , Chuan-Jian Zhong 1
1 Department of Chemistry, State University of New York at Binghamton, Binghamton, New York, United States
Show AbstractMixed-metal oxide nanoparticles with spinel structures, e.g., metal ferrite nanoparticles, represent an important class of metal oxides in which the metal dopant substitution constitutes a strategy for achieving high and tunable nanomagnetism for solid-state devices, biomolecular separation, specific targeting, or catalytic reactions in fuel cells and batteries. This report describes a novel core-shell structured ternary nanocube of MnZn ferrite synthesized by controlling reaction temperature and composition in the absence of conventionally-used reducing agents. The highly-monodispersed core-shell structure consists of an Fe3O4 core and an MnZnFe2O4 shell. The observation of Moiré pattern indicates that the core and the shell are two highly crystalline materials with slightly different lattice constants that are relatively rotated by a small angle. The ternary core-shell nanocubes display magnetic properties regulated by a combination of the core-shell composition, and exhibits an increased coercivity and the field-cooled/zero-field-cooled characteristic drastically different from regular MnZn ferrite nanoparticles. The ability to engineer the spatial nanostructures of ternary magnetic nanoparticles in terms of shape and composition offers the atomic-level versatility in fine-tuning the nanoscale magnetic properties. A detailed delineation among size, composition and shape for this class of core-shell nanocubes could lead to the design of advanced nanostructures useful for magnetic and catalytic applications.
9:00 PM - Z18.41
Analysis of Insulator in Spin Tunneling Magneto-Resistance Device.
Yosuke Yoshino 1 , Kazuo Shiiki 1
1 Department of applied physics and physico-imformatics, keio university, Yokohama, kanagawa, Japan
Show AbstractSpin tunneling magneto-resistance (TMR) devices, which consist of three layers of a ferromagnetic layer / an insulator / a ferromagnetic layer, are expected as high sensitive magnetic read heads. However it is reported TMR ratio decreases with increasing the bias voltage [1]. In this paper, the decrease in the TMR ratio has been investigated by using the simulator, Atomistix ToolKit[2].It is thought the characteristics of TMR devices greatly depend on the atomic structure of the insulator. When the TMR device has the ideal insulator, the TMR ratio becomes 51.4%, but when ferromagnetic impurities exist in the center of the insulator, the TMR ratio becomes 6.0%. Especially, when ferromagnetic impurities exist in the interface of the insulator / the ferromagnetic layer, the TMR ratio becomes 0.6%.When ferromagnetic impurities exist in the interface between the insulator and the ferromagnetic layer, the TMR ratio decreases from a bias voltage. This is thought new minority-spin bands are created by the ferromagnetic impurities existing at the interface for antiparallel magnetizations. Therefore, the resistance for antiparallel magnetizations becomes small, and TMR ratio decreases with increasing the bias voltage.It becomes clear that TMR ratio decreasing with increasing the bias voltage is caused by the mixture of ferromagnetic impurities at the interface of the insulator / the ferromagnetic layer.[1] A. M. Bratkovsky: Appl. Phys. Lett., 79, 1334 (1998).[2] http://www.cybernet.co.jp/quantumwise/
9:00 PM - Z18.42
Shape Controlled Core/Shell Magnetic Oxide Nanoparticles for Antenna Applications.
Matthew O'Malley 1 2 , Thomas Ekiert 1 2 , Angela Griner 1 3 , Cory Flynn 1 3 , Brandon Yocum 1 3 , Jennifer Lippold 1 3 , Mallory Lyle 1 3 , Derek Mirre 1 3 , Max Alexander 1
1 , Air Force Research Laboratory (AFRL/RXBC), Wright Patterson AFB, Ohio, United States, 2 , Universal Technology Corporation, Dayton, Ohio, United States, 3 , Southwestern Ohio Council for Higher Education (SOCHE), Dayton, Ohio, United States
Show AbstractFe3O4Patch antennas with improved conformal antenna gain, reduced antenna aperture size, and improved bandwidth control are of interest to an increasingly mobile world. To obtain these improvements internal efforts are directed at developing new magnetic oxide nanoparticle/polymer composites with independently modifiable permeability and permittivity (μ = ε ≈3-5) with low electrical losses (tan δ < 0.001) at ever increasing frequencies. Our approach to achieving independently engineered permittivity and permeability, while maintaining low electronic loss, consists of producing shape controlled core/shell magnetic nanoparticles. The methods of synthesis utilize microwave and traditional heating to perform hydrothermal and solvothermal reactions. Solvothermal decomposition of iron (III) acetylacetonate and cobalt (II) acetylacetonate is performed using alcohols of varying length and degrees of branching resulting in production of spherical nanoparticles with diameters of 8-16 nm and 3-7 nm for Fe3O4 and CoFe2O4, respectively. Microwave methods consistently result in smaller particles, but are produced in 30 minutes compared to 48 hrs via the traditional solvothermal method. Successive growths using traditional heating are used to produce larger monolithic particles as well as core/shell systems (e.g. Fe3O4/CoFe2O4). High aspect ratio Fe3O4 nanoneedles (10x100 nm) are produced using a yttrium assisted hydrothermal synthetic technique resulting in nanoneedles with μr up to and exceeding 15. Methods of characterization include electron microscopy (TEM, SEM), X-ray diffraction, X ray photoelectron spectroscopy, and SQUID magnetometry.
9:00 PM - Z18.43
Hysteretic Current-Voltage Behavior of Titanium and Hafnium Dioxide Nanoparticle Memristive Devices.
Zachary Rice 1 , Magnus Bergkvist 1 , Joseph Van Nostrand 2 , Nathaniel Cady 1
1 , College of Nanoscale Science & Engineering, Albany, New York, United States, 2 , Air Force Research Laboratory, Rome, New York, United States
Show AbstractMetal oxides, such as TiOx, HfOx, CuOx, and ZnOx, exhibit memristive switching behavior. While this switching behavior has been primarily observed in devices fabricated from thin film materials, there is a growing body of work on resistive switching in nanomaterials/nanoparticles [1-4]. The objective of the research presented herein is to study the influence of particle size and crystallinity on the resistive switching characteristics of titanium and hafnium dioxide nanoparticles. Titanium and hafnium dioxide nanoparticles were synthesized by solution-based hydrothermal methods using titanium isopropoxide and hafnium dichloride oxide octahydrate precursors, respectively. The structure of the titanium dioxide nanoparticles was tailored from crystalline (anatase and rutile) to amorphous, with the particles sizes ranging from 10nm-200nm. The hafnium dioxide nanoparticles were monoclinic in crystal structure with a size of ~25nm. These particles were dispersed into a 6% hydrogen silsesquioxane (HSQ) solution, which was subsequently spun onto Cu-coated wafers and cured. Device fabrication was completed by patterning Ni top electrodes on top of the assembly using a shadow mask. Electrical characterization of the TiO2 nanoparticles in thin films of HSQ revealed a hysteretic current-voltage behavior, similar to that observed in memristive switching. For example, when sweeps were performed from 0V to 3V, the devices became less resistive. After sweeping in the negative direction (0 to -3V), the resistance state returns to a higher resistance state. It was found that the conductivity of the device was not only influenced by the direction of the applied electric field; the number of sweeps in a given voltage regime and the polarity and magnitude of the voltage also impacts the resistance of the device. Because Au nanoparticles have been demonstrated previously in memristive thin films, they were also incorporated with TiO2 nanoparticles into HSQ thin films. Hysteretic IV behavior was also observed for these samples. Similar devices with HfO2 have been fabricated and are currently being tested to understand the memristive properties of HfO2 nanomaterials.[1]Y. Yang, J. Ouyang, L. Ma, R.J.-H. Tseng, and C.-W. Chu, “Electrical Switching and Bistability in Organic/Polymeric Thin Films and Memory Devices,” Advanced Functional Materials, vol. 16, May. 2006, pp. 1001-1014.[2]B. Mukherjee and M. Mukherjee, “Nonvolatile memory device based on Ag nanoparticle: Characteristics improvement,” Applied Physics Letters, vol. 94, 2009, p. 173510.[3]J. Ouyang, “Application of nanomaterials in two-terminal resistive-switching memory devices,” Nano Reviews, vol. 1, May. 2010, pp. 1-14.[4]J.C. Scott and L.D. Bozano, “Nonvolatile Memory Elements Based on Organic Materials,” Advanced Materials, vol. 19, Jun. 2007, pp. 1452-1463.
9:00 PM - Z18.44
Characterization of Extraordinary Transmission through Hole Arrays in a Metallo-Dielectric Metamaterial across the Visible.
Emily Ray 1 , Rene Lopez 1
1 Physics and Astronomy, University of North Carolina, Chapel Hill, North Carolina, United States
Show AbstractWe report the characterization of extraordinary transmission through hole arrays in a 4 pair Al2O3-Ag metamaterial with 20.0 nm thicknesses across the visible. Using ion beam-milled square hole arrays with 400 nm periodicity, we examine the spectral response of transmission and reflection for hole diameters from 250 nm to 50 nm. Simulations and inspection of the dispersion curve reveal that the surface plasmons generated by the periodicity are outside the region of tuned enhanced transmission of the metamaterial. However, in this region, the metamaterial mimics a film of Ag with the equivalent thickness even though half of the Ag has been replaced by Al2O3. The metamaterial exhibits an increased spectral response of approximately a factor of 2 over the Ag film and shows transmission peaks that are predicted from both the Ag plasmon dispersion curve at 575 nm and 590 nm as well as those unique to the metamaterial dispersion near 700 nm. Also, the transmission peak centered around 700 nm has a wider full width half max and possesses a shoulder that extends into the red up to 850 nm. The transmission trends are independent of diameter size variation from 250 nm to 150 nm, but there is an increased transmittance that varies by a factor of 4 with diameter, which agrees well with simulation. The 50 nm diameter holes exhibited an almost featureless spectrum as was predicted by simulation.
9:00 PM - Z18.45
Terahertz Dielectric Response and Optical Conductivity of ITO Nanowhiskers.
Chan-Shan Yang 1 , Chia-Hua Chang 2 , Mao-Hsiang Lin 1 , Pei-Chen Yu 2 , Ci-Ling Pan 1
1 Physics, National Tsing Hua University, Hsinchu Taiwan, 2 Photonics, National Chiao Tung University, Hsinchu Taiwan
Show AbstractTin-doped Indium-Oxide (ITO) nanorods or nanocolumns were recently shown to exhibit broadband and omni-directional antireflective properties that are attractive for application in solar cells and light-emitting diodes. The ITO nanowhiskers, with side branches, exhibit similar characteristics. In this work, we report a Terahertz time-domain spectroscopic (THz-TDS) studies of the ITO nanowhiskers.Our ITO whiskers were grown on high-resistivity silicon wafers by using oblique-incidence electron beam deposition. The target was 95 wt. ‰ In2O3 and 5 wt. ‰ SnO2. The substrate was tilted at a deposition angle of 70° with respect to the incident vapor flux. During deposition, the temperature of substrates was controlled at 250°C~260°C. High-resolution TEM images of the samples reveal a structure of ITO trunks with side branches. X-ray diffraction analysis shows that the whiskers are crystalline with a lattice constant of 5.18 Å.Transmission and reflection THz-TDS studies show that the real parts (n) of the frequency dependent complex refractive indices of the ITO whiskers decrease slowly with increasing frequency, and the imaginary parts (κ) are always smaller than n (0.2~2 THz). For the complex conductivities (Re{σ}, Im{σ}) of the ITO whiskers, we find that Re{σ} increases slowly as the frequency increases, while, Im{σ} increases at higher THz frequencies and is always negative. For whiskers of thicknesses from 418 nm to 698 nm, the plasma frequencies are found to be in the range of 864 ~ 920 rad×THz, and the scattering times lie in the range of 60.4~68.9 fs. The mobility and carrier concentration of the above ITO whiskers are determined to be 2.1~25.6 cm2V-1s-1 and 7~8×1019 cm-3, respectively. Such electrical characteristics compared favorably with those of the ITO thin films. We attribute the larger values of scattering time of ITO whiskers to their better crystallinity.
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Anodized Ni Thin Layers by Atomic Force Lithography and Resistance-Switchable NiO Nanostructures.
Nuri Lee 1 , E. Kim 1 , C. Meny 2 , W. Jo 1
1 Department of physics, Ewha Womans University, Seoul Korea (the Republic of), 2 Département Magnétisme des Objets NanoStructurés (DMONS) IPCMS, The Centre National de la Recherche Scientifique (CNRS), Strasbourg France
Show AbstractAnodized metal-oxide nanostructure is studied by atomic force lithography (AFL). We prepared Ni thin films by RF magnetron sputter and anodized oxidation process was performed by scanning probes. Ni nanolayers have been prepared by rf-magnetron sputtering and e-beam evaporation. The as-gown exhibits a wide range of resistivity from tens to hundreds of μΩcm, depending on growth rate and deposition pressure. Ni films Thickness of the Ni films was changed from 1 to 70 nm in order to examine the thickness dependence of oxidation process. The oxidized structure looks always protruded as the Ni layer is applied by external bias. NiO has a rock-salt structure and the band gap of 3.6 eV. Microscopic chemical analysis was performed by Auger electron spectroscopy and Raman scattering spectroscopy. It seems that there is a minimum thickness to give rise to an oxide island. Electrical properties of NiO nanostructures were measured with a metal-coated cantilever on a nanometer scale. A switchable resistance out of the current-voltage curves indicates that the NiO nanodots and nanowires are potential for memory devices. Current level of the nanodots is a few nA at 1 V. From the interdistance between the fabricated NiO nanodot arrays, an integrated intensity is estimated as 1.5 Gbits/in2.
9:00 PM - Z18.48
High Mobile Electron Gas at LaAlO3/SrTiO3 Heterointerface.
Shanshan Su 1 , Jeong Ho You 1
1 Department of Mechanical Engineering, Southern Methodist University, Dallas, Texas, United States
Show AbstractHeterostructures consisting of two perovskite band insulators, LaAlO3 (LAO) and SrTiO3 (STO) have received much attention due to the presence of high mobile two-dimensional electron gas (2DEG) at the interface. In this work, we have calculated carrier distributions and band structures in a LAO film stacked on a STO substrate containing a n-type interface by solving the Schrödinger equation self-consistently with the Poisson equation. It is found that the interface remains non-conducting up to four unit cells of LAO. For five or higher unit cells, the interface becomes conducting due to a significant overlap between the STO conduction band and the LAO valence band. About 80 % of electrons are localized within 7 nm from the interface forming two-dimensional electron gas, and multi-subbands are occupied indicating multi-channel conduction. Mobility of 2DEG has been calculated using the linearized Boltzmann equation including scattering mechanisms of acoustic phonon, polar optical phonon, and remote ionic charged layers in LAO. The calculated mobility matches well with available experimental data. At low temperature, the mobility is limited by the remote ionic charged layers in LAO. At higher temperature, the polar optical phonon is the dominant scattering center. The acoustic phonon scattering becomes an important scattering mechanism at intermediate temperature.
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Influence of Carrier Transport in Individual SnO2 Nanowire FETs by Surface Passivation.
Junghwan Huh 1 2 , Min-Kyu Ju 1 , Doyoung Jang 1 , Jong-Heun Lee 3 , Gyu-Tae Kim 1
1 School of Electrical Engineering, Korea University, Seoul Korea (the Republic of), 2 Semiconductor Research Institute, Korea University, Seoul Korea (the Republic of), 3 Department of Materials Science and Engineering, Korea University, Seoul Korea (the Republic of)
Show Abstract For the metal oxide nanostructures, the electrical properties are dominantly affected by the surface effects such as the chemical adsorption/desorption and the oxygen vacancy. However, conventional dc analysis employed to study the surface effects can not clarify the influence of dynamic responses at the surface although the surface reactions of metal oxide nanostructures (cf. ZnO or SnO2 nanowires) play a key role in the performance of electronic devices. In this study, we investigated the passivation effects on the electrical transport of individual SnO2 nanowire field effect transistors (FETs) using the noise characterization. The electrical characteristics of the SnO2 FETs were improved by coating the PMMA (polymethylmethacrylate) on SnO2 nanowire surfaces. Moreover, most of devices exhibited the positive shift of the threshold voltages owing to the change of carrier concentrations according to the surface passivation. From the low frequency (LF) noise measurement, the unpassivated devices exhibited the higher level of drain current noise power spectrum (SId). In contrast, the SId of the passivated devices decreased. More importantly, the LF noise behavior in both unpassivated and passivated devices can be described with the carrier number fluctuations associated with the charge carrier trapping and release at the oxide-semiconductor interface. These results suggest that the dynamic responses at the surface or the depletion layer can strongly affect the carrier transport in the SnO2 nanowire devices. Also we found that the PMMA passivation layer of metal oxide nanostructures can significantly reduce surface reactions which can induce the higher noise in the nanostructure devices.
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The Characterization of Electronic State from Surface to Several Nanometer Region on MgO:Si Thin Film.
Mikihiko Nishitani 1 , Mutsumu Fukada 1 , Masaharu Terauchi 1 , Tessei Kurashiki 1 , Yasushi Yamauchi 2 , Yukihiro Morita 1
1 , Osaka university, Suita , Osaka, Japan, 2 , National Institute of Material Science, Tsukuba Japan
Show AbstractRecently, it is reported that the secondary electron emission coefficient is improved by adding a small amount (about 0.03 at %) of Si to MgO film though it has not come to clarify the mechanism. For the understanding of the secondary electron emission process, we have tried to characterize the electronic state of the outer-most surface (the first layer from the surface of the material) of MgO:Si films measured by helium meta-stable de-excitation spectroscopy (MDS). Additionally, the XPS measurements, which contained the information about the electronic state around the depth of the several nm from the surface, were carried out to acquire the basis of the outer-most surface. In our experiment, the plasma discharge characteristics of the MgO:Si films without exposing in the atmosphere after the film deposition has been improved with an increase with the Si content in the MgO film. But, the MgO:Si (1 at %) thin film showed the higher discharge voltage compared with the pure-MgO thin film and MgO:Si (0.01 at %) thin film with exposing in the atmosphere. As for the measurements of MDS and XPS on those MgO thin films with exposing the films in the atmosphere, the thin film of MgO: Si (1at %) showed the peak shift to lower energy side of a kinetic energy of the electron in the MDS spectrum compared to the other MgO films, and any differences were not detected in the valence band spectra of XPS. However, the change in the O1s spectrum according to an increase in the Si content let us speculate that the increase of the Si content in the MgO film made the surface hydroxide and carbonate quickly. Essentially, the addition of Si to MgO of at least about one atomic percent improves the discharging characteristics of MgO:Si film. However, those surfaces quickly change to the hydroxide and/or carbonate with the increase of Si addition. In fact, it seems that the secondary electron emission properties of MgO:Si are decided by the result of those trade-offs.
9:00 PM - Z18.51
Analysis of Current Screen Layer by Current Spectroscopy.
Masaki Ishigaki 1 , Kazuo Shiiki 1
1 Department of Applied Physics and Physico-Informatics, Keio University, Yokohama, Kanagawa, Japan
Show AbstractCurrent-perpendicular-to-plane giant magnetoresistance (CPP-GMR) device, which has a potential for high signal-to-noise ratio, is a promising candidate for next-generation magnetic sensing device. Noise in CPP-GMR junctions with low resistivity decreases, but apparent MR ratio also decreases because of parasitic resistance from leads. Therefore, it has been attempted to confine current in the junction and control resistance by inserting the current screen layer (CSL) which is a nano-oxide layer with a current-confining path. However, it has not been clarified how current flows in the CSL. In this study, characteristics of current in the CSL-CPP-GMR were analyzed by current spectroscopy. Current spectrum of CSL-CPP-GMR was measured by the modulation method. The positive direction of the bias voltage was defined as the direction where a current flowed from a free magnetization layer to the pinned magnetization layer. The measurement temperature was 4K and 77K. Modulation voltage was 50 μV. A peak was measured around 10mV in current spectrum at 4K for the antiparallel configuration. At the voltage where the peak appears, it is thought that current flows in current-confining path. The peak was not measured at 4K for parallel configuration and at 77K for both configurations. In our previous work[1], a peak was measured at the positive voltage for antiparallel configuration and at the negative voltage for parallel configuration at 77K. The following two mechanisms are thought regarding this phenomenon. First, a peak becomes small at low temperature and the peak is thought to be buried in noise. In previous measurement[1], the device was cooled by LN2. On the other hand, in this measurement, the device was cooled by cryostat. The noise of cryostat is so large that the peak might not be seen. Second, it depends on temperature whether or not current flows in a certain path. In conclusion, it is clarified that how current flows in the CSL depend on temperature, especially in the current-confining path.[1]S. Ono, K. Horikiri, R. Nakao, K. Shiiki, Submitted to IEEE Trans. Magn.
9:00 PM - Z18.52
N-Type Nanowire Field Effect Transistors with Al-Doped Zirconia Gate Dielectrics Grown by Atomic Layer Deposition.
Min Young Bae 1 , Jeong Sook Ha 1
1 , Korea University, Seoul Korea (the Republic of)
Show AbstractThe choice of gate dielectric materials is expected to play an important role in the electrical performance of nanowire field effect transistors (FETs). As the device scales down, it is required to minimize the thickness of dielectric film which deteriorates the insulating property of conventional silicon dioxide (SiO2) due to electron tunneling. As an alternative, aluminum oxide (Al2O3) has been widely used owing to its higher dielectric constant and lower leakage current than SiO2 film. In this paper, we report on the growth and the effect of high-k dielectric Al-doped ZrO2 on the device performance of n-type metal oxide nanowire field effect transistors. Since ZrO2 has higher dielectric constant of 20 but poorer insulating property than Al2O3, doping of Al onto ZrO2 solved its demerits as gate dielectrics. Al-doped ZrO2 film was grown by atomic layer deposition (ALD) with variation of the extent of Al2O3 ALD cycle. n-type ZnO and SnO2 nanowires were grown by chemical vapor deposition and transferred onto the device substrates via sliding transfer technique. The transfer curves obtained from the nanowire FETs exhibited the improvement in the performance such as threshold voltage and sub-threshold swing when Al-doped ZrO2 film was used. We will discuss the optimization of the growth condition and the effect on the device performance.
9:00 PM - Z18.53
Metal-Oxide-Metal Diodes for Nanorectennas.
Richard Osgood 1 , Stephen Giardini 1 , Joel Carlson 1 , Megan Hoey 1 , Lauren Belton 1 , Gustavo Fernandes 2 , Jin Ho Kim 2 , Jimmy Xu 2 , Prakash Periasamy 3 , Philip Parilla 3 , Joseph Berry 3 , Ryan O'Hayre 3 , David Ginley 3 , Matthew Chin 4 , Barbara Nichols 4 , Madan Dubey 4
1 , US Army Natick Soldier Research, Development, and Engineering Center, Natick, Massachusetts, United States, 2 , Brown University, Providence, Rhode Island, United States, 3 , Colorado School of Mines, Golden, Colorado, United States, 4 , US Army Research Laboratory, Adelphi, Maryland, United States
Show AbstractMetal-Insulator-Metal (MIM) diodes can be extremely fast, if their capacitance is low enough that the electron tunneling transit time dominates the response. For 10 nm thick insulators, transit time is of order (10 nm)/vf ~ 10^-14 sec, where vf is the Fermi velocity in the metal. The insulator in these diodes is usually an oxide, produced either by anodizing the bottom metal layer (difficult with patterned metal), or by depositing an oxide (for example, using Atomic Layer Deposition or ALD). Oxide deposition is preferred if the bottom metal must be etched to minimize capacitance, although some oxides are difficult to deposit. At NSRDEC, we have developed a quantitative model of the diode conduction, using the quantum mechanical states of the trapezoidal potential barrier in the oxide. We compare the predicted current densities of this model to the measured current density, for NiO-, Nb2O5-, Al2O3-, and TiO2-based diodes with varying oxide thicknesses (< 20 nm) and varying diode areas (20 um to 500 um squares). Both modeling and experiment reveal > 7 orders of magnitude change in current density over 1-2 volts. Oxide thicknesses are determined with cross-sectional TEM, and barrier heights (often much lower than literature values) are estimated from the measured current-voltage characteristic. We discuss how the image potential alters the predictions for the current density. We incorporate oxide-based MIM diodes with horizontal Ag nanoantenna arrays to form a “nanorectenna”, which rectifies the high frequency (~100s of THz) alternating currents generated in the nanoantennas by incident visible and near-infrared light. We observe a response to pulsed lasers from these nanorectennas (thus excluding slower thermal effects), measure the efficiency of converting vis/nir light into electrical current, and discuss the optoelectronic response in terms of photoemission within the MIM diode vs. high-frequency rectification.
9:00 PM - Z18.54
Gaussian Distribution of Schottky Barrier Heights on SnO2 Nanowires.
Cleber Amorim 1 , Olivia Berengue 1 , Luana Araujo 1 , Edson Leite 2 , Adenilson Chiquito 1
1 Departamento de física, Universidade Federal de São Carlos, São Carlos, São Paulo, Brazil, 2 Laboratório Interdisciplinar de Eletroquímica e Cerâmicas, Departamento de Química, Universidade Federal de São Carlos, São Carlos, São Paulo, Brazil
Show AbstractThe study of low-dimensional structures has received wide attention due to their distinguished performance in electronics, optics and photonics [1,2]. Such characteristic features make nanostructured materials optimal for use in gas sensor, field effect transistors and bio-chemical sensors, for instance [1-3]. Several studies have been conducted about nanostructures synthesis and characterization, but better understanding of the electrical contact-nanostructure junctions and the underlying mechanisms of injection are required. In order to contribute to this issue, it was chosen tin oxide (SnO2) nanowires due to their distinctive applications [1-3]. SnO2 presents an n-type semiconductor character with a gap of 3.6 eV, the samples were grown by vapor-liquid-solid mechanism (4) and thus, the samples were not intentionally doped. The collected material was analyzed by using x-ray diffraction (XRD, Rigaku diffractometer model DMAX 2500), field emission gun scanning electron microscopy (FEG-SEM) measurements. They were then used for building field effect transistors; titanium electrodes were defined by conventional lithographic techniques onto oxidized silicon substrates. The resulting devices were built in well know back-gate metal-oxide-semiconductor structure.Current-voltage characterization was conducted under different conditions: drain-to-source current were monitored for different gate voltages at distinct temperatures. From transconductance measurements the mobility of the devices were estimated to be 5 cm2/V.s in agreement with literature [1,5,6]. For a gate voltage of -1V the channel was turned off. The transfer curves were obtained from IDS versus VG plots at a constant VDS and in the linear regime of IDS. Also, an on/off ratio of ~104 was obtained. Finally, current-voltage data were analyzed based on well-known Schottky-Mott theory. Parameters such as barrier height, ideality factor and series resistance were estimated at different temperatures.Schottky barrier height showed a small deviation of the theoretical value mainly because the barrier was considered fixed as described by ideal thermionic emission-diffusion model. These deviations have been explained by assuming the presence of barrier height inhomogeneities [7,8]. Such assumption can also explain the high ideality factor as well as the Schottky barrier height and ideality factor dependence on temperature.References[1] Dattoli, Eric N.; et. al., Nano Lett., 7, p. 2463, 2007.[2] Kolmakov, A et. al.,. Nano Lett., 5, p. 667, 2005.[3] Lu, J. G.; et. al., Mat. Sci. Eng., R 52, p. 49, 2006.[4] Wagner, R. S. and Ellis, W. C., Appl. Phys. Lett., 4, 89, 1964.[5] Michael S. A. et. al., J. Phys. Chem. B, 107, p. 659, 2003.[6] Cheng, Y. et al., Appl. Phys. Lett., 89, 093114, 2006.[7] Werner, J.H. and Güttler, H. H., J. Appl. Phys., 69, p. 1522, 1991.[8] Freeouf, J.L., et. al., Appl. Phys. Lett. 40, p. 634, 1982.
9:00 PM - Z18.55
Correlation between Filament Distribution and Resistive Switching Property in Binary-Transition-Metal-Oxide Based Resistive Random Access Memory.
Hayato Tanaka 1 , Kentaro Kinoshita 1 2 , Masataka Yoshihara 1 , Satoru Kishida 1 2
1 engineering, Tottori University, Tottori, Tottori, Japan, 2 engineering, Tottori University Electronic Display Research Center, Tottori, Tottori, Japan
Show Abstract We reported that filaments can be formed without a forming process by introducing oxygen vacancies into the NiO layer of a Pt/NiO/Pt structure utilizing dry etching [1]. Such kind of filaments, termed native filaments (NFI), is therefore formed into the fringe area of memory cells during the dry etching process for formation of the cells structure. The existence probability of NFIs increases with increasing the length of the fringe of the memory cell (L). This suggests that there are filaments which insufficiently connect the top and bottom electrodes even in memory cells that require the forming process. Therefore, it is expected that the relation between the memory property and the number of filaments (N) can be obtained by evaluating the L-dependence of memory properties. In this paper, L-dependence of current-voltage (I-V) characteristics was investigated with the Pt/NiO/Pt memory cells fabricated using the dry etching. It was shown that both set voltage (Vset) and its dispersion decrease with increasing L. A model which explains the dispersion of Vset is proposed on the basis of these results. NiO films with the thickness of 20 nm were deposited on Pt/Ti/SiO2 substrates by using RF reactive sputtering method, followed by the deposition of Pt-top electrode (TE) with the thickness of 50 nm. During the deposition, the pressure of Ar + O2 gas was retained at 0.5 Pa (Ar : O2 = 0.45 Pa : 0.05 Pa). Then, both the Pt-TE and the NiO film were formed into L ×L μm2 = 1 × 1, 2 × 2, 4 × 4, 8 × 8, 10 × 10, and 20 × 20 μm2 by using photo lithography and reactive ion etching (RIE) in the mixture gas of Cl2 and Ar (Cl2/Ar = 0.48/0.12 Pa), where etching power was configured source/bias = 700 W / 400 W. L-dependence of I-V characteristics of Pt/NiO/Pt/Ti/SiO2 (Pt/NiO/Pt) memory cells were measured by semiconductor parameter analyzer (Agilent 4155C). Vset distributions fit to Gauss function, and the mean value of Vset (<Vset>) and full width at half maximum (FWHM) decreased with increasing L. This result suggests that the increase of N decreases both <Vset> and the FWHM of Vset distribution. These experimental results present a model based on the following assumptions (i)-(iii): (i) Filaments have each Vset, which obeys Gaussian distribution. (ii) Only the filament which has the lowest Vset sets to a low resistance state, and the other filaments keep current Vset’s. (iii) Only one filament exists in the memory cell with L = 1 μm and N is proportional to L. The results of the simulation agreed well with the experimental results. The consistency with the experimental data confirmed the validity of the proposed model. [1] T. Yoda, et al ., phys status solid (c) 8, 546 (2011).
9:00 PM - Z18.56
Comparison of MoOx/4H-SiC Schottky Contacts Formed by Annealing after Reactive Sputtering and Oxidation Annealing of Molybdenum.
Myeong Sook Oh 1 , Myeong Soo Huh 1 , Bong Seob Yang 1 , Do Hyun Lee 1 , Hyeong Joon Kim 1
1 , Department of Materials Science and Engineering, Seoul Korea (the Republic of)
Show AbstractFor stable device operation in high temperature circumstances, the formation of Schottky contacts with high schottky barrier height and low reverse leakage property is required. In previous report, RuO2 and IrO2 were used as Schottky material and characterized electrically, however these oxides are known for having low thermal stability. In this paper, molybdenum dioxide (MoO2) having better thermal stability(decomposing at 1100 °C) and high work function ( < 6.0 eV) was adopted and MoOx/4H-SiC Schottky contacts were characterized. MoOx thin films on 4H-SiC were formed by two different methods, that is, annealing after reactive sputter deposition and oxidation annealing of Mo metal, respectively. Forward characteristics of two contacts were nearly identical, but the reverse characteristics of the contacts were significantly different. The reverse leakage current level of sputtered- and oxidation annealed-MoOx/SiC are about 10-2 ~ 10-3 A/cm2 and 10-9 A/cm2 at -100V, respectively. These unusual electrical properties may be attributed to their nano-structural differences in the MoOx/SiC interface. Through TEM analysis, we could observe MoOx/SiO2/MoSix/SiC multi layers in oxidation annealed contact, i.e. SiO2/ MoSix double layer as interfacial layer was newly formed by annealing. Thick SiO2 layer formed uniformly may act as the leakage blocking layer under reverse bias and thin MoSix layer cause comparatively low SBH under forward bias. Meanwhile MoOx/SiC contacts annealed after reactive sputtering showed the partially formed clods of SiO2 in interfacial region. This results in high reverse leakage current density.
9:00 PM - Z18.58
Electrical Properties of Magnesium Carbon Co-Sputtered Thin Films Applied Post Hydroxylation Treatment.
Masafumi Chiba 1 , Daisuke Endo 1 , Mikihiko Maizono 2 , Mikiteru Higashi 1 , Hideo Kiyota 3
1 Mat. Chem., Tokai Univ., Numazu, Shizuoka, Japan, 2 Mat. Sci. and Tech., Tokai Univ., Numazu, Shizuoka, Japan, 3 Mech. Sys. Eng., Tokai Univ., Kumamoto, Kumamoto, Japan
Show AbstractIndium oxide doped with tin oxide, or ITO, has been widely used as an electrode material for flat panel displays [1]. However, the rare metal in ITO is a limited natural resource. The research group of us succeeded in developing a material composed solely of elements with abundant reserves [2]. We present the results of analyzing the electronic structure of an Mg-based compound based on its electrical conductivity [3]. Preparation of Mg-C thin films was performed in an Ar gas atmosphere at room temperature under a pressure of 0.5 Pa with disks of Mg and graphite placed on the electrode. A new transparent and electrically conductive material, Mg(OH)2-C, was formed after reacting the Mg-C film with moisture in air. On average, its transmittance of visible light was 90%. The properties were observed by X-ray photoelectron spectroscopy (XPS). Moreover, the mechanism for the effect of carbon on the electrical conductivity of Mg(OH)2 was examined on the basis of XPS spectra and DV-Xa molecular orbital calculations. The value of the band gap shows that Mg(OH)2 is an insulator. It was revealed that a new orbital appears when the number of substituting carbon atoms increases in the Mg(OH)2 lattice. It was possible to measure the new orbital that consisted of C-2s and C-2p. In addition, a comparison between the calculated electronic state around the valence band and the result measured by XPS of the obtained film reveals that they are in extremely close agreement. This suggests that there exists a mechanism that supports electrical conduction in the Mg(OH)2-C compounds. Acknowledgements: This work was supported in part by Grant-in-Aid for Challenging Exploratory Research 22656076 of Japan Society for the Promotion of Science (JSPS). The authors would like to thanks Prof. Dr. T. Kuji and Dr. T. Honjo of Tokai University for their contribute, as well as Prof. Dr. T. Ishii and Prof. Dr. K. Kuramasu of Kagawa University for useful technical advice. References: [1] T. Minami, Semicond. Sci. Techn., 20, S35 (2005). [2] T. Kuji, T. Honjo, M. Chiba, T. Nobuki, and J. –C. Crivello, e-J. Suff. Sci. Nanotech., 6, 15(2008). [3] M. Chiba, M. Higashi, H. Kiyota, M. Maizono, and T. Kuji, TMS (The Minerals, Metals and Mat. Soc.), 2011 Suppl. Proc., 3, 605(2011).
9:00 PM - Z18.59
Optimizing the Switching Uniformity of HfO2-Based RRAM by Inserting Hf Thin Layer.
Ching Hsiang Peng 1 , Wen Yuan Chang 1
1 , National Tsing Hua University, Hsinchu Taiwan
Show AbstractIn this study, the effects of inserting Hf thin layer on reversible resistive switching (RS) behaviors of HfO2 thin films is discussed. By inserting Hf thin layer, the oxygen vacancies of HfO2 thin film can be increased which improve the uniformity of RRAM devices. For this reason, the Pt/Hf/HfO2/TiN structure were deposited. The HfO2 thin films were sequentially deposited on TiN bottom electrode by atomic layer deposition, and Pt/Hf metal were fabricated by DC sputtering method. According to the X-ray photoelectron spectroscopy (XPS) analysis, the inserting Hf layer makes HfO2 thin films to be lack of oxygen without post-annealing. The Pt/Hf/HfO2/TiN memory device shows the reproducible resistive switching behavior, low operation voltage/current, stable high/low resistance and there is no data loss found in the non-destructive readout test under 0.1V. The retention characteristics performed over 105 s at room temperature and 150oC, respectively. The aforementioned results demonstrate the possible application memory of the Pt/Hf/HfO2/TiN memory device.
9:00 PM - Z18.6
Synthesis and Characterization of CeO2 Nanoparticles by Low Temperature Hydrothemal and Solvent Thermal Process.
Eric Teo 1 , Ming Lin 2 , Ziyuan Fu 1 2 , Siliang Song 1 2 , Seng Chee Ng 1 2 , Jun Cong Tan 1 2
1 School of Engineering, Republic Polytechnic, Singapore Singapore, 2 Materials Science & Characterisation Lab, Institute of Materials Research and Engineering, Singapore Singapore
Show AbstractCeria has been aggressively explored for applications as a fuel cell electrolyte or in catalytic converter due to its high oxygen ion conductivity, or as a UV absorption material. It is proven that the properties and applications of ceria nanoparticles are related to their morphologies and sizes. This ability to control the shape and morphology of CeO2 nanoparticles allows the corresponding tuning of their chemical and physical properties. Most of the applications require the use of non-agglomerated nanoparticles, as aggregated nano-particles lead to inhomogeneous mixing, poor sinterability and compromised properties. However, nano-crystals with a primary particle size < 5 nm have a strong tendency to agglomerate.In this work, nano-crystalline particles of CeO2 have been synthesized by a low temperature hydrothermal and solvent thermal synthesis process. Using the precursors of Ce(NO3)3.6H2O:NaOH in different mixing ratio, using polyvinylpyrrolidone (PVP) as the surfactant, the CeO2 particles were synthesized via 24 h hydrothermal and solvent thermal process treatment at reaction temperature of 100 oC and 180 oC using Teflon-lined hydrothermal autoclave. We have optimized the conditions for the two synthesized methods, hydrothermal and solvent thermal, to yield highly crystallized particle with controllable shape, sizes and morphology. X-ray diffraction (XRD) and high-resolution transmission electron microscope (HR-TEM) analysis were used to characterize the crystalline and morphology of the synthesized CeO2 nanoparticles. The optimal reaction condition to prepare the CeO2 of the desired octahedron shaped fluorite structure was established. Based on the results, the hydrothermal synthesis method yields nanocrystalline CeO2 sizes of ~6 nm, while the solvent synthesis method yields nanocrystalline CeO2 sizes of 2-3 nm at the optimal conditions. The hydrothermal synthesis method produced better particles in terms of crystallinity and morphology under HR-TEM. Temperature also plays a part in crystallinity and sizes of the CeO2 nanoparticles. The crystallinity and size of the CeO2 nanoparticles increases when using higher treatment temperature for both hydrothermal and solvent thermal methods. The growth mechanism of the shape and morphology of the CeO2 will also be discussed.
9:00 PM - Z18.60
Optically Transparent and Electrically Conductive Ceramic Materials.
Jonathan Rajala 1 , Mitra Yoonessi 2 3 , George Chase 1
1 Chemical and Biomolecular Engineering, The University of Akron, Akron, Ohio, United States, 2 , Ohio Aerospace Institute, Cleveland, Ohio, United States, 3 , NASA Glenn Research Center, Cleveland, Ohio, United States
Show AbstractElectrospinning is a simple and low cost method used to produce polymeric nanofibers. The chemistry of the electrospun polymer solution can be modified by adding a ceramic precursor of metal salts to produce ceramic fibers with heat treatment after the polymer fibers are formed. Some of these ceramic materials are optically transparent and electrically conductive (OTEC) materials. The goal of this work is to produce OTEC fibers that may be used to increase electrical conductivity properties of polycarbonate without adversely affecting its transparency. Ceramic fibers of indium tin oxide (ITO), zinc oxide (ZnO), aluminum oxide (AlO) and indium doped zinc oxide (IZnO) were synthesized with diameters less than 300 nm. The percent transmission range of light over a spectrum of 400 nm to 800 nm wavelength using UV-Vis spectrophotometry is 80-90% for the IZnO fibers on a glass slide. When the same sample is tested for surface conductivity, it performs as a semiconductor with a measurement of 1.21x10-8 S. While ITO nanofibers are well reported in literature, IZnO nanofibers are not reported on as much and have cost advantages in using less indium while also displaying OTEC characteristics. Potential applications for these materials include flat panel displays, solar cells, smart windows, and sensors.
9:00 PM - Z18.61
Insight into Distribution and Switching Operation of ReRAM Filaments Based on Variation Analysis of Memory Characteristics.
Kentaro Kinoshita 1 2 , Hayato Tanaka 1 , Masataka Yoshihara 1 , Satoru Kishida 1 2
1 Department of Information and Electronics, Tottori University, Tottori , Tottori, Japan, 2 , Tottori University Electronic Display Research Center, Tottori , Tottori, Japan
Show Abstract On the basis of Vset-distribution in NiO-ReRAM, we proposed a switching model that Vset of a single filament is given according to Gaussian distribution and Vset-distribution of a whole of a memory cell is decided by a group of the filaments [1], where Vset is a set voltage. Based on the model, Vset of a memory cell is decided by the lowest Vset of the Vset’s of the filaments existing in the cell. Considering the correlation between reset and Joule heat (Vreset2/RLRS) [2], the variation of Vset can be an origin that causes the variation of Vreset, where Vreset and RLRS are a reset voltage and a resistance in low resistance state. In this paper, the dependence of electric properties of Pt/NiO/Pt memory cells on cell area (S) was measured and the correlation between Vreset-distribution and Vset-distribution was estimated. A NiO film with thickness of 20 nm was deposited on Pt/Ti/SiO2 substrates by RF reactive sputtering, followed by the deposition of Pt-top-electrode (TE) with the thickness of 50 nm. During the deposition, the pressure of Ar + O2 gas was retained at 0.5 Pa (Ar : O2 = 0.45 : 0.05 Pa). Then, both the Pt-TE and the NiO film were formed into S (= L × L μm2) = 2 × 2 - 20 × 20 μm2 by using reactive ion etching. The L-dependence of Vreset-distribution showed that the average of Vreset is almost independent of L and the variation of Vreset decreases with increasing L. This result is consistent with the proposed model on the points that a memory cell is reset to a high resistance state by repairing the one filament which had the lowest Vset and the variation of Vset affects the variation of Vreset. The L-dependence of the probability that Δ(1/dn) [= 1/dn-1-1/dn] is positive, P(Δ(1/dn) > 0), was calculated from n-times successive switching cycles. Here, we assumed that a filament consists of a series of oxygen vacancies connecting a top and bottom electrodes and that n-th reset is completed by oxidizing the anode side of the filament until the oxidized thickness reaches the enough thickness, dn, to stop the reset reaction [3]. That is, positive Δ(1/dn) means that d obtained by n-th reset is larger than d obtained by (n-1)-th reset. The average P(Δ(1/dn) > 0) for n = 1-10 increased from 50 % to 60 % with increasing L from 1 μm to 20 μm, whereas the average P(Δ(1/dn) > 0) for n = 11-40 was 50 % independent of L. This result is consistent with our model in which only the filament which has smallest d (∝Vset) operates among all the filaments. Since the number of filaments in the cell is proportional to L [1], the probability that d increases after every reset process increases with increasing L.[1] H. Tanaka et al., MRS 2011 fall meeting submitted, [2] Y. Sato et al., APL90, 033503(2007), [3] K. Kinoshita et al., APL89, 103509 (2006).
9:00 PM - Z18.62
Optical and Thermal Detection Functionality of Inclined-Oriented CaxCoO2 Thin Films Based on the off-Diagonal Thermoelectric Effect.
Kouhei Takahashi 1 , Tsutomu Kanno 1 , Akihiro Sakai 1 , Hideaki Adachi 1 , Yuka Yamada 1
1 , Panasonic Corporation, Soraku-gun, Kyoto, Japan
Show AbstractThermoelectric (TE) materials enable direct conversion of heat into electricity. During the last few decades, unusual TE properties have been discovered in specially designed materials such as nanowires, nanocomposites and superlattices. The off-diagonal thermoelectric (ODTE) effect is one of such unconventional phenomena which develop in anisotropic materials with inclined crystal orientations. The ODTE effect is unique in the sense that a large surface in-plane voltage can be generated by applying a very small temperature difference ΔT in the surface out-of-plane direction. This feature is prominent for thin film samples. For example, in thin films with thicknesses of less than 100 nm, the voltage via the ODTE effect can be 105 times larger than that generated via the ordinary TE effect. Here, we report development of an optical/thermal detection functionality of inclined-oriented thin films of layered cobaltite CaxCoO2 by utilizing the ODTE effect. Samples examined here are CaxCoO2 thin films grown on n-plane sapphire single crystal substrates in which the c-axis is inclined-oriented from the film surface by 30°. CaxCoO2 exhibits large anisotropy in the Seebeck coefficient between parallel and perpendicular to the c-axis. The present films thus satisfy the theoretical requirements to develop the ODTE effect. In fact, upon illumination of a Nd:YAG pulse laser with an intensity of 1 mJ/cm2, we observed generation of large film in-plane voltages of several 10 V for films with thicknesses of less than 150 nm. We identified that this large film in-plane voltage is associated with the film out-of-plane ΔT introduced by laser heating. The films characterized here exhibited a potential to generate film in-plane voltages of up to 1 V by applying film out-of-plane ΔT of merely 1 K. This indicates that the inclined CaxCoO2 films can act as sensitive optical sensors, which operates by detecting small-ΔT applied in the film out-of-plane direction. The responses of the inclined CaxCoO2 films to thermal radiation were also measured using a blackbody furnace. The results showed that the inclined CaxCoO2 films enable detection of objects at temperatures above 33°C. The present optical/thermal detection based on the ODTE effect does not require a membrane bridge structure which is essential in conventional thermopile-type detectors, and thus, exhibit advantages over the thermopiles regarding response speed and device fabrication process.
9:00 PM - Z18.63
Fabrication of Epitaxial VO2 Nanostructured Thin Films and Their Electronic Properties.
Hidefumi Takami 1 , Teruo Kanki 1 , Kenichi Kawatani 1 , Hidekazu Tanaka 1
1 ISIR, Osaka Univ., Ibaraki, Osaka, Japan
Show AbstractVanadium dioxide (VO2) shows orders-of-magnitude changes in resistance around 340 K, accompanied by structural deformation between the tetragonal rutile phase with a metallic state at high temperature and the monoclinic phase with an insulating state at low temperature. In terms of nano-spatial characteristic in the correlated materials including VO2, the inhomogeneous magnetic and/or electronic phases derived from correlated electrons are present in nature. These nano-scaled domains work on an important element in their physical properties. In fact, each domain behavior against temperature or a magnetic field dependence remarkably reflect to the electronic properties in sub-micro sized oxide thin films which is a comparable order with a domain size instead of spatial averaged electronic properties in general thin films. From a view point of electronic applications such as a Mott-FET, electrical control of the single domain is strongly interesting, expecting drastic change of physical properties by small perturbations. In this research, we fabricated epitaxial VO2 nano-structured thin films on Al2O3 (0001) substrates. As a first step, VO2 thin films were conventionally prepared by a pulsed laser deposition technique. For the nano patterning of the thin films, we performed nanoimprint lithography (NIL) after spin-coating of organic resists on the thin films and successfully obtained patterned resists. The imprinted patterns on the resists were transferred to the underlayer VO2 film using reactive ion etching (RIE) process. Next, in order to put Au/Ti electrodes onto the VO2 nano-lines, we performed NIL process with precise positioning control. In this twice NIL process, Au/Ti electrode can be obtained at appropriate position on the VO2 lines. In this meeting, we will explain a detail process of fabricating VO2 nanostructures and report their transport properties.
9:00 PM - Z18.64
Theoretical Calculation of the Work Function of Modified Indium Tin Oxide with Novel Self-Assembled Monolayer.
Qi Wei 1 , Munkhbat Battulga 1 , Khishigjargal Tegshjargal 1 , Dashzeveg Rentsenmyadag 1 , Davaasambuu Sarangerel 1 , Chimed Ganzorig 1
1 Department of Chemical Technology, School of Chemistry and Chemical Engineering, Ulaanbaatar Mongolia
Show AbstractThe work function is the major parameter of the specific material for the usage of electronic devices. In this study we investigated the work function change of Au(111) surface with the 1-carboxyl-4-amino-2-aza-3-oxo-[2.2.2] bicyclooctane as a self-assembled monolayer (SAM) with various terminal groups such as –NH2, -Boc, and -Fmoc by Molecular Orbital ab initio method. The calculated work function changes are compared to each other. Our results of calculation indicated that there is correlation between dipole moment of isolated molecule and dipole moment on surface of SAM.
9:00 PM - Z18.65
Highly Ordered ZnO-SnO2 Epitaxial Heterostructures with Enhanced Photocatalytic Performance.
Shiting Ling 1 , Guangwei She 1 , Fuqiang Li 1 , Wensheng Shi 1 , Xiangmin Meng 1
1 Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing China
Show AbstractNanoscale heterostructures have attracted more and more attention in recent years owing to the multifunctional and integrated request for the nanodevices. As important oxide semiconductors, both SnO2 and ZnO have been intensively studied due to their outstanding properties and potential applications in nanoscale electronics, optics, sensors and other novel devices. In this study, we used a facile two-step thermal evaporation method to synthesize the highly ordered ZnO-SnO2 hierarchical nanodendrites. The SnO2 nanowire trunks in the nanodendrites were first prepared on an alumina substrate and then used as template for the growth of the ZnO nanowire branches in the second step. The XRD and detailed HRTEM investigation revealed that the ZnO branches with [001] direction are epitaxial grown from the (-101) crystal plane of the SnO2 trunks with a good lattice match. The epitaxial relationship between ZnO and SnO2 promises the fast and effect transfer and diminished recombination of the charge carriers. And with the large surface areas, the as-prepared ZnO-SnO2 nanodendrites exhibited an enhanced photocatalytic performance in the degradation of the methyl orange under the UV light illumination.
9:00 PM - Z18.67
Potential Dependent Absorption in ZnO Quantum Dots: Determining Band Edges and Density of State Characteristics as a Function of Particle Size.
Jesper Jacobsson 1 , Tomas Edvinsson 1
1 Department of materials chemistry, Uppsala University, Uppsala Sweden
Show AbstractZnO quantum dots (Q-dots) in the size range 4-10 nm have been synthesized by thermal hydrolysis in alkaline zinc acetate solution. Ensambles of Q-dots in the solid state were prepared in form of thin transparent films for spectro-electrochemical measurements. By a precise control of the electrochemical potential and thus the Fermi level at the back-contact, it was possible to form a steady-state condition of populated states in the conduction band of the quantum dots. This lead to a depletion of the optical absorption and a shift in the absorption onset as a function of the applied potential. This is similar to the Burstein-Moss shift observed in degenerate semiconductors. From the absorption change it is possible to extract the flat band potential and the position of the valence- and conduction band edges as well as density of state characteristics. In particular, we show how this can be applied and how the density of state characteristics is different for different particle sizes due to the quantum confinement. With the developed method we have been able to follow the position of the band edges as a function of particle size which previously has been found difficult to obtain for nanoparticles with traditional electrochemical methods like Mott-Schottky measurements.
9:00 PM - Z18.68
Effects of Size and Load on Transport Properties of Nanoscale Metal-Oxide Interfaces.
Ramsey Kraya 1
1 , University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractNanomaterials wills serve as the foundation of future electronics, greatly improving efficiency and capabilities due to enhanced control of interfaces at the nanoscale. In this work the effect of contact size and loading conditions on the transport characteristics of Au nanoparticle – SrTiO3 interfaces is investigated using scanning probe techniques. First, Au nano-island/reduced Nb doped SrTiO3 interfaces were electrically characterized by cAFM. The main observed result is the transport dependence on the island size and the transition from bias dependent resistance to ohmic contact response. Conductivity increased exponentially with decreasing interface size. Second, the effect of various loading conditions on the transport characteristics at Au nanoparticle – oxidized Nb SrTiO3 interfaces was investigated. Two types of interfaces were identified – one robust against applied load, and the other affected by small variations in load with improved performance with increasing load. The broader impacts of this work on the future of nanoelectronics will be discussed.
9:00 PM - Z18.69
Coupling of Colloidal CuInS2 Nanocrystals with TiO2 and ZnO Nanotubes for Fabrication of Solar Cells.
Rick Eyi 1 , William Wilson 1 , Jiang Wu 1 , Reddy Vanga 1 , Omar Manasreh 1
1 Electrical engineering, University of Arkansas, Fayetteville, Arkansas, United States
Show AbstractWe report solar cells consisting of an inorganic semiconductor, p-type CuInS2 (CIS) nanocrystals, and n-type TiO2 nanotubes. CuInS2 was chosen among the chalcopyrite compounds such as Cu(In,Ga)Se2,(CIGSe) or Cu(In,Ga)(S,Se)2, for the solar cells, because of its high optical absorption coefficient. The nanocrystals were prepared by reactive rapid thermal processing, using Cu and In precursors in the presence of sulfur vapor. The cristallinity of the particles was confirmed using XRD and TEM. The semiconductor TiO2 and ZnO nanotubes have been synthesized using an electrochemical deposition technique from an aqueous solution, using respectively Ti and Zn as starting material and platinum as the counter electrode. Two different simple techniques, not requiring exposition of the sample to high temperature, were used to couple the nanocrystals with the tubes. First an ink of CuInS2 was made and deposited on the layer of TiO2 and ZnO nanotubes, grown respectively on a Ti and a Zn foil, using a spin-coater. The thickness of the layer of CIS was controlled by changing the viscosity of the ink, the spinning time and speed. Second, tubes were dipped in a solution containing nanocrystals for different time durations. Then the samples were removed and cleaned using acetone to remove non coupled nanocrystals. Some solar cells were fabricated using uncapped CuInS2 nanocrystals and others with CIS capped with a layer of ZnS, used here as a buffer layer, between the CIS and the tubes. For the front contact, a thin and transparent layer of ITO was deposited on the sample using E-beam evaporation. The maximum efficiency of the solar cells was found, by playing with ink thickness, the spinner speed and duration, by modifying the dipping time, by adding or not the buffer layer.
9:00 PM - Z18.7
A Large Scale Quantum Chemistry Study on the Stability of Precious Metal Catalyst on CeO2 Based Oxide.
Sunho Jung 1
1 Chemical Engineering, Tohoku University, Sendai Japan
Show AbstractCeO2 is widely used for the support material of automotive exhaust catalyst. The interaction between precious metal particle and oxide support is an important factor regarding the particle growth of precious metal (PM) under high temperature. Even though Pt/CeO2 has a high inhibitive performance of the particle growth of PM, the thermal stability of CeO2 is not good for having a high surface area of the support. For this reason, the commercialized support materials contain ZrO2 and small amount of rare earth elements (RE) to improve the thermal stability of the support. Therefore, the interaction between PM and CeO2 based oxide in an atomic scale is essential for having a high inhibitive performance. Regarding the information in atomic scale, quantum chemistry approaches are effective and support some experimental findings. However, PM/Oxide systems are difficult to handle because of their high computational cost. In the present study, to clarify the effect of the RE and mixing ratio of CeO2/ZrO2 on the interaction, we evaluated the stability of PM on the RE doped CeO2-ZrO2 using a large scale quantum chemistry method. For the large scale quantum chemistry calculation and structural relaxation, original tight-binding quantum chemistry method “Colors [1]” and molecular dynamics program “NEW-RYUDO [2]” were employed, respectively. In the tight-binding calculation, interatomic bond energy is represented by the summation of orbital energy, coulombic interaction and short-range exchange-repulsion energy. To estimate the interaction between PM/Support, we deposited Pt particle on ZrO2 (ZR) Ce0.25Zr0.75O2 (C1Z3) Ce0.25Zr0.71La0.04O1.98 (C1Z3L), Ce0.75Zr0.25O2 (C3Z1) and compared the each interaction. We obtained the partial density of states of each model. To compare the each interaction, we focused on the orbital overlap between Pt 5d and O 2p. The overlap region between the two orbitals with ZR was small compared with that with Cerium containing supports. Pt/C3Z1 showed Ce 4f occupation on the overlap region while the Ce 4f occupation with Zr-rich support was quite small. This indicates that Pt particle is stable on a Ce-rich support because of the interaction among Pt 5d, O 2p and Ce 4f orbitals. We then evaluated the charge of Pt particle on each support to evaluate how easy the oxidation occurs in each PM/Support model. The order of positive charge of each Pt particle was C3Z1 > C1Z3L > C1Z3 > ZR. This is in reasonable agreement with experimental result [3]. We will discuss the average charge of each atom of the supports and bond energy between Pt/Support.
9:00 PM - Z18.70
Multi-Frequency Electron Magnetic Resonance Spectroscopy Investigations of Ni Nanocubes Embedded in MgO.
Saritha Nellutla 1 , Sudhakar Nori 2 , John Prater 3 , Jagdish Narayan 2 , Alexej Smirnov 1
1 Department of Chemistry, North Carolina State University, Raleigh, North Carolina, United States, 2 Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States, 3 Materials Science Division, Army Research Office, Raleigh, North Carolina, United States
Show AbstractIn spite of interesting magnetic properties displayed by the ferromagnetic nanoparticle (FM-NP) arrays, the spin physics behind these properties is not yet completely understood. In contrast to the traditional magnetometry techniques which measure the bulk magnetic properties of these NPs, electron magnetic resonance (EMR) spectroscopy directly detects, with a high degree of accuracy, the electronic spin properties. This presentation will discuss the EMR studies of the heat treated Ni-doped MgO crystals containing epitaxially oriented FM Ni nanocubes (NCs). Room temperature orientation dependence of the crystal with respect to the applied magnetic field at 9.5 GHz identifies three types of Ni NCs viz., (a) FM NCs with their easy magnetization axes parallel to the external field direction, (b) superparamagnetic NCs and (c) FM NCs with their hard magnetization axes parallel to the external magnetic field direction. Variable temperature (120 – 490 K) and high-frequency/high-field (9.5 – 360 GHz/0.3 – 15 T) EMR measurements further support the presence of different types of NCs. Our EMR results are consistent with the magnetization and TEM studies, where a broad distribution of blocking temperatures (TB) and sizes were observed [1,2]. To our knowledge, this report represents one of the very few systematic EMR studies performed on partially oriented NCs, demonstrating the power of EMR spectroscopy as an analytical tool in not only understanding the magnetic and spin properties of nanoscale systems but also the role of defects in ferromagnetic properties of systems such as ZnO [3]. 1. J. Narayan, S. Nori, D. K. Pandya, D. K. Avasthi and A. I. Smirnov, Appl. Phys. Lett. 93, 082507 (2008)2. J. Narayan, S. Nori, S. Ramachandran and J. T. Prater, JOM, 61, 76 (2009)3. S. Mal, S. Nori, C. Jin, J. Narayan, S. Nellutla, A. I. Smirnov and J. T. Prater, J. App. Phys. 108, 073510 (2010)
9:00 PM - Z18.71
Experimental Characteristics of SiO2 and Al2O3-ZrO2 Thin Film Layer for OLED Moisture Barrier.
Ung Soo Lee 1 , Myeong Sook Oh 1
1 Material Science, Seoul National University, Seoul Korea (the Republic of)
Show AbstractIn recent years, several organic light-emitting device (OLED) technologies such as transparent OLED, top-emitting OLED (TOLED), and flexible OLED (FOLED) have been developed. It was well known that some of the organic materials and low work function metals used in OLED device are sensitive to moisture and oxygen, which lead to the degradation of devices. Encapsulation technique is necessary to protect OLED from oxygen and water vapor. At present, the most popular encapsulation technique is to use a glass or metal lid. However, these lids are thick and heavy, which limits the applications of OLED in mobile and flexible displays. There has also been considerable interest in developing the encapsulation of OLED using thin films instead of a glass or metal lid. The film must have very good impermeability and a high optical band gap to let the emitted light pass through. Multilayer barriers recently have been reported to achieve very low permeability on polyethylene terephthalate substrates. Permeation through thin film barriers is controlled by defects ; defect size and defect density in thin film inorganic layers are the critical parameters which define the barrier performance of both single and multilayer moisture barrier. To enhance barrier property, it is important that we obtain high packing density and reduce pinhole of nanometer size. Especially pinhole of nanometer size is mainly created by particle contamination. So when is deposited, good particle coverage characteristic like ALD(Atomic Layer Deposition) film is necessary to be moisture barrier. Multilayer barrier can also enhance impermeability characteristic. Once pinhole happen to be created, it is seldom sealed. So single layer is limited to be effective moisture barrier. If we adopt two or three kinds of deposit process, due to the new interface between two layer, it will be effective to seal the pinhole. First, in this experiment, SiO2 film is deposited about 30nm thickness by Plasma Enhanced Atomic Layer Deposition (PEALD) using bis-diethylamino-silane (BDEAS) and oxygen (O2) at low temperature (100 degrees). PEALD-SiO2 films were characterized by AES and XRR. SiO2 films processed at 100 degrees had low carbon contents about 1% and good density comparable to those of 300 degrees SiO2. As the second layer Al2O3-ZrO2 was deposited about 70nm thickness by magnetron sputtering at ultra-low-pressure (0.5mTorr). Using ultra-low-pressure, density of thin film was enhanced by about 15% compared to conventional pressure(5mTorr). The packing density of Al2O3-ZrO2 film at same pressure(0.5mTorr) was enhanced as increase of the ratio of ZrO2, and it was maximum at ZrO2 of 70% ratio. Its density of ZrO2 of 70% ratio was 4.1g/cm3. It is higher than ZrO2 of 100% ratio, 3.7g/cm3. The high packing density is due to increasing sputter kinetic energy in ultra-low-pressure and interstitial structure of Al2O3-ZrO2. It can be expected to obtain high impermeability compared to Al2O3 single material or conventional pressure(5mTorr).
9:00 PM - Z18.72
Three-Dimensional Nanostructures for Photoelectric Devices.
Seong-Je Park 1 , Sang-Won Jee 2 , Joondong Kim 1 , Yun Chang Park 3 , Jun-Hyuk Choi 1 , Jun-Ho Jeong 1 , Jung-Ho Lee 2
1 Nano-Mechanical Systems Research Center, Korea Institute of Machinery and Materials, Daejeon Korea (the Republic of), 2 Materials and Chemical Engineering, Hanyang University, Ansan Korea (the Republic of), 3 Measurement and Analysis Division, National Nanofab Center (NNFC), Daejeon Korea (the Republic of)
Show AbstractAn efficient three-dimensional (3D) nanostructure photoelectric device is presented. An Al-doped ZnO (AZO) coating was applied to lithography-free patterned Si nanopillars and spontaneously formed a radial heterojunction (n-AZO/p-Si) photodiode having a quality ideality factor of 1.64. A significantly enhanced photocurrent of 5.45 mA/cm2 was obtained from the 3D nanostructure relative to that of a planar substrate (1.1 mA/cm2). This enhancement is induced by enlargement of the light-active surface area and an anti-reflection effect. Due to the intermediate refractive index of AZO, the reflection was distinctively reduced in the air-Si system. It discusses an effective approach for realizing nanostructured photoelectric device.
9:00 PM - Z18.8
Electrochemical Impedance Spectroscopic Investigations on ZnO Coated TiO2 Photoelectrodes for Dye Sensitized Solar Cells.
Mariyappan Shanmugam 1 , Mahdi Farrokh Baroughi 1
1 Electrical Engineering and Computer Science, South Dakota State University, Brookings, South Dakota, United States
Show AbstractRecent studies have shown that major recombination process in the bulk of nanoparticle based TiO2 is governed by the surface defect states rather than influenced by scattering mechanisms in the bulk of TiO2. Surface states of TiO2 which are close to the conduction band edge actively participate in the process of electron trap and recombination with electrolyte. Photoelectrodes with core-shell structure have shown significant reduction in electron trap and hence reduced recombination. A thin energy barrier, growing another metal oxide layer on TiO2 surface, can engineer the density and activity of electronically active defects in TiO2/electrolyte interface. Electrochemical impedance spectroscopy (EIS) is widely used to probe the quality of TiO2/electrolyte interface in terms of electron transport, accumulation and recombination. In this paper we present dye sensitized solar cells (DSSCs) with sol-gel processed ZnO coated TiO2 photoelectrodes and EIS investigation on the factors that govern photovoltaic performance of DSSCs. Nanoporous TiO2 colloidal paste was deposited onto ITO coated glass with TiO2 compact layer and it was sintered at 450C°C for 30 minutes. Zinc Acetate dehydrate and 2-Propanol were used as precursors to prepare ZnO at 80°C. This solution was dip coated onto the mesoporous TiO2 surface. Ruthenium 535 bis-TBA (also known as "N719") was used as the sensitizer and Iodolyte AN-50 (I-/I3-) redox electrolyte was used as an electron donor to the dye. A 40 nm thin film of Pt was deposited on another ITO coated glass as a counter electrode. DSSCs were fabricated using the two electrodes with a spacer.Deposition of ZnO on TiO2 was confirmed by X- ray photoelectron spectroscopy. A significant improvement in the open circuit voltage (VOC) and overall photoconversion efficiency of the DSSC with ZnO coated TiO2 compared to a DSSC with no ZnO coating confirmed the density and activity of TiO2 surface states were suppressed by ZnO and resulted in enhanced photovoltaic performance. EIS studies have shown that charge transfer resistance, in case of DSSC with ZnO, was reduced which confirmed electron recombination from TiO2 to electrolyte via TiO2 surface states was suppressed. Improved VOC of the DSSC suggest that there is a significant shift in the conduction band edge relative to the redox potential of the electrolyte due to the increase in electron density in the TiO2. References[1] O’Regan, B.; Gratzel, M. Nature 1991, 353, 737.[2] Kay, A.; Grätzel, M. Chem. Mater. 2002, 14, 2930.[3] Palomares, E. Clifford, J. N.; Haque, S. A.; Lutz, T.; Durrant, J. R. Chem. Commun. 2002, 14, 1464.[4] Fabregat-Santiago. Et. Al., J. Phys. Chem. C 2007,111, 6550.
9:00 PM - Z18.9
Electrical Transport Properties of Spin-Coated Thin Films Composed of ITO Nanoparticles.
Akira Fujimoto 1 2 , Kota Yoshida 3 , Masami Nakamoto 4 , Toshinobu Ohno 4 , Mari Yamamoto 4 , Yukiyasu Kashiwagi 4 , Masashi Saitoh 4 , Shinya Furuta 5 , Katsuhiro Takai 5
1 Applied Physics, Faculty of Engineering, Osaka Institute of Technology, Osaka Japan, 2 Nanomaterials Microdevices Research Center, Osaka Institute of Technology, Osaka Japan, 3 Department of Biomedical Engineering, Graduate School of Engineering, Osaka Institute of Technology, Osaka Japan, 4 , Osaka Municipal Technical Research Institute, Osaka Japan, 5 , Tomoe works co., Ltd., Osaka Japan
Show AbstractTin (Sn) doped indium oxide (ITO) is well-known transparent conductive oxide and has been widely used in a large variety of electronic devices. Most of the researches on ITO system are mainly focused on the samples grown by physical manufacturing processes such as a sputtering method, which need high vacuum and expensive experimental setups. In order to produce ITO nanoparticles (NPs), recently new inexpensive chemical synthesis which is performable in the air has been developed. However, solid state properties of the films composed of the ITO NPs are not well understood. In this study, we will clarify the Sn concentration and grain size dependence of the electrical transport properties. Furthermore, we have been trying the growth of indium oxide based dilute magnetic semiconductors doped transition metal.ITO NPs were produced by the chemical thermolysis with different initial ratio of the precursor complexes, indium and tin carboxylates. We obtained some kinds of ITO NPs doped with Sn in the amount of 1% (ITO-1), 3% and 5.5% (ITO-5). The controllable average size of these ITO NPs was about 10 nm. The ITO NPs dispersed in toluene were spin-coated on a corning glass substrate. Then the samples were dried at 150 degree centigrade for 20 min and at 500 degree centigrade for 30 min in the air. The thickness of the fabricated ITO films was estimated to be 50 nm. As a result of X-ray diffraction measurements, (222) diffraction peak of cubic indium oxide was clearly observed for the above-mentioned three types of samples with different concentration. Furthermore the half maximum full-widths of the (222) diffraction peak were broadened slightly with Sn doping level. The increase of Sn concentration is accompanied by the lattice strain and disorder. Sheet carrier concentrations obtained by Hall measurements were almost constant with varying temperature for the same three types of samples. Sheet resistance of ITO-1 film was largest of all the samples at room temperature. However, sheet resistance of ITO-5 film rose more dramatically than that of other samples with decreasing temperature, originating from the difference in crystallinity. Moreover, variable range hopping conduction is predominant at low temperatures for the ITO-5 film.We also measured transverse magnetoresistance (MR) under the magnetic field perpendicular to the film surface up to 6 T and down to 4.4 K. Negative MR was observed for all the three samples. The negative MR of ITO-5 film is probably attributed to the interference of different hopping paths. On the other hand, the negative MR for ITO-1 film results from the effect of weak localization (WL) due to the quantum interference effect of the scattered electron wave. The inelastic scattering time at crystal defects and grain boundary is evaluated from the MR data analysis based on WL theories.