Symposium Organizers
Zhang-Lin Zhou Hewlett-Packard Labs
Clement Sanchez College de France
Michael Popall Fraunhofer ISC
Jian Pei Peking University
NN3: Poster Session: Display Applications of Hybrid Materials
Session Chairs
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
NN1: Display Applications of Hybrid Materials
Session Chairs
Hongzheng Chen
Jong-Souk Yeo
Tuesday PM, April 26, 2011
Salons 1-2 (Marriott)
9:30 AM - **NN1.1
Low Power Reflective Display with Print-like Color.
Jong-Souk Yeo 1
1 Nano Science Engineering, School of Integrated Technology, Yonsei University, Yonsei Korea (the Republic of)
Show AbstractReflective displays have seen tremendous growth recently with their application to eBook readers and other retail environments. This growth continues to drive technology development in related frontplane and backplane technologies, and especially in their integration required to provide compelling color solutions. Currently there is an extraordinary diversity of technologies vying to become the next generation of color e-Paper. This presentation will provide a review of major e-Paper technologies, including a technical breakdown based on device physics, visual requirements, and standards compared to conventional print. Some of the novel technologies are electro-optic switching with electronic inks of hybrid nanomaterials. While many innovations are being made with further investments, we still have much work remaining in order to bridge the gap between reflective electronic displays and print-on-paper.
10:00 AM - NN1.2
Colloidal Aluminum-doped Zinc Oxide Nanocrystals for Electrochromic Devices.
Raffaella Buonsanti 1 , Guillermo Garcia 1 , Anna Llordes 1 , Brett Helms 1 , Delia Milliron 1
1 The Molecular Foundry, LBNL, Berkeley, California, United States
Show AbstractColloidal nanocrystals (NCs) are synthesized in solution using wet-chemical approaches and consist in an inorganic crystalline core stabilized by a shell of organic surfactants. This organic component makes them distinct from nanomaterials prepared by methods such as laser ablation or chemical vapour deposition. Indeed, surfactants play an important role during NC nucleation and growth, leading to a fine tuning of their size, shape, and composition and, therefore, of their physical-chemical properties. Equally significant, surfactants facilitate dispersion of the NCs post-synthetically in a wide variety of solvents.[1,2] Consequently, colloidal NCs can be used as a nanoink printable on different substrates for diverse technological applications. [3]Herein, we report the colloidal synthesis of size- and composition-controlled aluminum-doped zinc oxide (AZO) NCs. AZO is a transparent conductive oxide (TCO) and is emerging as a promising alternative to the commonly used indium tin oxide (ITO). Indeed, AZO films can show electrical and optical performance comparable to ITO at substantially lower material cost.[4] By a careful manipulation of the reaction conditions and considering in particular the role played by the surfactants, we have reached an unprecedented level of control over both the size and the doping content of AZO NCs. The NC chemical and structural identity has been investigated by a combination of techniques including powder X-ray Diffraction (XRD), high resolution transmission electron microscopy (HRTEM) analysis, energy dispersive spectroscopy (EDS), and inductively coupled plasma atomic emission spectroscopy (ICP-AES). Optical properties across a broad spectral range have been correlated with these results to assess the efficacy of aluminum dopant incorporation and activation. Finally, we also briefly outline the technological potential of this promising material with some preliminary results on the integration of these novel AZO NCs in an electrochromic device of interest for smart windows.1. Yin, Y.; Alivisatos P. Nature 2005, 437, 6642. Peng, X. Nano Res. 2009, 2, 425-4473. A. Rogach, D.V. Talapin, H. Weller “Applications of semiconductor nanocrystals” in Colloids and Colloidal Assembly, F.Caruso Editor, 2004, Wiley-VCH Verlag GmbH&Co4. Minami, T. Semicond. Sci. Technol. 2005, S35–S44
10:15 AM - NN1.3
Silica-on-silicon High Rejection Filters Using Organic-Inorganic Hybrids.
Rute Ferreira 1 2 , Carlos Vicente 1 2 3 , Vasco Fernandes 1 2 3 , Luis Carlos 1 2 , Veronica Bermudez 4 , Paulo Andre 1 3 , Edison Pecoraro 3
1 Physics, University of Aveiro, Aveiro Portugal, 2 CICECO, Universidade de Aveiro, Aveiro Portugal, 3 Instituto de Telecomunicações, Universidade de Aveiro, Aveiro Portugal, 4 Chemistry/CQ-VR,, University of Trás-os-Montes e Alto Douro, Vila Real Portugal
Show AbstractThe increase of traffic on the existing telecommunications networks and the need for more energy friendly solutions is driving the introduction of fiber optics telecommunications systems into metropolitan and access networks. In this context, the use of integrated optical devices in the development of passive optical networks (PON) can be viewed as a very valid solution to reduce the cost of implementing this type of technology, due to the low unit cost of each device, which results from a mass manufacturing [1]. The typical integrated optics fabrication process uses the semiconductor production technology, which includes lithographic or etching techniques that are complex, expensive and time consuming. In recent years, to overcome these advantages, the sol-gel method was successfully applied to the processing of integrated optics devices, namely on the synthesis of organic-inorganic hybrids (OIH) materials [2]. OIH materials are a technologically key class of advanced multifunctional materials that fulfill the challenging strict requirements of the beginning of the century: higher levels of sophistication, miniaturisation, recyclability, reliability and low energy consumption with potential to be used as low-cost components in optical networks operating at high bit rates [3]. Sol-gel derived OIH based on methacrylic acid (McOH) modified zirconium tetrapropoxide, Zr(OPrn)4, (di-ureasils-ZrOMc) have been used in integrated optics devices for the next generation of optical networks. Emphasis was given to passive (planar and channel waveguides, couplers and multimode interference splitters) [3,4] and active (lasers and optical amplifiers) [3,5] optical architectures of monoliths and films on glass substrates. In this work we will produce planar waveguides of di-ureasils-ZrOMc on oxidized silicon substrates by spin coating method. The films characterization will be done by spectroscopic ellipsometry in order to measure the thickness, rugosity and refractive index dependence on the wavelength. Direct UV-laser writing will be used to record high-rejection optical filters with controlled refractive index, filtering wavelength peak, bandwidth, and optical rejection. References[1] Prat J, “Next-Generation FTTH Passive Optical Networks: Research towards unlimited bandwidth access”, Springer Netherlands, 2008.[2] Sanchez C, Julian B, Belleville O, Popall M, J. Mater. Chem. 2005, 15 3559.[3] Ferreira RAS, André PS, Carlos LD, Optical Materials 2010, 32, 1397, and references therein. [4] Fernandes VR, Vicente CMS, Wada N, André PS, Ferreira RAS, Optics Express 2010, 18, 16580.[5] Pecoraro E, García-Revilla S, Ferreira RAS, Balda R, Carlos LD, Fernández J, Optics Express 2010, 18, 7470.FundingThis work was supported by Fundação para a Ciência e a Tecnologia, FEDER, COMPETE (PTDC/CTM/72093/2006) and COST Action MP0702. Carlos Vicente acknowledges the FCT grant (SFRH/BD/41943/2007).
10:30 AM - NN1.4
Characterization of Charge Injection and Transport in Organic Light Emitting Diodes Based on NPB and Alq3.
Wudyalew Wondmagegn 1 , Nikhil Satyala 1 , Huiping Jia 2 , Manuel Quevedo-Lopez 2 , Srinivas Gowrisanker 2 , Husam Alshareef 3 , Harvey Stiegler 2 , Unnat Bhansali 2 , Ron Pieper 1 , Bruce Gnade 2
1 Electrical Engineering, University of Texas at Tyler, Tyler, Texas, United States, 2 Materials Science and Engineering, University of Texas at Dallas, Dallas, Texas, United States, 3 Materials Science and Engineering, King Abdullah University of Science & Technology, Thuwal, Thuwal, Saudi Arabia
Show AbstractIn order to understand the interplay of the various critical parameters of organic light emitting diodes (OLEDs), the injection and transport properties of charge carriers in the devices have to be investigated. In this work, the electrical properties of typical OLEDs having a structures of metal/NPB/PEDOT:PSS and metal/Alq3/PEDOT:PSS(Al) are numerically investigated with Silvaco’s Atlas simulation program. The electrical modeling is based on Poisson’s equation coupled with the drift-diffusion equations that contain Poole-Frenkel field-dependent mobility, charge carrier trapping, and the Langevin bimolecular recombination process. The input data to the simulation include material parameters, device structure, and model parameters. Once the simulation results and experimental data are in good agreement, the dominant contribution of the charge transport process has been identified by variation of the electrode materials. The simulation results indicated that in both devices the current is limited by the majority carriers. However the turn on voltage shows some dependence on the minority carriers. Previous reports demonstrated that the current in an OLED is bulk limited and not injection limited. In contrast our simulation results indicated that bulk-limited currents and injection limited currents could both be important to consider depending on the work function of the respective electrodes. From the results we observed that an injection barrier of about 0.2 eV resulted in a bulk limited current in both NPB and Alq3. Our simulations for Alq3 electron-only and OLED required a trap density in the order of 1018cm-3 to obtain good agreement with experiment. However, simulations for NPB hole-only and OLED produced a match with experiment with a trap density as low as 1016cm-3.
10:45 AM - NN1: Display
BREAK
11:15 AM - **NN1.5
Microcapsules-based Materials for Electrophoretic Display.
Runying Dai 1 , Gang Wu 1 , Weigang Li 1 , Yu Rong 1 , Hongzheng Chen 1
1 Dept. of Polym. Sci. & Eng., Zhejiang University, Hangzhou China
Show AbstractElectrophoretic displays (EPDs), the rewritable non-light-emitting display devices based on the movement of colored pigments inside a low dielectric liquid media as a voltage is applied, have attracted a great deal of academic and commercial interests due to the combination of the advantages of both electronic displays and conventional paper, including paper-like high contrast appearance, ultra-low power consumption, thinness, flexibility etc. Fabrication of electrophoretic ink by microcapsulating the electrophoretic suspension into individual microcapsules is one way to realize such application. However, there are still some limitations to limit its commercial application, such as the dispersion and the electrophoretic mobility of charged particles due to the nano-particles aggregation, the barrier property and stability of microcapsule wall due to the suspension releasing, etc. In this work, systematic studies on the preparation of electrophoretic particles and microencapsulation by complex coacervation method were carried out to solve the mentioned problems. The obtained microcapsules can be quasi-monolayer coated on ITO-PET substrate and driven by static mode to obtain a matrix character display prototype.Acknowledgments This work was financially supported by the National High-tech Research Development Program (863 Program) of China (Grant No. 2008AA03A331) and the Science & Research Program of Zhejiang Province (Grant No. 2009C21024).
11:45 AM - NN1.6
Hybrid Infrared-to-visible Up-conversion Device.
Do Young Kim 1 , Jae Woong Lee 1 , Galileo Sarasqueta 1 , Dong Woo Song 1 , Kaushik Roy Choudhury 1 , Franky So 1
1 Dept of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractRecently, we reported an organic infrared up-conversion device capable of converting 0.83 µm near infrared (NIR) light to green light by incorporating an organic NIR sensitizing layer with an organic light emitting device (OLED). In order to enhance the device performance, it is important to extend the spectral sensitivity to longer wavelengths. Here, we demonstrated hybrid infrared (0.7 µm ~ 1.6 µm)-to-green up-conversion devices using PbSe nanocrystals (NCs) as a NIR sensitizer and Irppy3 as an organic emitter. The hybrid devices have the following structure: ITO/ZnO nanoparticles (NPs) (25 nm)/PbSe NCs (50 nm)/1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) (45 nm)/Irppy3:4,4-N,Ndicarbazole-biphenyl (CBP) (30 nm)/tris[3-(3-pyridyl)-mesityl]borane (3TPYMB) (45 nm)/Al (100 nm). A ZnO NPs thin film was used as a hole blocking layer, a PbSe NCs thin film was used as an NIR sensitizing layer, TAPC was used as a hole transport layer, CBP doped with 7% Irppy3 was used as a phosphorescent light emitting layer, and 3PTYMB was used as an electron transport layer. A control OLED with Irppy3 as an emitter was also fabricated and its external quantum efficiency is about 20%. The luminance-current-voltage (LIV) characteristics were measured in the dark and the spectral response was measured from 0.7 µm to 1.7 µm. Without NIR excitation, electroluminescence was not observed until the applied voltage reached 17 V. When the device was irradiated with infrared light, electroluminescence was observed at 8 V. The hybrid up-conversion device shows the photon (IR)-to-photon (Green) conversion efficiency up to 3.9 %. Also, the green emitted light in hybrid up-conversion device shows a linear dependence with the optical power density.
12:00 PM - NN1.7
ZnO-based Transparent Anodes for Organic Light Emitting Devices.
Karthik Sivaramakrishnan 1 , Terry Alford 1
1 School of Materials, ASU, Tempe, Arizona, United States
Show AbstractZnO/Au/ZnO (ZAZ) electrodes were evaluated as transparent electrodes for organic light-emitting devices (OLEDs). The electrodes exhibited substantially enhanced conductivity (about 8x10-5 Ω-cm) over conventional indium tin oxide (ITO) electrodes and photopic average transmittance of ~85%. OLEDs fabricated with the ZAZ electrodes showed reduced leakage compared to control OLEDs on ITO and reduced ohmic losses at high current densities. At a luminance of 25000 cd/m2, the lum/W efficiency of the ZAZ electrode based device improved by about 5% compared to that of the ITO-based device. A normalized intensity graph of the color output from the green OLEDs shows that ZAZ electrodes allow for a broader spectral output in green wavelength region of peak photopic sensitivity compared to ITO. The results have implications for electrode choice in display technology
12:15 PM - NN1.8
Cadmium Selenide and Indium Phosphide Quantum Dots for Hybrid Inorganic-organic LED Devices: One-pot and Large-scale Syntheses, Surface Modifications as well as Purification Process.
Tonino Greco 1 , Christian Ippen 1 , Armin Wedel 1
1 Functional Materials and Devices, Fraunhofer Institute for Applied Polymer Research, Potsdam Germany
Show AbstractIn recent years, high attention has been attributed to the application of inorganic luminescent nanoparticles for light-emitting devices. The most promising ones are the quantum dots (QDs) based on core-shell semiconductor materials due to their tunable and highly efficient emission properties as well as their thermal and photochemical stability. Despite the wide research on the synthesis of cadmium selenide/zinc sulfide (CdSe/ZnS) only few approaches have been attended to achieve fast and large-scale fabrications for industrial applications. The use of QDs as light-emitting materials in OLED (organic light-emitting diodes) technologies requires highly purified and surface-modified nanomaterials. For the CdSe system, published syntheses procedures were adapted and optimized in regard to parameters like the type of precursors and stabilizers, their concentration and ratio, the reaction conditions as well as regarding the shell formation. A facile and fast purification procedure was developed to prepare the QDs for spin-coating techniques. QDs with high quantum yields (>50%) and narrow emission (FWHM < 30 nm) could be fabricated on a multi-gram scale. OLED devices were assembled successfully by spin-coating these QDs to thin films. The main scope of current research on QDs is the substitution of the inherent toxic cadmium-based QDs by more environmentally friendly materials like indium phosphide (InP). First approaches show the potential of this system although optimal synthesis conditions are less known in literature. In order to receive high-quality materials suitable for OLED devices the synthesis of InP QDs with narrow band emission as well as high quantum efficiencies are currently under investigation. On the basis of the optimized InP/ZnS synthesis and adapted surface modification we could fabricate the first hybrid organic-inorganic LED device based on non-toxic InP QDs. The multi-layer OLED device could be even assembled on flexible polymer substrates.
12:30 PM - NN1.9
Enhanced Light Out-coupling of Organic Light Emitting Diodes: Spontaneously Formed Nano Facet-structured Refractive Index Modulation Layer.
Kihyon Hong 1 , Hak Ki Yu 1 , Kisoo Kim 1 , Sunjun Kim 1 , Illhwan Lee 1 , Jong-Lam Lee 1
1 Materials Science and Engineering, POSTECH, Pohang Korea (the Republic of)
Show AbstractIn the organic light emitting diodes (OLEDs) the majority of the light generated in the organic material is confined in the transparent anode (indium tin oxide, ITO) and glass substrate due to the large difference in the refractive indices n between their layers (nITO=1.9, nglass=1.5). This has resulted in out-coupling efficiencies (ηout) expressed as the ratio of surface emission to all emitted light of only around 20%. Many techniques such as micro-lens to the glass substrate, photonic crystal, high refractive index substrate, and so on have been studied to enhance ηout. In this work, we have demonstrated that nano-facet structured refractive index modulation layer (RIML) could enhance the out-coupling efficiency in OLEDs. The nano-facet structured RIML could be fabricated without additional lithography steps or pattering process. Thus, we believe that the proposed nano-facet structure RIML can contribute the realizing high efficiency OLEDs.. For the RIML materials, nano-facet structured MgO (n=1.73) and ZrO2 (n=1.84) layers which can reduce the total internal reflection at the glass/ITO interface were deposited using electron beam evaporation method. Formation of MgO nano-facet is simple and low cost process without additional lithography or patterning process because it is formed spontaneously due to material anisotropic characteristics of MgO between crystal orientations.The emission from OLEDs is in general assumed to be Lambertian distribution. Thus, generated light should propagate toward all direction. From the classical Snell’s law, low-angle mode (<52.14°, with nITO=1.9, nglass=1.5) can be extracted toward glass substrate at the glass/interface. However, the high angle mode (>52.14°) induced the total internal reflection at the interface, resulting the propagation within the glass substrate and ITO electrode. In the case of OLEDs with nano-facet structured RIML, the high angle mode that would otherwise be trapped by glass/ITO interface can enter the RIML region, and are refracted into a direction towards the substrate normal. In addition, the RIML will not affect the rays that are originally emitted into the forward viewing cone. When the nano-facet structured MgO incorporated between glass substrate and ITO anode, the luminance value increased from 28750 to 34200 cd/m2 and power efficiency improved about 34 %.In conclusion, we demonstrated that the light out-coupling efficiency of OLEDs can be enhanced by the use of RIML with nano-facet structure. The nano-facet structured RIML could be formed without additional lithography or patterning process. The luminance value at 220 mA/cm2 increased from 28750 to 34200 cd/m2 by using nano-facet structured RIML. Using the RIML of MgO/ZrO can increase the power efficiency (@10 mA/cm2) of OLEDs about 34.7 %. The nano-facet structured RIML redirects light confined in the ITO layer and glass substrate towards the substrate normal, thereby enhanced light out-coupling of OLEDs could be achieved.
NN3: Poster Session: Display Applications of Hybrid Materials
Session Chairs
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
6:00 PM - NN3.1
High Hole Mobility Hole Transport Material for Organic Light-emitting Devices.
Dal Ho Huh 1 , Sung-hyun Jung 1 , Kyoungmi Lee 1 , Miyoung Chae 1 , Jang Hyuk Kwon 1 2
1 , Samsung Cheil Industries, Uiwang-si Korea (the Republic of), 2 , Kyung Hee University, Seoul Korea (the Republic of)
Show AbstractA new hole-transporting material, 5,10,15-triphenyl-5H-diindolo[3,2-a:3’,2’-c]carbazole (TPDI) has been synthesized and evaluated in terms of material performances. It shows excellent hole mobility (3.2×10-3 cm2/V.s), one order higher than that of NPB (4,4’-bis(N-phenyl-1-naphthylamino)biphenyl), and a good HOMO (highest occupied molecular orbital) level of 5.3 eV. Fabricated blue organic light-emitting devices (OLEDs) exhibit about 1.0 V voltage reduction and 30% external quantum efficiency (EQE) improvement by incorporating TPDI as a hole transport layer. In the green phosphorescent OLEDs, the driving voltage improves about 1.8 V and the EQE increases about 52%. The TPDI is capable of efficient hole transport not only in improving the performances of fluorescent blue OLEDs but also in other phosphorescent OLED devices
6:00 PM - NN3.10
Improved Field Emission Stability from Carbon Nanotube Composites for Field Emission Display Devices.
Archana Pandey 1 , Abhishek Prasad 2 , Yoke Yap 3 , Mark Engelhard 4 , Chongmin Wang 5
1 Physics, Michigan Tech University, Houghton, Michigan, United States, 2 Physics, Michigan Tech University, Houghton, Michigan, United States, 3 Physics, Michigan Tech University, Houghton, Michigan, United States, 4 EMSL, Pacific Northwest National Laboratory, Richland, Washington, United States, 5 EMSL, Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractCarbon nanotubes (CNTs) composites have potential to be the next generation field emission display (FEDs) devices. However, field emission from as-grown CNTs suffers from high threshold electric field, poor life time stability and low emission site density due to screening effects etc. Lithographically prepared catalyst films are expensive and are not compatible for future display devices with large areas. In this work, we show that lithography free as-grown CNT films can have low emission threshold field and high emission density. We have further reduced screening effects and work function of as-grown CNT films and created the novel CNT matrices by addition vapor- and/or liquid- phase deposition. The fabrication method of our CNT matrices is as follows. First, CNT films were grown by plasma-enhanced chemical vapor deposition. These as-grown samples were then subjected to the deposition of magnesium oxide (MgO) and strontium titanate (SrTiO3) by pulsed-laser deposition. The coating of MgO and SrTiO3 on as-grown VA-MWCNTs was confirmed by transmission electron microscopy (TEM), Energy-dispersive X-ray spectroscopy (EDS) and x-ray photoelectron spectroscopy (XPS). We also found that the emission properties of these MgO and SrTiO3 coated samples can be further improved by filling the void spaces between VA-MWCNTs by poly-methyl methacrylate (PMMA) by drop coating and polishing to open the tips. Long term emission stability and emission site density were enhanced manifold for these CNT matrices when compared to as grown CNTs. Furthermore, these CNT matrices can continuously emit electrons for longer hours without significant degradation. Based on our theoretical simulation, a new emission model was then proposed to explain the enhanced performances of our CNT matrices. All these results will be discussed in the meeting. *E-mail address:
[email protected] (A. Pandey)This work was supported by the Defense Advanced Research Projects Agency (Contract number DAAD17-03-C-0115 through the U.S. Army Research Laboratory), and the U.S. Department of Army (Grant number W911NF-04-1-0029 through the City College of New York). A portion of the research was performed using EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research located at Pacific Northwest National Laboratory.
6:00 PM - NN3.11
Improving OLED Efficiency, Stability and Dynamic Range by Efficient Heat Dissipation.
Alex Zakhidov 1 , Sebastian Reineke 1 , Bjoern Luessem 1 , Karl Leo 1
1 IAPP, TU-Dresden, Dresden Germany
Show AbstractOne of the main reasons for organic light emitting diodes (OLED) instability and small dynamic range is heat. Even though, state of the art OLEDs achieve reasonable power efficiency, most of the energy applied to OLED device goes into heat. Therefore, it is crucial to efficiently dissipate heat generated inside the devices. Here we introduce simple yet very efficient method of heat dissipation by immersing OLED device into hydrofluoroether (HFE) fluids. It has been reported, that HFEs do not damage organic semiconductor and thus can be used as encapsulation media [1]. HFE also have high thermal conductivity and can efficiently dissipate the heat. By employing HFE we were able to dramatically improve OLED operating dynamic range, stability and efficiency at high brightness. [1] Al. A. Zakhidov, J.-K. Lee, H. H. Fong, J. A. DeFranco, M. Chatzichristidi, P. G. Taylor, C. K. Ober, G. G. Malliaras, Advanced Materials, 2008, 20, 3481.
6:00 PM - NN3.2
Single Carrier Devices for the Understanding of the Voltage Drift in Organic Light Emitting Diodes.
Julien Boizot 1
1 LETI/LTCV, CEA Grenoble, Grenoble Cedex 9, Isere, France
Show Abstract Although the lifetime and reliability of OLEDs have been improved greatly over the last decades, a complete understanding of the device degradation mechanisms remains elusive. More specifically, studies have been done to understand the origin of the driving voltage increase observed with operating time: we propose in this paper to understand this phenomenon using single carrier devices deposited on Si substrates and using doped injection layers. Those specific devices are indeed very appealing because of simplified device structure and because they allow the extraction of crucial electrical parameters, such as material conductivities, interfacial capacitances and carrier mobilities in organic semiconductors. Single carrier devices represent a very interesting tool for the understanding of full stack design and voltage drift origin, especially in the perspective of doing OLED-on-CMOS components with an operating voltage inferior at 4V and where the least voltage drift during lifetime can thus have a strong impact on the device performances. We report here on the study of basic single carrier devices consisting in a single layer under test, symmetrically sandwiched between electrically doped injection layers of same composition and equal thickness. In each case, voltage drift occuring when applying a constant current through the device was recorded and I-V curves before and after this stress were systematically analyzed. An analysis with the SETFOS software from FLUXiM company using classical theoretical models of carrier injection and carrier transport was finally used to determine electrical parameters by fitting experimental I-V curves. Our typical device structure is a top-emitting OLED based on doped injection layers. We first demonstrate the ohmic contact between the doped electron injection layer (4,7-diphenyl-1,10-phenanthroline or Bphen) and the Ag semi-transparent cathode. Then we show a way to improve the conductivity of the doped hole transport material (2,2',7,7'-tetra(N,N-di-tolyl)amino-spiro-bifluorene or Spiro-TTB) by optimizing its doping in order to get a similar ohmic contact at the AlCu reflective anode interface. Two very common materials in the field of organic semiconductors were then analyzed: N,N’-di(naphthalen-1-y1)-N,N’-diphenyl-benzidine (α-NPD) between doped Spiro-TTB layers and tris(8-hydroxy-quinoline) aluminum (Alq3) between doped Bphen layers. We thus show here the unipolar behavior of Alq3 and we also confirm the bipolar behavior of NPB. We have also studied the influence of the thickness of our materials under test and we eventually showed that the voltage drift was mainly due to the degradation of Alq3 when crossed by a hole-current.
6:00 PM - NN3.3
Highly Efficient Organic Light-emitting Diodes Using Graphene Anode.
Tae-Hee Han 1 , Seong-Hoon Woo 1 , Youngbin Lee 2 , Jong-Hyun Ahn 2 , Tae-Woo Lee 1
1 Deptartment of Materials Science and Engineering, POSTECH (Pohang University of Science and Technology), Pohang Korea (the Republic of), 2 SKKU Advanced Institute of Nanotechnology (SAINT) and Center for Human Interface Nano Technology (HINT), Sungkyunkwan University, Suwon Korea (the Republic of)
Show AbstractWe realized the highly efficient organic light-emitting diodes(OLEDs) using multilayered graphene anode which was modified with self-organized polymeric hole injection layers (HILs). Traditionally, indium-tin-oxide (ITO) has been used as transparent anode for OLEDs. The ITO anode, however, has many drawbacks for fabrication of organic electronic devices such as increasing cost, brittle substrate, and diffusion of indium and tin atoms into overlying organic films during the device operation. In order to overcome these issues, there is a strong need for alternative transparent and flexible electrodes like graphene. Although graphene has unique electrical properties as a promising transparent conductor, there is significant disadvantage for application to electrodes of OLEDs. The relatively low work function of graphene (~ 4.4 eV) compared with that ITO anode (~4.8 eV) makes the hole injection unfavorable because of high injection barrier at interface between anode and organic layers. Our polymeric hole injection layer (HIL) has gradient work function and thus makes holes injected easily to the organic layer despite high injection barrier for holes at interface between graphene anode and organic layer. We demonstrated that when our polymeric HIL is introduced on top of graphene anode, the nearly ohmic contact is formed between graphene anode and organic layers by using Dark Injection Space Charge Limited Current transient measurement. On the other hand, the case with general conducting polymeric HIL, PEDOT:PSS, shows quasi-ohmic contact which has ~ 0.2-0.3 of injection efficiency. Furthermore, we realized very high and much higher luminous efficiency of OLEDs with graphene anode than those with ITO anode by using our workfunction tunable polymeric HIL in fluorescent small-molecule OLEDs. This kind of strategy to tune the work function of graphene anode with workfunction tunable self-organized polymeric HIL paves a way to very efficient replacement of ITO anode with flexible graphene anode even with much improved device performance.
6:00 PM - NN3.4
Nanocomposites Comprising Graphene Nanosheets and Conjugated Polymer--Poly(9,9-dioctylfluorene-alt-thiophene).
Raymond Tsiang 1
1 Chemical Engineering, National Chung heng University, Min-Hsiung, Chiayi Taiwan
Show AbstractNanocomposite comprising Poly(9,9-dioctylfluorene- alt-thiophene) (PDOFT) and graphene sheets has been customly synthesized for investigation of the effect of graphene on the morphological and electroluminescent properties. Spectroscopic evidence from UV/Vis and photoluminescence shows that the existence of graphene does not alter the optical characteristics of PDOFT, and both solution samples and thin films emit green light. Meanwhile, the insignificant change in PL quantum efficiency indicates that graphene does not have significant effects on the transfer of excitation energy, the occurrence of self-quenching and the formation of excimer. However, the electric conductivity increases with an increase in the amount of graphene. The ionization potential(HOMO) and the electron affinity(LUMO) measured from the cyclic voltammetry lead to the determination of the optical band gap (Egchem.). When used to fabricate an optoelectronic device, the threshold voltage decreases with an increase in the graphene content until an excessive amount of graphene causes an unbalance on the electron and hole mobilities. The device fabricated with PDOFT/graphene with a 5% graphene content has a maximum luminescence of 5908 cd/m2 at a voltage of 9.5 V. The corresponding power efficiency at this maximum luminescence is 0.38 cd/A which is much higher than the device fabricated with pristine PDOFT. From the Admittance spectroscopy of the device, the electron mobility has been proved to increase with the graphene content.
6:00 PM - NN3.6
Polyimide Substrates for the Flexible Display Show Definite Thermal Expansion Property?
Youngsuk Jung 1 , Yooseong Yang 1 , Sangmo Kim 1 , Jungha Chae 1 , Taigyoo Park 1
1 , Samsung Advanced Institute of Technology, Yongin-si Korea (the Republic of)
Show AbstractAs the mobile display market is expanded, light and portable materials and devices are being actively developed. A substrate is one of the important components in the display devices that determines the performance, reliability, and even the price of the devices. A glass substrate, which is widely used currently, has excellent properties such as transparency, high heat resistance, low moisture uptake, low oxygen permeability, low coefficient of thermal expansion (CTE), and so forth. Though its many kinds of merits, the glass substrate hardly satisfies the needs of the future mobile display technologies, in terms of lightness and flexibility. Developments of new low-cost flexible plastic substrates are so being required to flexible displays to fully exploit the various advantages that can offer. Aromatic polyimides can be a promising candidate as the plastic substrate due to their excellent thermal stabilities, chemical resistance, and dielectric properties. However, the color problem of polyimides is the most significant issue in optical and electronic device applications. Most polyimides between UV and the visible area have strong absorption, rendering their color close to yellow or brown, and it is known to be originated from the easy formation of inter- or intra-molecular charge transfer (CT) complexes in the polymer chains. CT complex formation also affects the thermal properties of the thermally treated polyimide films. This makes the films to show different thermal expansion behavior. The dependant CTE may cause the incompatibility between the organic substrates and the inorganic compartment in the flexible devices. So the selection of the candidate polyimides cannot be more circumspective. In this report, we find the origin and the probable mechanism that gives the different CTE value, and then prepare organic-inorganic hybrid materials with the thermally definite polyimides and organosilicate materials. Through the hydrolysis and polycondensation of the amino functionalized silane with alkyl chain linked silsesquioxanes, new organosilicate additives are developed. These new additives into the polyimides provide both the optical and thermal property improved hybrid polymer films.
6:00 PM - NN3.7
Polarized Phosphorescent Organic Light-emitting Devices Adopting Mesogenic Host-guest Systems.
Yu-Tang Tsai 6 , Su-Hao Liu 5 , Ming-Shiang Lin 1 , Li-Yin Chen 1 , Yun-Hua Hong 1 , Chih-Hung Tsai 1 , Anurach Poloek 2 , Yun Chi 2 , Chien-An Chen 3 , Shaw H. Chen 3 , Hsiu-Fu Hsu 4 , Chung-Chih Wu 1 5 6
6 Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei Taiwan, 5 Graduate Institute of Electronics Engineering, National Taiwan University, Taipei Taiwan, 1 Department of Electrical Engineering, National Taiwan University, Taipei Taiwan, 2 Chemistry Department, National Tsing-Hua University, Hsin-Chu Taiwan, 3 Chemical Engineering Department, Rochester University, Rochester, New York, United States, 4 Chemistry Department, Tamkang University, Taipei Taiwan
Show AbstractWe report successful realization of workable polarized phosphorescent organic light-emitting devices (OLEDs) by combining a newly developed mesogenic phosphorescent Pt(II) complex and a mesogenic oligofluorene host to form the corresponding mesogenic host-guest emitting system. In the host-guest film, the mesogenic Pt(II) complex tend to aggregate and self-assemble into the columnar stacking arrangement, exhibiting metal-metal-to-ligand charge transfer (MMLCT) emission of the Pt(II) complex. Both the host molecules and guest aggregates in the host-guest films were successfully aligned by using the rubbed conducting polymer as the alignment layer. With such aligned host-guest films, polarized red-emitting OLEDs were successfully implemented, showing an EL polarization ratio of ~2, a maximal brightness exceeding 2000 cd/m2, and a cd/A efficiency up to 2.4 cd/A. Due to the particular alignment mechanism of guest aggregates and the unique MMLCT emission mechanism, the polarized OLED exhibiting stronger electroluminescence perpendicular to the rubbing direction than along the rubbing direction.
6:00 PM - NN3.8
High-efficiency Polymer Light-emitting Diodes by Using Various Organic Salts as Electron Injection Layers.
Chen-Hao Wu 1 , Sung-Nine Hsieh 1 , Ten-Chin Wen 1
1 Chemical Engineering, National Cheng Kung University, Tainan Taiwan
Show AbstractPolymer light-emitting diodes (PLEDs) have attracted great attention because of their potential applications in flexible displays and their low-cost production. Low work function metals are commonly used as a cathode to enhance electron injection. However, they are susceptible to oxygen and moisture. To improve the long term stability, it is desirable to use a high work function metal (such as Al, Ag, and Au) as a cathode. Inserting a thin layer such as inorganic salt, conjugated polyelectrolyte, and surfactant is useful in significantly improving the efficiency of PLEDs.Recently, our group has demonstrated that the high device performance can be achieved by using a series of organic salts as electron injection layers in PLEDs. It is confirmed that the thin organic salt layers inhibit the detrimental quenching sites in cathode interface and lower the electron injection barrier due to the effect of molecular dipole between cation and anion. To understand the influence of using different cations to the electron injection, we select two organic salts AS and BS (they are similar in structure but with different cations) as electron injection layer in our devices: indium-tin-oxide (ITO)/poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid (PEDOT)/poly(9,9-dioctylfluorene) derivative (PF)/AS or BS/Al structure. The performance of device with AS/Al cathode is 10.1 cd/A and 33197 cd/m2 at 7 V, and that with BS/Al cathode is 11.2 cd/A and 29937 cd/m2. The using of these salts largely enhances both electroluminescence efficiency and luminance as compared to the device with Al cathode (1.2 cd/A and 113.88 cd/m2). Additionally, the ultra-violet photoelectron spectroscopy reveals that both these salt layers effectively lower the work function of PF surface and result in the lowering of the electron injection barrier in the same degree. In this study, we verify that using AS/Al and BS/Al cathode can fabricate high performance PLEDs. These salts are low-cost and solution processible, therefore it is ideal for fabricating high-performance PLEDs with them.
Symposium Organizers
Zhang-Lin Zhou Hewlett-Packard Labs
Clement Sanchez College de France
Michael Popall Fraunhofer ISC
Jian Pei Peking University
NN5: Hybrid Materials for Switching Device, Memory, Photonic Devices
Session Chairs
Wednesday PM, April 27, 2011
Salons 1-2 (Marriott)
2:30 PM - **NN5.1
Hybrid Organic–Inorganic Photonic Materials: From Luminescent Nanothermometers to Integrated Optics Substrates for the Next Generations of Optical Networks.
Luis Carlos 1
1 Physics and CICECO, University of Aveiro, Aveiro Portugal
Show AbstractOrganic-inorganic hybrids are a technologically key class of advanced multifunctional materials that fulfill the challenging strict requirements of the beginning of this century: higher levels of sophistication and miniaturisation, recyclability, reliability and low energy consumption. The potential of these tailor-made materials, that are already entering niche markets [1], is basically due to the synergistic combination of organic, inorganic, and even biological components in a single system at the nanosize level. Their properties are then not just the sum of the individual contributions of both organic and inorganic phases; the role of their inner interfaces is also predominant. The realization of cost effective, eco-friendly and sustainable electronic and photonic components based on sol-gel derived organic-inorganic hybrid matrices has received increasing attention in the past years, being actually a highly attractive scientific and technological challenge [2,3].The talk presents examples of organic-inorganic hybrids that can be used as integrated optics (IO) substrates in the new generation of optical networks and non-contact luminescent micro and nanoscale thermometers. For IO substrates, emphasis will be given to approaches for materials processing and refractive index control that permits the design of passive and active applications in long haul/metro (NIR range) and access/indoor (visible range) optical architectures, particularly, planar and channel waveguides, couplers, filters, Y and MMI power splitters, and lasers. The molecular thermometers reported, based on Ln3+-containing organic-inorganic hybrids, are self-referencing, allowing absolute measurements in the 10–350 K temperature range [4]. The temperature sensitivity reached is up to 4.9% K−1, 1.5 times larger than the highest value reported so far, and the thermometers exhibit high photostability in long-term use. To obtain high-resolution 2-dimensional temperature mapping, a judicious choice of the host matrix enables processing the thermometer material as a film. Finally, the combination of the molecular thermometer with a nanometric magnetic/luminescent host matrix provides the device multifunctionality at the nanoscale.The collaboration of C.D.S. Brites, P.P. Lima, N.J.O. Silva, A. Millán, V.S. Amaral and F. Palacio, for the nanotermometers, and of R.A.S. Ferreira and P.S. André, for IO, is gratefully acknowledged. [1] L. Nicole, L. Rozes, C. Sanchez, Adv. Mater. 2010, 22, 3208–3214[2] R. A. S. Ferreira, P. S. André, L. D. Carlos, Opt. Mater. 2010, 32, 1397–1409[3] L. D. Carlos, R. A. S. Ferreira, V. de Zea Bermudez, S. J. L. Ribeiro, Adv. Mater. 2009, 21, 509-534.[4] C. D. S. Brites, P. P. Lima, N. J. O. Silva, A. Millán, V. S. Amaral, F. Palacio, L. D. Carlos, Adv. Mater. 2010, 22, 4499–4504
3:00 PM - **NN5.2
Nanostructured Coatings for Optical Applications Involving Light Conversion.
Thierry Gacoin 1 , Geraldine Dantelle 1 , Amelie Revaux 1 , Joelle Corde 1 , Jean-Pierre Boilot 1
1 , CNRS - Ecole Polytechnique, Palaiseau France
Show AbstractSoft chemistry routes allow the elaboration of hybrid materials combining different constituent at the nanometer scale : polymeric oxides with a controlled porosity obtained from sol-gel condensation, nanoparticles obtained through colloid chemistry and functional organic species. This allows the elaboration of a large variety of materials with original properties, which may find numerous applications as functional coatings. In the last few years, our group has been involved in this field of research for the development of light converting coatings for displays, lightning and photocatalytic devices. We mainly focussed our attention on processes of elaboration that involve the dispersion of pre-formed nanoparticles within a dielectric host matrix. First step is the synthesis of nanoparticles through colloid chemistry. We mainly investigated systems exhibiting luminescent properties such as rare earth doped oxides and photocatalytic particles derived from TiO2. The development of particles with optimized absorption and emission properties led us to work on an original process allowing the production of well dispersed colloidal particles obtained after high temperature treatments up to 1000°C. Luminescent particles obtained with this method exhibit high emission yields due to their excellent crystallinity and absence of defects. As shown in the case of doped TiO2, this process was also successfully applied for the elaboration of particles which composition cannot be obtained using conventional colloid chemistry.Second step is the incorporation of the nanoparticles within a silica film deposited onto the desired substrate (usually glass). Depending on the application, the organic template approach was used to control the porosity of the film and its refractive index. Starting from colloidal dispersions, films are obtained using a sol containing both the particles and sol-gel precursors of the matrix that will mainly act as a binder. Different deposition techniques were investigated, but we focused our attention on spray deposition that allows, after optimization, the elaboration of films with good optical transparency even for thicknesses up to a few microns.Finally, we will discuss on our strategy to develop film with optimized properties by playing on dielectric properties of multilayer coatings and structuration by imprint lithography. The basic idea is here to control light propagation phenomena, both to enhance the film absorption by increasing the pathlength of the excitation light and to control light extraction in the case of luminescent films. Applications of this strategy will be shown for the design of functional coatings such as self cleaning coatings, plasmonic devices and phosphor conversion layers in white GaN LEDs.
3:30 PM - NN5.3
Nanotextured Oxide/Prussian Blue Analog Nanocomposites: Towards Tailor-made Nano-scale Electronic Devices.
Anne Bleuzen 1 , Giulia Fornasieri 1 , Merwen Aouadi 1 , Emilie Delahaye 1
1 ICMMO-ECI, Universite Paris-Sud, Orsay France
Show AbstractPrussian blue and analogs (PBA) have attracted growing attention over the past decade because of the diversity and tunability of their electronic properties. The possible control of their magnetic properties following external stimuli particularly makes them good candidates for future molecular memories or switching devices.[1] The successful integration of such functional objects into real applications depends however on an additional processing step to control their shape, size and organization in, or at the surface of, a solid matrix.In order to shape and organize functional components into a solid matrix, solids exhibiting well-defined pore size, pore shape and pore organization, which can besides be deposited onto various substrates are particularly suited. Nano-structured oxides elaborated via sol-gel chemistry combined with surfactant micelle templating gather all these capabilities. We present here our recent studies focusing on the elaboration of sol-gel porous oxide/ photomagnetic CoFe Prussian blue analogs nanocomposites. Several strategies have been developed to control the PBA formation within the porosity of the solid matrix exclusively.[2-4] The chemistry of PBA in confined condition can be adjusted to retain the switching properties even in nanosized PBA particles. The study of the effect of the processing step on the switching properties of the nanocomposites in comparison with the properties of bulk compounds is in progress.[5] [1] A. Dei, Angew. Chem. Int. Ed., 44, 1160-1163, 2005.[2] G. Fornasieri, A. Bleuzen, Angew. Chem. Int. Ed., 47, 7750-7752, 2008.[3] P. Durand, G. Fornasieri, C. Baumier, P. Beaunier, D. Durand, E. Rivière, A. Bleuzen, J. Mater. Chem., 20, 9348-9354, 2010.[4] S. Lepoutre, D. Grosso, C. Sanchez, G. Fornasieri, E. Rivière, A. Bleuzen, Adv. Mater., 22, 3992–3996, 2010.[5] G. Fornasieri, M. Aouadi, P. Durand, P. Beaunier, E. Rivière, A. Bleuzen, Chem. Commun., 46, 8061-8063, 2010.
3:45 PM - NN5.4
Thiol-ene Reaction derived Sol-gel Oligosiloxane Hybrid Material for Optical Application.
Joon-Soo Kim 1 , SeungCheol Yang 1 , Hyung-Jin Park 1 , Byeong-Soo Bae 1
1 Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon Korea (the Republic of)
Show AbstractPhoto-polymerization is the powerful tool to be applied in the field of numerous coating industries, especially optical applications. The dielectric constant of materials acts as a key factor to decide these applications. For instance, the low dielectric material is required for the passivation layer to avoid the crosstalk in the electric device while the high dielectric material is suitable for the core material for the optical waveguide. Thus, the photo-curing system applied dielectric materials have been researched and widely used for various optical applications. The thiol-ene reaction is known as the click chemistry since it is the direct reaction of sulfur containing compounds with alkenes. In contrast to typical photo-polymerization, the thiol-ene reaction has low oxygen inhibition and less shrinkage than typical photo-polymerization due to its low gelation time. Thus, the thiol-ene reaction is increasingly applied to various research fields in polymer functionalization and macromolecular synthesis with these advantages. Also, it results high yield of target product from starting material and has strong tolerance to many different reaction conditions and solvents. And the sulfur atom has high optical refraction compared with other organic atoms, which can be widely applied for optical materials. Even though the thiol-ene reaction has such excellent various merits, the bad odor and stability of solution have limited its applications in industry fields. In this research, the sol-gel process was used to synthesize odorless and stable thiol containing solution. The sol-gel process has received much attention in the synthesis of inorganic-organic hybrid materials over the years since stable chemical combination of inorganic and organic components in low temperature process is possible through it. This technical process provides the desirable properties of both components within one chemical compound. We synthesized thiol and vinyl containing oligosiloxane respectively by non-hydrolytic sol-gel condensation of oranoalkoxysilane (mercaptopropyltrimethoxysilane, vinyltrimethoxysilane) and diphenylsilanediol. These highly condensed resins were mixed with photo-initiator. It can be photo-cured by UV (365nm) light by thiol-ene reaction in air. And it was patterned through photo-mask. The fabricated siloxane hybrid material has high refractive index (n=1.58 at 633nm) and dielectric constant (ε=4.134) due to the existence of sulfur and phenyl groups, and low leakage current (2.79nA/cm2 at 1MV/cm) to be applied in optics and displays as the optical material. It also has high thermal stability (5% weight loss temperature=364°C) with high transparency (∼90% at 450nm).
4:00 PM - NN5: photonics
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4:30 PM - **NN5.5
High Thermally Stable Hybrid Materials for Optical Interconnects.
Tetsuo Sato 1
1 , Nissan Chemical Industries, LTD., Funabashi Japan
Show AbstractOptical materials in the optical circuit board are required to overcome soldering process. In detail, the material should not have absorption and shape changes after several tens of seconds heating at around 250 oC. For such application field, we have developed a novel organic-inorganic hybrid material having a high thermal stability and low absorption at telecom wavelength.The hybrid material was designed to solvent less resin, which is curable with heating at 150 oC or UV exposure at room temperature, for the sake of device fabrication activity. We have demonstrated to fabricate a coating layer by spin-coating technique or a bulk body sample by curing in molds, and obtained a high uniformity cured materials even in 1cm-thick. Transparency of the cured material at telecom wavelength was 0.10 dB/cm at 850 nm, 0.12 dB/cm at 1060 nm, 0.29 dB/cm at 1310 nm, and 0.45 dB/cm at 1550 nm. These values are good low attenuation for the Near-IR optical communication in optical interconnects. Without any further treatment such as post bake, the cured materials showed a high thermal stability. The temperature of 5 % weight loss was over 400 oC, and the transparency hardly changed after 1 min heating at 300 oC.In addition, the cured material showed a high refractive index of n=1.60 at 633 nm and a low curing shrinkage about 4.7 %. From these properties, the developed organic-inorganic material is expected to be beneficial for the optical interconnection such as micro lenses and optical packages.
5:00 PM - **NN5.6
Ultra-short Laser Pulses for 3D Patterning of Hybrid Materials - a Scalable Technology for Optical and Life Science Applications.
Ruth Houbertz-Krauss 1
1 Competence Team Hybrid Materials for Microsystems and Micromedicine, Fraunhofer-Institut fuer Silicatforschung ISC, Wuerzburg Germany
Show AbstractOptical technologies open up a wide field of novel applications when combined with electronics or (bio-)medicine. Many efforts have been made to develop laser light sources in order to continuously increase their application potential. With the postulation of two-photon absorption in 1931 and the invention of ultra-fast lasers which led to the experimental demonstration of this effect in 1997, many new applications were addressed, and the interaction of ultra-short laser pulses with polymer or glass materials is of high technological interest. Non-linear absorption initiated by focusing ultra-short laser pulses into materials is particularly used for the 3D free-form fabrication of functional structures among which are waveguides, metamaterials, or scaffold structures for biomedical applications. Since the triggered reactions are strongly confined to the focal region, the fabrication of 3D microstructures is performed simply by moving the focal volume in 3D through the materials, providing a scalable technology. However, up to now only smaller scale structures of only several 100 µm with some examples of waveguides which were written on a several cm scale in length were demonstrated. The generation of complex free-form 3D structures in custom-designed multifunctional materials such as inorganic-organic hybrid polymers (ORMOCER®s ) provides the key feature for combining the design possibilities of 3D fabrication with the power of multifunctional materials. Not only the material’s optical and electrical properties can be tailored, but also their thermal and mechanical properties. Additionally, suitable functionalization creates binding sites for, e.g. biomolecules and cells in order to also enable micromedicine and biomedical applications. The scalability of the method ranging from the sub-100 nm regime to the cm range will be demonstrated by examples from optical to biomedical applications. Registered by the Fraunhofer-Gesellschaft für Angewandte Forschung e.V.
5:30 PM - NN5.7
Magnetically Responsive Photonic Structures.
Yongxing Hu 1 , Yadong Yin 1
1 Department of Chemistry, University of California,Riverside, Riverside, California, United States
Show AbstractMagnetically responsive photonic crystal structures have been fabricated by the assembly of superparamagnetic iron oxide colloidal particles in solution phase using external magnetic fields. The colloids form 1-dimensional (1-D) chain-like structures with regular interparticle spacing along the direction of the magnetic field so that the system strongly diffracts light. The diffraction peak can be tuned across the entire visible spectrum by simply changing the strength of magnetic field. Modification of the particles’ surface with inorganic silica layer or organic silane groups renders the tunable photonic structures compatible in nonaqueous systems. The color of the photonic crystal structure can be fixed by photochemically immobilizing the structure in a polymer matrix. Also the miniaturization of the photonic crystals can be realized by fixing the single photonic chain with inorganic coatings. These magnetically responsive photonic structures have great potential in applications such as optoelectronic devices, sensors, and color displays.
5:45 PM - NN5.8
Effect of Light Intensity on Schottky Barrier Widths and I-V Characteristics of Polymer Heterojunction Photodiodes.
Ali Guvenc 1 , Emre Yengel 1 , Guoping Wang 1 , Cengiz Ozkan 2 3 , Mihrimah Ozkan 1
1 Electrical Engineering, University of California, Riverside, Riverside, California, United States, 2 Mechanical Engineering, University of California, Riverside, Riverside, California, United States, 3 Materials Science and Engineering, University of California, Riverside, Riverside, California, United States
Show AbstractThe Schottky barriers that forms on the interface between aluminum and organic semiconductor of polymer heterojunction photodiodes based on poly(3-hexylthiophene): [6,6]-phenyl-C61-butyric acid methylester blend, has been investigated according to Mott-Schottky curves. We focused on the effect of light intensity on the Schottky barrier widths and I-V characteristics of the devices. Comparison of the mathematical models and experimental data measured under different light intensities indicate a dependency of Schottky barrier to the light intensity.
Symposium Organizers
Zhang-Lin Zhou Hewlett-Packard Labs
Clement Sanchez College de France
Michael Popall Fraunhofer ISC
Jian Pei Peking University
NN9: Poster Session: New Material Synthesis, Sensor and Biology Applications
Session Chairs
Thursday PM, April 28, 2011
Salons 7-9 (Marriott)
NN7: Hybrid Nanomaterials for Energy Conversion and Solar Cell
Session Chairs
Thursday PM, April 28, 2011
Salons 1-2 (Marriott)
9:00 AM - **NN7.1
Nanomaterials and Nanocoatings for Energy Storage Applications.
Kai Moeller 1
1 Electrochemical EnergyStorage and Conversion, Fraunhofer Institute for Silicate Reearch, Wuerzburg Germany
Show AbstractTodays electrochemical energy storage market is dominated by nickel metal hydrid batteries, lithium-ion batteries and supercapacitors. The presentation will give examples for the use of nanomaterials and nanocoatings to improve important properties such as energy density, power density, and safety of the different energy storage systems.Among the energy storage devices, supercapacitors enable a much faster storage and release of charge than battery systems, and therefor have a excellent power density. The mechanism of energy storage involves the formation of an electrochemical double layer at the high surface area of the used electrode materials. The disadvantage is that the energy is only stored at the surface of the particles, unlike in a battery, where (slow) faradaic reactions of the bulk electrode active material give much higher energy densities. Commercial supercapacitors based on activated carbon electrodes have, due to the increase of the performance and decrease in cost during the last three years, found their way to the mass market. These state-of-the-art supercapacitors do not satisfy all actual requirements for the use in, e.g., automobiles: The energy density is for applications in the power train not sufficient. For a new generation of supercapacitors with optimized energy and power densities new electrode concepts will be presented. Here the use of hybrid electrodes with pseudocapacitive storage materials seems promising, since these have a significant higher charge storage capability. Coming from the other side, batteries, especially lithium-ion systems, have catched up a lot in terms of power density mostly due to the use of nanomaterials. Concerning this topic, strategies to improve the rate capability and the safety of lithium-ion batteries will be discussed.
9:30 AM - NN7.2
Molecular Design of New Squaraines for Efficient OPVs: Tuning Absorption, Energy Levels and Morphology.
Siyi Wang 1 , Vyacheslav Diev 1 , Lincoln Hall 1 , Peter Djurovich 1 , Mark Thompson 1
1 chemistry, University of southern california, Los angeles, California, United States
Show AbstractWe have previously demonstrated that the squaraine 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] (SQ) can be applied as a donor layer in planar heterojunction organic photovoltaic (OPV) devices. However, bulk heterojunction devices show low fill-factors (FF) that arise from the relatively low hole transport mobility of SQ. Hence, squaraines with better charge transport properties are desired. Here we present a new promising family of diarylamino-substituted squaraines that lead to OPVs with improved performance. A facile synthetic route for both symmetrical and unsymmetrical aryl squaraines (>50% yield in gram quantity) will be discussed. These new aryl squaraines show better organization in thin films and film morphology. Symmetrical squaraines with phenyl, 1-naphthyl or 2-naphthyl substituents absorb between 660-690 nm in solution and up to 800 nm in films and are effective as a donor layers in single heterojunction OPVs prepared by spin casting techniques. Despite having similar optical and electrochemical properties, aryl squaraines can lead to devices with different Voc depending on film morphology. A series of unsymmetrical squaraines with different absorption profiles have also been synthesized and show absorption maxima blue shifted to 530 nm (solution). OPV devices with high efficiency can be fabricated by blending these unsymmetrical and symmetrical squaraines. Improved performance in this case is due to a panchromatic EQE response (>15%) throughout the visible solar spectrum, up to 800 nm, with peak maxima at 550 nm (EQE = 30%) and 670 nm (EQE = 20%).
9:45 AM - NN7.3
Greatly Enhanced Performance of a Nanotube/Silicon Solar Cell by Electronic Gating.
Pooja Wadhwa 1 , Andrew Rinzler 1
1 Department of Physics, University of Florida, Gainesville, Florida, United States
Show AbstractSingle wall carbon nanotubes (SWNTs) and related sp2 bonded carbons provide a unique metallic system possessing a low density of electronic states that unlike normal metals allows their Fermi level to be readily shifted via chemical charge transfer doping or electrical gating. This characteristic of SWNTs is exploited to demonstrate control over the built-in potential in a SWNT film/n-Silicon Schottky junction solar cell. The natural porosity of the SWNT film permits access to the junction by an ionic liquid electrolyte gate. This gate electronically modulates the Fermi level offset, a junction interface dipole and an induced field developed across the depletion layer in n-Si thus modulating the performance characteristics of the cell. In the steady state the gate neither consumes nor dissipates power. Under standard test conditions of AM1.5G, the as produced (before electronic gating) device exhibits a power conversion efficiency of 8.5% with an open circuit voltage of 0.52 V, a short circuit current density of 22.1 mA/cm2, and a fill factor of 0.75. With electronic gating from +0.75 V to -0.75 V, the power conversion efficiency in a single device is continuously and reversibly changed from 4% to 11%.
10:00 AM - NN7.4
Energy Storage Elements Based on Hybrid Organic/Inorganic Nanomembranes.
Carlos Bof Bufon 1 , Jose Cojal Gonzales 1 , Dominic Thurmer 1 , Daniel Grimm 1 , Matin Bauer 1 , Oliver Schmidt 1 2
1 Institute for Integrative Nanosciences, IFW-Dresden, Dresden Germany, 2 Material Systems for Nanoelectronics, Chemnitz University of Technology, Chemnitz Germany
Show AbstractIn this work, we demonstrate that self-assembly methods combined with standard top-down approaches are suitable for fabricating three-dimensional ultra-compact hybrid organic/inorganic electronic devices, such as self-wound capacitors (UCCaps), manufactured in parallel on a single chip. To the best of our knowledge, the inorganic version of our UCCaps exhibit capacitances per footprint area higher than their state-of-the-art planar counterparts and specific energy comparable with supercapacitors (~0.55 Wh/kg).Due to the synthetic tailorability of molecular systems, their incorporation in inorganic elements gives rise to novel devices with almost limitless chemical and biological functionalities. Therefore, in addition to reducing the device footprint by the rolling process, we were able to incorporate a self-assembled monolayer (SAM) of phosphonic acid in between the oxide layer and the capacitor metallic plate. The integration of organic molecules provides further free parameters to tune the properties and extend the range of applications of the final self-wounded device. For instance, the systematic change of the SAM’s chain length allowed us to precisely control both the leakage current and the effective capacitance of the UCCaps: the growth of a single monolayer of octadecane phosphonic acid (ODP) on top of an Al2O3 layer represented a suppression of the leakage current in about 6 orders of magnitude. Similar to previously reported works, the current through the hybrid dielectric layer drops following an exponential dependence on the chain length with a decay coefficient β equal to 0.66± 0.03 Å-1. Furthermore, by the evaluation of the capacitance dependence on the chain length, we were able to experimentally determine the dielectric constant of phosphonic acid SAM’s.While small size of such energy storage system may limit their application range to low power systems, we believe that rolled-up supercapacitors with high specific energy could find many uses in energy autonomous systems where other supercapacitor structures would be far too bulky. In this case, the UCCaps could be directly combined with energy harvesters in a stand-alone compact module. Furthermore, replacing the phosphonic acids by magnetic molecules may represent a route towards organic spin-electronics in the near future.
10:15 AM - NN7.5
Synthesis and Chemical Passivation of Silicon Quantum Dots for Solar Cell Application.
Ingrid Anderson 1 , Rebecca Shircliff 2 , Benjamin Lee 3 , Chandra Macauley 4 , Bhavin Jariwala 5 , Sumit Agarwal 5 , Pauls Stradins 3 , Reuben Collins 1
1 Physics, Colorado School of Mines, Golden, Colorado, United States, 2 Chemistry, Colorado School of Mines, Golden, Colorado, United States, 3 , National Renewable Energy Lab, Golden, Colorado, United States, 4 Chemical Engineering, Montana State University, Bozeman, Montana, United States, 5 Chemical Engineering, Colorado School of Mines, Golden, Colorado, United States
Show AbstractNanomaterials have the potential to revolutionize photovoltaics with the promise of new physics, novel architectures and low cost synthesis. Silicon quantum dots, relative to their II-VI counterparts, are understudied due to the difficulty of solution synthesis and chemical passivation. However, silicon is still an attractive solar cell material, providing an optimal band gap, low toxicity, and a very solid body of physical understanding of bulk silicon to draw from. We have synthesized silicon quantum dots with plasma enhanced chemical vapor deposition, and have developed a method for chemical passivation of these silicon quantum dots that can be used on particles created in a variety of ways. This versatile method utilizes oxidation via wet chemical etch and subsequent siloxane bond formation. The attachment of a silane to the SiOx shell leads to stability of the silicon core for over a month in air, and individual particles can be seen with TEM; thus a stable, colloidal suspension is formed. The future for this technique, including increasing quantum yield of the particles by changing the nature of the oxide, will be discussed.
10:30 AM - NN7.6
Matrix-assisted Energy Conversion in Nanostructured Piezoelectric Arrays.
Donald Sirbuly 1 , Xianying Wang 2 3 , Kanguk Kim 1 , Yinmin Wang 2 , Michael Stadermann 2 , Aleksandr Noy 2 4 , Alex Hamza 2 , Junhe Yang 3
1 NanoEngineering, UC San Diego, La Jolla, California, United States, 2 Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States, 3 School of Materials Science and Engineering, University of Shanghai for Science and Technology, Shanghai, Shanghai, China, 4 School of Natural Sciences, UC Merced, Merced, California, United States
Show AbstractHere we discuss a new hybrid energy harvesting platform, based on nanostructured piezolelectric arrays embedded in an environmental-responsive matrix, which can self-generate electrical power from non-mechanical energy sources. A proof of principle device is designed, fabricated, and tested using vertically aligned ZnO nanowires and heat as the local energy source. The device layout takes advantage of the collective stretching motion of piezoelectric ZnO NWs, induced by the shape-change of the matrix polymer, to convert the thermal energy into direct current. The responsive nature of polymeric matrices to various stimuli makes this nanostructured piezoelectric architecture a highly versatile approach to scavenging energy from a multitude of environments including fluid-based and chemical-rich systems.
10:45 AM - NN7.7
Transparent Silver Nanowire-polymer Composite Electrodes for Stretchable and Efficient Polymer LEDs and Solar Cells.
Zhibin Yu 1 , Qingwu Zhang 1 , Lu Li 1 , Qibing Pei 1
1 Materials science and engineering, UCLA, Los Angeles, California, United States
Show AbstractTransparent silver nanowire (AgNW)-polymer composite electrodes were prepared. The figure of merit sheet resistance was 12 ohm/sq with 82% transmission and lower than 5 nm surface roughness. The electrodes could be stretched by up to 16% with only a small increase of sheet resistance. Polymer light emitting diodes (LEDs) were fabricated using the AgNW/polymer anode and an alkoxyphenyl substituted yellow emissive poly(1,4-phenylene vinylene) as the emissive layer. The maximum luminous efficiency was 14.0 cd/A, comparable to similar LEDs fabricated on an ITO/glass substrate. Polymer solar cells based on a blend of poly(3-hexylthiophene) and phenyl-C61-butyric acid methyl ester had power conversion efficiency over 3% under standard AM 1.5 illumination. The efficiency is comparable to similar solar cells on an ITO/glass substrate. Both the LEDs and solar cells are highly flexible and can be stretched by up to 10% without loss of performance.
11:00 AM - NN7: solar cell
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11:30 AM - NN7.8
Synthesis and Characterization of (4,5-diaza-9,9’-spirobifluorene) Functionalized Donor/ Acceptor Conjugated Polymer for Solar Cell Application.
Chia-Hsin Lee 2 1 , Yi-Chen Ho 2 , Hsueh-Chung Liao 2 , Wei-Fan Su 2 , Cheng-Si Tsao 1 , Charn-Ying Chen 1
2 Material Science and Engineering, National Taiwan University, Taipei Taiwan, 1 Division of Nuclear Fuel and Materials, Institute of Nuclear Energy Research, Taoyuan County Taiwan
Show AbstractTwo novel (4,5-diaza-9,9’-spirobifluorene) functionalized donor/ acceptor low bandgap conjugated polymers PZFDPP (K117) and PZFBTZ(K108) have been synthesized via Stille coupling. Their band gaps were determined by absorption spectroscopy and cyclic voltammetry to be ~1.5 eV and ~2.0 eV for K117 and K108 respectively. The pyridine moiety of the copolymer exhibited good affinity toward hydrophilic TiO2 nanorods, so they were used to modify the surface of TiO2 nanorods. The modified nanorods were blended with P3HT to fabricate hybrid solar cell. An increase of power conversion efficiency was observed at 2.6 times and 2.3 times for K108 and K117 respectively as compared with that of pyridine modified TiO2 nanorods. The results are due to the reduced charge recombination.
11:45 AM - NN7.9
Electrospun TiO2 Nanofibers for Organic-inorganic Hybrid Photovoltaic Cells.
Surawut Chuangchote 1 , Takashi Sagawa 1 , Susumu Yoshikawa 1
1 Institute of Advanced Energy, Kyoto University, Uji, Kyoto, Japan
Show AbstractRecently, polymer-based organic solar cells have attracted a great interest in terms of lightweight, printable and flexible photovoltaic devices. In order to improve the cell efficiencies, the combination of organic and inorganic semiconductor as hybrid organic-inorganic photovoltaic cells has been extremely reported. One-dimensional (1D) nanostructured metal oxides are promising electrodes for photovoltaic devices due to their high conductivity as a direct path for charge transport. Among these various nanostructured metal oxides, TiO2 is an attractive oxide, because of its processability and appropriate band gap. In this work, a simple and controllable fabrication of TiO2 nanofibers by electrospinning and their applications to the electron transporting layer for hybrid organic-inorganic photovoltaic cells will be reported. TiO2 nanofibers were directly electrospun onto an indium tin oxide (ITO) on glass substrate from a solution in methanol of polyvinylpyrrolidone (PVP), titanium(IV) butoxide, and acetylacetone. The nanofiber electrode obtained was consequently subjected to calcination at 450 °C. Solution of blended poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was spin coated on the TiO2 electrode, followed by thermal annealing and deposition of Au electrode. After photovoltaic characterizations, it was found that hybrid organic-inorganic photovoltaic cells made of TiO2 nanofibers exhibited remarkable improvement of the cell efficiencies in terms of photocurrent density and open circuit voltage as compared with those of reference, TiO2 flat film. Maximum energy conversion efficiency of hybrid organic-inorganic photovoltaic cells made of TiO2 nanofibers of 1.11% could be obtained (efficiency of the reference = 0.28%).
12:00 PM - NN7.10
C60:LiF Hole Blocking Layer for Improved Environmental Stability of Bulk Hetero-junction Solar Cells.
Dong Gao 1 , Michael Helander 1 , Zhibin Wang 1 , Danny Puzzo 1 , Mark Greiner 1 , Zhenghong Lu 1
1 Materials Science & Engineering, University of Toronto, Toronto, Ontario, Canada
Show AbstractOrganic photovoltaics (OPVs) have attracted considerable interest due to their potential to be manufactured at low cost using solution processing. Significant effort has been devoted in recent years to improving the efficiency of OPVs using a variety of different materials processing strategies. Power conversion efficiencies (PCEs) greater than 5% are now routinely reported based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) bulk-heterojunctions. In addition to high efficiency, a long lifetime is also equally as important to make OPVs a cost competitive and sustainable technology. However, despite the overwhelming work dedicated to incremental improvements in efficiency, there are very few studies to develop new pathways to improve device lifetime and environmental stability. There is therefore great interest in new materials that can deliver both high performance and long lifetime OPVs.The predominant degradation mechanism in OPVs is a result of the ingress of moisture and oxygen into the device.[6-9] Most device structures are based on indium tin oxide (ITO) as anode and a low work function metal as cathode. Unfortunately, low work function metals are highly reactive, and oxidize readily upon exposure to moisture and oxygen. The active layer is also degraded by exposure to moisture and oxygen. The high mobility of C60 and fullerene derivatives—the most commonly used acceptor materials in OPVs—is reduced by several orders of magnitude by air exposure. Moisture and oxygen in the presence of light may also contribute to photo-oxidative bleaching of the active layer. For the above mentioned reasons OPVs degrade extremely rapidly in ambient air. Without hermetic packaging, typical half-lives are on the order of several hours for P3HT:PCBM devices.Packaging OPVs with an epoxy resin sealed glass cap is commonly used in research labs to encapsulate devices for pro-longed lifetime testing. Encapsulating OPVs with a glass cap greatly improves device stability and lifetime. However, glass cap packaging is only feasible for small-area devices fabricated on rigid glass substrates. To realize the low cost potential of OPVs requires processing on large-area flexible substrates. Thin film encapsulation schemes are thus necessary, but cannot yet meet the ultra-low moisture and oxygen permeation rates required for long lifetime OPVs. Improved environmental stability of OPVs is thus highly desirable to reduce the stringent requirements for ultra-low moisture and oxygen permeation rates through the device packaging.In this work we report C60:LiF nano-composite as an electron transporting and a hole-blocking layer for OPVs, with improved PCE and an impressive enhancement in device stability. The excellent environmental stability and high conductivity make the C60:LiF nano-composite a versatile buffer layer to enable high performance OPVs with long lifetime.
12:15 PM - NN7.11
Ultrafast Dynamics of `Hot’ Charge-Transfer States in Organic Photovoltaic Materials.
Artem Bakulin 1 , Vlad Pavelyev 2 , Akshay Rao 1 , Dmitri Paraschuk 3 , Paul van Loosdrecht 2 , Maxim Pshenichnikov 2 , Richard Friend 1
1 Cavendish Laboratory, University of Cambridge, Cambridge United Kingdom, 2 Zernike Institute for Advanced Materials, University of Groningen, Groningen Netherlands, 3 Faculty of Physics and International Laser Center, Lomonosov Moscow State University, Moscow Russian Federation
Show AbstractThe importance of vibrationally ‘hot’ charge-transfer (CT) states for the formation of free (unbound) charges in the plastic photovoltaic devices is intensely debated at the moment. The CT state is a bound pair of charges residing at the interface of donor and acceptor organic materials. A number of studies [1,2] suggest that the conversion of singlet exciton to the hot CT state is directly followed by an ultrafast generation of free charges. In this framework, charge separation is assumed to be much faster than the “slow” relaxation of the hot state downhill the CT manifold. An alternative viewpoint is that the formation of free charges is typically mediated by the relaxation to the ‘cold’ (lowest in energy) CT state and, therefore, the hot CT state is not important for the performance of organic photovoltaic devices.[3,4] This scenario assumes relaxation within the CT band to be much faster than the formation of free charges. Understanding the actual charge-dissociation mechanism is critical for developing the optimal band structures of photovoltaic materials which is the key parameter for improving plastic solar cells efficiency. The aforementioned hypothesises can be potentially verified by comparing the CT state relaxation and dissociation rates. The typical times of free-charge formation were previously estimated to be longer than 10 ps. However, the rate of intraband relaxation within charge-transfer states manifold has never been studied till date. In this contribution, we propose a three-pulse ultrafast (near-IR pre-pump)–(IR pump)–(IR probe) spectroscopy to investigate the intraband relaxation of CT states. The experiment is designed to estimate the relaxation time constant and the contribution of the vibrationaly-assisted hopping to the dissociation of the CT states. We apply the developed technique to study CT state dynamics in a number of organic donor-acceptor blends. As the first step along this venue, we exploit formation of the ground-state CT complex in the photovoltaic materials. [3,4] Here the CT manifold is directly populated with the first near-IR pulse. After thermalization, the cold CT state is excited to the hot state with the second, IR-pump, pulse. The re-thermalization of the hot state back to the bottom of the CT manifold is then monitored by the third IR-probe pulse. Our preliminary results indicate that the CT-state relaxation is extremely fast, occurring at the timescale of 100’s fs. This signifies that in the photovoltaic materials the dissociation of the hot CT states should be even faster to compete with intraband relaxation. Most likely, the formation of free charges at the donor-acceptor interface occurs through the thermally activated hopping from the low-lying CT states to the free-charge states manifold.[1] H. Ohkita et al., JACS, 130, 3030 (2008)[2] J. Bredas et al., Acc. Chem. Res., 42, 1691 (2009)[3] A.A. Bakulin et al., Chem. Phys. Lett., 482, 99 (2009)[4] J. Lee et al, JACS, 132, 11878 (2010)
12:30 PM - NN7.12
Effect of Au Nanopillar Arrays on the External Quantum Efficiency of a Bulk Heterojunction Organic Solar Cell.
Shu-Ju Tsai 1 2 , Mihaela Ballarotto 1 3 , Danilo B. Romero 1 3 , Warren N. Herman 1 3 , Raymond J. Phaneuf 1 2 3
1 , Laboratory for Physical Sciences, College Park, Maryland, United States, 2 Materials Sceicence and Engineering, University of Maryland, College Park, Maryland, United States, 3 Electrical and Computer Engineering, University of Maryland, College Park, Maryland, United States
Show AbstractWe report on a systematic experimental and numerical study of the effect of periodic of Au nanopillar arrays of different widths and pitches, on the external quantum efficiency and optical absorption of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM)-based BHJ solar cells. We observe an overall decrease in efficiency relative to cells without nanopillars, but find an increase within a range of wavelengths from ~640-720 nm [1]. We find that the corresponding resonance is of mixed nature, with contributions from plasmon excitation and interference within the cavity formed by the electrodes. We discuss the issue of where the energy associated with extra extinction (i.e. absorption plus scattering) in the presence of Au nanopillar arrays with smaller width goes, and we find that the joule heating is responsible. Finally we discuss how to mitigate this effect, and to improve the efficiency of such devices.[1] Shu-Ju Tsai, M. Ballarotto, D. B. Romero, W. N. Herman, H.-C. Kan, and R. J. Phaneuf, "Effect of gold nanopillar arrays on the absorption spectrum of a bulk heterojunction organic solar cell," Optics Express, 18, A528 (2010).
NN9: Poster Session: New Material Synthesis, Sensor and Biology Applications
Session Chairs
Friday AM, April 29, 2011
Salons 7-9 (Marriott)
9:00 PM - NN9.1
Synthesis of Cobalt Ferrite Nanoparticle/polymer Hybrid for Magnetic Hyperthermia.
Koichiro Hayashi 1 , Kazuki Maeda 1 , Makoto Moriya 1 , Wataru Sakamoto 1 , Toshinobu Yogo 1
1 EcoTopia Science Institute, Nagoya University, Nagoya University, Nagoya, Aichi, Japan
Show AbstractFunctional inorganic nanoparticle/organic hybrid materials have attracted attentions because of their beneficial 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 chemoselective synthesis of cysteine-modified magnetite nanoparticles via click chemistry for magnetic hyperthermia [1]. This paper describes the synthesis of water-soluble cobalt ferrite (CFO) nanoparticle/polymer hybrid through the hydrolysis and functionalization of iron and cobalt methacrylate. The structure of Co-Fe methacrylate complex was analyzed by single-crystal X-ray analysis. The crystal was found to consist of two Co and four Fe metals coordinated with organic ligands. The complex was copolymerized with 2-hydroxyethyl methacrylate, and then hydrolyzed to form CFO nanopartilce/polymer hybrid. The hybrid was analyzed by FT-IR, DTA-TG, powder XRD, and VSM. The size and magnetic properties of the hybrid was controlled by selecting the hydrolysis conditions. The magnetization of CFO nanoparticle/polymer hybrid revealed the maximum value at 8.6 nm in diameter. The hybrid generated heat by applying an AC magnetic field. The specific absorption rate (SAR) in water was 26.1 W g−1 normalized at 1 MHz and 100 Oe. The CFO nanoparticle/polymer hybrid is expected for the future application in multifunctional nanomedicine with hyperthermia and MRI.1.K. Hayashi, K. Ono, H. Suzuki, M. Sawada, M. Moriya, W. Sakamoto and T. Yogo, Chem. Mater., 22, [12] 3768 (2010).
9:00 PM - NN9.10
Mesoporous Graphitic Carbon (IV) Nitride: A Chemosensor for Selective Optical Sensing of Metal and Anions.
Eun Zoo Lee 1 , Young-Si Jun 2 , Yun Suk Huh 3 , Arne Thomas 4 , Won Hi Hong 1
1 Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon Korea (the Republic of), 2 Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, California, United States, 3 Division of Material Science, Korea Basic Science Institute, Daejeon Korea (the Republic of), 4 Institute of Chemistry, Technische Universitat Berlin, Berlin Germany
Show AbstractWith recent advances in industry, large amount of toxic and carcinogenic metals and anions have been released into the environment, which strongly raised the interest in biological and environmental monitoring of such compounds. Optical sensing system are intensively investigated because they promise to combine sensitivity, fast and easy detection, biocompatibility and adaptability to a wide variety of assay conditions. Up to now, various optical sensors based on azo-coupled macrocycles, porphyrin and phenanthroline derivatives have been described for the detection of a wide range of metal ions. Recently, the application of mesoporous materials to optical sensing has also brought remarkable success. There is however still growing demands for more advanced optical sensing system with lower detection limit and faster kinetic response. We have induced graphitic carbon nitride (g-C3N4) to have 3D cubic nanostructure through nanocasting approach. 3D cubic mesoporous g-C3N4 (c-mpg-C3N4), as all-in-one chemosensor playing roles of ligand, fluorophore and supporting material, enables extremely simple detection of metal ions and is highly selective and sensitive to Cu2+. Considering the properties of present chromogenic/fluorescent receptors, it seems that nanostructured g-C3N4 would be a promising alternative. The electronic structure of g-C3N4 is adjustable by coupling events of protons or metals to the surface. The surface functionalities of g-C3N4, i.e. -NH2/-NH-/=N-, are well-characterized ligands exhibiting high adsorption capability for metal ions through chelation or redox reaction. Finally, an additional supporting material is not necessary because it is possible to tailor its nanostructure by using any kind of silica hard template.While the detection of anions that can be potentially harmful to the environment or human is important, cyanide is one of the most concerned anions due to its lethal toxicity. We have combined the ability of Cu2+ to affect electron transfer across g-C3N4, with that of cyanide anion to bind Cu2+ to create a novel, sensitive and selective fluorescent sensor.
9:00 PM - NN9.12
Detection of Genomic DNA Using Magnetic Nanobeads.
Teresa Zardan Gomez de la Torre 1 , Jenny Goeransson 1 2 3 , Mattias Stroemberg 1 , Camilla Russell 2 , Peter Svedlindh 1 , Mats Nilsson 2 , Maria Stromme 1
1 Department of Engineering Sciences, Uppsala University, Uppsala Sweden, 2 Department of Genetics and Pathology, Uppsala University, Uppsala Sweden, 3 , Q-linea AB, Uppsala Sweden
Show AbstractMagnetic nanobeads have a high potential as carriers for biomolecules (e.g. DNA and proteins) in different life science applications (e.g. biosensors and magnetic separation) because of the high physical and chemical stability and the potentially low-cost of production. Substrate-free biosensors often involve labeling magnetic beads, exhibiting Brownian relaxation behavior, with probe molecules for recognition of specific target molecules. Hybridization of target molecules to the probes causes a hydrodynamic size increase of the magnetic nanobeads, corresponding essentially to the size of the target molecule. This brings on a decrease in the Brownian relaxation frequency, defined by the position of the peak in the imaginary part (m'') of the complex magnetization (m = m’- im'') spectrum, of the beads since the frequency is inversely proportional to the hydrodynamic size of the beads. A frequency shift, thus, confirms the presence of target molecules. The concentration of the target molecules can then be monitored as a corresponding decrease of the amplitude of the Brownian relaxation peak of the free beads. The volume-amplified magnetic nanobead detection assay (VAM-NDA) uses this strategy. The VAM-NDA has up to now been demonstrated for the detection of synthetic DNA molecules. These studies have mainly served to characterize features of the assay and to optimize the performance of the assay. In this study, the VAM-NDA has for the first time been applied for detection of real genomic DNA from Escherichia coli cells by implementing a solid-phase-based molecular probing and amplification protocol that can be executed in 80 minutes. A semiquantitative response was achieved with a limit of detection of 50 bacteria. This limit of detection is relevant for diagnosis of several infectious diseases such as urinary tract infection, diarrhea, and respiratory tract infections.
9:00 PM - NN9.13
Label Free DNA Detection Using Large Area Graphene Based FET Biosensors.
Shirui Guo 1 , Cengiz Ozkan 3 2 , Mihrimah Ozkan 2 1
1 Chemistry, UC Riverside, Riverside, California, United States, 3 Mechanical Engineering, UC Riverside, Riverside, California, United States, 2 Electrical Engineering, UC Riverside, Riverside, California, United States
Show AbstractWe describe the fabrication of highly sensitive graphene based field effect transistor (FET) biosensors with a cost-effective approach and their application in label-free Deoxyribonucleic acid (DNA) detection. Chemical vapor deposition (CVD) grown graphene layers were used to achieve mass production of FET devices via conventional photolithographic patterning. Non-covalent functionalization of the graphene layer with 1-Pyrenebutanoic acid succinimidyl ester ensures high conductivity and sensitivity of the FET device. The present device could reach a detection limit as low as 1nM. Introduction of gold nanoparticles increased the detection limit to pM which demonstrates the capability of hybrid nanomaterials for biosensor.
9:00 PM - NN9.14
ZnBeMgO Thim Films for Ultraviolet Detection by Sol-gel.
Jose Liriano 1 , Neeraj Panwar 1 , Ram Katiyar 1
1 Physics, University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractDuring this decade, the band gap modulation of ZnO films has been achieved by alloying it with much wider band gap semiconductor MgO (7.8eV). However, there exists a miscibility gap in the ZnO-MgO binary system due to the structural difference and the large lattice mismatch between ZnO and MgO. Mg+2 ions can replace 33% of Zn+2 ions without changing the structure of ZnO and beyond that phase segregation between hexagonal ZnO and cubic MgO has been observed in Zn1-xMgxO alloy. During this time, another binary system ZnBeO, with wide band gap, has also been proposed. ZnBeMgO films have been deposited on c-axis oriented sapphire substrates by pulsed laser deposition (PLD) technique with the increased bandgap from 3.7eV to 4.9eV with the incorporation of different amount of Be and Mg into ZnO matrix. Here, we have studied the Zn1-x-yBexMgyO films on sapphire (Al2O3) substrates by the novel and cheaper spin coating method.Starting materials were dissolved in 2-methoxyethanol and monoethanolamine (MEA) used as solvent and stabilizer respectively. The molar concentration of the solutions was 0.5M. The solutions were coated on the substrates rotated with 3000rpm for 30s. The films were then dried at 300°C for 10 min for evaporating the solvents and removal of organic residuals. This process of coating and heating was repeated 10 times. These films were later annealed at 550°C for 90 min. The optical studies have been performed with UV-VIS spectrometer in the wavelength range 190-800nm. XRD patterns of the films revealed that the pristine film has a wurtzite type structure. No extra peaks corresponding to BeO or MgO could be noticed in the XRD patterns of the films. From the optical measurements it was observed that for the pristine ZnO film, the cutoff wavelength was 364nm which decreased for example to 280nm for Zn0.6Be0.1Mg0.3O film which is quite well in the solar blind region. Other measurements like I-V and Raman are in the process and will be presented.The authors would like to acknowledge NASA-URC for the financial support for this work.
9:00 PM - NN9.15
Enhancement of the Electrical Conductivity in PEDOT:PSS Films Using Dimethyl Sulfate.
Roman Lopez-Sandoval 1 , Isidro Cruz-Cruz 2 , Marisol Reyes-Reyes 2
1 Advanced Material, IPICYT, San Luis Potosi, San Luis Potosi, Mexico, 2 IICO, Universidad Autonoma de San Luis Potosi, San Luis Potosi, San Luis Potosi, Mexico
Show AbstractA significant increase of the electrical conductivity of PEDOT:PSS films, brought about by the addition of dimethyl sulfate (DMS, (CH3)2SO4), while preserving the films’ excellent flexibility and visible-light transparency, is reported. The electrical and morphological properties of the films were studied as a function of DMS concentration. At an optimal concentration of around 1:25 (DMS to PEDOT:PSS), the conductivity of the films is enhanced by a factor on the order of 1880 times that of pristine PEDOT:PSS films. Extensive spectroscopic measurements using absorbance, Raman and FTIR techniques, as well as structural characterization by AFM microscopy, were performed. These measurements support the idea that the mechanism responsible for the conductivity enhancement is the partial replacement of the PSS- segments by SO4-2 anionic sulfates when a small amount of DMS is added to a PEDOT:PSS solution. This mechanism is associated with an increase of doping and this doping can be understood in the following manner: due to that the SO3- ions of the PSS segment only carry one negative charge, it is more probable for them to create polaronic states, whereas the SO4-2 ions are double charged, increasing the possibility of creating bipolaron carriers in the PEDOT backbone. In this way, the partial replacement of the PSS- segments by SO4-2 ions increases the bipolaron population by an ion exchange process and, as a consequence, the doping level is increased.
9:00 PM - NN9.17
Photonic Crystal Structures Created by Magnetic Assembly of Nonmagnetic Particles.
Le He 1 , Yadong Yin 1
1 , UC Riverside, Riverside, California, United States
Show AbstractWe report the rapid formation of photonic crystal structures by magnetic assembly of uniform nonmagnetic polystyrene particles in ferrofluids (magnetic holes). Magnetic manipulation of submicrometer magnetic holes has been difficult due to their weak magnetic dipole moment. Increasing the dipole moment has been limited by the instability of ferrofluids toward aggregation at high concentration or under strong magnetic field. By taking advantage of the superior stability of highly surface-charged magnetite(Fe3O4) nanocrystal-based ferrofluids, we have been able to successfully assemble 185 nm nonmagnetic polymer beads into photonic crystal structures, from 1D chains to 3D assemblies as determined by the interplay of magnetic dipole force and packing force. In a strong magnetic field with large field gradient, 3D photonic crystals with high reflectance (83%) in the visible range can be rapidly produced within several minutes, making this general strategy promising for fast creation of large-area photonic crystals using nonmagnetic particles as building blocks.
9:00 PM - NN9.4
Outstanding Radiation Performance of an All-carbon Nanotube Patch.
David Stollberg 1 , Fabio Urbani 3 , Amit Verma 2
1 Georgia Tech Research Institute, Georgia Institute of Technology, Atlanta, Georgia, United States, 3 Department of Engineering, The University of Texas at Brownsville, Brownsville, Texas, United States, 2 Electrical Engineering & Computer Science, Texas A&M University-Kingsville, Kingsville, Texas, United States
Show AbstractThe last several years have seen a significant interest in carbon nanotubes (CNTs) for antenna applications. In particular such applications show great potential for the utilization of CNTs for terahertz (THz) or infrared (IR) operations. However the use of these dimensionally challenged materials for lower frequency applications, such as microwaves and millimeter-waves, which constitute a significant portion of commercial applications, has not been exhaustively explored. Within those frequency bands, microstrip antennas (MSA) have proved to be excellent radiators for many applications. Aircraft and ship antennas, satellite communications, mobile radio, and biomedical are just few of the application areas of such devices. In this work we report the development and characterization of a MSA with a patch composed entirely out of multi-wall CNTs on a silicon substrate, fabricated to behave as a microwave radiator in the X-band (8-12 GHz). The patch CNTs were grown vertically using thermally enhanced chemical vapor deposition. These CNTs achieved a relatively uniform height of approximately 40 µm with diameters ranging from approximately 20 nm – 40 nm.One of the important challenges facing the utilization of nano-materials for electronic applications is the need to fabricate reliable contacts. In fabricating our antenna, we overcame the contact problem by using a feeding technique known as the aperture-coupled configuration where the electromagnetic field is coupled from the microstrip line feed to the radiating patch through an electrically small aperture or slot cut in the ground plane. The coupling aperture is usually centered under the patch. This feeding technique eliminates the need to electrically connect the CNT patch with a co-planar metallic microstrip line, which in turn significantly minimizes practical manufacturing difficulties. This feeding mechanism therefore, we believe, will become the method of choice for nano-materials based MSAs, and other applications involving nano-materials.The experimental characterization of the patch showed excellent response. In particular, a left-shift in the resonance peaks was observed. This points towards significant potential for antenna miniaturization, since, as a rule-of-thumb, the antenna size is generally inversely proportional to the frequency of operation. The structure also showed very promising reliability under different operating conditions. Such structures, given their outstanding performance, novel design, and ease and reliability of development, open up a new domain of scientific and technological innovation, and have significant promise for system-on-chip, space application, and other specialized applications.
9:00 PM - NN9.5
Synthesis of Photomagnetic Prussian Blue Analogues - Silica Nanocomposites: Study of Critical Synthetic Parameters.
Giulia Fornasieri 1 , Merwen Aouadi 1 , Valerie Briois 2 , Emilie Delahaye 1 , Anne Bleuzen 1
1 ICMMO-ECI, Université de Paris-Sud, Orsay France, 2 , Synchrotron SOLEIL, Gif sur Yvette France
Show AbstractIn the past decade CoFe Prussian blue analogues (CoFe PBA) have attracted growing interest owing to the tunability of their magnetic properties by external stimuli that make them good candidates for future optical memories or switching devices.[1] Several works report on the comprehension of the phenomenon and on the optimization of the precipitation in aqueous solution to control CoFe PBA stoichiometry and obtain reproducible switching properties.[2] Nevertheless the design of PBA-based electronic devices requires an additional processing step to elaborate a nanocomposite material with full control on the stoichiometry, the size, the shape and the organisation of PBA particles. The confined precipitation of CoFe PBA particles by impregnation of a Co(II)-containing mesoporous monolith with a ferricyanide solution, as already reported by the authors, can lead to PBA - silica nanocomposites with photomagnetic behaviour.[3] The reported elaboration strategy allows controlling the size and the organization of the CoFe PBA particles in the silica matrix.In this work, we focus on the chemistry of precipitation of PBA within the ordered mesoporosity of silica monoliths. To determine the critical parameters and fully control the synthesis of the photoactive CoFe PBA in the silica pores cobalt K-edge X-ray absorption spectroscopy was performed. This study showed that cobalt cation chemistry is the keystone species of the entire process. The local environment and the electronic structure of the cobalt cation undergo several modifications during the elaboration process: first the solubilisation of the cation as an octahedral complex in the polymeric matrix, then the deprotonation by thermohydrolysis to give a tetracoordinated negatively charged low condensed species, and finally the formation of the 3D coordination network of CoFe PBA with the electronic transfer leading to the photomagnetic Co(III)(LS)-Fe(II)(LS) pairs.This study is a mandatory step to fully control the precipitation of CoFe PBA in the porosity of silica matrix giving nanocomposites with optimised switching properties.[1] a) M. Verdaguer, G. Girolami, in Magnetism: Molecules to Materials (Eds. J. S. Miller, M. Drillon) Wiley-VCH, Weinheim, 2005; b) S.-I. Ohkoshi, K. Hashimoto, Electrochem. Soc. Interface 2002, 34-38; c) A. Dei, Angew. Chem. Int. Ed. 2005, 44, 1160-1163.[2] a) O. Sato, T. Iyoda, A. Fujishima, K. Hashimoto, Science 1996, 272, 704-705; b) A. Bleuzen, C. Lomenech, V. Escax, F. Villain, F. Varret, C. Cartier dit Moulin, M. Verdaguer, J. Am. Chem. Soc. 2000, 122, 6648-6652; c) J.-D. Cafun, G. Champion, M.-A. Arrio, C. Cartier dit Moulin, A. Bleuzen J. Am. Chem. Soc. 2010, 132, 11552-11559.[3] a) G. Fornasieri, M. Aouadi, P. Durand, P. Beaunier, E. Rivière, A. Bleuzen, Chem. Commun. 2010, 46, 8061-8063. b) P. Durand, G. Fornasieri, C. Baumier, P. Beaunier, D. Durand, E. Rivière, A. Bleuzen, J. Mater. Chem. 2010, 20, 9348-9354.
9:00 PM - NN9.6
Advanced Soft Lithograpgy for Nano-scale Resolutions;Organic/Inorganic Hybrid Siloxane for Stamping Materials.
Kyung Choi 1
1 , University of California, Irvine, California, United States
Show AbstractThe ability to fabricate small patterns on flexible substrates has received considerable attention due to potential applications in low coat plastic/ organic/molecular electronics. In microfabrication, 'soft lithography' has been widely used in stamping and printing processes for fabricating small features at a low cost. It is an alternative to conventional UV photolithography. However, conventional stamp materials based on poly (dimethyl)siloxane (PDMS) have shown limitations, especially at the submicron ranges, due to its low mechanical toughness. Since the resolution of soft lithography techniques is relied on the elastomeric elements, these limitations have motivated us to develop stiff, photocured silicon rubbers, which satisfy a set of our multiple demands, such as enhanced physical stiffness, good elastomeric properties, low linear polymerization shrinkage, photocurability, and freedom from stress. A new version of stamp materials with adjustable physical toughness has been developed for advanced soft lithography.
9:00 PM - NN9.7
Synthesis and Characterization of Hybrid Organic/Inorganic Particles for Biomolecules Separations.
Beatrice Muriithi 1 , Nicole Lawrence 1 , Kevin Wyndham 1 , Ken Glose 1 , Jessica Sargent 1 , Ed Bouvier 1 , Nadya Brady 1 , Susan Serpa 1 , Tom Walter 1
1 , Waters Corporation, Milford, Massachusetts, United States
Show AbstractSize exclusion chromatography (SEC) in an analytical technique that uses porous particles to separate analytes molecules of different size based on their size and not their interaction with the stationary phase. It’s mostly effective in separating larger molecules such as proteins and is therefore considered as one of the primary methods of analyzing proteins aggregation. Traditional silica based SEC stationary phases suffer from interactions with the analyte molecules and therefore, requires high ionic strength mobile phase to mitigate protein adsorption. In this poster, we introduce the synthesis and characterization of a new SEC packing material based on ethylene bridged hybrid (BEH) technology. These materials have reduced surface silanol activity resulting into a decrease in secondary interactions compared to silica based particles. In addition, these hybrid particles have been made to withstand the high pressures in Ultra-performance Liquid Chromatography (UPLC®) while maintaining pore sizes large enough for high resolution.
9:00 PM - NN9.9
Synthesis of Lithium Doped ZnO Nanowires for Stable P-type Conduction.
JunSeok Lee 1 , HyeWon Nam 1 , SangHyo Lee 1 , WonBae Ko 1 , SeungNam Cha 2 , JongMin Kim 2 , JinPyo Hong 1
1 Physics, HanYang University, Seoul Korea (the Republic of), 2 Frontier Research Lab., Samsung Institute of Advanced Technology, Yongin-si Korea (the Republic of)
Show AbstractWe report the synthesis of highly vertical oriented p-type ZnO nanowires (NWs) using aqueous solution, where lithium nitrate was used as a dopant source. The Li-doped ZnO NWs were prepared on sapphire substrates using a hydro-thermal synthesis. Physical properties of various Li-doped ZnO NWs were confirmed by transmission electron microscopy (TEM), temperature dependent photoluminescence (PL) measurements, and electron energy loss spectroscopy (EELS). Results of low temperature PL measurements of undoped, as-grown Li-doped, and annealed Li-doped ZnO NWs NWs display clear differences in various peaks that were associated with the donor and acceptor states in each NWs. Especially, post annealing on as-grown Li-doped Zn NWs significantly influence the thermally induced migration of interstitial Li atoms in as-grown Li doped NWs and then Li substitution of Zn. The promising electrical features of Li-doped p-type ZnO NWs after annealing reproducibly demonstrate a hole concentration of 3.36 × 107 cm-3 and a field-effect mobility of 2.52 cm2 V-2 s-1. Finally, time dependence of n-type ZnO thin film/p-type Li-doped ZnO NWs diode structure indicates stable rectification characteristics, providing strong evidence on the formation of stable p-type Li-doped ZnO NWs.
Symposium Organizers
Zhang-Lin Zhou Hewlett-Packard Labs
Clement Sanchez College de France
Michael Popall Fraunhofer ISC
Jian Pei Peking University
NN10: New Material Synthesis, Characterization and Properties
Session Chairs
Marc Drillon
Laurence Rozes
Friday AM, April 29, 2011
Salons 1-2 (Marriott)
9:00 AM - **NN10.1
Development of New Polymer Systems and Quantum Dots - Polymer Nanocomposites for Low-cost,Flexible OLED Display Applications
Lihua Zhao 1 , Zhang-Lin Zhou 1 , Zengshan Guo 2 , Jian Pei 2 , Samuel Mao 3
1 , HP Labs, Palo Alto, California, United States, 2 , Peking University, Beijing China, 3 , University of California-Berkeley, Berkeley, California, United States
Show AbstractRecently, significant progress has been made toward application of organic (small molecule/polymer) light-emitting diodes (OLEDs) in full color flat panel displays and other devices. However, current technologies for OLEDs in the market are still very limited, especially in terms of cost and flexibility. Our goal is to create the display that is light weight, flexible, thin, extremely low cost, video capable, brilliant color as well as low power consumption. We believe that plastic and roll-to-roll (R2R) manufacturing will be key enablers toward this goal. This presentation will provide a brief introduction of our R2R manufactured flexible backplane on plastic and mainly discuss our recent progress in achieving all solution processed multilayer and multicolor OLEDs pixels as well as our development of hybrid organic/inorganic quantum dot(QD)-polymer nanocomposites in order to take advantages from the both regions. Our method for fabricating multilayer OLEDs structures has shown great compatibilities with many state-of-the-arts emissive polymers/even small molecules to achieve RGB colored and white OLEDs. The research findings on hybrid QD-polymer nanocomposites system appeared promising in providing excellent color stability and device robustness.
9:30 AM - NN10.2
Mechanism of Multiple Heck Reaction.
Feng Zhou 1 , Jianwei Zheng 2 , Michael Sullivan 2 , Haibin Su 1 2
1 , Nanyang Tech. Univ., Singapore Singapore, 2 , Institute of High Performance Computing, Singapore Singapore
Show AbstractThe recent discovery of multiple Heck reactions stimulate great interests in unravelling its fundamental mechanism. The nanocomposites processed experimently are described as octavinylsilsesquioxane based compounds, which are proven to have higher performances than standard organic materials used in current OLEDs and also offer new perspectives that very promising in the research field. In this work, we have investigated the detail mechanism by ab initio approach. Particularly, the Kinetic and solvent effects are addressed, which is very desirable to guide further experimental work in this important field.
9:45 AM - NN10.3
Non-lithographic Patterning of Oxide Embedded Group IV Nanocrystals Using Sol-Gel Chemistry.
Jose Rodriguez Nunez 1 , Melanie Johnson 1 , Jonathan Veinot 1
1 Chemistry, University of Alberta, Edmonton, Alberta, Canada
Show AbstractOxide embedded Silicon and Germanium nanocrystals (OE-Si/Ge-NCs) are of great interest in the field of photonics. Bulk Silicon and Germanium are indirect bandgap semiconductors and thus exhibit low quantum efficiencies. However, at sizes below their corresponding Bohr exciton radii they become luminescent. This luminescence has been attributed to quantum confinement of carriers in the nanocrystals.Our group has demonstrated a method to obtain gram quantities of Si and Ge nanocrystals embedded in an oxide matrix using commercially available precursors. We have also demonstrated patterning of luminescent OE-Si-NCs using e-beam lithography which may be of great use in optoelectronic applications. Recently, non-lithographic patterning techniques have become very attractive because they are cost effective and straightforward. In this talk I will present a new method to pattern OE-Si/Ge-NCs using block copolymers of Polystyrene-b-Poly-4-Vinylpyridine (PS-P4VP).The basicity of the pyridine units is at the heart of this patterning technique. The P4VP block catalyzes the hydrolysis of the Si and Ge precursors acting as nanoreactors where the semiconductor nanocrystals can deposit. Nanodiscs of approximately 5-10 nm in height and 40-60 nm in diameters (as measured by AFM) can be deposited on silica, silicon, and highly ordered pyrolitic graphite. The particle-particle acing can be partly controlled by the molecular weight of the PS block. This technique also allows us to pattern silver coated germanium nanodiscs by galvanic displacement. Furthermore, this non-lithographic patterning technique can be extended to other materials that undergo sol-gel reactions.
10:00 AM - NN10.4
Functionally Graded Hybrid Layers for High-performance Polymer/Silicon Adhesion.
Taek-Soo Kim 1 2 , Marta Giachino 1 , Nisha Ananthakrishnan 3 , Shawna Liff 3 , Reinhold Dauskardt 1
1 Department of Materials Science and Engineering, Stanford University, Stanford, California, United States, 2 Department of Mechanical Engineering, KAIST, Daejeon Korea (the Republic of), 3 , Intel Corporation, Phoenix, Arizona, United States
Show AbstractAdhesion of polymer epoxy layers to passivated silicon substrates is of critical concern for a wide range of emerging technologies including coatings for medical devices, solar photovoltaic devices, MEMS technologies and the reliable packaging of microelectronic devices. In many of these applications, the interface is exposed to complex mechanical loads, temperature fluctuations and the presence of environmental species like moisture which can greatly weaken the interface adhesion. As a result, the polymer epoxy tends to fail adhesively with significantly lower fracture energy compared to the cohesive fracture energy of the epoxy layer. In the present study, we demonstrate that the introduction of a compositionally and functionally graded hybrid adhesion layer at the epoxy/silicon interface can greatly increase the adhesion energy and completely inhibits interfacial failure related to moisture-assisted debonding. The hybrid layer was produced via sol-gel chemistry from epoxy-functionalized silane, 3-glycidoxypropyltrimethoxysilane (GPTMS), and a zirconium alkoxide, tetra n-propoxyzirconium (TPOZ). Through optimization of GPTMS/TPOZ ratio, solution aging time, stirring speed, curing temperature and time, we achieved ~80 nm thick hybrid layers with optimized adhesion. The outstanding functionality was found to be related to the graded composition of the resulting hybrid glass film. During condensation of the film, the epoxysilane rich molecules migrate towards the top of the layer, and the metal alkoxide toward the passivated silicon substrate. When such graded layers are properly optimized the interface adhesion exceeds the cohesive fracture energy of the epoxy layer, even in the presence of moist environments. Failure occurs cohesively in the epoxy layers at extremely high values of fracture energy, making the resulting interfaces capable of high performance bonding under complex loading and environmental conditions.
10:15 AM - NN10.5
Photoluminescent ZnS:Cu,Br Organic-soluble Nanocrystals Synthesized Using Br as a Co-activator.
Carley Corrado 1 , Jin Zhang 1
1 Chemistry and Biochemistry, UC Santa Cruz, Santa Cruz, California, United States
Show AbstractPhotoluminescent Cu-doped ZnS (ZnS:Cu) organic soluble nanocrystals (NCs) were synthesized via hot-injection method. The method employed to incorporate Cu into the ZnS lattice was through addition of a co-activator halide ion to co-dope the NCs. Tetraoctylammonium bromide was employed as the source of Br- ions. Using a halide co-activator has been done in the case of synthesizing aqueous-soluble ZnS:Cu NCs, but this is the first time it has been reported in an organic system. Organic soluble ZnS:Cu NCs are of special interest for their potential application in fabrication of electroluminescent devices. Optical characterization of the NCs was performed and comparison was made between pure ZnS, ZnS:Cu,Br, ZnS:Cu and ZnS:Br. Pure ZnS NCs exhibited near band-edge emission at 350nm. ZnS NCs with Cu (but no Br-) emitted in the same 350nm region with a lower PL emission intensity, they exhibited no signs of doping. ZnS:Br emitted in the range of 450-470nm, with very low intensity. The ZnS:Cu, Br NCs doped in a range of 0.1-1% Cu emitted in the same PL range, but with an increased intensity of emission ~5×. Extended X-Ray Absorbance Fine Structure (EXAFS) structural characterization of the ZnS:Cu NCs was performed and a change in the structure around the Cu-dopant with different concentrations of Cu was observed. The proposed structure of the Cu-doped ZnS and PL emission mechanism will be discussed.
10:30 AM - NN10.6
Nanoscale Thermal and Electrical Transport within Metal-organic Composites.
Samanthule Nola 1 , Yansha Jin 2 , Max Shtein 2 1 , Kevin Pipe 3
1 Macromolecular Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 3 Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractNanostructuring of materials potentially allows precise control over thermal and electrical transport, with the possibility of independently varying thermal and electrical conductivity, as well as other properties. Here we examine the effect of increasing metal nanoparticle concentration in an organic semiconductor. Specifically, we find that in films consisting of co-evaporated silver and copper phthalocyanine (CuPC, an archetypal organic photovoltaic material), electrical transport has a percolation-type behavior, with onset ca. 25 vol% silver. We attribute this to the aggregation of silver into nanoparticles during the deposition process, and the onset of particle-particle contact, forming percolating conduction paths at higher concentrations of silver. We also find that below the percolation threshold, there is a regime where electrical conductivity increases with silver content, but thermal conductivity decreases. We attribute this effect to scattering of propagating phonons in the CuPC matrix by silver particles, while electrical conduction is enhanced by silver acting as a dopant. These findings advance our understanding of organic-inorganic nano-composites and potential paths for controlling their thermoelectric behavior.
10:45 AM - NN10.7
Aligned Carbon Nanotubes Embedded in Polymer as Elastic Conductors.
Yingying Zhang 1 , Quanxi Jia 1
1 , Los Alamos National lab, Los Alamos, New Mexico, United States
Show AbstractStretchable electronics enable new applications in a wide range of fields. Carbon nanotube (CNT) ribbons, composed of bundles of aligned millimeter-long CNTs, represent a unique opportunity for high performance stretchable conductors. In this work, we embedded CNT ribbons in elastic poly(dimethylsiloxane) (PDMS) film (or CNT/PDMS films) and systematically investigated the dependence of film resistance on the tensile strains. A stable resistance with application of strain was achieved after the first several stretching/releasing cycles. The CNT/PDMS films fabricated by this approach are flexible, transparent, and show constant resistance under strains in the range of 0%-100%.
11:00 AM - NN10: NM
BREAK
11:30 AM - NN10.8
Surface Plasmons-molecules Hybridization: Toward New Materials.
Adi Salomon 1 , Genet Cyriaque 2 , Thomas Ebbesen 2
1 Chemical Physics, weizmann Institute of Science, Rehovot Israel, 2 , ISIS, Université de Strasbourg, Strasbourg France
Show AbstractWe show that molecular excited states can undergo strong coupling with surface plasmon modes of a sub-wavelength hole array. Following the strong interaction, new hybrid states with a Rabi splitting of about 0.3 eV are formed. These hybrid states are different from the original uncoupled modes in their energy levels, dispersion and dynamics. We show that the nature of the coupling and its strength are dependent both on the molecular concentration and the hole array parameters such as symmetry and periodicity. Such hybrid materials might be useful for optical device engineering.
11:45 AM - NN10.9
Oriented Crystal Growth and Multiple Local Infiltration of Organic Fluorescence/NLO Dyes in Dynamic Photonic Crystals.
Markus Geuss 1 , Brian Makowski 1 3 , Peter Nolte 2 , Daniel Pergande 2 , Stefan Schweizer 2 , Roland Salzer 8 , Patrick Mack 5 6 , Daniel Hermann 6 , Brent Vale 4 , Christoph Weder 1 3 , Ralf Wehrspohn 2 8 , Kurt Busch 6 , Kenneth Singer 4 , Martin Steinhart 7
1 Adolphe Merkle Institute, University of Fribourg, Marly Switzerland, 3 Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, Ohio, United States, 2 Institute of Physics, Martin-Luther-Univesity Halle-Wittenberg, Halle (Saale) Germany, 8 , Fraunhofer Institute for Mechanics of Materials, Halle (Saale) Germany, 5 Institut für Nanotechnologie, Karlsruhe Institute of Technology, Karlsruhe Germany, 6 Institut für Theoretische Festkörperphysik and DFG-Center for Functional Nanostructures (CFN), Karlsruhe Institute of Technology, Karlsruhe Germany, 4 Department of Physics, Case Western Reserve University, Cleveland, Ohio, United States, 7 Institute for Chemistry, University of Osnabrueck, Osnabrück Germany
Show AbstractIn recent years, photonic crystals (PhC) based on periodic porous silicon structures attracted significant interest driven by the demand for versatile and high-speed optical devices. A rather little explored approach to create a fast switching complete dynamic photonic band gap is the consecutive infiltration of patterns of individual pores in a 2-dimensional PhC with different nonlinear optical (NLO) materials. In the first part of this contribution we present a versatile technique that allows the infiltration of individual pores of silicon PhCs with optical tuneable organic materials such as low-molecular-weight dyes, liquid crystals or polymers. The method relies on direct writing lithography by a focused ion beam and sequential melt infiltration of several different dyes to create patterns with NLO filled pores for manipulating the flow of light inside the PhC. However, in contrast to simple isotropic (amorphous) materials infiltrated into dynamic PhCs crystalline materials need a more precise understanding of the crystallization process in the confinement of the pores. Therefore our second part is devoted to a detailed study of the crystallization and emission behavior of NLO dyes inside the pores of a PhC as a first step towards an understanding of the impact of crystallization conditions on the optical properties of this new class of optical devices. We present a simple and fast routine to form highly crystalline fluorescence/NLO dyes inside the pores. A complementary approach of X-ray texture analysis and fluorescence microscopy revealed that oriented crystal growth takes not only place in the confinement of small pores diameters <200 nm diameter as reported by others, but is already accessible at pore diameters in the micrometer range of macroporous silicon. As demonstrated by numerical simulations, this new approach to create dynamic PhCs may pave the way to the fabrication of a new class of devices, e.g., optical switches or multiplexers
12:00 PM - NN10.10
From Colloidal Nanocrystals to Functional Inorganic Nanocomposite Films.
Anna Llordes 1 , Ravisubhash Tangirala 1 , Raffaella Buonsanti 1 , Guillermo Garcia 1 , Brett Helms 1 , Angang Dong 1 , Delia Milliron 1
1 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractChemical conversion of hybrid organic-inorganic nanocrystal superlattices towards hybrid inorganic-inorganic nanomaterials appears as a very promising pathway to prepare novel functional inorganic nanocomposite films. The separate synthesis and processing of the nanocrystal and matrix phases enables compositional modularity, while allowing retention of the original superlattice assembly. Here, we report a novel solution-based method for preparing inorganic nanocomposite films, by the post-assembly displacement of organic ligands in nanocrystal superlattices via either chalcogenidometallate (ChaMs) or polyoxometallate clusters (POMs). In particular, we will focus on the chemical and structural conversion of the original organic-inorganic superlattice assembly to the final inorganic-inorganic nanostructured coating. Vibrational spectroscopy and electron microscopy as well as small and wide angle X-ray scattering techniques have been used to study the conversion pathway and its relationship to the final structure of the nanocomposites. The structural and morphological control at the nanoscale level will be also discussed and related to the synthetic procedure. This general methodology can be applied to reach a wide range of compositions and so, we have prepared nanocomposites of interest for photovoltaic, data storage, and electrochromic window applications. Here, we include new results on conversion of organic-metal oxide nanocrystals for application to electrochromic windows.
12:15 PM - NN10.11
Density Control of ZnO Nanorod Arrays on Mixed Self-assembled Monolayers.
Sungyoung Yun 1 , Xavier Bulliard 1 , Soo-Ghang Ihn 1 , Yeong Suk Choi 1 , Yungi Kim 1 , Dukhyun Choi 1 , Jae-Young Choi 1 , Woong Choi 1
1 , Samsung Advanced Institute of Technology, Yongin-si Korea (the Republic of)
Show AbstractThere has been great interest in ZnO nanostructures, such as nanorod arrays, because of their potential applications in energy conversion, optoelectronics, gas sensors and biomedical devices. For device applications, one of the most important characteristics to be controlled is the lateral density of ZnO nanorod arrays, since it can impact device performance such as field emission or cell adhesion. But, the development of a straightforward method for the systematic and accurate control of the nanorod density over a wide range remains a challenge. In this study, we controlled the density of ZnO nanorod arrays by using mixed self assembled monolayers (SAMs) composed of molecules with hydrophobic methyl end groups and hydrophilic amine end groups. As the molar ratio of amine groups in the mixed SAMs increased, the density of ZnO nanorods increased from 0 to 6X10^10 cm-2. For the given molar ratio of the amine end group, surface energy changed from 31 mN/m to 64 mN/m. While the dispersive component of surface energy showed weak correlation with the amine concentration, the polar component increased from less than 1 mN/m to 20 mN/m. This indicates that the reactive amine molecules induce the change of the nanorod density in our experimental system. These results suggest easier and finer way to control the density of ZnO nanorod density. Furthermore, the use of mixed SAMs can be applied to various substrates.
12:30 PM - NN10.12
Silicon Surface Functionalization and Dopant Concentration Dependencies of Conductive Polymer (PEDOT) Electrical Contacts on P- and N-Si Microwire Arrays.
Michael Walter 1 , Xueliang Liu 1 , Leslie O'Leary 1 , Nathan Lewis 1
1 Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, United States
Show AbstractThe interfacial electronic properties of poly(3,4-ethylenedioxythiophene) (PEDOT) on planar and microwire array silicon substrates were measured. The conductive polymer film was deposited on Si electrodes using either a solution processable (PEDOT:PSS) spin-coating method or through the photoelectropolymerization of ethylenedioxythiophene (EDOT) onto the surface. The conductive polymer contact was found to be sensitive to the surface functionalization (CH3-terminated or H-terminated) and to the conductivity/doping of both the silicon substrate and conductive PEDOT material. Highly conductive PEDOT exhibited ohmic contact between p-Si and n+Si substrates. Rectifying junctions were obtained with PEDOT on n-Si substrates with larger potential barrier heights observed for methylated n-Si samples. The versatility of using PEDOT to contact degenerately doped n+-Si electrodes is demonstrated showing ideal transparent metallic contacts for a p-n junction solar cell. The controllability of these organic/inorganic junctions leading to rectifying and ohmic contacts is also demonstrated on p- and n- Si microwire arrays. PEDOT/Si hybrid contacts can serve as the active photovoltaic junction or the connection between active layers in multi-junction devices, making conductive polymers such as PEDOT a viable material for solar energy conversion applications.
NN11: Mixed Applications of Hybrid Materials
Session Chairs
Eric Verploegen
Zhang-Lin Zhou
Friday PM, April 29, 2011
Salons 1-2 (Marriott)
2:30 PM - NN11.1
Neutron Reflectivity Studies of Organic Field Effect Transistors for Underwater Sensing Applications.
Eric Verploegen 1 2 , Anatoliy Sokolov 2 , Zhenan Bao 1 , Michael Toney 2
1 Chemical Engineering, Stanford University, Stanford, California, United States, 2 Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California, United States
Show AbstractOwing to their compatibility with flexible materials and simple fabrication methods, organic thin-film transistors (OTFTs) are particularly well suited for low-cost chemical and biological sensors. Additionally, the synthetic versatility of organic materials provides endless routes to impart functionality for specifically targeted chemical interactions. The transistors used in this study consist of a poly-4-vinylphenol (PVP) dielectric layer, and an organic semiconductor 5,5′-bis-(7-dodecyl-9H-fluoren-2-yl)-2,2′-bithiophene (DDFTTF) as the semiconducting layer. The OFET device properties are altered when submerged in an aqueous environment, but still exhibit stable transistor performance. Upon the introduction of specific analytes of interest the transistor performance is further altered. By measuring the device performance, i.e. charge carrier mobility, as a function of analyte concentration these devices can be used as underwater chemical sensors. Currently, there is an incomplete knowledge of how the device morphology and in turn the device properties are affected by the presence of the analyte. We are use neutron reflectivity to investigate the swelling of the polymer dielectric and the organic semiconductor layers in order to gain a deeper understanding of how the microstructure of these devices is affected by the aqueous analyte solution. Neuron reflectivity allows for the in-situ characterization of the thin film layers in the semiconductor device while submerged in the aqueous analyte solution. Through these experiments we observe ~ 8% increase in thickness upon exposure to H¬2O. Upon the addition of MeOH the polymer films an additional 4% swelling of the dielectric was observed. These results are corroborated with capacitance measurements of the polymer dielectric. A capacitance increase was observed when the polymer dielectric was submerged in H2O. An additional increase in the capacitance occurred when MeOH was added to the aqueous sample environment. Much of the previous work in this field has focused on the interactions of the analyte with the semiconducting layer. These results indicate that when designing an OFET device for use as a chemical sensor, the interactions of the aqueous analyte solution with the semiconducting layer AND the dielectric layer must be considered.
2:45 PM - NN11.2
An Evaluation of Doping Efficiencies of Metal Oxides for Organic Charge Transporters.
Yiu Him Chan 1 , Shu Kong So 1
1 Department of Physics, Hong Kong Baptist University, Kowloon Tong Hong Kong
Show AbstractOrganic thin-film transistor (OTFT) technique was used to investigate the effects of dopants on N’-diphenyl-N,N’-bis(1-naphthyl)(1,1’-biphenyl)-4,4’diamine (NPB) and other hole transporters. Different transition metal oxides (TMOs) including molybdenum oxide (MoO3), vanadium oxide (V2O5), tungsten oxide (WO3) were employed as dopants. Using temperature dependent OTFT measurements, important parameters such as carrier mobility, carrier concentration, activation for carrier generation, and the energetic disorder of the doping system can be extracted by TFT technique alone. Generally, all TMOs form p-dopants and the conductivities increase drastically after doping. Among the TMOs, MoO3 appears to be the most effective p-type dopant. It generates the largest free carrier concentration (1.4x1017cm-3) and has the least activation energy (~134meV) for a modest doping concentration of ~5%. Detailed carrier transport analysis indicates that, the carrier mobilities were slightly reduced. It appears that the increase of free carrier concentration is the deciding factor in the conductivity enhancement in TMO-doped NPB.
3:00 PM - NN11.3
High Electron Mobility and Photoconductivity in CdSe and CdSe/CdS Nanocrystal Arrays Bridged with Molecular Metal Chalcogenide Ligands.
JongSoo Lee 1 , Maksym V Kovalenko 1 , Jing Huang 1 , Daesung Chung 1 , Dmitri V Talapin 1
1 Chemistry, The University of Chicago, Chicago, Illinois, United States
Show AbstractColloidal nanocrystals (NCs) with precisely controlled composition, size and shape can be used as the building blocks for electronic and optoelectronic devices. Stable NC colloids are naturally suitable for solution-based fabrication of large area devices using spin coating, dip coating or inkjet printing. Here we show that colloidal solutions of semiconductor NCs capped with molecular metal chalcogenide complexes (MCCs) can provide a useful pathway toward low-temperature fabrication of thin film semiconductors with high electron mobility and photoconductivity. The arrays of 3.9-nm CdSe NCs with In2Se42- surface ligands showed electron mobility higher than 15 cm2V-1s-1, while preserving tunable electronic structure of quantum-confined semiconductors. This methodology can be extended to different NCs (e.g., to CdSe/CdS core-shells) and different inorganic surface ligands (e.g., Sn2Se64-). High carrier mobility, combined with size-tunable direct-gap electronic structure, makes MCC-capped NCs very attractive for photodetector applications. As an example, the arrays of In2Se42--capped CdSe/CdS core-shell NCs were used to fabricate photoconductive detectors with the depectivity (D*) exceeding 1013 Jones and millisecond response time.
3:15 PM - NN11.4
Organic Complementary Circuits with Floating-gate Structure.
Tomoyuki Yokota 1 , Tsuyoshi Sekitani 1 , Takashi Nakagawa 1 , Yoshiaki Noguchi 1 , Ken Takeuchi 1 , Ute Zschieschang 2 , Hagen Klauk 2 , Takao Someya 1 3
1 Electric and Electronic Engineering, The University of Tokyo, Tokyo Japan, 2 , Max Planck Institute for Solid State Research, Stuttgart Germany, 3 Institute for Nano Quantum Information Electronics, The University of Tokyo, Tokyo Japan
Show AbstractWe have demonstrated threshold voltage control of organic complementary inverter circuits with a floating gate structure and self-assembled monolayer (SAM) gate dielectrics. Each threshold voltage of p-type and n-type organic transistors can be systematically controlled with charging a floating gate because the charge in the floating gate changes the electric field between the control gate and semiconductor. Utilizing the floating-gate structure, we fabricated an organic complementary 5-stage ring oscillator and succeeded in control its oscillations by changing the floating gate charge.
These inverters were fabricated by vacuum evaporation and solution processes. First, 30-nm-thick Al layer were thermally evaporated through a shadow mask as Control gate. Second, we formed control gate dielectric layers. Then 30-nm-thick Al layer were evaporated on the control gate dielectric layers and formed floating gate dielectric layers. The control and floating gate dielectric layers consisted of thin layers of aluminum oxide and molecular SAMs (n-octadecylphosphonic acid) [1, 2]. A thin aluminum oxide layers with a large density of hydroxyl groups for molecular adsorption were formed by oxygen-plasma treatment (300W 30 min) and a SAM layers were prepared from a 2-propanol solution at room temperature. Purified pentacene or hexadecafluorocopperphthalocyanine (F16CuPc) was deposited in vacuum through a shadow mask to form a 50-nm-thick as p- or n-type organic semiconductors on the floating gate dielectric layer, respectively. A 50-nm-thick Au layer was evaporated through a shadow mask to form the source and drain electrodes.
The threshold voltages of the p- and n-type transistors are shifted independently and systematically from +2.4 to –1 V and from –0.3 to +1.5 V, respectively, after applying –6 V and +6 V, respectively to the control gate electrode of the p-type and n-type transistor. Using these transistors, we have succeeded in controlling the threshold voltage of organic complementary inverter circuits.
This work is partially supported by Special Coordination Funds for Promoting, JST/CREST and KAKENHI (Wakate S). One of the authors (T.Y.) is grateful to the research fellowships for young scientists of JSPS.
[1] H. Klauk, U. Zschieschang, J. Pflaum and M. Halik, Nature 445, 745 (2007).[2] T. Sekitani, T. Yokota, U. Zschineschang, H. Klauk, S. Bauer, K. Takeuchi, M. Takamiya, T. Sakurai, and T. Someya, Science. 326, 11 (2009). 3:30 PM - NN11.5
Towards a Room Temperature Organic Spin Valve : Structural, Magnetic and Transport Properties of Fe3O4/PTCTE/Co Devices.
Mathieu Palosse 1 4 , Elena Bedel-Pereira 1 4 , Isabelle Seguy 1 4 , Christina Villeneuve 1 4 , Thomas Blon 3 4 , Christophe Gatel 2 4 , Benedicte Warot-Fonrose 2 4 , Jean-Francois Bobo 2 4 5
1 , LAAS-CNRS, Toulouse France, 4 , Université de Toulouse, UPS, INSA, INP, ISAE; LAAS; CEMES, Toulouse France, 3 , LPCNO-INSA, Toulouse France, 2 , CEMES-CNRS, Toulouse France, 5 GLAM - MSE, Stanford University, Stanford, California, United States
Show AbstractOrganic semiconductors currently attract considerable interest due to their use in electronic and optoelectronic devices such as organic light emitting diodes (OLEDs), organic field effect transistors (OFETs) and organic solar cells. Recently an entirely new route, which explores the use of the electron spin degree of freedom in organic materials, has been opened [1, 2]. Organic semiconductors have appealing characteristics that make them suitable for spin transport media, such as long spin relaxation times in these molecules and the advantage of simple device fabrication techniques.Organic Spin valves (OSV) are multilayer devices composed of two ferromagnetic (FM) electrodes separated by an organic semiconductor spacer layer. Most studies of spin injection in organic semiconductors focus on hybrid junctions with La0.67Sr0.33MnO3 (LSMO) as bottom electrode because of its nearly 100% spin polarization at low temperature. However LSMO electrodes do not allow efficient spin injection at room temperature since this material presents a low Curie temperature (TC) of about 300 K. In order to overcome this drawback, organic spin valves with high TC magnetic contacts (NiFe and Co) have been prepared but only very small MR has been observed at 10 K showing that the spin injection efficiency is very low [3]. Magnetite (Fe3O4) has a nearly 100% spin polarization, high TC (850 K) and offers a good resistance to air exposure, which makes it a good candidate for organic spintronics applications.This paper describes first steps in preparation of a spin valve device based on a perylene derivative (PTCTE: tetraethyl perylene 3,4,9,10 tetracarboxylate) sandwiched between magnetite and cobalt ferromagnetic electrodes. Fe3O4/PTCTE (300 nm)/Co devices were prepared by dc and rf sputtering respectively for the Co and Fe3O4 electrodes and vacuum sublimation for the organic layer. First, magnetic properties of the Fe3O4 and Co electrodes versus temperature were investigated by magneto-optical Kerr effect (MOKE) technique and Vibrating Sample Magnetometer (VSM). VSM studies of the Fe3O4/PTCTE/Co stacks evidence spin-valve behaviour with magnetically uncoupled electrodes down to 20 nm PTCTE. For thinner organic layers, loss of SV behaviour is due to coupling through pinholes or intermixing and degradation of the organic spacer. These results were correlated with a morphological study by atomic force microscopy (AFM) of each layer, tunnelling AFM for the investigation of inhomogeneity of current distribution in the stacks, electron microscopy and electron energy loss imaging for interface chemical profiling. Finally, current-voltage characteristics of the devices will be presented and compared with previous results obtained with NiFe/PTCTE/Co structures. References [1] V. Dediu et al, Solid State Com., 122, 181 (2002)[2] Z.H. Xiong et al, Nature, 427, 821 (2004)[3] J. F. Bobo et al, IEEE transmag, 46, 2090 (2010)
3:45 PM - NN11.6
Large Area Self-assembly of Ferrimagnetic Nanoparticle Composites on Lithographically Defined Substrates.
Qiu Dai 1 , Alshakim Nelson 1
1 , IBM Almaden Research Center, San Jose, California, United States
Show AbstractFerro- and ferrimagnetic nanocrystals generate considerable interest by virtue of their potential application in ultrahigh density magnetic recording media. We have successfully synthesized 18 nm cobalt ferrite (CoFe2O4) nanocrystals which are ferrimagnetic at 298 K (Hc = 1000 Oe, saturation magnetization = 80 emu/g). The particles are readily stabilized by the block copolymer, polyacrylic acid-b-polystyrene (PAA-b-PS), which minimizes the magnetic dipolar coupling interactions between the nanocrystals. The PAA block displaced the oleic acid surfactants on the particle surface to enable the diblock copolymer to provide colloidal solubility and stability in a variety of solvents. The self-assembly of these polymer-nanoparticle complexes into thin films will be presented. We observed that when these complexes are spincast onto lithographically patterned substrate, the topographical patterns can be used to guide the polymer-coated nanoparticles into well-ordered assemblies over large areas. The type of assembly formed (whether linear or circular) was dependent upon the shape of the lithographic pattern, as well as the spincasting conditions. This approach provides a facile method for a simple and fast method to form assemblies of nanoparticle-polymer complexes over a large area.
4:00 PM - NN11: Mix
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4:30 PM - NN11.7
Zinc Oxide Based Organic-inorganic Hybrid p-n Junction Using Aluminum Doped Zinc Oxide Thin Film as Transparent Conducting Electrodes.
Budhi Singh 1 , Subhasis Ghosh 1
1 SPS, SPS-JNU, Delhi, Delhi, India
Show AbstractZnO is a direct band gap (Eg=3.3eV) semiconductors and shows a great deal of interest in future green technology. As compared to other materials such as Indium Tin Oxide (ITO), ZnO is nontoxic, inexpensive, abundant, and chemically and thermally stable under plasma processes used for solar cell manufacturing. As grown ZnO is normally n-type but the difficulty of p-type doping is still remained to be solved. So, it is difficult to fabricate ZnO based p-n homo- junctions. For this reason, several hybrid p-type organic/n-type ZnO junctions have been proposed in recent years [1, 2]. Also both the ZnO and organic materials have great potential for low cost electronic devices. Hybrid devices may play a significant role also in the field of non-volatile memory (NVM) and RF-ID technology, where the requirement for high density and low cost devices motivate the research for innovative device architectures. In this abstract we present a hybrid p-n junction based on p-type zinc phthalocyanine (ZnPc) and n-type ZnO for applications where cost is prime concern such as NVM, RF – ID tags and solar cells. Aluminum doped ZnO (AZO) films on quartz substrate were grown by RF sputtering. XRD data of the AZO films show pronounced c-axis orientation resulting in strong 2θ (002) peak that corresponds to wurtzite ZnO structure. The average grain size was ~ 143 nm and the RMS surface roughness was below 1.2nm. Minimum resistivity of 2.63 x 10-4 Ω cm was observed at the 2% doping level. In order to achieve the optimal device performance, 2% AZO thin film is used as transparent conducting electrode as an alternate to ITO films. The device structure used for hybrid p-n junction was AZO (300nm)/ ZnO (200nm)/ZnPc (200nm)/Au (40nm). Current-voltage characteristics of the hybrid p-n junction structure exhibit rectifying behavior similar to that in conventional inorganic p-n junction diode. The current density of the device was as high as 0.3mA/cm2 at 2V and gives a rectification factor greater than 104. Capacitance- voltage (C-V) characteristics show that the device exhibits a strong voltage dependence of its capacitance, indicating the presence of depletion layer. The application of a forward bias reduces the width of the space charge region. When bias reaches the built in potential, Vbi, the space charge region disappears and a collapse of the capacitance is observed [3]. In the reverse bias region a plot of 1/C2 vs. bias yields a straight line. The extrapolation of this plot of is used to find the built in potential barrier, Vbi= 0.6V and the effective doping concentration is 6.12x 1014 cm-3[4].References: [1] S. Coe, W.K. Woo, M. Bawendi, and V. Bulovic, Nature (London) 420,800(2002).[2] Jong H. Na, M. Kitamura, M. Arita, and Y. Arakawa Appl. Phys. Lett. 95, 253303 (2009).[3] K. Harada, A.G. Werner, M. Pfeiffer, C.J. Bloom, C.M. Elliott, and K. Leo, Phys. Rev. Lett. 94,036601 (2005).[4] S.M. Sze, Physics of semiconductor devices, 2nd ed. (Wiley,New York, 1981).
4:45 PM - NN11.8
Optically Functional Organic-inorganic Hybrid Materials from Solvent-free Condensation Reactions.
Masahide Takahashi 1
1 Graduate School of Engeneering, Osaka Prefecture University, Sakai, Osaka, Japan
Show AbstractOrganic-inorganic hybrid materials mainly consisting of siloxane chain (silicone) are receiving much attention as highly functional materials for electronics and photonics. Most of the hybrid material presently available is based on siloxane-based materials prepared by sol-gel and related techniques. Recently, the present authors have been reporting organic-inorganic hybrid materials with alternating copolymer structures obtained through solvent-free condensation reactions using acid-base reaction and alcohol condensation.[1-3] It is possible to obtain hybrid materials in complete solventless conditions, which offers simpler route and higher yield to obtain final products than other liquid phase preparation methods. The obtained materials are characterized by their unique structrue of main oxo chains, which is oxide alternating copolymer structure such as –(O-M(1)-O-M(2))n-, M: Si, P, Ti, Zr, Sn, B, and so on. The alternating oxo chain could be modified by organic functional groups to attain advanced characteristics for specific applications. We are mainly concerning the development of optical functionalities using such new hybrid materials, and have reported several materials for low-attenuation waveguiding, thermo-optical application, re-writable holographic memories, low-threshold cavity lasers, and so on.[4-6]In this presentation, we will introduce the fundamentals of the solvent-free condensation reactions and their advanced applications in photonics.[1] M. Mizuno; M. Takahashi; Y. Tokuda; T. Yoko, Chem. Mat., 2006, 18, 2075.[2] E.S. Kang; M. Takahashi; Y. Tokuda; T. Yoko, J. Mater. Res., 2006, 21, 1286.[3] M. Mizuno; M. Takahashi; Y. Tokuda; T. Yoko, J. Sol-Gel Sci. Technol., 2007, 44, 47.[4] E.S. Kang; M. Takahashi; Y. Tokuda; T. Yoko, Appl. Phys. Lett., 2006, 89, 131916[5] H. Takashima; H. Fujiwara; S. Takeuchi; K. Sasaki; M. Takahashi, Appl. Phys. Lett., 2007, 90, 10113.[6] H. Kakiuchida; M. Takahashi; Y. Tokuda; T. Yoko, Adv. Func. Mater., in press.
5:00 PM - NN11.10
Silicon Nanoparticles Stabilized with Organic Molecules: Building Blocks for Printable Electronics.
Juergen Nelles 1 , Ulrich Simon 1
1 Institute of Inorganic Chemistry, RWTH Aachen University, Aachen, NRW, Germany
Show AbstractGrowing interest in silicon nanoparticles (SiNPs) has evolved during the last years, as they may have many potential applications, e.g. in bioimaging or optoelectronic devices. Our research focuses on the applicability of SiNPs as basic components in printing inks for the fabrication of printable electronic devices. For this purpose, we first conducted a bottom-up liquid phase synthesis of SiNPs in the size range of 1,2 nm up to 6 nm with narrow size distribution as well as their chemical surface stabilization by hydrosilylation or silanization, respectively, in order to prevent the SiNPs from oxygenation due to oxygen or humidity from the ambience. Based on this, we systematically varied the chemical composition of the organic stabilizing molecules, which serve as electrically transparent barriers between the particles in compact layers. These layers were deposited on interdigital electrodes and studied by means of impedance spectroscopy over a wide temperature and frequency range.In this study we compared as-prepared SiNPs as well as freshly etched ones formed in a gas phase process, both terminated with hydrogen, with silicon nanoparticles stabilized using a hydrosilylation procedure with 1-hexene, 1-octene, 1-dodecene, allylamine, allylmercaptan and 4-pentenoic acid, respectively. The charge transport through the nanoparticle films was found to be thermally activated and thus can be described according to classical electron hopping transport models. It is demonstrated that the activation energy of the electron transport scales with the thickness and permittivity of the respective organic molecules. Hence, structure-property relations as well as design rules for desired conducting properties can be derived. Furthermore first devices have been fabricated using a field effect transistor configuration, so that first steps towards printable electronics could be realized based on SiNPs.