Symposium Organizers
Valentin Craciun University of Florida
Dhananjay Kumar North Carolina A&T State University
Stephen J. Pennycook Oak Ridge National Laboratory
Kaushal K. Singh Applied Materials, Inc.
I1: Nanostructures and Thin Films: Magnetic and Electrical Properties
Session Chairs
Valentin Craciun
Dhananjay Kumar
Tuesday PM, March 25, 2008
Room 2001 (Moscone West)
9:15 AM - I1.1
Modulation of the Magnetic Anisotropy of Magnetite in Fe3O4/BaTiO3(100) Epitaxial Structures.
Carlos Vaz 1 2 , Jason Hoffman 1 2 , Agham-Bayan Posadas 1 2 , Charles Ahn 1 2
1 Applied Physics, Yale University, New Haven, Connecticut, United States, 2 Center for Research on Interface Structures and Phenomena, Yale University, New Haven, Connecticut, United States
Show AbstractA defining characteristic of complex oxides is the display of a wide variety of magnetic and dielectric behavior. Such multifunctional behavior has driven much research effort towards the control of the material properties by means of external applied fields, aiming both at the understanding of the electronic behavior of these strongly correlated systems and at the prospect of device applications. While the 'classical' ferroic materials such as YMnO3 and BiFeO3 continue to raise interest, recent advances in the growth of epitaxial oxide multilayers have enabled the fabrication and study of composite material heterostructures, where the properties of the individual components are engineered to yield an overall multiferroic behavior. In this context, we have investigated the effect of strain induced by a BaTiO3(001) substrate on a 10 nm epitaxial magnetite (Fe3O4) film grown by off-axis magnetron sputtering. We exploit the fact that BaTiO3 exhibits a series of structural phase transformations as a function of temperature to induce different strains on the magnetite film. X-ray diffraction measurements show that the magnetite films grows in registry with the BaTiO3(001) substrate. SQUID magnetometry and magnetoresistance measurements carried out as a function of temperature after magnetic saturation show a series of discontinuities that we attribute to changes in the strain of magnetite via elastic coupling to the BaTiO3 substrate. Magnetic hysteresis loops carried out at several temperatures (before and after each transformation in the BaTiO3) elucidate the variation of the effective anisotropy of the Fe3O4(001) film. We discuss the possibility of using the piezoelectricity of BaTiO3 layers to modulate the magnetic anisotropy of magnetite films.
9:30 AM - I1.2
Selective Adsorption of Organosilanes along One-dimensional Si Oxides at Step Edges of Si(111) Surfaces.
Akina Yoshimatsu 1 , Takushi Shigetoshi 1 , Junichi Uchikoshi 1 , Mizuho Morita 1 , Kenta Arima 1
1 Department of Precision Science and Technology, Osaka University , Suita, Osaka, Japan
Show Abstract The purpose of this study is to form novel one-dimensional nanostructures using one-dimensional Si oxides along Cu nanowires at step edges of Si(111) surfaces. Studies of the formation of low-dimensional nanostructures have attracted considerable interest because the spatial confinement of electrons in these structures results in discrete quantum states. This phenomenon is not only interesting from a fundamental point of view, but can also lead to the realization of novel nanodevices. Chemical and electrochemical methods, as the bottom-up approach, are believed to be promising approaches for achieving the mass production of nanostructures. Recently, it has reported that Cu nanowires are selectively formed at step edges of flat Si(111) surfaces composed of terraces and steps. In this study, we show that the flat Si(111) surfaces with Cu nanowires can be a template for the formation of novel one-dimensional structures by organic molecules. Among organic molecules, we use octadecyltrichlorosilane (CH3-(CH2)17- SiCl3 ,OTS) which is used as a resist in lithography processes. Samples were cut from single-side-polished silicon (111) wafers (0.1° miscut in the <11-2> direction, phosphorus-doped, 0.8-1.2 Ωcm). To remove organic contaminants, the samples were immersed in a solution (H2SO4 (97 wt%):H2O2 (30 wt%) = 4:1 (by volume)) for 10 min. Then, to remove an oxide layer, the samples were immersed in a diluted HF solution (HF (50 wt%):H2O=1:100(by volume)). To create an atomically flat surface, the samples were subsequently immersed in ultra-low dissolved oxygen water (LOW) for 30 min in N2 atmosphere. Then, the wafers were immersed in LOW containing 10 ppm Cu ions for 10 s at room temperature (referred to as the 2nd LOW hereafter). The 2nd LOW was prepared by adding a Cu standard solution (10,000 ppm Cu in 5 % HCl solution) to LOW. Next, the samples were immersed in OTS solutions for 1 s. The immersion into OTS solutions was performed in N2 ambient, because OTS reacts easily with water. AFM images show that one-dimensional structures with bright dots, of which the average height is 2.0 nm, are formed at step edges of Si(111) surfaces . The bright dots correspond to OTS molecules. On the other hand, we did not find apparent adsorption of OTS molecules at step edges of Si(111) surfaces without Cu nanowires. It is likely that adsorbed Cu atoms accelerate oxidation around step edges, which forms one-dimensional Si oxides on Si(111) surfaces[1]. It is well known that OTS molecules easily react with SiO2. These are the reason for the formation of one-dimensional structures by OTS molecules. Our results presents the possibility in which the Si(111) surface with one-dimensional Si oxides will be a template for novel nanostructures with various functional organic molecules. [1] Akina Yoshimatsu, Takushi Shigetoshi, Junichi Uchikoshi, Mizuho Morita, and Kenta Arima (Submitted)
9:45 AM - I1.3
Electronic Structural Properties of SrRuO3 Ultrathin Films on SrTiO3 Substrates.
Young Jun Chang 1 , Soo-hyon Phark 1 , Tae W. Noh 1
1 ReCOE, Department of Physics and Astronomy, Seoul National University, Seoul Korea (the Republic of)
Show AbstractHeterostructures between different oxide perovskite compounds attracts lots of attention due to its potential application in oxide electronics. One fundamental question that we have to face in utilizing the heterostructures is just how thin film can maintain their own physical properties. The ferromagnetic metal SrRuO3 films on the band insulator SrTiO3 provide a good model system to test the thickness limit of ferromagnetic metallic properties in the complex materials. We fabricated ultrathin films of SrRuO3 on TiO2 terminated SrTiO3 by pulsed laser deposition. We carefully controlled thicknesses of the SrRuO3 films from one to 50 monolayers by monitoring the growth mode with high-pressure reflection high energy electron diffraction and checked the thicknesses with X-ray reflectivity measurements. Atomic force microscopy studies show clear step-terrace structures of the films, which reflects 2-dimensional growth mode. Temperature-dependent resistivity measurements revealed that the atomically flat films are metallic down to the 2-unit-cell thickness. As the film thickness decreased, the conductivity increased and the ferromagnetic transition temperature decreased. However, the ferromagnetic transition signature in the resistivity curve could not be observed for the 2-unit-cell SrRuO3 films. We investigated thickness-dependent electronic structural changes of SrTiO3 layer by in-situ scanning tunneling spectroscopy. The electronic structural evolution will be discussed with the predictions of the first principles calculations.
10:00 AM - **I1.4
Nanowire-Based Multiferroic Oxide Heterostructures
Arunava Gupta 1
1 MINT Center, Department of Chemistry, Chemical and Biological Engineering, University of Alabama, Tuscaloosa, Alabama, United States
Show AbstractThe coupling of magnetic, electronic and shape altering properties, referred to as the magneto-electric (ME) effect, allows for dual functionality in a single-phase or composite material system. For example, an applied electric or magnetic field will induce a magnetization or polarization response, respectively, and in a composite system the response is mediated by mechanical stress: magnetostriction induced mechanical deformation and piezoelectric effect induced electric fields. We have fabricated and studied the ME properties of 1D nanowire composites consisting of ferroelectric materials, such as barium titanate (BTO), with ferrimagnetic nickel iron oxide (NFO). The core-shell nanocomposite is deposited on magnesium oxide (MgO) nanowire templates using pulsed laser deposition. A reproducible process has been developed for the growth of single crystalline magnesium oxide (MgO) nanowires with a square cross-section. The wires are grown at temperatures of 900-925°C using a vapor-liquid solid (VLS) growth process using Mg3N2 as a precursor with mixed oxygen (0.01%)/argon carrier gas. They are synthesized either as a dense array using a very thin pre-deposited gold film, which acts as a catalyst, or with lower density and controlled diameter using monodisperse gold nanoparticles. The MgO nanowires are grown on (001) MgO) and Si substrates. While the wires grow vertically aligned on MgO, they display random orientations on the silicon substrate. The vertical MgO nanowires grown on MgO substrate are used as a template for the coaxial growth of BTO and NFO layers using PLD. Work done in collaboration with G. Kim, R. Martens, G. B. Thomson, and B. Kim (University of Alabama), and G. Srinivasan (Oakland University).
10:30 AM - I1.5
Polymer Template Directed Chemical Solution Synthesis of Single-Crystalline La0.7Sr0.3MnO3 Nanowires.
Narcis Mestres 1 , Adrian Carretero-Genevrier 1 , Teresa Puig 1 , Awatef Hassini 1 , Alberto Pomar 1 , Judith Oro 1 , Jaume Gazquez 1 , Felip Sandiumenge 1 , Xavier Obradors 1 , Etienne Ferain 2
1 Institut de Ciencia de Materials de Barcelona, CSIC, Consejo Superior de Investigaciones Científicas, CSIC, Cerdanyola Spain, 2 , Université Catholique de Louvain UCL, Louvain la Neuve Belgium
Show Abstract10:45 AM - I1:Nano1
BREAK
11:15 AM - I1.6
Spontaneous Outcropping of Self-assembled (Sr,La)Ox Nanodots in Ferromagnetic La0.7Sr0.3MnO3 Films Derived from Chemical Solutions.
Cesar Moreno 1 , Patricia Abellan 1 , Awatef Hassini 1 , Angel Perez del Pino 1 , Felip Sandiumenge 1 , Jose Santiso 1 , Teresa Puig 1 , Xavier Obradors 1
1 , ICMAB-CSIC, Bellaterra, Catalonia, Spain
Show AbstractA new mechanism is proposed for the generation of self-assembled nanodots at the surface of a film based on a spontaneous outcropping of the secondary phase of a nanocomposite epitaxial film. Epitaxial self-assembled (Sr,La)Ox nanodots, as determined by electron energy loss spectroscopy, have been formed through this mechanism at the surface of La0.7Sr0.3MnO3 (LSMO) epitaxial films deposited on SrTiO3 (STO) substrates. The films were grown by chemical solution deposition using metallic propionates based solvents, and annealed at temperatures in the range 900C – 1000C under flowing oxygen gas for different annealing times up to 12h. The final thickness of the films was in the range 20 – 26 nm. X-ray reciprocal space mapping reveals that the film is fully strained. Annealing at 1000C causes the transition from a granular to flat surface, and annealing at this temperature for extended periods causes the spontaneous appearance of (Sr,La)Ox polyhedral nanodots on the surface of the film. The size and concentration of the nanodots was tuned by adjusting the precursor composition and annealing conditions, from a few to several tens of nanometres in height, and from ~4 to ~15 dots per square micrometer, as determined by analysis of atomic force microscopy images. High resolution transmission electron microscopy analysis reveals that the nanodots penetrate into the LSMO film, exhibiting a three-dimensional epitaxy, with matching distances of 0.4055 nm and 0.4048 nm, parallel and perpendicular to the LSMO film, respectively. Thus, the c-axis of the LSMO film becomes tensile stretched around the buried part of the nanodots, while the in-plane parameters are kept tensile stressed throughout the whole interface with the STO substrate. This results in a volume expansion of the LSMO unit cell of 2.5% around the nanodots. Analysis of HRTEM images reveals that the stress state induced by the nanodots may even induce a local transition from the rhombohedral structure to the films to an orthorhombic or monoclinic one around the nanodots. On the other hand, the strain values determined for LSMO regions not influenced by the nanodots yield a Poisson ration of 0.38, indicating that the film preserves its structural integrity between the zones of influence of the nanodots. Isothermal magnetization loops revealed that the macroscopic behaviour corresponds to an in-plane easy axis orientation, as expected for in-plane tensile LSMO/STO films. Thus, the overall in-plane macoscopic magnetic anisotropy is preserved in the presence of the nanodots, indicating that it is dominated by shape anisotropy affects. We suggest that the driving force for the nanodot formation is the minimization of the elastic strain energy of the nanocomposite film and the mechanism is a generalization of the classical Stranski-Krastanov growth mode also involving phase separation.
11:30 AM - I1.7
Ferroelectric Field Effect Tuning of the Electronic and Magnetic Properties of Colossal Magnetoresistive Oxides.
Jason Hoffman 1 2 , Hajo Molegraaf 3 , Xia Hong 1 4 , Jean-Marc Triscone 3 , Charles Ahn 1 2
1 Applied Physics, Yale University, New Haven, Connecticut, United States, 2 Center for Research on Interface Structures and Phenomenon, Yale University, New Haven, Connecticut, United States, 3 DPMC, Université de Genève, Geneva Switzerland, 4 Physics, Penn State Universtiy, State College, Pennsylvania, United States
Show AbstractIn order to control the electron spin state in devices, the magnetic properties of the constituent materials are of paramount importance. In this respect, strongly correlated oxides are promising candidates for such devices because of the multitude of physical properties that they exhibit, which in principle allows one to control the electron and spin transport via applied electric or magnetic fields. In this work, off-axis RF magnetron sputtering was used to deposit La1-xSrxMnO3 (LSMO) films with high crystalline quality and atomically smooth surfaces. Magneto-optical Kerr effect (MOKE), SQUID magnetometry, and magnetotransport measurements performed on thick films (30-40nm) show bulk-like behavior: the Curie temperature corresponds well with the metal-insulator transition temperature.Chemical substitution is the traditional tool used to tailor the electrical and magnetic properties of LSMO. Here, we use an electrostatic approach, the ferroelectric field effect, to tune the magnetotransport properties of LSMO thin films. Epitaxial ferroelectric Pb(ZrxTi1-x)O3 (PZT) / LSMO heterostructures were fabricated using off-axis RF magnetron sputtering. X-ray diffraction reveals c-axis oriented growth of PZT, with a typical root-mean-square (RMS) surface roughness of ~5Å. Using the polarization field of the ferroelectric, we have reversibly tuned the carrier density and magnetotransport properties of the LSMO films. Using the magneto-optical Kerr effect (MOKE), we observed a 30K shift in the ferromagnetic Curie temperature of LSMO upon switching the polarization direction of PZT. This result is in good agreement with the 35K shift in Tc observed in magnetotransport measurements for LSMO thin film heterostructures with similar thickness and composition.
11:45 AM - I1.8
Tuning Electronic Transport of Thin-film Pervoskites with Strain: The Role of Anisotropy.
Franklin Wong 1 , Virat Mehta 1 , Seung-Hyub Baek 2 , Rajesh Chopdekar 1 3 , Chang-Beom Eom 2 , Yuri Suzuki 1
1 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 2 Materials Science and Engineering, Univeristy of Wisconsin, Madision, Madison, Wisconsin, United States, 3 Applied and Engineering Physics, Cornell University, Ithaca, New York, United States
Show AbstractMuch of the recent efforts to realize functional perovskite interfaces have concentrated on exploiting charge transfer at polar heterojunctions. A system of current interest is the LaTiO3(LTO)-SrTiO3(STO) Mott insulator-band insulator interface where the localized carriers in the bulk of the Mott insulator LTO has been predicted to delocalize at or near the interface due to abrupt changes in the Ti valence, thereby creating a confined metallic interfacial layer. It should be noted that strain in LTO films should profoundly alter their electronic structure and hence transport properties, as many the bulk pseudo-cubic perovskites Mott insulators are sensitive to the details of their orthorhombic distortion. Using pulsed-laser deposition and starting with a pressed La2Ti2O7 powder target, the thermodynamically stable bulk phase, we have grown (001) LaTiO3 (LTO) perovskite thin films. Cross-section transmission electron microscopy and four-circle x-ray diffraction have confirmed the growth of a homogeneous perovskite phase, with no noticeable second phases. Using standard four-point van der Pauw and Hall transport measurements, we have observed a metal-insulator transition (MIT) in LTO films controlled by biaxial epitaxial strain. Electronic transport characteristics ranging from metallic to semi-metallic to insulating can be attained in LTO thin films when deposited on (001) SrTiO3, (001) (LaAlO3)0.3(Sr2AlTaO6)0.7, and (001) LaAlO3 substrates, respectively. Among the films on different substrates, resistivity values range over two orders of magnitude at room temperature and seven orders at 5K. The strain-induced tetragonal distortions in the films, as quantified by x-ray diffraction, lowers the overall crystal symmetry and lifts the degeneracy of some electronic bands as well as changes their dispersion, creating anisotropy that cannot be routinely attained in the bulk. We propose the MIT in LTO thin films can be explained by the transfer of electron population from a large-bandwidth itinerant band to a small-bandwidth localized polaron band. We demonstrate how the structural anisotropy gives rise to this electronic anisotropy and illustrate the importance of using a multiple band model to understand (even on a qualitative level) the electronic conduction in LTO thin films. The conceptual model that we have developed is a general one that can be applied to other related materials, and we will suggest new opportunities to tune the properties of perovskite oxide thin films by exploiting strain.
12:00 PM - **I1.9
Magnetic Coupling at Epitaxial Manganite-Bismuth Ferrite Interfaces Grown by Molecular Beam Epitaxy.
Ramamoorthy Ramesh 1
1 Department of Materials Science & Engineering and Department of Physics, University of California-Berkeley, Berkeley, California, United States
Show AbstractThe creation of new functional heterostructures may enable a new generation of devices based on electrical control of magnetic properties. Until recently the knowledge of the appropriate materials to make such devices possible did not exist, but with the rebirth of interest in multiferroic and magnetoelectric materials this may become a reality. The algorithm involves the utilization of both the intrinsic coupling present in magnetoelectric, multiferroics like BiFeO3 (BFO) – where ferroelectricity and antiferromagnetism are coupled – as well as extrinsic coupling – like that present between a ferromagnet and an antiferromagnet – to create the first generation of this new class of device. In this work we have produced fully epitaxial heterostructures in which we can probe the nature of coupling between functional materials and understand how to engineer such systems for creation of new spin-based logic, memories, and devices. We report the growth and characterization of multifunctional systems based on the ferromagnet La0.7Sr0.3MnO3 (LSMO) and the multiferroic, antiferromagnet BFO using laser-MBE synthesis techniques to achieve atomic level control of the heterostructures. The nature of the coupling in the heterostructures has been probed using a variety of magnetic measurements including SQUID magnetometry and synchrotron-based, chemical specific x-ray measurements. From this analysis we have found that the heterostructures exhibit classic negative exchange bias interactions – a shift of the hysteresis loop as well as enhancement of the coercive field. The nature of this coupling has been examined as a function of both BFO and LSMO thicknesses, temperature, strain state, and more. Measurements aimed at understanding the nature of the coupling at the interface, including synchrotron based scattering experiments, will be discussed as well.
12:30 PM - I1.10
Control of the Early Stacking Sequence in Oxide Heterostructures on SrTiO3(001).
Romain Bachelet 1 , Federico Valle 1 , Jose Santiso 2 , Ingrid Infante 1 , Franco Rigato 1 , Nico Dix 1 , Florencio Sanchez 1 , Josep Fontcuberta 1
1 , ICMAB-CSIC, Barcelona Spain, 2 , Centro de Investigación Nanociencia y Nanotecnología, Barcelona Spain
Show AbstractIt is well-known that the surface morphology and the chemical termination of ABO3(001) perovskite-type substrates (i.e. AO and/or BO2) drive the early stack of subsequent functional layers. In this communication, with the example of the most-commonly used perovskite-type substrate for growth of oxide heterostructures, namely SrTiO3(001), we show that well-defined surfaces with atomic steps and flat terraces can be obtained by annealing in air at high temperature. Moreover, taking advantage of the SrO surface segregation with temperature and time on fully TiO2-terminated surfaces, we demonstrate that the chemical termination ratio can be well-controlled in a full range of 0 to 100% without destroying the “step and terrace” morphology. These results are revealed by phase imaging by amplitude-modulation atomic force microscopy and the impact on the early stacking sequence is shown through the pulsed laser deposition of (sub)monolayers controlled by in-situ high pressure reflection high energy electron diffraction.
12:45 PM - I1.11
Interface-charge-coupled Ferroelectric Hysteresis Resistance Switching in Pt-ZnO-BaTiO3-Pt Heterojunctions: A Physical Model Approach.
Venkata Voora 1 , Tino Hofmann 1 , Mathias Schubert 1 , Matthias Brandt 2 , Nurdin Ashkenov 2 , Lorenz Michael 2 , Grundmann Marius 2
1 Department of Electrical Engineeringand, and Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 2 Institut für Experimentelle Physik II, Universität Leipzig, Leipzig Germany
Show AbstractWe present a simple continuum model for the frequency and voltage dependencies of resistance and capacitance in heterojunctions composed of wurtzite-structure (piezoelectric) ZnO and perovskite-structure (ferroelectric) BaTiO3. The ionic wurtzite-structure (ZnO) and pervoskite structure (BTO) lattice polarizations couple at their common interface, and cause strong asymmetric electro-optic and electric hysteresis behavior. Control of slight n-type conductivity in ZnO allows to produce electrical resistance switches by employing the depletion layer at the ZnO interface. The ferroelectric state within the BTO controls and sets the overall heterostructure conductance, and which may be used in memory applications. We compare our model to voltage and time dependent capacitance measurements, and find excellent agreement over large bias and frequency regions. Temperature dependent measurements reveal the complete disappearance of the hysteresis at the paraelectric phase transition, which is further corroborated by electro-optic Raman and Ellipsometry measurements. From these investigations we conclude that BTO ferroelectricity is the driving cause of the hysteresis, instead of trap charges injected through the interfaces. Our model approach further allows us to access the spontaneous piezoelectric interface charge of ZnO from the electrical experiments.
I3: Poster Session: Nanostructures and Thin Films: Electric, Magnetic and Ferroelectric Properties
Session Chairs
Wednesday AM, March 26, 2008
Salon Level (Marriott)
9:00 PM - I3.10
Size Effect on Phase Transitions in Strained Ultrathin BaTiO3 Films Studied by Ultraviolet Raman Spectroscopy.
Dmitri Tenne 1 , Paul Turner 1 , Jonathan Schmidt 1 , Arsen Soukiassian 2 , Michael Biegalski 2 3 , Xiaoxing Xi 2 , Susan Trolier-McKinstry 2 , Darrell Schlom 2
1 Physics, Boise State University, Boise, Idaho, United States, 2 , Pennsylvania State University, University Park, Pennsylvania, United States, 3 , Oak Ridge National Laboratory, Oak Ridge , Tennessee, United States
Show AbstractWe have applied ultraviolet (UV) Raman spectroscopy for studies of phase transitions in a series of ultrathin BaTiO3 films with layer thicknesses varied from 4 to 25 unit cells. The films were grown by molecular beam epitaxy on SrTiO3 (001)-oriented substrates. UV Raman spectroscopy data show that the 5-unit cell thick single BaTiO3 film commensurately grown on SrTiO3 substrate becomes polar at the temperature ~75 K. The ferroelectric phase transition temperature varies in a very broad range as a function of layer thickness, being as high as about 850 K for the 10-nm-thick (25 unit cells) BaTiO3 film, even though the latter is partially relaxed. Multilayer structures containing several BaTiO3 layers separated by SrTiO3 layers have significantly higher phase transition temperatures compared to single BaTiO3 films of the same thicknesses. This work was supported in part by NSF and Research Corporation.
9:00 PM - I3.11
Optical Detection of SiN Stress Layer Induced Carrier Mobility Enhancement in Silicon.
Frank Wirbeleit 1 , Victoria Pedrero 2 , Dominik Thron 1 , Rolf Stephan 1 , Udo Schalke 2
1 , Advanced Micro Devices, Dresden, Sachsen, Germany, 2 Darmstadt University of Technology, Institute for Semiconductor Technology, D-64289 Darmstadt Germany
Show AbstractStrain engineering is a key element for improving MOSFET device performance in todays advanced microelectronic technology. Strained SiN layers are well established for the generation of near surface strain effects for carrier mobility enhancement in this field. However, non destructive detection of electrical effects from strain layers has not been resolved, especially during the processing of patterned wafers. Since optical measurements are well established for non destructive thickness measurements in semiconductor manufacturing, the plasmon shift of those spectra can be used to investigate stress induced carrier mobility enhancement, as shown in this work. This provides direct access to the effectiveness of the applied near surface strain in the device. By this novel method, SiN films at different stress levels and under different process conditions are investigated on blanket SOI wafers in the first part. On these wafers, the optically detected spectra shift is correlated with standard wafer bow and RAMAN stress measurement results. Furthermore, the optical shift in thickness measurement spectra of SiN films was analyzed on structured films after different process treatment steps, such as plasma resist strip, low temperature anneal and rapid thermal anneal as well. These results are correlated to the electrical performance of microelectronic test structures. Based on this, the relative variation of the stress levels of SiN films after different process treatments, and the impact on carrier mobility in microelectronic devices is shown. For example, optical reflective spectra taken from a measurement pad with a SiN film on top of an SOI silicon layer (bi layer stack) after plasma treatment or rapid thermal anneal do no show a significant difference. However, after a furnance anneal of 600°C and 20 minutes a shift in optical reflective spectra is visible. This is related to a change in the SiN layer stress level and increased near surface electron mobility in the under laying silicon material as a consequence. By this work, process related stress engineering is supported and technology related stress altering factors become obvious. More detailed data will be discussed in this work.
9:00 PM - I3.13
Photo-induced Deposition of Nanostructured Thin Films by UV-exposure of Heteroleptic Ti-alkoxide Solutions.
J. David Musgraves 1 , Barrett Potter 1 , Timothy Boyle 2
1 Materials Science and Engineering, University of Arizona, Tucson, Arizona, United States, 2 Advanced Materials Laboratory, Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractPhotoexcitation at λ = 248 nm of hydrous pyridine solutions containing a water-stable, heteroleptic titanium alkoxide precursor (OPy)2Ti(TAP)2 [where OPy = pyridine carbinoxide and TAP = 2,4,6 tris(dimethylamino)phenoxide] produced an insoluble,oxide-containing, nanostructured thin film on glass substrate surfaces in contact with the solution during irradiation. Deposition only occurs in the illuminated region of the substrate allowing physical relief structures to be photopatterned directly from solution. SEM analysis of the dried film indicates that the films possess a randomly interconnected structure of irregularly shaped, low aspect ratio nanopores (average size <100 nm). Photodeposited film thicknesses show a monotonic increase with UV-fluence. Films ranging from 30 nm to 300 nm in thickness have been deposited. A Raman scattering investigation of the solid photoproduct reveals vibrational structure consistent with the presence of Ti-based hydrolysis and condensation products as well as unreacted alkoxide ligand moieties indicating that the ultraviolet irradiation of these solutions destabilizes the precursor, leading to the partial photocatalysis of intermolecular linking reactions. Excitation wavelength-dependent studies indicate that photon energies resonant with π-π* transitions present in the cyclic ligand groups of the alkoxide, and in the solvent itself, are most effective in forming solid phase. In contrast, excitation energies resonant with the charge transfer band present in the Ti-alkoxide molecule produce only limited changes in vibrational resonances associated with the OPy and TAP ligands with no observable film deposition. Such studies, in conjunction with modifications in solution chemistry, are used to develop insight into the primary processes contributing to film assembly. The propensity for oxide phase development and evolution during subsequent thermal processing of the photodeposited films will also be discussed._____________This work partially supported by the Department of Energy - Office of Basic Energy Sciences and the United States Department of Energy under contract number DE-AC04-94AL85000. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the United States Department of Energy.
9:00 PM - I3.14
Effect of Doping Molecular Monolayers on Charge Transport Through Si / Organic Monolayers / Metal Junctions.
Oliver Seitz 1 , Ayelet Vilan 2 , Hagay Cohen 2 , Antoine Kahn 3 , David Cahen 2
1 Chemistry and Chemical Biology Dept., Rutgers University, Piscataway, New Jersey, United States, 2 Materials and Interfaces Dept., Weizmann Institute of Science, Rehovot Israel, 3 Electrical Engineering Dept., Princeton University, Princeton, New Jersey, United States
Show Abstract9:00 PM - I3.15
Ab initio Thermodynamics of Oxygen Defective Rutile: The Magneli Phases.
Leandro Liborio 1 , Nicholas Harrison 1 2
1 Department of Chemistry, Imperial College London, London United Kingdom, 2 , CLRC, Daresbury Laboratory, Daresbury, Warrington, United Kingdom
Show Abstract9:00 PM - I3.16
Accumulation and Dissipation of Oxygen Vacancies on Oxide Surface using Atomic Force Microscopy.
Wonyoung Lee 1 , Minhwan Lee 1 , Young-Beom Kim 1 , Fritz Prinz 1 2
1 Department of Mechanical Engineering, Stanford University, Stanford, California, United States, 2 Department of Materials and Science Engineering, Stanford University, Stanford, California, United States
Show AbstractCharge transfer reactions on solid oxide surfaces have been extensively studied in the fuel cell literatures, especially solid oxide fuel cells (SOFCs) because the reaction kinetics on oxide surfaces often presents a significant limitation to the fuel cell performance. [1-3] In addition, changing the surface oxidation state in a spatially varying fashion raises the possibility of inducing significant charge gradients that, in turn, may facilitate orienting or breaking up molecular structures. The accumulation of charged surface vacancies may facilitate the entry of oxide ions into the underlying substrate of oxide ion conductors. Without continued application of an electrical field the accumulation of charges may be temporary, due to charge rearrangement and transport. Therefore, characterizing the accumulation and dissipation of charge concentration on the oxide surface provides the opportunities for understanding the surface reactions and performance enhancement. Here, we present a methodology that allows the introduction of the localized charge accumulation, and the characterization of the dissipation of accumulated charges using atomic force microscopy (AFM), so that the quantitative data can be extracted. We examined gadolia doped ceria (GDC) and yttria stabilized zirconia (YSZ) due to their applicability in SOFCs. The tiny AFM tip was used both an electrode for applying a local electric bias as well as a probe to detect the distribution of oxygen vacancies on oxide surface. Anodic bias was applied to the probe with respect to the bulk counter-electrode, causing local oxygen vacancy formation. The well-established Kelvin probe microscopy (KPM) technique was adopted to observe the local charge distribution on the surface after the bias application. [4] The resulting surface potential maps can be converted to charge density maps with the help of Poisson’s equation.Applying an anodic bias with the probe in air generates a surface charge adjacent to the applied electric field. This observation appears consistent with the accumulation of oxide ion vacancies on the oxide surface. A sequence of surface potential maps after applying an anodic bias at different temperatures suggests that surface charge concentration can be related to the rate of oxide ion conductivity on the electrolyte surface. The activation energy for diffusion was obtained as 0.56eV, implying that the majority of oxide ion vacancies diffuse on the surface rather than into the electrolyte bulk. [1] B. Luerben, J. Janek, S. Günther, M. Kiskinovac and R. Imbihlb, Phys. Chem. Chem. Phys. 4, 2673 (2002).[2] I. Kosacki, C.M. Rouleau, P.F. Becher and J. Bentley and D.H. Lowndes, Electrochem. Solid. St. 7, A459 (2004).[3] M.K. Nowotny, T. Bak, J. Nowotny, C.C. Sorrell, K.E. Prince and S.-J.L. Kang, Adv. Appl. Ceram. 104, 154 (2005). [4] M. Nonnenmacher, M.P. O’Boyle and H.K. Wickramasinghe, Appl. Phys. Lett. 58, 2921 (1991).
9:00 PM - I3.17
In situ X-ray Studies of La0.7Sr0.3MnO3 Thin Films at Elevated Temperature and Oxygen Partial Pressure.
Tim Fister 1 , Jeff Eastman 1 , Dillon Fong 1 , Peter Baldo 1 , Matthew Highland 1 , Paul Salvador 2 , Kavaipatti Balasubramaniam 2 , Joanna Meador 2 , Paul Fuoss 1
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractAs a prototypical strongly correlated electron material, La1-xSrxMnO3 (LSMO) displays a wealth of fascinating magnetic and electronic phenomena and is a pivotal component in many technological devices, such as solid oxide fuel cells (SOFC). A key area of interest is understanding the structural and chemical changes that occur at the LSMO surface and at interfaces between LSMO and other complex oxides. Using in situ x-ray scattering and spectroscopy at the Advanced Photon Source, we examine the behavior of La0.7Sr0.3MnO3 (001) epitaxial thin films at elevated temperatures (up to 800°C) and under a range of oxygen partial pressures (pO2 ≤ 150 Torr). The films, ranging from 6-200 nm thick, are grown by pulsed laser deposition onto SrTiO3, DyScO3, and NdGaO3 single-crystal substrates, resulting in well-defined compressive or tensile strain states. Strontium, lanthanum, and manganese concentration profiles are measured as a function of film thickness, strain state, temperature, and oxygen partial pressure. At temperatures and pressures characteristic of operating SOFCs, we find clear evidence of strontium segregation, with an amount independent of the oxygen atmosphere. We discuss these results in the context of chemical bonding and its impact on the surface structure of LSMO. This work is supported by the U.S. Department of Energy under Contract No. DE-AC02-06CH11357.
9:00 PM - I3.18
Microstructural Investigations of Hafnium Aluminum Oxide Films.
Doina Craciun 1 , Gabriel Socol 1 , Emanuel Axente 1 , Aurelian-Catalin Galca 3 , Valentin Craciun 1 2
1 Laser, National Institute for Laser, Plasma and Radiation Physics, Bucharest-Magurele Romania, 3 , National Institute of Materials Physics, Bucharest-Magurele Romania, 2 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractA great amount of research has been dedicated in the past decade towards finding an alternative gate dielectric to replace silicon dioxide in Si MOSFET devices. A higher dielectric constant, thermodynamic stability with Si, a film/Si interface with a low density of defects and chemical inertness are among the most important requirements. HfO2 has shown excellent promise owing to its high thermodynamic stability with Si and higher permittivity (k > 19 – 22). However, the main drawback with HfO2 is its low re-crystallization temperature (~450 oC) with the eventual emergence of its characteristic monoclinic polycrystalline phase upon post deposition annealing.It is well known that aluminum oxide has a larger band-gap (~8.8 eV) and a lower oxygen diffusion coefficient in comparison to hafnium oxide. From a materials science viewpoint, alloying of hafnium oxide films with aluminum oxide can significantly improve the thermal stability by introducing lattice strains which help in delaying the onset of crystallization by hindering easy movement of individual atoms upon increase in temperature. The onset of crystallization can be pushed to higher temperatures. However, there would be an inevitable decrease in the overall permittivity due to the permittivity differences among the individual constituents. It is therefore necessary to optimize the Al2O3 content to improve the thermal stability without degrading the final capacitance due to its lower permittivity. We have used the combinatorial pulsed laser deposition (C-PLD) method to deposit films with lateral Al gradients across the sample surface. Films were afterwards annealed at 900 oC for various time durations and their microstructure analyzed to find out what Al concentrations are necessary to ensure thermal stability of various films and multilayer structures.
9:00 PM - I3.19
Thermal Stability of Epitaxial SrTiO3 Thin Films on Si (001).
Grace Yong 1 , Rajeswari Kolagani 1 , Sanjay Adhikari 1 , William Vanderlinde 2 , Lourdes Salamanca-Riba 3 , Yong Liang 4 , Stephan Friedrich 5
1 Physics, Astronomy & Geosciences, Towson University, Towson, Maryland, United States, 2 , Laboratory for Physical Sciences, College Park, Maryland, United States, 3 Materials and Nuclear Engineering, University of Maryland, College Park, Maryland, United States, 4 Physical Science Research Labs, Motorola Labs, Tempe, Arizona, United States, 5 Advanced Detector Group, Lawrence Livermore National Lab, Livermore, California, United States
Show AbstractEpitaxial SrTiO3 on Si(001) is important for application as a high κ (Kappa) gate oxide and is also suitable as a buffer layer for the subsequent growth of other perovskite oxide thin films to enable integration of perovskite oxide functionality with Si. For the latter application, the thermal stability of the interface structure in epitaxial SrTiO3 thin films grown by molecular-beam epitaxy on Si (001) becomes a key issue since most of the perovskite layers are grown at relatively high temperatures (750-850°C). SrTiO3 and Si are intrinsically thermodynamically unstable in proximity to each other, with some reduction of the SrTiO3 and oxidation of the Si to be expected. We have used x-ray diffraction and micro-analytical techniques including optical microscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) to study the thermal stability of epitaxial SrTiO3 thin films grown by molecular beam epitaxy (MBE) on Si (001). Elemental composition of the amorphous interface layer (AIL) and of the epitaxial SrTiO3 film will change during various thermal treatments and gas environments encountered in the subsequent growth of other oxide layers.
9:00 PM - I3.2
Synthesis and Properties of Magnetic Particle/Organic Hybrid.
Koichiro Hayashi 1 , Makoto Moriya 1 , Wataru Sakamoto 1 , Toshinobu Yogo 1
1 EcoTopia Science Institute, Nagoya University, Nagoya, Aichi, Japan
Show AbstractFunctional inorganic nanoparticle/organic hybrid materials have attracted attentions because of their benefitical properties of each phase. Magnetic nanoparticle/organic hybrid materials have various applications, such as recording media, printing agent, ferrofluid, magnetic resonance imaging, hyperthermia. The authors reported the synthesis of spinel ferrite particle/organic hybrid materials through controlled hydrolysis of iron- and metal-organic compound below 100 centigrade[1,2]. This paper describes in situ synthesis of magnetite particle/organic hybrid and its fundamental properties of heat generation. Magnetite particle/organic hybrid was synthesized from iron acetylacetonate and its derivative below 100 centigrade. XRD analysis revealed crystalline spinel particles were formed in the organic matrix. The crystallinity of spinel particles was dependent upon the processing conditions, and increased with increasing hydrolysis water and time. The dispersion of crystalline particles below 10 nm in the organic matrix was confirmed by TEM and SAD. The magnetic properties of the hybrids were analyzed by VSM and SQUID. The BH curve of the nano-sized spinel oxide particle/organic hybrid showed no remanence at room temperature. On the other hand, particles above 10 nm were also formed in the hybrid depending upon the reaction conditions. The hybrid exhibited a hysteresis at room temperature. The heat generation due to magnetic hysteresis loss was confirmed for the hybrid in a high frequency magnetic field. The temperature distribution of agar phantom was also investigated.1.T. Nakamura, W. Sakamoto and T. Yogo, J. Mater. Res., 21, 1336 (2006).2. Y. Hayashimoto, W. Sakamoto and T. Yogo, J. Mater. Res., 22, 1967 (2007).
9:00 PM - I3.21
Study of the Stress Behaviour with Temperature in Oxygen Ions Conductors.
Samuel Rey-Mermet 1 , Paul Muralt 1
1 Ceramics laboratory, Ecole Polytechnique Fédérale de Lausanne EPFL, Lausanne Switzerland
Show AbstractCeria doped gadolinia Ce0.8Gd0.2O2-x (CGO) and yttira stabilized zirconia Zr0.92Y0.08O2-x (YSZ) in form of thin films are candidates for electrolytes in microfabricated Solid Oxide Fuel Cells (μSOFCs). In order, to improve the power density of the μSOFCs, and to reduce their temperature of operation, the electrolyte should have the geometry of a thin membrane, thus requiring the control of mechanical stresses in these materials. CGO and YSZ were investigated in the form of 100 to 300 nm thick films deposited by reactive magnetron sputtering. These measurements are performed at temperatures up to 700°C in air. As-deposited YSZ films grown at 500°C are subject to a compressive stress of approximately -800 MPa. In CGO samples, the stress after deposition amounts to even -1 GPa. Such compressive stress cannot be explained by thermal expansion mismatch, which should rather lead to tensile stress. We propose that this effect is due to the formation of oxygen vacancies in the films during cooling under low oxygen pressure (vacuum). Indeed, cooling down the YSZ film in 80 mTorr of pure oxygen reduced the stress to -500 MPa. Thus the number of vacancies in the film directly affects the value of the compressive stress. In YSZ, the introduction of an oxygen vacancy leads to an increase of the lattice volume and to a compressive stress. In CGO, the lack of oxygen ions is known to be balanced by a change of the valence of the cerium ions from +IV to +III. The lattice expands and the film develops a compressive stress, as the Ce+III ions are bigger than Ce+IV ions. Ramping the temperature up to 700°C, the films first show a compressive contribution (up to about 400 °C), due to the thermal mismatch between the oxides and the silicon. After this compressive part, in both films, an exponentially growing tensile stress contribution is added to the baseline caused by thermal mismatch. By subtracting the thermal mismatch stress from the data, it is possible to monitor this tensile contribution. We suggest that this part is due to the incorporation of oxygen ions in the films. The activation energies were derived from the Gibbs factor governing the temperature dependence and were obtained as 0.46eV in CGO and 0.40eV in YSZ. These energies are close but somewhat lower than the measured activation energies for ionic conductivity measured across the film (0.58eV in CGO and 0.69eV in YSZ). Upon cooling down, the films undergo further stress reduction due to thermal expansion mismatch. Back to room temperature, the stress is strongly reduced by -60% in CGO and -75% in YSZ. It is thus imperative to anneal such films before membrane fabrication. The scientifically interesting question is whether the mechanical stress reduces diffusion activation energies. The rigidity and/or thermal expansion are different after the annealing cycle. Whereas the YSZ film seem to be softer or expand less, the CGO film shows the opposite effect thus becomes stiffer or expands more.
9:00 PM - I3.22
Effect of the Surface Structure of Thin Layers on Their Reactivity.
Fedor Dultsev 1
1 , Institute of Semiconductor Physics SB RAS,, Novosibirsk Russian Federation
Show Abstract9:00 PM - I3.24
Room Temperature Ferromagnetism in Co and Ni Incorporated Rf-Sputtered TiO2 Thin Films
Nitin Malik 1 , Nikhil Kumar 1 , Kanwal Bhatti 1 , Sujeet Chaudhary 1
1 Physics, Indian Institute of Technology Delhi, New Delhi India
Show AbstractThe future of the spin based electronics is limited by various fundamental challenges. One such challenge is the requirement of a material which can ensure integration of electronic, photonic and magnetoelectronic capability so as to ensure new device functionalities not available at the moment. In this regard, the oxide based dilute magnetic semiconductors produced by doping the transition metal (TM) ions into oxide semiconductors have attracted a great deal of interest. It has been reported that the TiO2 exhibits ferromagnetism (FM) with a Curie temperature above room temperature when doped with a few atomic percent of cobalt (Co) or another TM ion. However, the observed FM character in the Co:TiO2 films is often attributed to formation of cobalt clusters. While the FM behavior in case of TM doped SnO2 and In2O3 system is established to be an intrinsic effect owing to the carrier mediated nature of the observed FM behavior, the case of TM:TiO2 continues to be unclear. It is yet to be established whether TiO2 can be made intrinsically FM while retaining its semiconducting and transparent character.In the recent past, we have intensively investigated ZnO and SnO2 systems while doping them with TM ions. Continuing with our efforts for hunting transparent FM semiconductors, we have also fabricated cobalt and nickel incorporated TiO2 thin films on quartz and saphhire substrates using reactive rf-magnetorn sputtering technique with oxygen serving as the oxidant. The structural, optical and magnetic properties of these Co/Ni doped TiO2 thin films have been analysed in detail. The X-ray diffraction investigations show that while the crystalline phase starts above 350°C, pure rutile phase of TiO2 forms in-situ in a small substrate temperature window near 650°C. These films, possessing optical transmission in excess of 70%, were found to exhibit FM behavior in their M-H data recorded at 300K. The saturation magnetization of the FM contribution in the films seems to depend proportionally on doping concentration of cobalt and nickel. For both kinds of substitutions (Co and Ni), the optical investigations of Co/Ni:TiO2 films reveal a red shift in the energy gap of TiO2. When vacuum annealed at 500°C for 3 hrs, the saturation magnetization in case of Co:TiO2 system was found to increase significantly, indicating the formation of Co clusters. Most importantly, the subsequent air annealing of the vacuum annealed Co:TiO2 thin films showed that the saturation magnetization decreased and more or less got stabilized thereafter. We believe that oxidation of the cobalt clusters or formation of the CoTiO3 phase arrests the formation of cobalt clusters finally leading to the intrinsic ferromagnetic character in the transparent and somewhat insulating Co:TiO2 system. High temperature VSM studies reveal that the Curie temperature of the Co- and Ni doped TiO2 thin films is certainly above 300°C. More details would be presented in the conference.
9:00 PM - I3.25
MeV Si ions Bombardment Effects on the Properties of Nano-layers of SiO2/SiO2+Ag.
Sadik Guner 1 2 , Satilmis Budak 3 , Claudiu Muntele 1 , Cydale Smith 4 , Daryush Ila 1
1 Department of Physics, Center for Irradiation of Materials, Alabama A&M University, Normal, 35762, Alabama, United States, 2 Department of Physics, Fatih University, 34500, Büyükçekmece / Istanbul Turkey, 3 Department of Electrical Engineering, Alabama A&M University, , Normal, 35762, Alabama, United States, 4 NASA-MSFC , MSFC, 35801, Alabama, United States
Show AbstractWe have grown alternating SiO2/SiO2+Ag multi-nano-layered system where the SiO2Ag layers were 5-20 nanometers and SiO2 buffer layer were 5-10 nanometer. The layered systems were made at 50 to 100 periods. Using interferometry as well as in-situ thickness monitoring, we measured the thickness of the layers; using Rutherford Backscattering Spectrometry (RBS) measured the concentration and distribution of Ag in SiO2. The optical absorption, electrical conductivity, thermal conductivity and the Seebeck coefficient of the layered structure was measured at various temperatures before and after bombardment by 5 MeV Si ions. The energy of the Si ions were chosen such that the ions are stopped in the silicon substrate and only electronic energy due to ionization is deposited in the layered structure. The optical absorption of the layered systems was measured using optical photo absorption spectrometry. The electrical conductivity measured using both Van der Pauw method and cross plane I-V method. Thermal conductivity of the thin films was measured using an in-house built 3w thermal conductivity measurement system. Using the measured Seebeck coefficient, thermal conductivity and electrical conductivity we calculated the figure of merit (ZT). We will report our findings of change in the optical properties, change in the figure of merit as a function of the bombardment fluence. Contact author: Daryush IlaAcknowlegment: Research sponsored by the Center for Irradiation of Materials, Alabama A&M University and by the AAMURI Center for Advanced Propulsion Materials under the contract number NAG8-1933 from NASA, and by National Science Foundation under Grant No. EPS-0447675.
9:00 PM - I3.26
Plasma and Photochemically Assisted Growth of Chromium Oxide Films by Chemical Vapor Deposition.
Jinwen Wang 1 2 , Arunava Gupta 2 1 , Tonya Klein 1 2
1 Chemical & Biological Department, Unversity of Alabama, Tuscaloosa, Alabama, United States, 2 Center for Materials for Information Technology, Unversity of Alabama, Tuscaloosa, Alabama, United States
Show AbstractChromium dioxide (CrO2) is a half-metallic ferromagnetic material, which makes it a promising material for magnetoelectronic devices. Because of its phase metastability, it is difficult to get large single crystals of CrO2. Powders and thin films are likely to possess multiple phases of chromium oxide (Cr2O3) and chromium dioxide. In order to explore conditions for epitaxial Cr2O3 and CrO2 film growth, plasma enhanced chemical deposition (PECVD) and laser assisted CVD were used to grow thin films on various substrates including c-cut sapphire, TiO2 (100)/(110) substrates as well as oxidized Si (100) wafers. Two precursors, chromium hexacarbonyl (Cr(CO)6) and chromyl chloride (CrO2Cl2), were tried at substrate temperatures between 200–500 degree C. Epitaxial Chromium oxide (Cr2O3) thin films were observed on both c-cut sapphire (Al2O3) and TiO2 (100) substrates. Physical and chemical properties of films grown under different reaction environments are compared using XRD, SEM/EDAX, XPS, AFM, and AGM. Further investigation has been done to find the appropriate parameters for CrO2 growth under low pressure conditions.
9:00 PM - I3.27
Cation Site Occupancy and Valence in Non-Equilibrium Spinel Oxide Thin Films.
Brittany Nelson-Cheeseman 1 , Rajesh Chopdekar 2 1 , Michael Toney 3 , Elke Arenholz 4 , Yuri Suzuki 1
1 Materials Science and Engineering, University of California - Berkeley, Berkeley, California, United States, 2 School of Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, 3 Stanford Synchrotron Radiation Laboratory, Stanford Linear Accelerator Center, Menlo Park, California, United States, 4 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractMagnetic thin films can exhibit properties markedly different from the bulk due to the effects of surfaces or interfaces, strain state and non-equilibrium synthesis. This is particularly true in magnetic spinel oxide thin films, where the magnetic properties are determined by the ferrimagnetic interaction among the transition metal cations with octahedral and tetrahedral coordination. A departure from equilibrium cation valences and site occupancies can cause a dramatic change in the magnetic properties. We have investigated epitaxial thin films of the ferrimagnetic spinels NiMn2O4 (NMO) and NiFe2O4 (NFO) that both exhibit anomalous magnetic behavior in thin film form. While NMO exhibits two magnetic transitions in the bulk (a collinear moment configuration below 100K and a canted moment configuration below 60K), epitaxial thin films grown on SrTiO3 and MgAl2O4 substrates exhibit a single magnetic transition at 60K. Resonant X-ray diffraction (RXS), X-ray absorption spectroscopy (XAS), and X-ray magnetic circular dichroism (XMCD) have been used to investigate both the chemical and magnetic structure of NMO thin films. RXS indicates that the cation site occupancy does not differ markedly from bulk samples, but both RXS and XAS show that differences in the relative amounts of Mn2+, Mn3+ and Mn4+ may play a role in the difference in magnetic properties. The NFO films also show a departure from bulk magnetic properties, exhibiting a significant increase above bulk magnetization values with decreasing film thickness. Ultrathin NFO films with enhanced magnetization have been characterized by both XMCD and RXS methods in order to investigate if any changes in cation valence and site occupancy are the cause of such properties when compared to thicker films. Preliminary data shows Ni and Fe XMCD lineshapes similar to that of bulk NFO, but with different relative peak intensities.
9:00 PM - I3.29
The Anisotropy Induced by Magnetic Alignment on Ni-Zn Ferrite Thick Films.
Ming Da Yang 1 , Mean Jue Tung 1 , Shi Yuan Tong 1
1 , Industrial Technology Research Institute, Hsinchu, Taiwan Taiwan
Show Abstract9:00 PM - I3.3
A Raman Scattering Investigation of the Magnetic and MI Transition in Rare Earth Nickelates.
Cecile Girardot 1 2 , Kreisel Jens 1 , Stephane Pignard 1
1 LMGP-Minatec, Grenoble Institute of Technology, Grenoble France, 2 , Schneider Electric, Grenoble France
Show Abstract9:00 PM - I3.30
Gallium Oxide Tin Films Prepared by Hydrothermal Decomposition of Gallium Nitrate Ga(NO3)3 on Cleaved Surface of Layered InSe Single Crystals.
S. Drapak 1 , Z. Kovalyuk 1
1 , I.M. Frantsevich Institute of Materials Science Problems, National Academy of Sciences of Ukraine, Chernivtsi Ukraine
Show Abstract9:00 PM - I3.31
Nanopatterned Optical and Magnetic La0.6Ca0.4MnO3 Arrays: Synthesise, Fabrication, and Properties
Ming-Chung Wu 1 , Chih-Min Chuang 1 , Yu-Ching Huang 1 , Chin-Feng Lin 1 , Yang-Fang Chen 2 , Wei-Fang Su 1
1 Department of Materials Science and Engineering, National Taiwan University, Taipei Taiwan, 2 Department of Physics, National Taiwan University, Taipei, Taiwan. , Taipei Taiwan
Show AbstractWe have fabricated a unique periodic structure with tunable optical and magnetic properties using water-developable La0.6Ca0.4MnO3 electron beam resist. The resist can be developed in a nontoxic and environmental friendly manner using pure water. Additionally, the resist is capable to exhibit both positive and negative resist behaviors depending on the electron beam dosage. Thus, these special characteristics are used to fabricate periodic structure on a thin film which has controlled optical reflectance properties with one fixed design electron beam pattern (i.e. without changing the geometries and lattice constants of the periodical structures) by simply changing the electron beam dosage only. At the same time, our approach provides a simple and convenient route for the fabrication of nanometer scale magnetic patterns, which serve as the building blocks in the search for novel properties of periodic magnetic arrays such as magnetics and magnetic photonic crystals.
9:00 PM - I3.32
Structure and Dynamics of the Water/amorphous Silica Interface.
Hui Zhang 1 , Ali Hassanali 1 , Yun Kyun Shin 1 , Sherwin Singer 1 , Chris Knight 1
1 Chemistry, The Ohio State University, Columbus, Ohio, United States
Show AbstractThe interface between amorphous silica and water is one of the most ubiquitous and technologically relevant surfaces. Starting with well- known interaction models for bulk amorphous silica (BKS) and bulk water (SPC/E), we have constructed a empirical force field for the water/amorphous silica interface based on ab initio fragment calculations. The model allows for undissociated (-SiOH) and dissociated (-SiO-) silanol groups. The heat of immersion predicted by the model agrees well with experimental data. Using this model, we performed moleculardynamics simulations to explore the structure and dynamicalproperties of the interface that are relevant to fundamental electrochemical processes. Electroosmotic flow was observed in the simulations under the influence of an applied electric field. These studies allow us to evaluation long-standing models of the electrical double layer near silica, such as the nature of the Stern layer, whether a distinct co-ion layer is present, and the degree of ion and solvent mobility near the surface. Results will be presented on the ion distribution near the silicasurface, and the ion and solvent mobility in the presence of an electric field. Specifically, the degree to which ions are mobile within the Stern layer will be described.
9:00 PM - I3.34
Properties of Lead-free Ferroelectric Na1/2Bi1/2TiO3-BaTiO3 Thin Films Obtained by PLD and RF-PLD.
Nicu-Doinel Scarisoreanu 1 , Floriana Craciun 2 , Ruxandra Birjega 1 , Maria Dinescu 1
1 Lasers, NILPRP-Magurele, Bucharest Romania, 2 , CNR-Istituto dei Sistemi Complessi, Rome Italy
Show Abstract Sodium bismuth titanate (Na1/2 Bi1/2)TiO3, pure or in solid solution with BaTiO3, (1–x)Na0.5Bi0.5TiO3–xBaTiO3, can be a promising lead-free ferroelectric material for replacing the most used commercial materials, PZTs, due to environmental problems created by the toxicity of lead. In bulk it has attractive properties such as remanent polarization of 38μCcm−2 and a coercive field of 73kVcm−1 at room temperature, with a relatively high Curie temperature. In this work, the morphological, structural and dielectric properties of the relaxor ferroelectric NBT-BT thin films with x = 0.06, prepared by pulsed laser deposition and radiofrequency assisted pulsed laser deposition on different substrates were investigated. A parametric study concerning the influence of substrate temperature, RF power, laser wavelength and the reactive gas pressure was carried out. The deposited layers were characterized by XRD, SEM, AFM and TEM. Dielectric and ferroelectric properties were investigated by using an impedance analyzer and a RT 66A Ferroelectric Test System.
9:00 PM - I3.35
Structural and Optical Properties of SrxBa1-xNb2O6 Thin Films Growth by PLD and RF-PLD.
Nicu-Doinel Scarisoreanu 1 , Ruxandra Birjega 1 , Maria Dinescu 1 , Dan Pantelica 2 , Cornel Ghica 3 , Leona Nistor 3
1 Lasers, NILPRP-Magurele, Bucharest Romania, 2 , HH - NIPNE, Bucharest Romania, 3 , NIMP, Bucharest Romania
Show Abstract Strontium barium titanate, SrxBa1-xNb2O6 (SBN:x), is a ferroelectric material with interesting optical and electrical properties, having a relatively complicated crystal structure of tetragonal tungsten-bronze type(TTB). Because of high cost of single-crystal production, growing epitaxialy SBN thin films has become very attractive. By using pulsed laser deposition and radiofrequency assisted pulsed laser deposition, we report the growth of highly oriented strontium barium niobate (SrxBa1-xNb2O6) thin films on MgO (100), starting from stoichiometric single-crystal and ceramic targets, respectively. The effects of the oxygen partial pressure, the presence of radiofrequency plasma during the deposition and cooling periods and the substrate temperature have been studied from the structural, morphological and optical point of view with the help of XRD, AFM, SEM, TEM and SE (spectro-ellipsometry) techniques. The composition of the SBN thin films has been determined by RBS measurements which were conducted using a 12C beam provided by the van de Graaff tandem accelerator of NIPNE-HH. The RBS analysis showed that the films have stoichiometric composition identical to the target material.
9:00 PM - I3.36
Investigation of Micro-structural Properties of BaTiO3 Thin Films by Pulsed Laser Deposition.
Kesava Yellareddy 1 , Jerome Wolfman 1 , Romain Bodeux 1 , Cecile Autret-Lambert 1 , Monique Gervais 1 , Francois Gervais 1
1 LEMA, UMR 6157 CNRS-CEA, University FR Tours, Tours France
Show Abstract9:00 PM - I3.37
Influence of Strain on Phase Transitions in Short-period BaTiO3/SrTiO3 Ferroelectric Superlattices.
Jonathan Schmidt 1 , Paul Turner 1 , Dmitri Tenne 1 , Arsen Soukiassian 2 , Xiaoxing Xi 2 , Darrell Schlom 2 , Yulan Li 2 , Long-Qing Chen 2 , Ram Katiyar 3
1 Physics, Boise State University, Boise, Idaho, United States, 2 , Pennsylvania State University, University Park, Pennsylvania, United States, 3 , University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractA Raman study of the strain effect on phase diagram and lattice dynamics of BaTiO3/SrTiO3 superlattices with variable magnitude of substrate-induced strain will be presented. High quality short-period BaTiO3/SrTiO3 superlattices have been grown on rare earth scandate (GdScO3, DyScO3, SmScO3) as well as SrTiO3 substrates. Using Raman spectroscopy with ultraviolet excitation allowed the observation of phonons and determination of the ferroelectric phase transition temperature as a function of strain in superlattices. Experimental Raman results will be compared with the thermodynamic phase-field model calculations of strain-temperature phase diagrams and ferroelectric polarization as a function of temperature and strain. This work was supported in part by NSF, DOE and Research Corporation.
9:00 PM - I3.38
Nanostructuration of SrRuO3 layers grown by Chemical Solution Deposition
Giannantonio Busato 1 , Susagna Ricart 1 , Teresa Puig 1 , Narcis Mestres 1 , Xavier Obradors 1
1 Institut de ciència de materials de Barcelona, ICMAB, Consejo Superior de Investigaciones Cientificas, CSIC, Bellaterra Spain
Show AbstractChemical solution deposition techniques are appearing as a very promising methodology to achieve epitaxial oxide thin films at a low cost. In particular, intense effort is being carried out to develop routes for all chemical nanostructured YBCO superconducting films. Ferromagnetic conductive oxide SrRuO3 has many interesting properties like high electrical conductivity, crystal structure compatibility with many other technically important metal oxides and high thermal and chemical stability. Moreover, the phase compatibility between YBa2Cu3O7 and SrRuO3 makes it very suitable for studying new physical phenomena associated to magnetic pinning of flux lines.Two different homogeneous precursor solutions have been employed. A metalorganic decomposition route based on Ru(C5H7O2)3 and Sr(C5H7O2)2 as starting materials, and a polymeric solution based on strontium nitrate and ruthenium chloride precursors. Precursor solutions were spin coated onto LaAlO3 (001) (LAO) single crystal substrate. The as-coated thin films were afterwards heat treated at processing temperature in the range of 600-800° C with different gas fluxes. The film growth was examined by XRD theta-2theta and pole figure analysis, evidencing a good epitaxial quality of SrRuO3 thin films (100) orientated showing a cube on cube growth type. Film surface analysis, magnetic and transport properties will be presented and the feasibility developing new SrRuO3 nanostructuration routes will be discussed..We acknowledge the financial support from MEC (MAT2005-02047, NAN2004-09133-C03-01, MAT2006-26543-E); Generalitat de Catalunya (Pla de Recerca SGR-0029 and CeRMAE), and EU (NESPA, HIPERCHEM)
9:00 PM - I3.39
CuO/CeO2 Nanocomposites: Synthesis and Reactivity with NOX.
Antonella Glisenti 1 , Marta Natile 1 , Alessandro Galenda 1 , Federico Scopel 1
1 Chemical Science, University of Padova, Padova Italy
Show Abstract9:00 PM - I3.4
Oxidation of NiSi and Ni(Pt)Si: Molecular vs. Atomic Oxygen
Sudha Manandhar 1 , Brian Copp 2 , Chiranjeevi Valmala 2 , Jeffry Kelber 1 2
1 Chemistry, University of North Texas, Denton, Texas, United States, 2 Materials Science and Engineering, University of North Texas, Denton, Texas, United States
Show Abstract9:00 PM - I3.40
Atomic Layer Deposition of Tin Oxide Films: On the Out-diffusion of Oxygen at Elevated Temperatures.
Gomathi Natarajan 1 , David Cameron 1
1 , ASTRaL, Lappeenranta University of Technology, Mikkeli Finland
Show AbstractMetal oxides including, tin oxide, tungsten oxide and titanium oxide have been playing an important role in gas sensors applications. Gas sensing is based on reducing or oxidizing reactions at the surface level of these oxides and the electrical conductance change. Hence, engineering and control of the film characteristics including electrical conductance is important. Atomic layer deposition (ALD) is a very controllable growth technique for thin films especially oxides. This presentation will describe the growth of SnO2 films by ALD and the determination of diffusion parameters of oxygen diffusion from the film surface at elevated temperatures.From our recent study, we found that the electrical conductance of ALD deposited tin oxide films was very much dependant on the atmosphere in which they were cooled down from after growth. For example, the samples which were cooled down in nitrogen showed much higher electrical conductance than the ones cooled down in oxygen atmosphere. This is connected to the out-diffusion of oxygen from the film surface into the reducing atmosphere at high temperatures (300-500oC). As a result of this, an oxygen depleted layer with a certain thickness (tdep) is formed at the surface. To investigate this out-diffusion in detail, the films were post annealed in nitrogen atmosphere at 500oC for different lengths of time. The film conductance increases up to certain annealing time (30 mins in this case), as the depletion layer thickness (tdep) increases. Any further increase in the annealing length does not show in any significant change in the sheet conductance, since the entire thickness will be oxygen depleted, i.e., tdep ≥ t (t- film thickness). A series of such experiments was done at different temperatures from 300-500oC. From these experimental results, the depletion layer thickness and diffusion parameters such as out diffusion rate and diffusion constant were determined.
9:00 PM - I3.42
Effect of microstructure on the Epitaxial FePt System.
Gopinath Trichy 1 , Jagdish Narayan 1
1 , North Carolina State University, Raleigh, North Carolina, United States
Show Abstract9:00 PM - I3.43
Photoconductivity in BiFeO3 Thin Films.
S. Basu 1 2 , L. Martin 1 2 , Y. Chu 1 2 , M. Gajek 1 2 , R. Rai 3 , X. Xu 3 , J. Musfeldt 3 , R. Ramesh 1 2
1 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 2 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Chemistry, University of Tennessee, Knoxville, Tennessee, United States
Show AbstractAlthough much recent attention on multiferroic materials like BiFeO3 (BFO) has been centered on the potential for development of novel memory devices based on the magnetoelectric effect, little attention has been given to understanding the optical properties of these materials. In this report we examine the possibility of optically excited photoconductivity in BFO thin films. It is thought that the large intrinsic polarization (~100 uC/cm2), tunable oxidation state in the B-site, and the theoretically predicted visible range band gap (~2.6eV) may lead to a large photo-ferroelectric effect in BFO. Thin film heterostructures including asymmetric [In2O3-SnO2 (ITO) (~300nm) / BFO (~250-300 nm) / SrRuO3 (SRO) (~50 nm)] and symmetric [ITO (300nm) / SRO (2 nm) / BFO (~250-300 nm) / SRO (50 nm)] device structures have been grown on SrTiO3 (111) substrates using ITO transparent electrodes to allow for optical excitation with a 100 mW/cm2 white light source. These films have been determined to be of high quality, are single phase, fully epitaxial, and exhibit excellent ferroelectric properties as measured via piezoresponse force microscopy and polarization-electric field hysteresis loop measurements. Optical transmittance measurements were completed from 4-730K in a range from 3000-190nm. Absorption spectra reveal excitations at 3.2 and 4.5 eV that are likely charge transfer in character and low temperature measurements indicate the possibility transitions that are excitonic in nature; the primary bandgap has been measured to be ~2.6eV, consistent with theoretical predictions. Significant differences in the light and dark current-voltage (IV) characteristics are found in fully oxidized heterostructures – current densities of 458 mA/cm2 and 720 mA/cm2 were measured at 2V for dark and light respectively. By controlling the oxygen-defect chemistry of BFO, through a series of low partial pressure anneals and cooling treatments, we have been able to further enhance and probe the nature of the optical excitation in BFO. A measurable increase in photoresponse is observed upon decreasing the cooling pressure following the growth of BFO thin films. For example an increase from 720 mA/cm2 to 1812 mA/cm2 was observed at 1V upon decreasing the pressure from 760 Torr to 1E-1 Torr of O2 under illumination.
9:00 PM - I3.45
Photoinduced Effects in Annealed Bi1-xCaxMnO3 Thin Films
Vera Smolyaninova 1 , K. Karki 1 , Rajeswari Kolagani 1 , G. Yong 1 , R. Kennedy, 1 , K. DeMarchi 1
1 Dept. of Physics, Astronomy and Geosciences, Towson University, Towson, Maryland, United States
Show AbstractDoped rare-earth manganese oxides (manganites) exhibit a wide variety of interesting physical phenomena. Application of magnetic, electric fields, and electromagnetic wave irradiation can induce different phase transitions in these materials. A photoinduced insulator to conductor transition in charge-ordered (CO) manganites is especially interesting from the point of view of creating photonic devices. Thin films of Bi0.4Ca0.6MnO3 exhibit large photoinduced effects associated with melting of the charge ordering by visible light and can support conducting and insulating phase coexistence on a submicron scale [1]. We have found significant increase of the photoinduced resistivity changes and the life time of the photoinduced conducting phase after annealing. The changes in current-induced effects will be also reported, and the possible origin of these effects will be discussed. This work is supported by the NSF grants DMR-0348939 and DMR-0453342. [1] V. N. Smolyaninova at al., Phys. Rev. B 76, 104423 (2007).
9:00 PM - I3.46
High Coercivity Co-ferrite Films with Columnar Structure by Sol-gel Method.
Yasuo Okazaki 1 , Shunji Yanase 1 , Shuichiro Hashi 1 , Hitoshi Ohashi 1
1 Engineering, Gifu University, Gifu Japan
Show AbstractCo-ferrite (CoFe2O4) has the highest value of magneto-crystalline anisotropy and magnetostriction among ferrite materials and has been researched as a candidate for high density magnetic recording media. For the applications of Co-ferrite, high coercivity of the Co-ferrite thin films is necessary. However, relatively low coercivity always limits the potential applications of Co-ferrite. Many intensive researches have been conducted in the world to obtain higher coersivity of Co-ferrite films by controlling the microstructure or doping with different element. A coercivity as high as 5.4 kOe was obtained in Co-ferrite powder prepared by chemical method and a coercivity in Co-ferrite films made by sol-gel method had been reported as low as 2.5 kOe. Here, we report a coercivity of as high as 7.7 kOe in Co-ferrite film prepared by a sol-gel method. After examining a mechanism to obtain high coercivity of CoFe2O4 films by sol-gel method considering crystallization procedure and microstructure of the films, we obtained a high coercivity of 6.3 kOe of Co-ferrite film on Corning glass substrate and 7.7 kOe on a thermally deposited silica substrate. These films with high coercivity showed columnar structure which appeared after annealing over 923K where the microstructure of the films changed from granular to columnar. The optimum crystallization condition of Co-ferrite films with high coercivity concerning with film thickness and grain size will be discussed.
9:00 PM - I3.47
Structure Function Properties of Pd/PC Nanocomposites for Detection of Sulfur Species.
Divakara A Meka 1 , Valmikanathan Onbattuvelli 2 , Sunder Atre 2 , Shalini Prasad 1
1 Department of Electrical and Computer Engineering, Portland State University, Portland, Oregon, United States, 2 Department of Industrial and Manufacturing Engineering, Oregon State University, Corvallis, Oregon, United States
Show Abstract Metal/polymer nanocomposites are one of the widely used materials for the sensor applications due to their tunable electrical properties. Here we present a Palladium (Pd)/ Polycarbonate (PC) nanocomposite which is being tailored to detect sulfur species. Since, palladium has a very high affinity towards adsorbing sulfur compounds, the Pd/PC nanocomposite acts as a transducer which translates the change in sulfur species concentration in air to an electrical signal. Carbon nanoparticles that are incorporated into the nanocomposite in order to improve the change in electrical signal resulted due to the adsorption of sulfur species. Synthesis conditions of Pd/PC nanocomposites were varied to control key nanoparticle characteristics such as size, distribution, concentration and surface chemistry. The consequence of these variations on nanocomposite properties and subsequent sensor performance were monitored. The goal of this project is to build a chemi-resistive SO2 sensor by using in-situ Pd/PC nanocomposite at elevated temperatures. This can be achieved by properly tailoring the in-situ Pd/PC nanocomposite by incorporating CNPs in order to improve the sensitivity. The measurement technique used in the detection is chemi-resistive sensing, is through resistance changes associated with the adsorption of gaseous agents onto the nanocomposite matrix. The sensor that is under development has a simple photolithography based fabrication scheme that can be executed on a non specialized wet bench, thus it is less expensive, highly reproducible and robust.
9:00 PM - I3.48
WITHDRAWN 02/21/08 The Dominant Ionization Processes in a RF Reactive Magnetron Plasma for Silicon Sub-oxide Deposition
Marites Violanda 1 , Frans Habraken 1 , Henrik Rudolph 1
1 Physics and Astronomy, Universiteit Utrecht, Utrecht Netherlands
Show AbstractTuesday, March 25WithdrawnPosterI3.48
9:00 PM - I3.49
High Temperature Oxidation Protective Chromium-Based Coatings Prepared by IBAD and PACVD Methods.
Frantisek Cerny 1 , Jaroslav Pitter 2 , Rudolf Stefec 1 , Jan Gurovic 1 , Daniel Tischler 1 , Svatava Konvickova 1
1 , Czech Technical University, Prague Czech Republic, 2 , ATG, s.r.o., Prague Czech Republic
Show AbstractProperties of chromium-based (chromium nitride and chromium oxide) films allow to use them as protective coatings of various objects against corrosion. There are many methods by which the chromium-based films can be prepared. These films were prepared also by Ion Beam Assisted Deposition (IBAD) method but only at low values of ion energy (below 2 keV). At high values of ion energy it would be possible to expect the improvement of adhesion and structural changes of the films. We have prepared the chromium-based films by high energy (90 keV) IBAD method and also by combination of IBAD and PACVD methods. We investigated properties of prepared films. In the case of chromium nitride we have obtained the mixture of two known crystalline phases or amorphous state of the film in the dependence on process parameters. Resulting films were hard and they had very high adhesion to the steel substrates. The films strongly supressed high temperature oxidation of stainless steel substrates.
9:00 PM - I3.5
Novel Methods for X-ray Reflectivity Analysis of Thin Films.
Jouni Tiilikainen 1 , Teppo Hakkarainen 1 , Harri Lipsanen 1
1 Micro and nanosciences laboratory, Helsinki University of Technology, Espoo Finland
Show AbstractNovel and simple methods are developed to invert x-ray reflectivity (XRR) data and calculate the accuracy of the determined parameters for thin film structures. Methods utilize Parratt's formalism combined with Nevot-Croce interfacial roughness in a curve calculation. In this formalism, one recursion cycle contains the calculation of reflectivity coefficient based on the previous coefficient and the three parameters, thickness, mass density and roughness. The calculation begins from the bottom substrate and continues until the surface is met. Due to the recursive nature of the formalism, there has been no good understanding how the inverting (fitting) procedure should be done computationally reasonably and what is the accuracy of the given algorithm.In this work, the use of simple but computationally very efficient genetic algorithms (GAs) using linear transformation techniques during a combination procedure is shown to be a very suitable approach to invert XRR data from difficult structures. It is shown by simulations that conventional approach without linear transformation techniques fails more often in global inversion process making it unsuitable for XRR analysis with difficult cases.GAs using linear transformation based on principal component or independent component analysis techniques are compared to conventional GA with a clear difference in performance.We have also developed a novel analysis method to study the given fitting solution in an objective way. In this novel accuracy analysis method, one approximates that the fit is the measurement and performs goodness-of-fit calculation between the ``measurement'' with Poisson noise and other noiseless solutions. The goodness-of-fit calculations are performed between a noiseless curve and at least one thousand noisy curves, each of them having their own arbitrary Poisson distributed noise events. In this method, one uses the p-value test for a null hypothesis which argues that another than the exact fit gives the best goodness-of-fit value. It turns out that the exactly known solution may not give the best goodness-of-fit value which is a consequence of Poisson noise and the applied goodness-of-fit measure. As a direct application, thenovel accuracy method gives lower limit for the error made in XRR analysis. For instance, the accuracy in the thickness of atomic-layer-deposited aluminum oxide on silicon is approximately within 0.18 nm but the thickness accuracy is better for materials having greater mass density. The implementation of the novel method for accuracy analysis is presented and it turns out that the method can be easily generalized for the analysis of an arbitrarily chosen parameter set.
9:00 PM - I3.50
Bonding Structure of Ultrathin Oxides on Si(110) Surface.
Yoshihisa Yamamoto 1 , Hideaki Togashi 1 , Atsushi Kato 1 , Maki Suemitsu 1 , Yuzuru Narita 2 , Akitaka Yoshigoe 3 , Yuden Teraoka 3
1 , Tohoku University, Sendai Japan, 2 , Kyushu Institute of Technology , Kitakyusyu Japan, 3 , Japan Atomic Energy Agency, Sayo-cho Japan
Show AbstractSi(110) surface has a higher hole mobility than on Si(001) by a factor of 1.5-2.5, which, as well as its expected usage in non-planer 3D devices, makes this surface quite promising in the next generation CMOS devices. In spite of these importance, knowledge on the oxidation kinetics on Si(110) surface has been quite insufficient. In this situation, we have studied initial oxidation process of Si(110)-16×2 clean surface by using real-time synchrotron radiation photoemission spectroscopy (SR-PES)[1] and scanning tunneling microscopy (STM)[2], and found a presence of a rapid initial oxidation[1] and preferential adsorption of oxygen at pentagon-pair adatoms[2]. The remaining issues, however, include unknown behavior of the surface core level shift during oxidation and the bonding states at the SiO2/Si interface. The former is indispensable in further clarification of the kinetics, while the latter is crucial in understanding the interface state that affects the channel mobility. In this study, we have investigated the bonding structure of ultrathin oxide films on Si(110) surface by real-time SR-PES experiments. Experiments were conducted at surface chemistry end-station settled at BL23SU in SPring-8. The oxidation temperature was 540 oC and the O2 pressure was 1.1×10-5 Pa. As a result, we found that one of the surface core-level shifts in Si 2p spectrum, related to the 1st and the 2nd layer Si atoms[3], decreases rapidly, coincident with the rapid initial development of the O 1s spectrum. This indicates high reactivity of the Si(110)-16×2 reconstructed surface with oxygen molecules. Among the oxide components in the Si 2p spectrum, Si3+ is always higher than Si4+ during oxidation up to 1 ML, contrary to the case on Si(001) surface. We currently understand this to be caused by a specific strain relaxation mechanism on this Si(110) surface. On Si(110) ideal truncated surface, there are two types of bond structure; one (A-bond) horizontally connects the 1st-layer Si atoms and is aligned along the [-110] direction while the other (B-bond) vertically connects the 1st- and the 2nd-layer Si atoms. A-bonds form a dense, chain-like structure and are prone to accumulate strain along the [-110] direction upon insertion of oxygen atoms between the bonds. It is therefore unlikely that oxygen insertion occurs to all the A-bonds on the surface even after the 1 ML saturation. B-bonds, on the other hand, are less dense than A-bonds, and may ease the oxidation strain by pushing the topmost Si atoms toward the vacuum. One possible picture is that the dominant Si3+ component in the 1 ML oxide arises from alternating oxidation of the surface A-bonds.[1]M. Suemitsu et al., Jpn. J. Appl. Phys, 46 (2007) 1888.[2]H. Togashi et al., Jpn. J. Appl. Phys, 46 (2007) 3239.[3]N. D. Kim et al., Phys. Rev. B, 75 (2007) 125309
9:00 PM - I3.52
Compositional Stresses, Diffusion, and Grain Boundary Effects in Large Grained and Nanocrystalline Ceria and Titania Films
Sunil Mandowara 1 , Sidharth Bhatia 1 , Janet Rankin 1 , Brian Sheldon 1
1 , Brown University, Providence, Rhode Island, United States
Show Abstract9:00 PM - I3.53
In situ Stress Measurements During Sintering of Pure and (Co, Li) Doped Cerium Gadolinium Oxide (CGO) Constrained Films to Understand Densification Mechanism.
Sunil Mandowara 1 , Jason Nicholas 2 , Lutgard De Jonghe 2 , Brian Sheldon 1
1 , Brown University, Providence, Rhode Island, United States, 2 Materials Science and Engineering Department, University of California, Berkeley, California, United States
Show Abstract9:00 PM - I3.54
Nanostructured CeO2 platforms for Resistive Oxygen Gas Sensing.
Shilpi Gupta 1 , Laxmikant V. Saraf 2 , Suntharampillai Thevuthasan 2 , Shalini Prasad 1
1 Electrical and Computer Engineering, Portland State University, Portland, Portland, Oregon, United States, 2 , Environmental Molecular Sciences Laboratory, Pacific Northwest National laboratory, Richland, Washington, United States
Show AbstractThe goal of the current project is the evaluation and analysis of ceria film, structure- function properties for rapid, resistive oxygen gas sensing. Ceria is known for its unique ability to lose or gain oxygen, which is of great interest to catalyst and solid oxide fuel cells. The defect migration is a major issue, which governs the properties like oxygen storage and oxygen conduction in ceria. The doping of trivalent elements including Y, Sm and Gd elements in ceria are expected to create oxygen vacancies and eventually influence virtually all types of transport properties like ionic and electronic properties. The overarching objective of this project is to study the effects of changes in surrounding conditions such as temperature, pressure, grain-size and film thickness on the transport properties.We have synthesized and fabricated fine pure and doped nanostructured ceria films using the sol gel process with different grain sizes ranging between 5-52 nm and the single crystalline ceria films using MBE and characterized them using several bulk surface sensitive capabilities. Conductivity in these films was measured as a function of temperature under various oxygen and vacuum conditions. Preliminary results show that response of the doped ceria film with smallest grain size is much faster than the others under the same conditions of temperature and pressure. Moreover response time of these films is few milliseconds with the change in the oxygen partial pressure. The operating range for the sensor is between 400°C to 800°C.Oxygen sensors have come into wide use in various fields like automotive and industrial applications. All these applications require the fast monitoring of the oxygen gas. We have addressed this issue by using cerium oxide grains as the active sensing material.
9:00 PM - I3.55
ALD-grown Titanium Dioxide Thin Films, their Structure and its Effect on their Photocatalytic Properties.
Marja-Leena Kaariainen 1 , Tommi Kaariainen 1 , David Cameron 1
1 , Lappeenranta University of Technology, Mikkeli Finland
Show AbstractUndoped and nitrogen doped titanium dioxide thin films were grown by using Atomic Layer Deposition (ALD). Titanium tetrachloride, distilled water and ammonium hydroxide were used as precursors. A series of film thicknesses of 3nm-260nm were deposited at temperatures of 350°C and 250°C. The photo activity and photocatalytic activity of the thin films were studied and the effect of the film structure on these properties was scrutinized. It was observed that at 350°C both undoped and doped titanium dioxide films grew first as anatase up to thickness of 30nm but changed into rutile dominant films as the thickness increased. Thin films deposited at 250°C possessed only anatase phase after thickness of 25nm. Thicknesses lower than 25nm did not show clear crystallinity in XRD measurement. The photocatalytic activity of the films was higher at those films having pure anatase structure. Yet the photocatalytic activity was higher at anatase film with a thickness of 15nm grown at 350°C than at thicker anatase films grown at 250°C. The reason for this may be the quantum well effect due to nanocrystalline structure of the very thin films. In addition the nitrogen doping improved the photo activity and the photocatalytic activity of the titanium dioxide films significantly.
9:00 PM - I3.56
Polymer Assisted Deposition of Thin Films
T Mark McCleskey 1 , Eve Bauer 1 , Anthony Burell 1 , Menka Jain 2 , Quanxi Jia 2 , Hongmei Luo 2
1 Materials Chemistry, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractWe have developed a new solution route for the deposition of thin films. This innovative technique uses aqueous solutions in which metals are bound to a water soluble polymers. The solution may then be applied to any type of surface in a variety of ways including spin coating or dip coating. Thermal treatment then removes both water and polymer at as low as 450 oC. Further annealing yields epitaxial, crack-free films. We have made a wide variety of stable solutions of over 30 metals. Stoichometry of the films is readily controlled by simply mixing solutions. We have made a wide variety of epitaxial films. Using lattice engineering to match the substrate with the desired fim we have been able to control both the phase of the film and the oxidation state in the case of uranium. Highly conformal coatings are obtained on a variety of surfaces including complex porous structures.
9:00 PM - I3.57
Perovskite Ferroelectric Thin films Grown by Polymer Assisted Deposition Technique.
Menka Jain 1 , Eve Bauer 1 , H. Yang 1 , A. Burrell 1 , T. McClesky 1 , R. DePaula 1 , Q. Jia 1 , H. Wang 2
1 Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Department of Electrical and Computer Engineering, Texas A&M University, College Station, Texas, United States
Show Abstract9:00 PM - I3.58
ALD of HfLaOx using tetrakis(ethylmethylamino)hafnium, tris(isopropylcyclopentadienyl)lanthanum and Ozone.
Rajesh Katamreddy 1 , Nathan Stafford 1 , Benjamin Feist 1
1 Delaware Research and Technology Center, American Air Liquide Inc., Newark, Delaware, United States
Show AbstractIn order to continue the pace of transistor scaling predicted by Moore’s law alternative high dielectric constant (high-K) materials are sought to replace SiO2 as gate dielectric material. Hf-based oxides are widely accepted as the most promising replacement materials with HfSiON to be incorporated as the first generation high-k material. Due to the relatively low dielectric constant of such oxides, materials with even more higher dielectric constant are actively sought for next generation gate and DRAM dielectrics. Although addition of Si to HfO2 enhances several structural and electrical characteristics of the film, it lowers the overall effective dielectric constant of the film. Addition of La2O3, a high-K (K~25) and wide bandgap (5.5.eV) material, to HfO2 film is a potential solution for obtaining higher-K films. La2O3 film has also been successfully used in between gate metal and high-K dielectric to tune the effective work function. One of the main challenges in incorporating HfO2 as dielectric is the thermal morphological stability of the film. HfO2 has been observed to crystallize at temperatures well below the standard post deposition annealing conditions; however, La2O3 is known to stay amorphous after high temperature post deposition annealing. Therefore, it is anticipated that La-doped HfO2 will remain amorphous after thermal treatment at high temperatures.In this work, HfLaOx films are deposited using tetrakis(ethylmethylamino) hafnium (TEMAH) and tris(isopropylcyclopentadienyl) lanthanum (La(iPrCp)3) with ozone as the co reactant. The ALD of individual HfO2 and La2O3 were performed using the above mentioned precursors and ALD process temperatures windows were determined. Since both the precursors are introduced under similar conditions for multi-metal oxide films their process temperature windows must overlap for their use in ALD of mixed multi-metal oxide. The ALD temperature windows of La(iPrCp)3 and TEMAH were observed to overlap between 150 and 225 oC. ALD growth rates of 1.1 Å/cycle for HfO2 and 0.6 Å/cycle for La2O3 were observed using respective precursors and ozone. HfLaOx films of different compositions were deposited by varying the number of alternating HfO2 and La2O3 monolayers. Compositions of such films were measured using Rutherford backscattering spectroscopy: composition tunability by ALD was then determined. The effect of La2O3 addition and the film composition on crystallization and electrical characteristics of HfO2 will also be presented.
9:00 PM - I3.59
A New Technique to Measure and Deliver Low Levels of Water Vapor into Atmospheric and Vacuum Processes.
Jeffrey Spiegelman 1 , Russell Holmes 1
1 , RASIRC, San Diego, California, United States
Show AbstractAs material processes move to the nanoscale, fine control of process chemistries becomes critical. Atomic Layer Deposition, Chemical Vacuum Deposition, Selective Gate Oxidation, as well as fabrication of Carbon Nanotubes all report the need to add water vapor from 50 sccm (40mg/min) to below 1 sccm ( 0.8 mg/min). Water vapor can be used for oxidation, cleaning and annealing of the nanoscale devices and thin films.At 0.8 mg/min, flow control of liquid water with a mechanical pump is difficult without pulsation. Because water is liquid at room temperature, a standard thermal mass flow controller for gas cannot be used. Instead bubblers are used. However, they do not provide consistent or repeatable delivery. They are affected by gas and liquid temperature, relative pressures as well as gas velocity, liquid height, thermal droop, and contamination build up. RASIRC has developed a new pervaporation device that selectively allows water to diffuse into a carrier gas stream. The liquid water never directly contacts the carrier gas, allowing for independent liquid and gas pressures. A nonporous, hydrophilic membrane provides very rapid diffusion of water vapor into the carrier gas stream. This allows for precise amounts of water vapor to be added to the carrier gas based solely on relative vapor pressures. To validate the performance of the device at very low flow rates into both atmosphere and vacuum process pressures, a heated humidity probe was used. This device was able to measure flow rates of 1 to 200 sccm in both vacuum and atmospheric pressure. The experimental results were compared with the expected theoretical dew point to validate the procedure. The humidity probe was used to measure both long term stability of the device and the instantaneous response time. Experimental results were compared to the expected time needed to change the water vapor concentration in the test volume.
9:00 PM - I3.6
Study of Coercivity-enhanced Ruthenium-doped La0.67Sr0.33MnO3 Thin Films for Pseudo Spin Valve Devices.
Yuk Kwan Chan 1 , Wang Fai Cheng 1 , Chi Wah Leung 1
1 Department of Applied Physics, The Hong Kong Polytechnic University, Hong Kong China
Show AbstractPseudo spin valves rely on the contrast in coercivities of magnetic layers to achieve distinct magnetization states, and to demonstrate noticable steplike giant magnetoresistance effect (GMR). Common schemes to achieve coercivity differences include variation in magnetic layer thicknesses, magnetostatic coupling due to shape anisotropy, or using magnetic materials with marked coercivity differences.The current investigation focused on 0.5wt% Ru-doped La0.67Sr0.33MnO (LSMRO) thin films. The material, in bulk or in thin film forms, has demonstrated enhanced coercivity compared with La0.67Sr0.33MnO3 (LSMO) . In this work we further studied its suitability to be employed as a ferromagnetic electrode in all-oxide pseudo spin valve structures. We have fabricated LSMRO epitaxial thin films on LaAlO3 substrates by pulsed laser deposition method. Curie temperatures (TC) of the films, as estimated from temperature-dependent resistance measurements and, further confirmed by magnetic hysteresis measurements, were above room temperature. Hysteresis measurements down to 80K showed that the coercivities of LSMRO films, as compared with that of LSMO, can be greatly enhanced. Anisotropic magnetoresistance (AMR) measurements of the films below 20 K showed a similar trend. Coercivity enhancement up to ten times the values of LSMO thin films of same thicknesses can be obtained at such temperatures, without greatly compromising TC and conductivity. Our work suggests the suitability of LSMRO thin films as ferromagnetic electrodes in pseudo spin valve.
9:00 PM - I3.60
Development and Study of Single-Chamber SOFCs with Extra Thin Nano-structured Electrolytes.
Zhigang Xu 1 , Dhananjay Kumar 1 , Jag Sankar 1
1 Mechanical Engineering, North Carolina A&T State University, Greensboro, North Carolina, United States
Show Abstract9:00 PM - I3.61
Preparation of PNZT Thin Films by Chemical Solution Deposition and Their Characterization.
Volkan Kayasu 1 , Macit Ozenbas 1
1 Materials Engineering, Middle East Technical University, Ankara Turkey
Show AbstractNiobium doped lead zirconate titanate thin films (PNZT) were prepared using a chemical solution deposition technique with nominal compositions, Pb(1-0.5x)(Zr0.53Ti0.47)1-xNbxO3 where x = 0.00 - 0.07. Single and multi-layered films were deposited onto (111)-Pt/Ti/SiO2/Si-(100) substrates by spin coating. PZT compositions near the morphotropic phase boundary (MPB) were chosen due to excellent ferroelectric and dielectric properties achieved in this area. The effects of sintering temperature, sintering time, thickness of the films and niobium doping were investigated with regard to phase development, microstructure, and ferroelectric and dielectric characteristics. From the results of XRD studies, the optimum sintering parameters were found as 600°C and 1 hour by keeping the thickness and composition of the films constant. Ferroelectric and dielectric measurements also supported this behaviour. PNZT thin films with different thicknesses between 250 nm and 870 nm were produced by multilayer coating method. The best results were obtained in double layered films which was 390 nm in thickness. The films were smooth, crack free and uniform. Ferroelectric behaviour of PNZT thin films were examined by hysteresis curves and C-V curves. Optimum doping was obtained in 1% Nb doped films. The properties were diminished in the films containing higher amounts of Nb doping. For 1% Nb doped [Pb0.985(Zr0.53Ti0.47)0.97Nb0.03O3] films, remanent polarization (Pr) of 20.6 μC/cm2 and coercive field (Ec) of 27.4 kV/cm were obtained. Dielectric properties of the films were examined by dielectric constant and tangent loss values. The maximum dielectric constant was achieved in 1% Nb doped films which was 689. The tangent loss values were between 2 and 4 %. It was observed that after 1% Nb doping, dielectric constant decreased significantly.
9:00 PM - I3.62
Transesterification Catalysts From Hydrotalcite-Like Precursors.
Gerald Macala 1 , Alexei Iretskii 2 , Mark White 3 , Peter Ford 1
1 Chemistry and Biochemistry, UCSB, Santa Barbara, California, United States, 2 Department of Chemistry, Lake Superior State University, Sault Ste. Marie, Michigan, United States, 3 School of Chemical Engineering, Mississippi State University, Mississippi State, Mississippi, United States
Show AbstractThe base catalyzed transesterification of triglycerides such as seed oils with methanol or ethanol produces a non-toxic, biodegradable, renewable, and clean burning fuel that can directly replace petroleum diesel in most applications. Commercial technology for this transesterification process to give biodiesel generally employs homogeneous bases such as NaOH or NaOCH3 in methanol solution as catalysts. We report here the preparation and characterization of new solid base catalysts based on transition metal doped hydrotalcite (Mg–Al layered double hydroxide) precursors potentially suitable for flow reactor applications. We also demonstrate that these doped materials are effective catalysts both for the model reaction with triacetin (glyceryl triacetate) and for the transesterification of soybean oil. The influence of metal dopant type and concentration, calcination temperature, and reaction conditions is described.
9:00 PM - I3.64
Quantitative Analysis of Fluorite to Perovskite Transformations in (Pb,La)(Zr,Ti)O3.
Chad Parish 1 , Geoff Brennecka 1 , Bruce Tuttle 1 , Luke Brewer 1
1 Materials Science and Engineering Center, Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractTypically, (Pb,La)(Zr,Ti)O3 (PLZT) ferroelectric thin films are fabricated with excess Pb precursor in order to compensate for volatile PbO lost during processing and avoid formation of sub-stoichiometric fluorite phase. Fluorite phase is non-ferroelectric and has inferior dielectric properties relative to the desired Pb-stoichiometric perovskite phase. Due to series mixing, even a small volume of surface fluorite can dominate the dielectric behavior of a mixed-phase material. This problem is aggravated when film thickness decreases as a relatively larger amount of Pb is lost. Recently, we have succeeded in showing that fluorite-crystallized PLZT can be reverse transformed to the perovskite phase via deposition of a PbO overcoat and subsequent annealing of the crystallized PLZT films. Specifically, we have demonstrated that both PZT and PLZT thin films (~250 nm thick) grown with Pb-deficient precursors exhibit phase reversibility and have minimal reaction with underlying electrode technology in marked contrast to stoichiometric or Pb-excess films. Here, we will present the TEM results that have led us to these observations in PZT and PLZT. Conventional and high-resolution TEM results indicated that large-grained perovskite formed on the bottom electrode, and fine-grained fluorite formed on top of the perovskite. HREM lattice images confirmed the phase identifications. Qualitative EDS x-ray spectroscopy in TEM showed depletion of Pb near the surface of the fluorite-bearing films, and replenishment in the subsequently converted films. X-ray spectrum imaging has further confirmed our phase identifications. We have also developed EDS quantification routines to measure the cation ratios in these materials, and will discuss the difficulties and results arising from EDS quantification in these samples.Sandia is a multiprogram laboratory operated by Sandia Corporation, a LockheedMartin Company, for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
9:00 PM - I3.65
Structural Evolution and Phase Transformations in La(Sr)-Cr(Mg,Ni)-O Thin Films.
Sergey Yarmolenko 1 , Kristofer Gordon 1 , Jag Sankar 1
1 Mechanical Engineering, North Carolina A&T State University, Greensboro, North Carolina, United States
Show AbstractLanthanum chromite based dense perovskite ceramic membranes with mixed ionic and electronic conductivities can be used for oxygen separation process and reforming of methane into syngas. La(Sr)-Cr(Mg,Ni)-O amorphous films doped by Sr, Mg and Ni were deposited on (La0.9Sr0.1)0.95Cr0.85Mg0.10Ni0.05O3 (LSCMN) perovskite ceramic membrane material and on Si/SiO2 substrates by pulsed laser deposition method. LSCMN was used as a target material. Annealing of these films in air was studied high temperature XRD and micro-Raman. Amorphous films exhibit two-step structural evolution resulting in nanoporous polycrystalline film when they heated up from room temperature to 800°C. At temperatures above 500°C amorphous films transform to dense polycrystalline films consisting of monoclinic phase La(Sr)Cr(Mg,Ni)O4 typical to already reported LaCrO4. At temperatures above 700°C this film irreversibly transforms into highly porous nanocrystalline film of orthorhombic phase La(Sr)Cr(Mg,Ni)O3. This effect can be used for creation of stress free porous coating on membrane with embedded nanoparticles of metals serving as catalysts in syngas reforming process.
9:00 PM - I3.66
Phase Stability of 10mol%Sc2O3-1mol%CeO2-ZrO2 Ceramics
Sergey Yarmolenko 1 , Svitlana Fialkova 1 , Devdas Pai 1 , Jag Sankar 1
1 Mechanical Engineering, North Carolina A&T State University, Greensboro, North Carolina, United States
Show AbstractScandia doped zirconia is very promising material for solid oxide fuel cells due to its high oxygen conductivity in the 800-1000°C temperature range. Cubic phase can be stabilized by small amounts of CeO2. 10mol% Sc2O3-1mol% CeO2-ZrO2 ceramics were sintered at temperatures 1100-1600°C at different heating rates and dwell time. Ceramics sintered at temperatures higher 1300°C exhibit slow phase transformation from cubic to rhombohedral (β) phase at temperatures 350-400°C. Analysis of c-β phase transition efficiency in the ceramics shows strong correlation between the rate and grain size. Microstructural changes on polished and thermally etched surfaces of cubic phase due to c-β phase transition studied by SEM, AFM and micro-Raman. However, β-c phase transition temperature (440°C) does not depend on sintering temperature of ceramics. This phase transition was studied by high temperature x-ray diffractometry (HTXRD) and differential scanning calorimetry methods. Coefficients of thermal expansion of cubic and β-phases were calculated from temperature dependence of lattice parameters obtained by HTXRD in the temperature range of 25-800°C. Hardness of the ceramics was studied by nano- and microindentation. Hardness of c- and β-phases is similar and very close to zirconia values. Indentation results indicate that phase transition is accelerated by stress.
9:00 PM - I3.67
Ag Bonding-Enabled LiNbO3 Layer Transfer
Kenneth Diest 1 2 , Melissa Archer 3 2 , Jennifer Dionne 2 , Young-Bae Park 2 , Matthew Czubakowski 2 , Harry Atwater 2 1
1 Materials Science, California Institute of Technology, Pasadena, California, United States, 2 Applied Physics, California Institute of Technology, Pasadena, California, United States, 3 Chemical Engineering, California Institute of Technology, Pasadena, California, United States
Show AbstractThroughout the past two decades, wafer bonding has become an invaluable technique within the electronics industry. The ability to directly bond two materials, with varying lattice constants and crystal orientations, has facilitated the development of entirely new fields of research, from microelectromechanical systems to Si-based optoelectronics. Recently, wafer bonding processes have been combined with thin-film layer transfer induced by ion implantation. The application of these two methods enables thin film single crystal layer transfer of a wide variety of semiconductors and ferroelectrics. A major difficulty with current layer transfer processes is the preparation of the two bonding surfaces through a combination of plasma activation, wet etching, and chemical mechanical polishing. We report a new method for bonding LiNbO3 films onto silicon substrates which removes the tight restrictions on surface characteristics while still allowing bonding. The bond is facilitated through a thin Ag layer between the LiNbO3 and Si and the technique allows single crystal thin films of a wide variety of materials to be transferred to virtually any type of substrate. Single cystal LiNbO3 layers were transferred onto silicon substrates by deposition of 400 nm of silver onto the top surfaces of both samples. The silvered surfaces were then bonded together at temperatures between 200 and 500°C. The distribution of grain orientations before and after the annealing process was examined using X-ray diffraction. The growth of Ag (111) grains during the bonding process effectively removes the original bonding interface. Focused ion beam images of the silver films before and after annealing show an increase in average grain size from 2.39x10^3 nm^2 to 3.08x10^4 nm^2, and after bonding, these grains extend from the LiNbO3 interface to the Si interface. These results were confirmed with cross-sectional transmission electron microscopy images of the bonding layer before and after annealing.
9:00 PM - I3.69
Galvanic Deposition of Pt on Si: Fundamentals and Applications.
Marta Cerruti 1 , Gail Hernandez 1 , Carlo Carraro 1 , Roya Maboudian 1
1 Chemical Engineering, UC Berkeley, Berkeley, California, United States
Show AbstractGalvanic deposition is a process that allows the deposition of metals on substrates with lower reduction potential. During this process, a salt of the metal is put in an aqueous solution in contact with the substrate. Due to the higher electrochemical reduction potential, the metal is reduced while the substrate is oxidized. If the solution contains an agent that can remove the product of substrate oxidation, the deposition can continue and metallic films can be deposited with a controlled thickness. This process has many advantages over usual thin film deposition techniques: it is cheap, fast, and easy, and can be used to coat surfaces that would be hard to reach with depositions performed in the gas phase. In the past, Au, Ag, Pt, Pd and Cu have been successfully deposited with galvanic technique on Si, Ge and other substrates. In the present work we study the chemical structure and morphology of Pt films galvanically deposited on Si. Using X-Ray Photoelectron Spectroscopy and Auger Electron Spectroscopy we were able to determine the formation of a PtSi layer at the early stages of the deposition, which is covered by Pt with increasing deposition time. We also studied the evolution of the morphology of the film with Atomic Force microscopy, and we used contact angle measurements and i-V measurements to characterize surface and electrical properties of the film. Moreover, we studied how the growth was affected by the concentration of HF in solution and by the use of poly-crystalline Si vs. (100) crystalline Si as substrates. At last, we applied this technique to coat real devices and performed tests to evaluate the properties of the Pt film coverage.
9:00 PM - I3.72
Nanostructured Tin Oxide Films for Gas Sensing Applications
Piao Liu 1 , Vijay Singh 1 , Suresh Rajaputra 1
1 electrical & Computer Engineering, University of Kentucky, Lexington, Kentucky, United States
Show AbstractNanostructured tin oxide films have been reported to be highly sensitive to reducing agents like Hydrogen and Ammonia. Our work is focused on the evaluation of nanostructured architectures to improve the gas sensing properties of these films at low temperatures, and preferably at room temperature. So far we have been successful in observing an excellent sensor response (18%) in nanostructured tin oxide based resistive sensors at 100C. Nanoporous tin oxide films were fabricated by a two-step anodization process. Tin sheets were anodized at 4C for different time duartion (1min-90 minutes) at constant currents (40mA-400mA), followed by a thermal oxidation. Nanoporous tin oxide films with thicknesses ranging from 4 to 8 microns on top of un-anodized tin substrate were obtained. Surface morphology of the anodized foils was examined through electron microscopy. X-ray diffraction studies revealed a tetragonal phase with lattice parameters a=4.737Å, c=3.186Å. The films were patterned with electrodes and their responses to cycles of ammonia (100ppm in N2) and pure N2 were recorded. The best response (17.6% change in resistance) was obtained when the sensor was tested at 100 C. We have also measured a sensitivity of 8% when exposed to 10 ppm of ammonia. This indicates that our sensor can be used to detect very low concentrations of ammonia gas. High surface area resulting from the nanoporous structure of the anodized SnO2 films could be responsible for the enhanced sensor response at relatively low temperatures (100 C) observed in our studies. Sensor characteristics such as response time, recovery, sensitivity are correlated with process parameters (anodization voltage, effective porosity).
9:00 PM - I3.8
Synthesis and Characterization of CuCr2O4 Thin Films for Spin-Based Devices.
Jodi Iwata 1 , Rajesh Chopdekar 2 1 , Virat Mehta 1 , Brittany Nelson-Cheeseman 1 , Franklin Wong 1 , Joanna Bettinger 1 , Marco Liberati 1 , Elke Arenholz 3 , Yuri Suzuki 1
1 Materials Science & Engineering, University of California, Berkeley, Berkeley, California, United States, 2 Applied Physics, Cornell University, Ithaca, New York, United States, 3 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractThe complex spinel oxides have been of recent renewed interest due to their potential in spin-based devices. It has been shown that magnetic junctions with an isostructural interface between half-metallic Fe3O4 electrodes and a magnetic barrier layer can give rise to significant junction magnetoresistance while also allowing us to probe magnetism at these interfaces. CuCr2O4 is an electrically insulating, magnetic material that is promising as a magnetic barrier. It is a tetragonally distorted normal spinel crystal with Cr3+ and Cu2+ cations occupying octahedral and tetrahedral interstitial sites, respectively. We report the first synthesis of CuCr2O4 thin films that have significant potential as a magnetic barrier layer due to its close lattice match with Fe3O4. CuCr2O4 films were grown by pulsed laser deposition on insulating (110) SrTiO3 (STO), (110) MgAl2O4 (MAO), and (001) MgO substrates. We have found that depositing CuCr2O4 films at 500°C in 15mTorr of O2 at an energy density of 1 J/cm2 followed by cooling in 100 Torr O2 yields films with magnetic properties similar to those of the bulk. X-ray diffraction of CuCr2O4 films on (110) MAO, and (001) MgO reveal single-phase films with epitaxial strain of -4.2% and -3.5%, respectively. Rutherford backscattering spectroscopy confirms the stoichiometry of our CuCr2O4 films. X-ray absorption spectroscopy (XAS) shows the presence of divalent Cu and trivalent Cr at the film surface indicating that bulk cation valence charge is preserved throughout the film. The consistent cation valence charge also suggests that in thin film form, like bulk CuCr2O4, Cr3+ continues to exist in octahedral interstices while Cu2+ occupies tetrahedral interstices. Magnetic properties were investigated using SQUID magnetometry. The CuCr2O4 thin films exhibit a Curie temperature, TC, of 125K and a magnetic moment of 0.78 μB/f.u, closely resembling bulk values(TC = 135K and magnetic moment between 0.4-0.8μB/f.u )[2,3]. The low magnetic moment is surprising as Hund’s rule calculations show that Cr3+ and Cu2+ are magnetic which suggests a magnetic moment of 5μB for CuCr2O4. However, the discrepancy in magnetization can be accounted for by the triangular cation configuration proposed by Yafet and Kittel in which Cr3+ cations are aligned anti-parallel to each other, and the Cu2+ cations are perpendicular, thus sitting along the axis of magnetization [3]. Finally, the insulating nature of bulk CuCr2O4 is preserved in thin film form as all films displayed highly insulating electronic behavior, thus making it appropriate as a magnetic barrier layer material [4].[1] N. Padmamanaban et al. J. Solid State Chem. 81, 250 (1989).[2] T.R. McGuire et al., Ceramic Age. 82, (1952) 22.[3] E. Prince, Acta Crystal. 10, (1957) 554.[4] K.S. De et al., J. Solid State Chem. 43, 261 (1982).
9:00 PM - I3.9
Synthesis of Ultra-Dense Highly Crystalline Y-doped BaZrO3 Films by Pulsed Laser Deposition Technique
Michael Sygnatowicz 1 , Ashutosh Tiwari 1
1 Materials Science & Engineering, university of utah, Saltlake city, Utah, United States
Show AbstractProton conducting materials such as Y-doped BaZrO3 (BZYO) have wide ranging applications such as steam electrolyzers, hydrogen pumps, solid electrolytes in fuel cells, and gas sensors. Electrical conductivity of BZYO-based systems at temperature ranges of 400oC to 600oC can be over 10-2 Scm-1, a vast improvement over conventional oxygen ion conducting materials. However, most of the work on BZYO so far has been focused on bulk samples with very little work reported on thin films. Here we report the synthesis and characterization of ultra dense thin films of BZYO on various substrates such as sapphire, silicon and iron. These films, which range in thickness from 5 nm to more than 50 μm, not only have the ability to act as low resistance electrolyte layers in fuel cells but also as fast response gas sensors. The thin film and high conductivity allows for the ability to rapidly detect hydrogen containing gases such as water and organic vapors while at the same time remaining translucent. A UV nanosecond pulse laser was used to ablate a BaZr0.8Y0.2O3 target in a vacuum chamber. The discharged plasma was deposited on sapphire and steel substrates at 600oC and 700oC. 35,000 laser pulses at 10 Hz resulted in a ~1.5 μm translucent layer. XRD characterization showed the desired BaZr0.8Y0.2O3 and substrate peaks with no sign of contaminant phases. Electrical conductivity measurements were done in dry conditions using the two probe method on the sapphire sample. At 600oC and 800oC the electrical conductivity was 0.1x10-2 and 0.9x10-2 Scm-1 respectively. Significant enhancement in the electrical conductivity was observed in wet air environment due to added hydrogen ion conduction. Grain size measurements using a sulfuric acid etching showed grains sizes from 4-20 μm. This means that our films are only one grain thick, avoiding the problem of grain boundary trapping in the out-of-plane direction. Further research is going on to compare in-plane and out-of-plane electrical conductivities to get a fundamental understanding about the critical role played by the grain boundaries in the electrical transport characteristics of BZYO system.
Symposium Organizers
Valentin Craciun University of Florida
Dhananjay Kumar North Carolina A&T State University
Stephen J. Pennycook Oak Ridge National Laboratory
Kaushal K. Singh Applied Materials, Inc.
I7: ZnO Nanoparticles and Thin Films
Session Chairs
Thursday AM, March 27, 2008
Room 2001 (Moscone West)
9:00 AM - I7.1
Synthesis of ZnO Nanoparticles Using a Modified Vapor Phase Transport Process
Tarek Trad 1 , Curtis Taylor 1 , Kyle Donley 1 , David Look 3 , Kurt Eyink 2
1 Mechanical Engineering, Virginia Commonwealth University, Richmond, Virginia, United States, 3 Semiconductor Research Center, Wright State University, Dayton, Ohio, United States, 2 U.S. Airforce Research Lab, United States Air Force, Dayton, Ohio, United States
Show AbstractThe interest in ZnO nanostrucures arises from their potential applications in excitonic-related devices including components of nanoscale circuitry, piezoelectric power generation, and hybrid organic-inorganic photovoltaic devices. Generally, nanoparticles of ZnO are synthesized chemically through complex, multi-step, and time consuming processes with limited control over size and composition. Vapor phase synthesis offers a facile route towards preparation of ZnO nanoparticles with controlled size, high chemical purity, and offers greater compatibility for solid-state device integration. In this work, ZnO nanoparticles with average diameter of 75 nm were successfully synthesized using a modified vapor phase transport (VPT) growth process. Nanoparticles were grown on Si(100) inside a quartz inlet tube (23 cm long, 1 cm diameter) placed inside a horizontal tube furnace with substrate temperatures as low as 280 °C, which holds an advantage over previously reported routes (VPT with substrate temperature of 440-460 °C). Scanning electron microscopy and photoluminescence spectroscopy characterization techniques were used to determine particle size and room-temperature photoluminescence respectively. Ultraviolet emission at 3.335 eV is strong and predominant in the PL spectra which is a high energy location with respect to the near-band-edge (NBE) emission around 3.26 eV commonly observed for ZnO thin films and bulk crystals. This might be attributed to the quantum-confined band-edge emission. The UV emissions are generated from the nanoparticles at room temperature and without any pre-treatment. Also, self –assembled ZnO mesoparticles (> 100 nm) were easily realized by increasing the growth time. Currently, this approach is being optimized in order to reach better control over particle diameter and height in an effort to realize ZnO nanodots with clear quantum size effects.
9:15 AM - I7.2
Solubility and Secondary Phase Segregation Relationship for Favorable Vs Unfavorable Dopants in Oriented/Epitaxial ZnO Films Grown by MOCVD
Laxmikant Saraf 1 , W. Hlaing Oo 2 , Z. Zhu 1 , C. Wang 1 , M. Engelhard 1 , D. Baer 1 , M. McCluskey 2
1 Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington, United States, 2 Department of Physics , Washington State University , Pullman, Washington, United States
Show AbstractIn order to get a wider acceptance for ZnO to be a truly multifunctional semiconducting oxide for its current and perceived usages in scientific disciplines such as thermoelectrics, ferroelectrics, optics, magnetism, dielectrics and environmental sensing, a great deal of efforts need to focused on a variety of p- as well as n-dopants. Adaptable nature of particular dopants in ZnO as oppose to unfavorable nature of other dopants has created a wide opportunity to gain fundamental insights related to mutual interaction among growth process, dopant related secondary phase segregation and their impact on physical and chemical properties. In general, due to minimization of grain boundary density, oriented or epitaxial ZnO thin films are better candidates to simplify the analysis and better project the scale of dopant solubility, carbon contamination, mobility of defects and their interdependent relationship. In this study, we focus our discussion on better solubility of Mn as a dopant as oppose to unfavorable nature Cr solubility in oriented and epitaxial ZnO films grown by MOCVD. Based on some recent evidences from a highly sensitive time of flight secondary ion mass spectrometry (TOF-SIMS), solubility differences as a function of ZnO film depth are quite clear. The overall interpretation of our results are based on analysis by low temperature conductivity measurements, AES, XPS, XRD, HRTEM, EXAFS, PL, RBS and PIXE. We have observed a strong relationship between growth properties of (Zn, Cr) O films and secondary phase formation corresponding to preferred phase accumulation region. Interestingly, trace carbon contamination has been observed to follow similar route. A suppression of conductivity in lightly Mn doped ZnO films was due to Mn2+ replacement with Zn interstitials. The growth on r-plane Al2O3 single crystal shows α-Al2O3[-101-1]//ZnO[0001] and α-Al2O3(10-1-2)//ZnO((2-1-10) with domains corresponding to growth modes α-Al2O3 (0001)//ZnO(0001), α-Al2O3 [11-20]//ZnO[10-10] and α-Al2O3 [11-20]//ZnO[10-10]. Observation of periodic dislocations at the interface demonstrates overall film relaxation and energy minimization approach for the second type of domain growth. A possible link between the location of interface stress accumulation and misfit dislocation will also be discussed. We study our results in details from a larger view point of homogeneous Mn distribution as oppose to non-homogeneous Cr distribution in ZnO films and their impact on physical and chemical properties.
9:30 AM - I7.3
Magnetization Behavior in Nickel Incorporated Nanocrystalline ZnO.
Dinesh Pandya 1 , Ajay Shankar 1 , Sayoji Goli 1 , Kanwal Bhatti 1 , Nivedita Ghosh 1 , Sujeet Chaudhary 1
1 Physics, Indian Institute of Technology Delhi, New Delhi India
Show AbstractFerromagnetic II-VI semiconductors, like transition metal doped ZnO, SnO2, TiO2 have emerged as potential candidate for spintronic devices [1]. The primary requirement for such materials is to have intrinsic and stable room temperature ferromagnetism. Among the II-VI oxide semiconductors, the Ni incorporated ZnO system has also been investigated recently. The reports indicate that the magnetic behavior of Ni:ZnO system depends critically on the sample morphology and the preparation techniques. In some cases, the Ni:ZnO samples are reported to be ferromagnetic, while in other cases they are reported to be paramagnetic[2]. Very recently, we have observed that compared to the conventional solid state sintering technique, the chemical route of synthesizing nanocrystalline Co:ZnO samples reproducibly exhibit stable ferromagnetic behavior [3]. In this paper, we report our results on the synthesis and the characterization of nanocrystalline powder samples of nickel incorporated zinc oxide (up to 10% Ni) prepared by chemical method. By dissolving zinc acetate dihydrate, nickel acetate and polyvinyl pyrrolidane dissolved in deionized water followed by its heating at 90°C to evaporate water, the fine powder of the reactants was obtained. This resultant powder was calcined at 600°C for 1h. A pellet sample was formed after grinding the calcined powder. These pellets were characterized by x-ray diffractometer (XRD) for phase analysis and by vibrating sample magnetometer for the magnetic properties. It was found that in addition to the wurtzite structure of ZnO, an additional NiO phase was also present. The dc-magnetization measurement performed at room temperature and high temperature revealed that the samples consisted of some ferromagnetic fraction along with a paramagnetic fraction. Based on magnetization measurements, we have negated the possibility of the presence of Ni clusters in these samples. The x-ray diffraction analysis revealed that with the increase in Ni concentration, a decrease in lattice parameters ‘a’ and ‘c’ of the unit cell was observed, which indicated the substitution of Zn+2 by Ni2+. The insulating nature of these nanocrystalline Zn1-xNixO samples suggest that the observed room temperature ferromagnetic behavior could be explained on the basis of bound magnetic polarons [4].[1] T. Dietl, H. Ohno, F. Matsukur, J. Cibert and D. Ferrad, Science 287 1019 (2000). [2] D. A. Schwartz, K. R. Kittilstved and D. R. Gamelin, Appl. Phys. Lett. 85, 1395 (2004).[3] K. P. Bhatti, S. Kundu, S. Chaudhary, D. K. Pandya and S. C. Kashyap, J. Phys. D: Appl. Phys.39, 4909 (2006), K. P. Bhatti, S. Chaudhary, D. K. Pandya and S. C. Kashyap, J. Appl. Phys. 101, 033902 (2007); ibid, 101, 103919 (2007).[4] A. Kaminski and S. D. Sarma, Phys. Rev. Lett. 88, 247202 (2002).
9:45 AM - I7.4
Fabrication of Thin Film Transistors with Zinc Oxide Channel Layer at Low Temperatures by High Rate Sputtering.
Paul Beecher 1 , Steven Wakeham 2 , Michael Thwaites 2 , Mary Vickers 3 , Caterina Ducati 3 , Stuart Speakman 1 , John Robertson 1 , William Milne 1 , Andrew Flewitt 1
1 Engineering, University of Cambridge, Cambridge United Kingdom, 2 , Plasma Quest Limited, Hook United Kingdom, 3 Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom
Show AbstractSputtered metal oxides, including zinc oxide (ZnO) and hafnium dioxide (HfO2), have recently been used as the channel semiconductor and gate dielectric layers respectively in thin film transistors (TFTs). These films can be deposited at room temperature by rf magnetron sputtering either directly from a ceramic target using argon gas or reactively from a metallic target using a gas mixture of argon and oxygen. In this work, a novel, high rate sputtering system (HiTUS) developed by Plasma Quest Ltd. was used for the deposition of both ZnO and HfO2 from metallic zinc and hafnium targets respectively in a gas mixture of oxygen and argon with no external substrate heating. The distinguishing feature of the HiTUS system is that the plasma is generated remotely from the target in a side-arm, using an inductively coupled, rf generator. Electromagnets guide the plasma onto the target, which is biased using a DC generator. Hence, the plasma density and target bias may be independently controlled.It was found that the conductivity of ZnO thin films (~100 nm) could be controlled by varying the partial pressure of oxygen used in the sputtering process. At high oxygen partial pressures, a very low conductivity semiconductor was produced with conductivities in the range of 10-6 to 10-9 W-1m-1 and an activation energy of conduction of 0.40 eV. As the oxygen partial pressure was reduced, the conductivity of the material increased to between 103 and 104 W-1m-1, whilst remaining optically transparent with an average transmission typically greater than 90% in the visible spectrum. The use of the remote plasma allows very high sputtering rates of up to 60 nm min-1 for the conducting ZnO. This is almost an order of magnitude faster than that achievable with conventional rf magnetron sputtering. HfO2 thin films (~100 nm) were found to have a high relative permittivity of 22.8, a high resistivity of over 1013 Ωcm and a high breakdown strength in excess of 10 MV cm-1. X-ray diffraction measurements suggest that this material has an amorphous structure. Bottom gate TFTs were fabricated on Corning 7059 glass substrates using a two mask, lift-off process. Chromium was used to form a gate contact. A 100 nm thick layer of HfO2 and ZnO formed the gate dielectric and channel respectively. A 50 nm layer of ZnO deposited at a reduced O2 partial pressure was used to form a source-drain charge injection layer. A double layer of chromium and aluminium formed the source-drain contacts. Devices show good electrical characteristics with switching ratios in excess of 104, threshold voltages of approximately 6 V, and device mobilities of approximately 0.2 cm2/Vs.
10:00 AM - **I7.5
Is Transition Metal incorporated ZnO an Intrinsic Ferromagnetic Semiconductor?
Sujeet Chaudhary 1 , Kanwal Bhatti 1 , Dinesh Pandya 1 , Subhash Kashyap 1
1 Physics, Indian Institute of Technology Delhi, New Delhi India
Show AbstractSpintronics refers to the study and investigation of material related aspects of the potential devices which specifically exploit the so far underutilized degree of freedom of the carriers, i.e., their spin. This has provided a worldwide research impetus to look for materials, e.g. transition metal (TM) incorporated II-VI oxides, which show stable and intrinsic ferromagnetic ordering at room temperature. The experimental findings on the room temperature ferromagnetism (RTFM) in ZnO:TM are at large variance, and both the nature and origin of RTFM are far from being clearly understood.We have extensively investigated the room temperature ferromagnetic character in the polycrystalline ZnO:Mn [1]and nanocrystalline ZnO:Co (both powder and thin films)[2,3] and ZnO:Ni samples. In the case of ZnO:Mn system, the polycrystalline bulk samples of (ZnO)1-x(MnO2)x were prepared by a modified solid-state reaction method. The low temperature (400°C) processed samples exhibited RTFM along with small amount of paramagnetic fraction. On sintering to higher temperatures of 900°C, the sample became single phasic and fully paramagnetic. The strength of the extrinsic RTFM in ZnO:Mn was found to scale with the amount of MnO2, rather than the ZnO.In case of ZnO:Co system, the nanocrystalline powder samples Zn1-xCoxO samples (with x upto 0.10) were synthesized by chemical method at 600°C. It was observed that all the as-calcined samples exhibited ferromagnetism along with small paramagnetic contribution. With increase in sintering in air, the oxides of cobalt starts forming and the saturation magnetization of the FM phase decreases until 800°C and then remains unchanged on further sintering up to 1000°C and above. The observed RTFM was found to be intrinsic in nature and presence of Co clusters is ruled out by varying the process conditions in careful and controlled manner. The RTFM in Zn1-xCoxO can be explained on the basis of bound magnetic polaron model. The correlated polarons give rise to the ferromagnetic fraction and the non-interacting polarons and Co ions, and oxides of cobalt formed the inevitable paramagnetic fraction of the sample. The high temperature magnetization (both iso-thermal and iso-field) confirmed that the TC of the Zn1-xCoxO system lie in the range of 450-495°C. The study of spray pyrolised ZnO:Co films supported the magnetization behavior observed in nanocrystalline ZnO:Co powders. A similar study on nanocrystalline powder samples of ZnO:Ni prepared by chemical method is also under active investigation. The results on ZnO:Ni would be presented separately in this meeting.[1] K. P. Bhatti, S. Chaudhary, D. K. Pandya and S. C. Kashyap, Solid State Commun. 136, 384 (2005), ibid, 140, 23 (2007). [2] K. P. Bhatti, S. Kundu, S. Chaudhary, D. K. Pandya and S. C. Kashyap, J. Phys. D: Appl. Phys.39, 4909 (2006)[3] K. P. Bhatti, S. Chaudhary, D. K. Pandya and S. C. Kashyap, J. Appl. Phys. 101, 033902 (2007), ibid, 101, 103919 (2007).
10:30 AM - I7.6
Effect of Spacer Layer Thickness on Magnetic Interactions in Self-assembled Single Domain Iron Nanoparticles.
Nicole Herndon 1 , Sang Ho Oh 1 2 , Jeremiah Abiade 3 , Devdas Pai 1 , Jag Sankar 1 , Dhananjay Kumar 1 2
1 Center for Advanced Materials and Smart Structures, Department of Mechanical and Chemical Engineering, North Carolina A&T State University, Greensboro, North Carolina, United States, 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Department of Materials Science and Engineering & Department of Mechanical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, United States
Show AbstractThursday, March 27New Abstract I7.6 @ 9:30 AMEffect of Spacer Layer Thickness on Magnetic Interactions in Self-assembled Single Domain Iron Nanoparticles. Dhananjay Kumar, North Carolina A&T State University, Greensboro, North Carolina.
10:45 AM - I7.7
Room Temperature Coherence and Electrical Enhancement of Spin Dynamics in ZnO.
Sayantani Ghosh 1 , Vanessa Sih 2 , David Stuerman 2 , David Awschalom 2 , H. Xu 3 , K. Ohtani 3 , Hideo Ohno 3 , S. Bae 4 , S. Wang 4 , S. Vaidya 5 , G. Chapline 5
1 School of Natural Sciences, University of California, Merced, Merced, California, United States, 2 Center for Spintronics and Quantum Information, University of California, Santa Barbara, Santa Barbara, California, United States, 3 Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communications, Tohoku University, Sendai Japan, 4 Department of Materials Science and Engineering, Stanford University, Stanford, California, United States, 5 , Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractA lot of attention has been focused on zinc oxide (ZnO) because of material properties that make it well-suited for applications in ultra-violet light emitters, transparent high-power electronics and piezoelectric transducers. The prediction of room temperature ferromagnetism in magnetically-doped ZnO, in addition to its small spin-orbit coupling (SO) and a naturally low abundance of nuclear spins, which is expected to contribute to long spin coherence times, has revealed the possibility that it may be an appropriate candidate for spintronic applications. Time-resolved Faraday rotation, transient absorption spectroscopy and time-resolved photoluminescence are used to monitor electron spin and charge dynamics in a wide variety of samples. These include commercially available bulk single crystals of ZnO, epilayers grown by pulsed laser deposition and epilayers grown by molecular beam epitaxy (MBE) on sapphire substrates. Measurements are performed over a range of temperatures, magnetic and electric fields. The bulk crystal yields a spin lifetime of 20 ns at 30 K. Epilayer samples show spin lifetimes ranging between 2 and 3 ns at 10 K (spin lifetime increases with increasing carrier concentration) with the spin precession persisting up to 280 K*. While weak SO coupling allows for long electron spin lifetimes, it also limits the coupling of the spin degree of freedom to an applied electric field. However, application of a dc in-plane electric field E is found to enhance the spin lifetime in the samples grown by MBE, while decreasing the Faraday rotation (FR) magnitude. At 20 K, the spin lifetime is electrically enhanced by a factor of two in the sample with the lowest carrier concentration. This enhancement decreases with increasing temperature and carrier density. In contrast to spin lifetime, the charge lifetime, obtained from transient absorption measurements, decreases with increasing E, while the radiative recombination time obtained from time-resolved photoluminescence (PL) shows no noticeable variation. It would appear that the application of the in-plane E has a two-fold effect: it enhances the initial absorption while simultaneously increasing the decay rate of the carriers. We speculate that the applied electric field provides enhanced carrier relaxation along non-radiative pathways, decreasing the charge lifetime while leaving the radiative recombination time unchanged. The increased density of photo-generated carriers leads to increased electron-electron interactions and hence, the reduced initial magnetization (given by the FR amplitude), while the faster depopulation of the carriers, as seen by the variation of charge lifetime, enhances the spin lifetimes.This work was supported by ONR MURI and NSF.* S. Ghosh, V. Sih, W. H. Lau, D. D. Awschalom, S.-Y. Bae, S. Wang, S. Vaidya. and G. Chapline, Appl. Phys. Lett. 86, 232507 (2005).
11:00 AM - I7:ZnO particles
BREAK
11:30 AM - I7.8
Correlation Between Microstructure and Optical Properties of ZnO Based Nanostructures Grown by MOCVD
Farid Falyouni 1 , Vincent Sallet 1 , Julien Barjon 1 , Alain Lusson 1 , Pierre Galtier 1
1 UVSQ-CNRS, GEMaC-UMR8635, Versailles France
Show AbstractIn this study, we investigate the correlation between structural properties of ZnO conical needles, assessed by Transmission Electron Microscopy (TEM), and their optical signature measured by low temperature cathodoluminescence (CL). Metallorganic Chemical Vapor Deposition (MOCVD) has been applied to fabricate ZnO nano-structures on sapphire substrate. A first set of nanostructures realized by this mean are conical needles with a very low aperture angle (~2.4°). These needles are several microns long and present a base diameter of 0.1 micron typically. TEM observation shows the excellent structural properties of these needles from their base up to the end of the tip. The growth axis of the cones is (0001). High resolution TEM observations show that the high crystalline quality is maintained at the surface without any noticeable perturbation of the atomic arrangement. Thus, these diameter varying wires are pertinent structures to study the effect of size shrinking on their optical properties. In order to probe the emission of the needles along their length, UV cathodoluminescence mapping has been performed at low temperature. As these conical needles exhibit a very low aperture angle, our aim was to correlate the evolution of the excitonic emission with the diameter of the needle at the analysed area. A clear blue shift of the overall excitonic emission is observed when the diameter of the probed area is decreased (i.e. close to the tip end). As this effect is observed on areas several tenth nanometres wide, the blue shift observed cannot be assigned to any confinement effect as it was already stressed. A more precise analysis could be performed at low temperature. The analysis of the PL spectra reveals that the blue shift is the result of a competition between (i) a high wavelength emission dominant on large diameter area and (ii) a low wavelength emission dominant on low diameter area of the needle. By comparison to what is observed on ZnO epitaxialy deposited by MOCVD on sapphire, we show that the high wavelength contribution is associated to some exciton bound to n-donor, whereas the low wavelength emission is associated to free exciton emission. The highest concentration of donor at the tail of the needles is likely to be related to some Al diffusion from the sapphire substrate as it has been previously reported. Thus, we conclude that the blue shift observed upon size shrinking is, in our case, not related to a surface contribution neither to some confinement effect but must be probably attributed to the improvement of the purity (in term doping level) of the ZnO needles close to their tip.Finally we report on the structural and optical properties of ZnO tubes fabricated by MOCVD without the use of any catalysis step.
11:45 AM - I7.9
Magneto-optical Studies of ZnO Based Dilute Magnetic Semiconductors Exhibiting Itinerant Magnetism.
James Neal 1 , Anthony Behan 1 , David Score 1 , Harry Blythe 1 , Anthony Fox 1 , Gillian Gehring 1
1 Physics and Astronomy, The University of Sheffield, Sheffield United Kingdom
Show AbstractDilute magnetic semiconductors have received huge interest recently due to their potential for use in spintronic applications. Of particular interest are thin films of ZnO doped with transition metals since they were predicted [1] to be ferromagnetic at room temperature and this effect was subsequently observed [2].We report magneto-optical measurements on room temperature ferromagnetic semiconductor thin films of ZnTMO (where TM = Co, Mn, V, Ti) co-doped with Al[3,4]. Films were grown by pulsed laser deposition on sapphire substrates. The magnetic circular dichroism as a function of energy and magneto-optical hysteresis loops at fixed energy have been measured at room temperature over an energy range of 1.5-3.8eV.Samples with a carrier concentrations and mean free paths that show metallic conductivity [4] exhibit robust ferromagnetism together with very strong magneto-optic signals and room temperature anomalous Hall data. This demonstrates the polarisation of the conduction bands and indicates that, when ZnO is doped into the metallic regime, it behaves as a genuine magnetic semiconductor.[1]T. Dietl, H. Ohno, F. Matsukura, J. Cibert, and D. Ferrand, Science 287, 1019-1022 (2000).[2]S. A. Chambers, T.C. Droubay, C.M. Wang, K.M. Rosso, S.M. Heald, D.A. Schwartz, K.R. Kittilstved, D.R. Gamelan, Ferromagnetism in Oxide Semiconductors, Materials Today, 9, 28 (2006)[3]J R Neal, A J Behan, R M Ibrahim, H J Blythe, M Ziese, A M Fox and G A Gehring, Phys. Rev. Lett. 96 197208 (2006)[4]A.J. Behan, A. Mokhtari, H.J. Blythe, D. Score, X-H. Xu, J.R. Neal, A.M. Fox and G.A. Gehring (Submitted to PRL)
12:00 PM - **I7.10
ZnO-based Photoluminescent Magnetic Nano-Powders and Thin Films
Ashutosh Tiwari 1 , Dhananjay Kumar 2 , Michael Snure 1 , Jeremiah Abiade 2
1 Materials Science & Engineering, university of utah, Saltlake city, Utah, United States, 2 Department of Mechanical Engineering, North Carolina A & T State University, Greensboro, North Carolina, United States
Show AbstractIn this paper we report some of our very exciting results about the observation of Room Temperature Ferromagnetism (RTF) in n-type Zn1-xCuxO (x=0.05) films and nanopowders and its disappearance on introducing additional electrons in the system. In order to introduce additional electrons in the system, a slight amount (1%) of Gallium was doped in the system. Nanopowders were prepared by a low temperature sol-gel technique while thin films were grown by pulsed laser deposition technique on c-plane sapphire substrate. A pulsed KrF excimer laser (Lambda Physik 210) with a wavelength of 248 nm was used for the deposition. The energy density and repetition rate of the pulsed excimer laser were 3-4 J/cm2 and 10 Hz, respectively. The targets used for deposition were synthesized by a sol-gel technique. Thin film deposition was performed at a substrate temperature of 650 oC with 1 mTorr of oxygen pressure. Films were characterized using X-ray diffraction (both θ-2θ scan and Φ-scan), transmission electron microscopy (TEM), optical absorption spectroscopy, Hall coefficient and magnetic property measurements. X-ray diffraction and TEM studies confirmed the high phase purity of both the nanopowder as well as thin film samples. In the case of thin film samples, only the diffraction peaks corresponding to (000l) family of planes of wurzite Zn0.95Cu0.05O were observed indicating strong c-axis alignment of the film. Optical absorption (α) studies showed that the absorption edge for Zn0.95Cu0.05O is located at slightly lower energy compared to undoped ZnO. By the extrapolation of α2 vs energy curve, we estimated the bandgap of Zn0.95Cu0.05O and ZnO as 3.1 eV and 3.5 eV, respectively. Decrease in the band-gap of Zn0.95Cu0.05O compared to undoped ZnO confirms the matrix incorporation of Cu in the system. Hall-measurements showed that the films are of n-type with a carrier-concentration of 3x1017cm-3. Magnetization measurements showed that the films exhibit room-temperature ferromagnetism with a saturation-magnetization of ~ 1.45 μB/Cu atom. When additional carriers were introduced in the films, ferromagnetism completely vanished. Our results show that the p-type nature of the film is not essential for realizing ferromagnetic characteristics, however, the concentration of n-type carriers should not exceed a critical value.
12:30 PM - I7.11
Real Time Spectroscopic Ellipsometry Studies of Zinc Oxide Deposition
Christian Fesenmaier 1 , Dean Levi 2
1 Electrical Engineering, Stanford University, Stanford, California, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractZinc oxide is increasingly being studied as a replacement for indium tin oxide as a Transparent Conducting Oxide (TCO) with a variety of uses from flat-panel displays to solar cells.In order to better understand the growth process and optical properties of ZnO, as well as provide for accurate control on the National Renewable Energy Laboratories’ TCO deposition system, undoped RF-sputtered ZnO films on silicon were analyzed in situ using Real Time Spectroscopic Ellipsometry (RTSE) and ex situ using Variable Angle Spectroscopic Ellipsometry (VASE). To our knowledge, this is the first example of in situ spectroscopic ellipsometry of the growth of ZnO in the literature. A large range of wavelengths (250-1000 nm) was measured in order to derive information about both free carrier absorption in the infrared and absorption above the bandgap in the ultraviolet. The effect of substrate temperature on the growth dynamics was also studied by taking measurements at room temperature, 100 °C, 200 °C, and 300 °C heater setpoint temperatures.For analysis of RTSE data, the ZnO dielectric function was modeled using spline functions, which allowed for maximum flexibility in the optical constants. VASE data were analyzed using parametric semiconductor models of the dielectric function in conjunction with the Drude free carrier model. Both methods included surface roughness as a Bruggeman Effective Medium Approximation (EMA) to allow for better insight into the film growth process, as surface roughness has been shown to correlate to changes in morphology.Analysis revealed a complex growth process consisting of two layers: a bulk material that increased in thickness as the growth proceeded and a growth zone at the top of the film that was indicated by infrared absorption not present in the bulk material. We surmise that this absorption at lower photon energies may be a result of defects or excess charge in the new growth. The thickness of this growth zone decreased at higher temperatures, indicating that the transition from growth zone to bulk material was likely thermally accelerated. The optical properties of the growth zone material also evolved over time more drastically during the high-temperature depositions for reasons we do not currently understand. We will report on additional experiments aimed at gaining a better understanding of the nature of the growth zone properties.Future work will focus on ZnO deposition on glass, which is significantly more relevant to most uses of ZnO as a TCO, but presents complications to the ellipsometry measurements because of weaker signal and back surface reflections. Using RTSE to study the addition of dopants to the ZnO film to increase conductivity is also being undertaken.
12:45 PM - I7.12
Transparent Oxide Semiconductors Obtained by PLD
Anna Vila 1 , Antonis Olziersky 1 , Joaquim Font 1 , Teresa Andreu 1 , Erik Koep 1 , Juan Ramon Morante 1
1 Electronics, University of Barcelona, Barcelona Spain
Show AbstractAlthough metal oxides have been extensively commercialized as transparent conductors for electrodes and interconnexions, there are still few applications as thin film semiconductors for electronic devices. In this work an analysis of structural, optical and electrical properties of semiconducting metal oxides deposited by pulsed laser deposition (PLD) is presented. Thin films with different compositions based onto zinc oxide have been prepared at room temperature. Additives such as Ga or In have been used, which influence the deposition process and give rise to layers with modified properties. A calibration of the deposition technique has been first established. Next, a variety of techniques including X-ray photoelectron spectroscopy, x-ray diffraction and electron microscopy techniques have been used to analyze the structure and composition of the obtained films and to compare the effect of the different additives. Optical characterization based onto optical transmission in the visible/UV range allowed also to determine energy gap and refractive index for each material, as well as thickness of each layer. Electrical characterization by 2- and 4-probes has been also undertaken, showing semiconductor behaviour and resistances of the order of 100 ohms for layers less than 1 um thick. These structural, compositional and optical properties have been correlated with the electrical ones. Annealing has also been performed on some of the films at temperatures in order to study crystallization for each composition and thickness. The high optical transmission of these films opens the possibility of their use in transparent electronics, and their relatively low resistance even without any annealing enables low-temperature easy cheap large-area processing if combined with polymer substrates.
I9: Nanoparticles, Structural, Electrical and Optical Properties
Session Chairs
Thursday PM, March 27, 2008
Room 2001 (Moscone West)
4:30 PM - **I9.1
Hall Effect in Ni-nanocrystallites Embedded in TiN Matrix on Sapphire.
A. Majumdar 1
1 , S. N. Bose National Centre for Basic Sciences, Kolkata India
Show AbstractThe detection of Hall effect in a single ~ 20 nm layer of Ni nanocrystallites embedded in TiN matrix over a wide temperature range of 5 to 350 K is a formidable task. This work focuses on the scaling behavior of the extraordinary Hall constant, Rs. An involved analysis of our very high-resolution Hall (B,T) data shows that the scaling exponent, n in Rs ~ ρn, where ρ is the Ohmic resistivity, is ~ 1. However, an earlier work on 5 bilayers of Ni nanoparticles (~ 65 nm) and TiN on silicon substrate reported n ~ 1.7, the same exponent as in bulk Ni. Theoretically, for homogeneous ferromagnets, n = 1 corresponds to Smit classical asymmetric scattering (clean limit) while n = 2 is attributed to the quantum mechanical side-jump scattering. The exponent of the scaling law in the present Ni/TiN system, n ~ 1, may be erroneously interpreted as coming from the Smit asymmetric scattering which is very unlikely to occur at such high temperatures of 350 K. Zhang had shown that, for inhomogeneous magnetic and non-magnetic multilayers, the scaling exponent could be smaller, greater or equal to 2 depending on whether the mean free path of the conduction electrons is temperature dependent only in the magnetic layers, only in the non-magnetic layers or in both the layers but with their ratio fixed. We have indeed found that the resistivity is strongly temperature dependent in the magnetic layer (Ni) and very weakly in the non-magnetic layer (TiN) and hence the exponent could understandably be much smaller than 2 even when the quantum transport dominates (dirty limit). However, the 5-bilayer Ni/TiN sample gave n ~ 1.7, probably because its much higher Ni thickness (65 nm), is well above the critical value predicted by the above theory for which one could again get n ~ 2.
5:00 PM - I9.2
Crystal and Electronic Structure of Iron Oxide Nanoparticles synthesized from Ferritin.
Michael Krispin 1 , Aladin Ullrich 1 , Florian Sedlmeir 1 , Siegfried Horn 1
1 Experimental Physics II, University of Augsburg, Augsburg Germany
Show AbstractNanosized transition metal oxide particles can be expected to show size dependent optical, magnetic and chemical properties with possible applications in catalysis and magnetic and optical devices. The size dependence of physical properties can be associated with an influence of particle dimension on the electronic structure of the material. It has already been shown, that catalytic and magnetic properties of nanoparticles might be quite different from bulk materials. An example are nanosized particles of the compound Fe2O3, which exhibit super-paramagnetism [1] and, at the same time, enhanced catalytic properties compared to bulk material [2]. Investigations of the electronic structure of Fe2O3 nanoparticles revealed, that the electronic excitation gap of the surface can be different from that of the bulk depending on the preparation process [3]. To shed further light on the differences between surface and bulk properties of Fe2O3 nanoparticles, we have investigated the size dependence of the crystal and electronic structure of nanosized iron oxide by extended x-ray absorption fine structure (EXAFS), scanning tunneling spectroscopy (STS), and conductive atomic force microscopy (CAFM). Iron oxide nanoparticles of diameters from 3nm to 6nm were produced by thermal treatment of horse spleen ferritin molecules and remineralized apo-ferritin molecules, respectively. The structure of these particles was compared to α-Fe2O3 (hematite) and γ-Fe2O3 (maghemite) nanopowder and ferrihydrite references before and after thermal treatment. The EXAFS spectra of the nanoparticles differ significantly from hematite, maghemite and ferrihydrite reference spectra and change systematically as a function of particle diameter, signalling a corresponding evolution of the structure. This can be explained by a core-shell model, in which the fraction of a γ-Fe22O3 like particle shell increases while the hematite core decreases with decreasing particle size. Measurements of the electronic structure show in addition to the known band gap of ~2.2eV for iron(III)oxides a new band gap of ~1.3eV. This Band gap seems to be independent of size but a result of the transition from a hydrated iron oxide core in the Ferritin to iron oxide.[1] C. Janzen, et al., J. Nanop. Res.5, p. 589, 2003[2] P. Li, et al., Appl Catal. B 43, p. 151, 2003[3] M. Preisinger et al., Phys. Rev. B 71, 165409, 2005
5:15 PM - I9.3
Molecular Precursor Routes to Bulk and Supported Nb-M Oxides (M = V, Mo, Y, Ta, Bi) Based on Stoichiometrically Well-defined Water-soluble Coordination Compounds.
Daisy Bayot 1 , Michel Devillers 1
1 Chemistry, Université Catholique de Louvain, Louvain-la-Neuve Belgium
Show AbstractNiobium-based oxide materials generate a broad interest because of their numerous applications in materials science, as ferroelectrics, ion conductors, and also as heterogeneous catalysts for several highly challenging processes, like the oxidative dehydrogenation of light alkanes and water photodecomposition. In that context, there is a clear need for the development of new chemical routes able to produce these materials with a high purity under various forms : bulk phases with adequate morphologies and textural properties, or highly dispersed supported phases for catalytic applications. Because the aqueous chemistry of niobium is restricted to very few compounds, we developed new water-soluble, stoichiometrically well-defined Nb coordination compounds that open new perspectives as molecular precursors for such materials. Oxo- or peroxo-complexes of Nb(+V) with high denticity carboxylate or polyaminocarboxylate (PAC) ligands have been synthesized, characterized from the spectroscopic point of view, and used as molecular precursors for Nb-M mixed oxides, with M = V, Mo, Ta, Y or Bi. In the peroxo compounds, the in situ oxidation of the nitrogen atoms of the PAC ligands into N-oxide groups has been evidenced. These precursor routes were applied successfully to a wide range of Nb-based phases. In the Y-Nb system, the cubic Y3NbO7 phase was obtained after calcination of the freeze-dried precursors at the moderate temperature of 650°C, and the distorted tetragonal YNbO4 phase was synthesized at 800°C and stabilized at room temperature without quenching. Similarly, the catalytically-relevant Nb2Mo3O14 phase was obtained in a pure form at 700°C (i.e. 100°C below the lowest temperature reported so far for its formation by the ceramic method), as bulk or silica-supported phase from a mixture of Nb and Mo oxooxalate complexes, the latter displaying a specific surface area in the range 60-70 m2/g. In addition, phases like NbVO5 and the high temperature triclinic β-BiNbO4, that are difficult to prepare, could be stabilized after doping with small amounts of Ta. Solid solutions for the systems Nb-Ta-V-O and Nb-Ta-Bi-O could also be obtained. XRD, Raman spectroscopy, N2 physisorption and SEM have been implemented to characterize the final materials from the structural, textural and morphological point of view. In some favourable cases, namely with tartaric acid, H5dtpa (diethylenetriaminepentaacetate) and H6ttha (triethylenetetraaminehexaacetate), stoichiometrically well-defined heterobimetallic Nb-Ta complexes were obtained and used as single source precursors for NbTaO5 solid solutions. With the tartrate complexes, the heterometallic precursor was shown to generate a mixed oxide with a higher specific surface area, i.e. 30 instead of 12-15 m2/g when using the multiple precursor method starting from a mixture of the corresponding homobimetallic compounds. The final materials were found to display a disordered porous character with meso- and macropores.
5:30 PM - I9.4
Visible Luminescence from DC Magnetron Sputtered ZnO with and without Ge.
Terje Finstad 1 2 , Jeyanthinath Mayandi 1 2 , Galeckas Augustinas 1 , Spyridon Diplas 1 2 , Anna Malou Petersson 1 , Balasundara Prabhu Rangasamy 1 2
1 Department of Physics, University of Oslo, Olso Norway, 2 Center for material science and nanotechnology, University of Oslo, Oslo Norway
Show Abstract