Vladimir Bulovic Massachusetts Institute of Technology
Seth Coe-Sullivan QD Vision, Inc.
Peter Peumans Stanford University
O1: Photovoltaics and Sensors
Tuesday PM, April 18, 2006
Room 3005 (Moscone West)
9:00 AM - O1.1
New Nano-Composite Materials for Radiation Detection.
Sonia Letant 1 , Tzu-Fang Wang 1 Show Abstract
1 Chemistry and Materials Science, LLNL, Livermore, California, United States
We will demonstrate that nano-composite materials based on semiconductor quantum dots have great potential for radiation detection via scintillation. While quantum dots and laser dyes both emit in the visible range at room temperature, the Stokes shift of the dyes is significantly larger. The scintillation output of both systems was studied under alpha radiation and interpreted using a combination of energy-loss and photon transport Monte Carlo simulation models. The comparison of the two systems, which allows the quantification of the role played by the Stokes shift in the scintillation output, opens up exciting possibilities for a new class of scintillators that would take advantage of the limitless assembly of nano-crystals in large, transparent, and sturdy matrices.This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.
9:15 AM - **O1.2
High Efficiency Organic Photovoltaic Cells with External Antennas.
Marc Baldo 1 , Tim Heidel 1 , Jon Mapel 1 , Kemal Celebi 1 , Madhusudan Singh 1 Show Abstract
1 , MIT, Cambridge, Massachusetts, United States
We describe an organic solar cell based on the photosynthetic model of physically separated electrical and optical photovoltaic components. Our cell consists of two parts. First, a conventional, thin-film heterostructure photovoltaic cell sandwiched between two metal contacts. And second, an external antenna deposited directly on top of the heterostructure cathode. The antenna is a thin film that absorbs light and transfers energy into the charge generating structure via surface plasmon polariton modes in the metal contacts. We present both numerical modeling of the device, and experimental results, demonstrating efficient energy transfer from the antenna to the charge generating heterostructure. By separating the electrical and optical functions of the cell, we can enhance absorption, without decreasing the internal quantum efficiency or degrading the electrical characteristics. Finally, we estimate the performance limitations of the external antenna structure.
9:45 AM - O1.3
Development of Conjugated Polymers with High Carbon Nanotube Affinities for Photovoltaic Devices.
Barry Thompson 1 , Kevin Sivula 1 2 , Jean Frechet 1 2 Show Abstract
1 Chemistry, University of California, Berkeley, Berkeley, California, United States, 2 Chemical Engineering, University of California, Berkeley, Berkeley, California, United States
We have designed a family of conjugated polymers with structural features intended to impart a high affinity for single-wall carbon nanotubes (SWNTs). The described polymers are primarily based on a polythiophene backbone as a means of producing polymers with electronic and processing characteristics similar to poly(3-hexylthiophene) (P3HT), which has proven so useful in polymer-fullerene solar cells. The specific recognition groups utilized for supramolecular interaction with the SWNTs are based on either pyrene or PmPV (poly (m-phenylenevinylene-co-2,5-dioctoxy-p-phenylenevinylene), both of which have been previously established as giving a strong non-covalent interaction with SWNTs. Random linear copolymers and graft copolymers are the focus of the work. The synthesis of PmPV and related oligomers with well-defined end-groups was realized through the Siegrist polycondensation enabling the use of a grafting-to technique with suitably functionalized polythiophene copolymers. On the other hand, the synthesis of pyrene-functionalized polythiophene copolymers was realized by direct copolymerization of 2-bromo-3-hexylthiophene and 2-bromo-3-(2-(pyren-1-yl)vinyl)thiophene. The electronic band structure of the synthesized polymers has been evaluated using electrochemical and spectroscopic techniques. The mobility of the pristine polymer samples has been compared with that of P3HT using field-effect conditions. Finally, polymers have been characterized for their interaction with SWNTs in solar cells. A morphological study has also been undertaken to elucidate the interactions of the polymers and the SWNTs and the role of these interactions in controlling film morphology and device performance.
10:00 AM - **O1.4
Polymer/nanoparticle Photovoltaic Devices.
Neil Greenham 1 Show Abstract
1 , University of Cambridge, Cambridge United Kingdom
I will describe recent progress in fabricating efficient photovoltaic devices based on blends of conjugated polymers with inorganic nanoparticles. Using CdSe tetrapods, solar power conversion efficiencies of close to 3% have been achieved by controlling the rate of solvent evaporation during spin-coating. This allows a vertical segregation of the tetrapods within the film, which assists in electron transport towards the appropriate electrode. I will also describe spectroscopic measurements of charge transfer and recombination at the nanoparticle/polymer interface.
11:00 AM - **O1.5
Nanocrystalline Semiconductor Junctions, Surface Confined Charge Transport and Interfacial Electron Transfer.
Michael Graetzel 1 Show Abstract
1 , Ecole Polytechnique de Lausanne, Lausanne Switzerland
The lecture describes electronic processes in hybrid materials comprising redox-active molecular species that are adsorbed by self-assembly at the surface of nanocrystaline oxide films. Photo-induced interfacial charge separation and cross-surface electron-or hole transfer are particularly intriguing processes, which have attracted wide spread attention. Charge propagation within the monomolecular films can be controlled by rational design of the molecular relay function. Similarly, molecular engineering of sensitizers allows photo-induced electron injection from an excited chromophore into the conduction band of the oxide nanoparticles to proceed quantitatively on a femtosecond time scale while the recapture of the charge by the oxidized sensitizer is many orders of magnitude slower. Applications of these systems in sensor, lithium ion batteries and photovoltaic devices will be demonstrated.
11:30 AM - O1.6
Solution-processed Hybrid Polymer-Quantum Dot Nanocomposite for Infrared Photodetection and Photorefractivity.
Kaushik Roy Choudhury 1 , Won Jin Kim 3 2 , Yudhisthira Sahoo 2 , Kwang-Sup Lee 3 2 , Paras Prasad 2 1 Show Abstract
1 Department of Physics, Institute for Lasers, Photonics and Biophotonics, University at Buffalo, Buffalo, New York, United States, 3 Department of Polymer Science and Engineering, Hannam University, Daejeon Korea (the Republic of), 2 Department of Chemistry, Institute for Lasers, Photonics and Biophotonics, University at Buffalo, Buffalo, New York, United States
The prospect of replacing electronic devices with faster, more efficient, more sensitive, and more reliable optical counterparts is a particularly fascinating driver for the development of new materials for optoelectronics. In this context, organic semiconductors and polymers, nanocrystal quantum dots (QDs), and their composites have attracted significant research efforts over the past two decades. The development of such multifunctional composites attributed with photoconductive and photorefractive properties with spectral response in the technologically important near-infrared wavelength range is highly desirable. We have successfully integrated high-quality solution-processible nanocrystal QDs (PbS, PbSe), active over a wide spectral range in the infrared (IR), organic molecules and polymers to fabricate efficient photoconductive and photorefractive devices operational at important optical communication wavelengths. Size tunable absorption in the semiconductor QDs enabled us to successfully sensitize the hybrid devices and tune their photoresponse in the IR. Efficient harvesting of photo-generated carriers led to high photocurrents at 1340 nm, yielding a photoconductive quantum efficiency among the highest reported to date. In the photorefractive composites, pronounced two-beam coupling effect was observed, leading to high optical gains achievable by low-power continuous-wave illumination, without the necessity of any lock-in techniques. Using colloidally-fabricated PbSe QDs, the photoresponse was further extended to 1550 nm. Dynamic holographic gratings were efficiently written in the composite leading to the first observation of net optical gain. A steady state diffraction efficiency of ~ 40% was obtained in the dynamic refractive-index gratings with appreciable response times. In order to enhance the photoconductive performance, the organic semiconducting molecule pentacene, which is of great interest for fabricating organic thin-film transistors, was successfully incorporated into the hybrid photoconducting composite. Pentacene is an excellent choice in this respect, having one of the highest reported mobilities and being environmentally stable. At the operating wavelength of 1340 nm, the photocurrent increases significantly as the amount of pentacene in the composite increases, resulting in a spectacular improvement of external quantum efficiency over previous results. Thus, a high-performance hybrid IR photodetector is successfully realized.
11:45 AM - **O1.7
Charge Transport and Electron Transfer at Organic-inorganic Interfaces in Field Effect Transistors and Photovoltaic Cells.
Michael McGehee 1 , Joseph Kline 1 , Chia Goh 1 , Bhavani Srinivasan 1 Show Abstract
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
12:15 PM - O1.8
High-Efficiency Polymer Solar Cells using Solution-Based Titanium Oxide Layer.
Kwanghee Lee 2 1 , Jin Young Kim 1 2 , Wanli Ma 1 , Alan Heeger 1 Show Abstract
2 Deaprtment of Physics, Pusan National University, Busan Korea (the Republic of), 1 Center for Polymers and Organic Solids, University of California at Santa Barbara, Santa Barbara, California, United States
We report that high efficiency polymer photovoltaic cells with ~5% power conversion efficiency under AM1.5 illumination have been achieved using titanium oxide (TiOx) as an optical spacer. Solar cells with a TiOx layer (deposited by a sol-gel process) between the active layer and the electron collecting aluminum electrode exhibit approximately 50% enhancement in power conversion efficiency compared to similar devices without the optical spacer. The TiOx layer increases the efficiency by modifying the spatial distribution of the light intensity inside the device, thereby creating more photogenerated charge carriers in the bulk heterojunction layer.
12:30 PM - **O1.9
Solution-Processed Photovoltaics Beyond 1 um Using Colloidal Quantum Dots
Edward (Ted) Sargent 1 Show Abstract
1 Electrical and Computer Engineering, University of Toronto, Toronto, Ontario, Canada
Solution-processed photovoltaics offer the attractive possibility of low cost of manufacture and deployment. Their power conversion efficiency limits their deployment to date. One contributor to low AM1.5 power conversion efficiency is polymer and organic photovoltaics' typical lack of absorbance beyond 700 nm. Half of the sun's power reaching the earth lies in the infrared. Multijunction solar cells separately and efficiently collecting blue, red, near-infrared, and short-wavelength infrared photons could lead to considerably more than a doubling in AM1.5 power conversion efficiency.Short-wavelength infrared photovoltaics are also of interest in thermophotovoltaics: the direct conversion of infrared power emitted by hot objects into electrical power.We will summarize progress towards efficient short-wavelength infrared photovoltaics, beginning with the first (very low efficiency) report [McDonald2005], subsequent progress (> 1% external quantum efficiency [Maria2005], and closing with our very latest findings.[McDonald2005]S. A. McDonald, G. Konstantatos, S. Zhang, P. W. Cyr, E. J. D. Klem, L. Levina, E. H. Sargent, "Solution-processed PbS quantum dot infrared photodetectors and photovoltaics," Nature Materials, vol. 4, no. 2, pp. 138-142, 2005.[Maria2005] Ahmed Maria, Paul W. Cyr, Ethan J. D. Klem, Larissa Levina, Edward H. Sargent, "Solution-processed infrared photovoltaics devices with >10% monochromatic internal quantum efficiency," Applied Physics Letters, vol. 87, 213112, 2005.
O2: Processes in Nanocrystal/Plasmon Enhanced Hybrids
Tuesday PM, April 18, 2006
Room 3005 (Moscone West)
2:30 PM - O2.1
Plasmonic Emission Enhancement from Metallodielectrics-Capped ZnO films.
Weihai Ni 1 , Jin An 1 , J.B. Xu 1 , H.C. Ong 1 Show Abstract
1 Physics, The Chinese University of Hong Kong, Hong Kong Hong Kong
2:45 PM - O2.2
Fabrication and Characterization of Transparent Hybrid Metal Nanoparticles/photopolymer Probes.
Olivier Soppera 1 , Abdellah Moustaghfir 1 , Daniel Lougnot 1 , Dominique Burget 1 , Lavinia Balan 1 , Renaud Bachelot 2 Show Abstract
1 Department of Photochemistry - UHA, CNRS UMR 7525, MULHOUSE France, 2 Laboratoire de Nanotechnologie et d'Instrumentation Optique - UTT, CNRS FRE 2671, Troyes France
Scanning Near Field Optical Microscopy (SNOM) has gained special interest in the last years since this technique allows to optically analyze and characterize the physico-chemical properties of surfaces with a sub-wavelength resolution. Today, several experimental techniques are used to fabricate SNOM aperture tips (by etching, micro-abrasion, electrical or thermal fusion, FIB…) but these processes suffer from a few drawbacks : high time consuming, low reproducibility and irregular shapes at the extremity. Consequently, such probes have characteristics (in terms of chemical composition and geometry) that limit not only the resolution but also the sensibility and/or the ratio signal/noise of the microscope. Today, it is still impossible to reach the theoretical resolution limit (a few nm) and the detection of the signals can hardly be achieved in the case of low-yield phenomena (Raman spectroscopy for example). A new technique to elaborate polymer microlenses at the end of optical fiber was recently developed. This process, based on photopolymerization, allows to create polymer lenses with sub-micronic diameter and with well-controlled geometry. The optical element is directly built at the end of the optical fiber, exactly aligned with the core of the fiber. Among other advantages, this process is easy to carry out and highly versatile to make tips with adjustable length and diameter.In parallel, we recently developed photopolymerizable resins that were compatible with the introduction of well-defined metallic nanoparticules (Au, Bi, …). We demonstrated that these resin were suitable to shape polymer tips doped with metal nanoparticles. The impact of the nanoparticules on the building of the hybrid probe is discussed. In addition, we analysed the spatial distribution of the nanoparticules in the polymer tip.The aim of this work is to graft a single nano-object at the very end of the optical fiber that can be used to enhance the near-field contribution of the electro-magnetic field by plasmon resonance either on illumination or collection mode. Considering the size and the geometry of the functionalized probe, the theoretical resolution is expected to go below 10 nm. Such performances would definitely demonstrate the potential of SNOM in the field of nano-optics. Applications of the nano-functionalized in the field of chemical or biological sensors are also to be expected.
3:00 PM - **O2.3
Hybrid Metal/Organic Devices - Towards Plasmolecular Electronics And Photonics.
Mark Brongersma 1 Show Abstract
1 Department of MS&E, Stanford University, Stanford, California, United States
The enormous growth of the semiconductor and communication industries has increased the demand for nanoscale electronic and photonic devices on a chip. I will discuss a number of chip-scale, hybrid metal/organic components that exhibit useful photonic and/or electronic functionality. First, I present a combined computational and near-field optics study on passive metal-optical (plasmonic) structures in which light can be manipulated at the nanoscale. I will then demonstrate how the unique properties of optically and electrically active molecules can be combined with plasmonic structures to open up a new area of research and device technologies: plasmolecular electronics and photonics. A number of devices will be discussed that are based on nanoscale metal-molecule-metal junctions in which one can control the flow of electrons based on optical signals or control the flow of light based on electronic signals. These devices enable an enhanced synergy between electronics, photonics, and plasmonics and form the basic building blocks for circuits of a more complex architecture. I will conclude by commenting on the prospects for such circuits.
3:30 PM - O2.4
Optical Characterization of CdSe Colloidal Quantum Dot/ MEH-PPV Polymer Nanocomposites Spin-cast on GaAs Substrates.
Adrienne Stiff-Roberts 1 , Abhishek Gupta 1 , Zhiya Zhao 1 Show Abstract
1 Electrical and Computer Engineering, Duke University, Durham, North Carolina, United States
Semiconductor colloidal quantum dots (CQDs) are typically used in photonic and electro-optic devices to sensitize polymers at a specific wavelength corresponding to the CQD size. Often, these nanocomposites are deposited on glass substrates in the form of sol-gel or Langmuir-Blodgett thin films. It is desirable to deposit CQD/polymer nanocomposites on semiconductor substrates for optoelectronic devices analogous to those achieved using Stranski-Krastanow quantum dots grown by epitaxy. CQD active regions should improve device performance due to: i) the ability to yield highly-uniform ensembles of nanostructures through size-filtering, and ii) the simplification of device design since quantum-sized effects are related to spherical CQDs. To date, there have been relatively few investigations of CQD thin-films deposited on GaAs or Si substrates. However, it is crucial to develop a better understanding of the optical properties of these hybrid material systems if such heterostructures are to be used for optoelectronic devices, such as infrared (IR) photodetectors. Several groups have demonstrated interband, near-IR sensitivity in CQD/polymer nanocomposites[Leatherdale,etal.,Phys.Rev.B,62,2669(2000).;McDonald,etal.,Appl.Phys.Lett.,85,2089(2004)]. The motivation and distinct approach for this work is the use of intraband transitions within CQDs for the detection of mid- and/or long-wave IR light. For this purpose, CQDs must be embedded in a potential barrier material, such as a polymer (considered theoretically by Binks [IEEEJ.Quant.Electron.,40,1140(2004)]). The CdSe CQD/MEH-PPV polymer nanocomposite material is well-suited for this application due to the ~1.5 eV difference between the corresponding electron affinities. Therefore, CdSe CQDs embedded in MEH-PPV should provide electron quantum confinement such that intraband transitions can occur in the conduction band. By depositing the CQD/polymer nanocomposite on epitaxial GaAs layers featuring various degenerate doping levels and measuring the corresponding optical properties (photoluminescence and Fourier transform IR spectroscopy), the feasibility of these intraband transitions will be demonstrated. Previously, we have demonstrated improved CQD ensemble uniformity due to the spin–cast deposition of CdSe/CdS CQD thin films on GaAs substrates, and we have demonstrated that spin-cast CQDs interact with GaAs substrates such that different doping characteristics of the substrate influence the structural and optical properties of the CQDs[Stiff-Roberts et al., EMC 2005, Santa Barbara, CA]. These results inform the current work in which the CQD/polymer nanocomposites are spin-cast on GaAs substrates.
3:45 PM - O2.5
Hot Excitation Transfer from Nanocrystals into Semiconductor Substrates
Siyuan Lu 1 , Anupam Madhukar 1 Show Abstract
1 , University of Southern California, Los Angeles, California, United States
Integration of epitaxical and colloidal semiconductor nanostructures into integrated hybrid structures can potentially open unprecedented functionalities that combine the strengths of the epitaxical nanostructure in optoelectronics with the versatility of the nanocrystal quantum dots (NCQDs) and their application in solution environment. Historically, the excitation transfer from adsorbed molecules into semiconductor substrate has been a well studied subject. The NCQDs, as artificial molecules, offer the opportunity to freely manipulate, through their size, composition, and surface functionalization, their energy levels and energy barriers to the energies in an underlining substrate. This opens the possibility of tailoring excitation (charge, energy) transfer between the NCQDs and the substrate of choice. Here we report on studies of optical response of InAs/ZnSe core-shell NCQDs functionalized with TOP (trioctylphosphine) molecules adsorbed in submonolayer coverages on GaAs (001) substrates. A principal finding is the evidence for excitation transfer out of directly excited NCQDs at a rate faster than the intra-dot relaxation to the ground state. This is indicated by the quenching of NCQDs luminescence when the excitation energy goes beyond a critical value just below GaAs bandgap. We present systematic studies of the photoluminescence excitation (PLE) behavior as a function of the temperature. The observed behavior substantiates the "hot" excitation transfer and provides some insights into potential mechanisms of such excitation transfer. The observation of “hot” excitation transfer from NCQDs to states arising from the presence of the interface, demonstrated for the first time, may have significant technological impact on the application of NCQDs in novel integrated hybrid nanostructures. This work is supported by DARPA/AFOSR under the DURINT program.
4:30 PM - **O2.6
Fowler-Nordheim Tunneling from Metallic Nanoparticles in a Semiconducting Host.
Campbell Scott 1 , Luisa Bozano 1 Show Abstract
1 , IBM Almaden Research Center, San Jose, California, United States
Several of the candidates for new nonvolatile memory elements are based on nanoparticles (NPs) blended into a polymeric host. It has been suggested [Bozano et al, J. Appl. Phys. 2004] that the NPs serve as charge traps. When the trapped charge density is high, the resulting space-charge field inhibits current flow. In another proposed mechanism [Ouyang et al, Nature Materials, 2004] the NPs act as donors to the charge transport acceptor species doped into the polymer. Distinguishing between these and other possible mechanisms will depend on quantitative analysis of transport and switching behavior. Here we address the field dependent rates of charging and discharging, extending Fowler-Nordheim theory to include the effect of charge conservation and the charge remaining on the NP. Taking into account the energy levels of NP and host, the polarization of the NP, its charge state and the image charge acting on the released electron, the rate of charge release (detrapping or ionization) is calculated. The range of rates is exponentially large: for example, for typical barrier heights, the detrapping rate from a singly charged NP in zero field varies from ~1E11 s^-1 at 1 nm diameter to less than 1E-9 s^-1 at 2 nm. The trapping rate depends on radius, and is strongly affected by the charge state of the NP and its neighbors. Several of the predictions of these calculation are testable by experiment.
5:00 PM - O2.7
Influence of the Surface Charge of Semiconductor Nanocrystals on Polyelectrolyte Multilayers.
Vamsi Komarala 1 , yury Rakovich 1 , Louise Bradley 1 , John Donegan 1 , Stephen Byrne 2 , Yury Gunko 2 Show Abstract
1 Physics, Trinity College Dublin, Dublin Ireland, 2 chemistry, Trinity College Dublin, Dublin Ireland
5:15 PM - **O2.8
Charge Transport and Excited State Dynamics in Polymer/Nanoparticle Blends
Sue Carter 1 , Stephanie Chasteen 1 , Veronica Sholin 1 , Daniel Simon 1 , Mike Griffo 1 , J. Campbell Scott 2 , Luisa Bozano 2 , Garry Rumbles 3 Show Abstract
1 Physics, University of California, Scotts Valley, California, United States, 2 , IBM Almaden Research Center, San Jose, California, United States, 3 , National Renewable Energy Laboratories, Golden, Colorado, United States
The blending of nanoparticles into a semiconducting polymer can lead to dramatic improvements in organic device performance through interesting modifications to both the polymer’s excited state dynamics as well as its charge transport. In the simplistic picture, nanoparticles quench the excited state exciton of the polymer and reduce the polymer’s carrier mobility by inducing charge traps; however, the introduction of nanoparticles can also increase the photoluminescence efficiency and greatly improve charge transport in the polymer. For example, we have shown that the addition of dielectric nanoparticles into an electroluminescent polymer, such as MEHPPV, can result in a large increase in the effective electric field across the devices and subsequently large increases in an OLED’s power efficiency. Furthermore, the addition of nanoparticles into photoconductive polymers can increase, as well as decrease, the photoluminescence efficiency and excited state decay in addition to modifying the polymer’s carrier mobility. In this talk, I will review the current theories and experimental results that describe the role of nanoparticles in modifying the electrical and optical properties of semiconducting polymers in the context of both OLED and photovoltaic devices. I will compare steady state and time resolved photoluminescence data with current-voltage characteristics taken on the same working device to elucidate the role that these effects ultimately have on device performance. I will also discuss our quasi-1D model that provides an adequate steady-state description of exciton generation and recombination as well as charge transport is polymer/nanoparticle blends. An interesting extension of these results is the study of blends of polymers with metallic nanoparticles, where competing effects, such as exciton quenching/charge trapping and surface enhanced fluorescence, occur. I will conclude by discussing our most recent results on understanding how metallic nanoparticles affect the charge dynamics in semiconducting polymers, focusing on the bistable memory effect and its role in polymer OLEDs and PVs.
5:45 PM - O2.9
Charge Transfer Between Semiconductor Quantum Dots and a Pi Conjugated Organic Polymer.
Don Selmarten 1 , Marcus Jones 1 , Garry Rumbles 1 , Pinrong Yu 1 , Jovan Nedeljkovic 1 , Sean Shaheen 2 Show Abstract
1 Center for Basic Science, National Renewable Energy Laboratory, Golden, Colorado, United States, 2 Center for Photovoltaics, National Renewable Energy Laboratory, Golden, Colorado, United States
O3: Poster Session: Hybrid Materials and Devices
Wednesday AM, April 19, 2006
Salons 8-15 (Marriott)
9:00 PM - O3.1
The Explanation of Interfacial Property in Liquid Lens with Multilayer System : Molecular View.
Jihye Shim 1 , Sung Soo Park 1 , JongYun Kim 1 , Hayong Jung 2 , JaeYoung Bae 2 Show Abstract
1 Central R&D Institute, Samsung Electro-Mechanics Co.,Ltd., Suwon Korea (the Republic of), 2 Opto-System Division, Samsung Electro-Mechanics Co.,Ltd., Suwon Korea (the Republic of)
Recently, micro optical systems employing electrowetting (liquid lens) have been focused on due to their small size and high dynamic tunability. Many works concentrated on the viability of these systems to microlens within the framework of mechanical and optical issues such as device structure, focal length, and dioptric power. However, there have been little research about the qualification of liquid which satisfies environmental conditions for electric device. As noted by Kuiper and Hendriks, the environmental condition for electric application is severe, so that a camera importing liquid lens should operate between -30 and +70 celcius degree. At low temperature, the freezing problem of liquid can be solved using a highly concentrated salt solution or an antifreezing solution. On the other hand, as the temperature increases, immiscible liquid materials at room temperature can blend, react among themselves, and produce an unexpected by-product. Nevertheless, the physical and chemical properties of liquid depending on the temperature have not been seriously considered in this area.We have investigated the change of the interface between conducting and non-conducting liquid layers as the temperature increases by using empirical molecular dynamics simulation and density-functional theory calculation. The stability of the liquid layers at high temperature was evaluated by simulation results such as the density profile of liquid components, their distribution near the interface, the interface width and chemical reactivity between them, which depends on the molecular species consisting of liquid and its concentration. We found that the organic solvent including halogen atoms, alkyl halide, easily penetrates into conducting liquid layer and reacts with its substances, which is added to increase a refractive index and density of non-conducting liquid. We also presented an optimized solution including the minimum organic solvent and satisfying the requisites for an optical device.  M. W. J. Prins, W. J. J. Welters, J. W. Weekamp, Science 291, 277 (2001). S. Kuiper and B. H. W. Hendriks, App. Phys. Lett. 85, 1128 (2004).
9:00 PM - O3.11
Preparation and Use of Modified Self-Assembled Thin Films for Detection of Bacillus anthracis Protective Antigen.
Aaron Anderson 1 , Andrew Dattelbaum 3 , Jennifer Martinez 3 , Jurgen Schmidt 2 , Basil Swanson 1 Show Abstract
1 C-PCS, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 MST-CINT, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 B-3, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Previously, our team developed assays for detecting cholera toxin and B. anthracis protective antigen using phospholipid bilayer membranes supported on a silica-coated waveguide detection platform. Lipid bilayer membranes offered excellent resistance to non-specific absorption for these assays. However, lipid membranes are not robust and do not endure either prolonged storage or use under harsh conditions. To overcome these limitations, we have developed a new self-assembly process to afford a polyethylene glycol (PEG) surface terminated with a fraction of biotin moieties that can be used in a variety of binding assays. In this presentation, we will describe the preparation and characterization of the PEG coatings on oxide surfaces, as well as their effectiveness in detection assays. These results will be compared to our previously developed assays using the lipid membrane systems. In particular, we will address issues of stability and non-specific absorption of biomolecules that make our newly prepared functionalized PEG surfaces advantageous for the detection of disease markers and pathogens.
9:00 PM - O3.12
Photo-Patternable Epoxy-Oligosiloxane Hybrid Materials (Epoxy Hybrimers) for Fabrication of Thermally Stable Microstructures
Kyung Ho Jung 1 , Eun-Young Lee 1 , Byeong-Soo Bae 1 Show Abstract
1 Materials science and engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon Korea (the Republic of)
Photosensitive polymer system such as acrylate and epoxy for application to the design of photo-resist (PR) which accompanies the structural change with UV dose can easily fabricate the microstructures by simple developing process. In particular, many researchers’ have interested in fabrication of microstructures with thick and high aspect ratio using high photosensitive polymers to apply for the dielectric materials of MEMS, RF or microwave devices. However, the fabricated microstructures are not resistent in high temperature since the photosensitive polymers are thermally unstable. In recent years, organic-inorganic hybrid materials which are thermally stable over polymers have been studied for application of electronic and optical devices. These organic-inorganic hybid materials can be photo-curable by incorporation of acryl or epoxy organics in the hybrid materials. Actually, it has been founded that acryl-based hybrid materials (acryl hybrimers) are photo-patternable to fabricate the microstructures integrated optical or electronic devices. In this study, we synthesized the photo-curable cycloaliphatic epoxy grafted oligosiloxane using simple non-hydrolytic sol-gel process and achieve the photo-curable epoxy hybrimers using epoxy polymerization with arysulfornium salts as a cationic initiator. We confirmed synthesis of epoxy-oligosiloxane nanoclusters by 29Si, 1H nuclear magnetic resonance (NMR) and Fourier transformation spectroscopy (FT-IR) and also measured the properties and the structures of epoxy-oligosiloxane nanoclusters with contents by small angle x-ray scatterings (SAX), matrix-assisted laser desorption-time flight (MALDI-TOF), gel permeation chromatography (GPC) and thermogravimetric analysis (TGA). We estimated UV polymerization behavior of epoxy hybrimers by solid state 13C NMR and FT-IR. We obtained over 90% degree of polymerization by just 30 second UV (365nm H lamp) exposure. We fabricated the thick films over 170μm on the substrate by single spin coating. Dielectric constant of films was 2~3 at 1MHz and refractive index was over 1.5 with low birefringence. For fabrication of thick and high aspect ratio microstructure, thick epoxy hybrimer film was spin coated on the substrate. Then we exposed UV on the film with Cr photo mask. Finally, we developed the pattern which had the high aspect ratio using developing solution (2-propanol and n-propyl acetate). The fabricated microstructures had over 100μm thick and 10:1 aspect ratio. These microstructures were not deformed even above 250 °C heat treatment. Therefore, it is expected that the epoxy hybrimer can be used as the photo-patternable dielectric materials in application of MEMS, RF and microwave devices.
9:00 PM - O3.13
Novel Organosiloxane-based Organic-Inorganic Hybrid Dielectrics for Organic Thin-film Transistors
Sunho Jeong 1 , Bong-Kyun Park 1 , Jooho Moon 1 Show Abstract
1 School of Advanced Materials Engineering, Yonsei University, Seoul Korea (the Republic of)
Using a thermal-crosslinkable organosiloxane-based organic-inorganic hybrid material, solution-processable gate dielectric layer for organic thin-film transistors (OTFTs) have been fabricated. The hybrid dielectrics were synthesized by the sol-gel process and an acid-catalyzed solution of tetraethylorthosilicate and methyltriethoxysilane was used as a precursor solution to produce the hybrid dielectrics by spin-coating. Heat-treatment conditions for the prepared hybrid dielectric were optimized to obtain the high-quality dielectric performance. The influence of heat-treatment temperature on a leakage current behavior was analyzed by studying the structural changes of the organosiloxane-based dielectric using Fourier transform infrared spectrometer. The surface of the synthesized dielectric was also modified by self-assembly molecules (SAMs) treatment to improve the leakage current behavior. The untreated hybrid dielectric and SAMs-treated hybrid dielectric exhibit the high breakdown E-field of 1 MV/cm and 1.4 MV/cm, respectively, with the same dielectric constant of 4.0. Atomic force microscopy reveals that the hybrid dielectrics have a smooth surface morphology with the rms value of 0.5 nm.
9:00 PM - O3.14
Synthesis of Photo-patternable Imide Hybrid Nanocomposite Using Amine and Methacryl Modified Oligosiloxane Nanoclusters.
Tae-Ho Lee 1 , Jong-Pil Jeong 1 , Byeong-Soo Bae 1 Show Abstract
1 Department of Materials Science and Engineering, Korea Advanced Science and Technology, Daejeon Korea (the Republic of)
Polyimides have been widely used as electronic materials in the large-scale integrated circuit industry, because of their outstanding features such as high thermal stability, high mechanical strength and excellent electrical properties. In particular, photosensitive polyimides with direct patternability are required because they can be used to simplify complicated processes and reduce processing cost. However, most of the photosensitive aromatic polyimides have dark colors and poor optical transparency in the range of visible lights. For optical applications such as waveguides and insulating layers in display devices, colorless photosensitive polyimides have to be developed without degradation of thermal stability and mechanical strengths. Inorganic-organic hybrid nanocomposites have attracted much attention as a useful synthetic route to enhance thermal stability and optical transparency of the polyimides. The incorporation of siloxane clusters and silica nanoparticles into polyimides could make it possible to fabricate desired materials. The use of siloxane clusters with various organic groups such as amine, epoxide and methacryl generated good compatibilities with polymers and additional functionalities. In this study, we fabricated new photosensitive imide hybrid nanocomposites using amine and methacryl modified oligosiloxanes nanoclusters (AMON). AMON synthesized by sol-gel process had excellent optical transparency and uniform sizes below 2 nm. Alicyclic dianhydrides were used for colorless polyimide precursors. Amine groups in AMON covalently bonded with alicyclic dianhydrides, producing amic acid and methcaryl groups in AMON generated photosensitivity in fabricated nanocomposites. After imidization, amic acids were converted to imide groups by ring closure and photosensitive imide hybrid nanocomposites (PINs) were prepared. The final structures of AMON and PINs were analyzed by 29Si nuclear magnetic resonance (NMR) spectroscopy, fourier transformed infrared (FT-IR) spectroscopy and small angle neutron scatterings (SANS). The thermal stability, optical transparency and mechanical strength depending on processing parameters of PINs were evaluated by TGA, UV-vis spectroscopy, tensile test and TMA. The negative-typed photo-patterning of PINs was prepared from PINs containing photoinitiator. The line and circular shaped patterns were obtained by conventional photo-lithography using high power mercury lamp (365 nm). The surface topology and resolution of patterns were observed by optical microscopy and scanning electron microscopy.
9:00 PM - O3.15
Dual Optical/Conductive doped photopolymer probes for Near Field Scanning Microscopy: Fabrication and characterization
Dominique Burget 1 , Lavinia Balan 1 , Olivier Soppera 1 , Daniel-Joseph Lougnot 1 Show Abstract
1 Departement de Photochimie Generale, Universite de Haute Alsace, Mulhouse France
9:00 PM - O3.17
Enhanced Photovoltaic Performance from Metal Nanoparticle Polymer Blends- The Role of Field Shaping.
Kyungkon Kim 1 , David Carroll 1 Show Abstract
1 Physics, The Center for Nanotechnology and Molecular Materials , Wake Forest University, Winston Salem, North Carolina, United States
We obtained improved poly (3 octylethiophene)(P3OT)/C60 bulk heterojunction photovoltaic devices by doping with stable and highly electrically conducting gold (Au) and silver(Ag) nanoparticles. Doped devices showed 50-70% improved efficiency with the Ag nanoparticles exhibiting greatest increase in efficiency. We suggest that a dominate mechanism for efficiency enhancment of the doped photovoltaic devices is the improved electrical conductivity through the introduction of dopant levels within the HOMO LUMO gap of the P3OT and the enhancement to active layer absoprtion due to nanoparticle scattering playing only a secondary role.
9:00 PM - O3.18
Polymer-Clay Hybrid Dielectric Layer for Flexible Organic Thin Film Transistors.
Sei Uemura 1 , Takehito Kodzasa 1 , Manabu Yoshida 1 , Satoshi Hoshino 1 , Kouji Suemori 1 , Noriyuki Takada 1 , Toshihide Kamata 1 Show Abstract
1 , National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan
Recently, much attention has been paid on the development of flexible devices for the future mobile devices such as mobile displays. In order to develop the flexible devices, the component materials should have flexibility. This is a reason why organic devices such as organic transistors and organic diodes have received much attention in these days. For these purpose, not only an active layer but also other parts should be prepared by flexible materials. Then, many try to develop an organic insulator, especially a polymer insulator, for the organic transistors. However, there are still many problems for the polymer insulator. For example, usually polymer is inferior to the characteristic of a gas barrier, then it often causes the decline of transistor performance. In this study, we have examined to develop an Organic/Inorganic hybrid thin film for the gate dielectric layer of an organic transistor to prevent the penetrated gas effects and improve the FET performance. We have prepared polymer transistor using polythiophene as an active layer. As a polymer gate dielectric, we have examined PVA and PMMA. The FET properties of the polymer transistor with simple PMMA or PVA gate insulator was strongly affected by the circumstance. The detailed analysis of the effect, we have revealed that the effect of the water is serious for such a FET performance. H2O affected not only on the polymer semiconductor layer but also on the polymer insulator layer. It has been known that clay has high gas barrier properties thus it can be a good candidate for the passivation material. However, it is not easy to prepare its film with flexibility and high quality by itself. Then, we have examined to prepare a hybrid thin film between polymer and clay (M0.2-0.6X2-3Si4O10(OH)2 ). The polymer/clay hybrid thin film was prepared by laminating their thin film each others from their solutions. In case that the clay layer thickness is enough thin, the polymer film kept its flexibility. The hybrid thin film was used as the gate dielectric of a polymer field effect transistor. In case of the PVA/clay hybrid thin film, the FET performance was not so improved. However, PMMA/clay hybrid thin film gives us remarkable improvement of the FET performance. The gate leak current was reduced more than one order, and the hysteresis of the out-put characteristics was disappeared. These results revealed that the hybridization of polymer and clay was effective to prevent the water influence on the transistor operation. It has been known that the clay has layered structure in its film. The gas and ions has been often intercalated in the layered structure. We also found from the structural study of the organic semiconductor layer that the clay layer act as a template to improve the structural orientation of the polymer semiconductor layer which was prepared on the dielectric layer. These may be reasons why the hybrid layer gave the improvement of the FET properties of organic transistors.
9:00 PM - O3.19
Linear Arrays Of Nanoparticles On Cellulose Nanofilaments Using Engineered Proteins
Qi Xu 1 , Shi-You Ding 1 , Marcus Jones 1 , Melvin Tucker 1 , Garry Rumbles 1 , Mike Himmel 1 Show Abstract
1 Basic Science and National Bioenergy Center, Natinal Renewable Energy Lab, Golden, Colorado, United States
9:00 PM - O3.2
Preparation and Characterization of Polymer-Metal Nanocomposites for Photovoltaic Applications.
Daniel Skorski 3 , Tyler Pounds 1 , Abhijit Biswas 2 , Hergen Eilers 2 , Grant Norton 1 Show Abstract
3 Materials Science and Engineering, Alfred University, Alfred, New York, United States, 1 Mechanical and Materials Engineering, Washington State University, Pullman, Washington, United States, 2 Applied Sciences Laboratory, Institute for Shock Physics, Washington State University, Spokane, Washington, United States
9:00 PM - O3.20
Dye-Sensitized TiO2 Solar Cells with P3HT Polymer Blended PCBM as Hole Transporter and Light Harvester.
Lewis Abra 1 , Robert Echols 1 , Michael Hiatt 1 , K. Steirer 1 Show Abstract
1 Physics, Cal Poly State University, San Luis Obispo, California, United States
9:00 PM - O3.21
Hybrid Polymer Based High Q Microcavity Biosensor.
Sudhaprasanna Padigi 1 , Mingdi Yan 2 , Andres La Rosa 3 , Shalini Prasad 1 Show Abstract
1 Electrical and Computer Engineering, Portland State University, Portland, Oregon, United States, 2 Chemistry, Portland State University, Portland, Oregon, United States, 3 Physics, Portland State University, Portland, Oregon, United States
Micro Photonic sensors have recently been the most intensively researched upon topic from the point of view of developing ultra-sensitive bio-chemical sensors. We are currently developing the High Q technology on a chip, towards the realization of ultra-compact and ultra-sensitive biosensor technology. We are investigating the possibility of using pH sensitive polymer material to create polymer micro-resonators on a chip. The micro-resonators are characterized by traveling wave whispering gallery modes (WGM). The micro-resonators are excited through evanescent coupling either by tapered optical fibers or through side-polished optical fiber. The device efficiency is characterized through the Finesse value and the Q-values, which indicate the sensitivity of the device in detecting the changes in the micro environment of the device. Based on the molecules of interest, the polymer can be chemically functionalized, resulting in the realization of an ultra-sensitive micro-photonic bio-sensor. The ultimate goal is to create an array of micro-photonic resonators on a single chip and functionalize each of them separately for different chemical and biological species. This would result in the detection of a hybrid mixture of chemical and biological species.
9:00 PM - O3.22
Morphology Study of a Hybrid Structure Based on Porous Silicon and Polypyrrole.
Ma. Concepcion Arenas 1 , Hailin Hu 1 , J. Antonio del Rio 2 , Ma. Elena Nicho-Diaz 3 Show Abstract
1 Solar Materials, CIE-UNAM, Temixco, Morelos, Mexico, 2 Theoretical Physic, CIE-UNAM, Temixco, Morelos, Mexico, 3 Polymeric Materials, CIICAp- UAEM, Cuernavaca, Morelos, Mexico
9:00 PM - O3.23
Photoresponsive Sol-gel Derived Hybrid Materials.
Lihua Zhao 1 , Matthias Vaupel 2 , Douglas Loy 3 , Kenneth Shea 1 Show Abstract
1 Chemistry, University of California, Irvine, Irvine, California, United States, 2 , Nanofilm Technologie, Goettingen Germany, 3 Department of Chemistry and Department of Material Science and Engineering, University of Arizona, Tucson, Arizona, United States
Photoresponsive materials are those with mechanical, electrical and/or optical properties that are modulated by light. Advances in photonics are often limited by the availability of multifunctional materials. Sol-gel derived hybrid materials that covalently integrate photoresponsive groups allow high loading and control of chromophore dispersion with reduction of dye mobility. The sol-gel matrix provides long-term stability. Here we report an optically transparent, thermally robust, sol-gel derived photoresponsive hybrid material. The materials are derived from a photodimer of 7-hydroxy-coumarin, a naturally occurring substance found in many species of plants. Irradiation at short wavelengths induces photofragmentation and produces a coumarin molecule that fluoresces (390 nm) upon irradiation at 350 nm. The photopatterns can be generated in thin films of this material through a photomask and revealed by fluorescence microscopy and imaging ellipsometry. The photopatterns can be “erased” by irradiation at 324 nm. These sol-gel derived hybrid materials have merit for creating optical circuitry, optical data storage, secure recognition, optical waveguides and interference filters.
9:00 PM - O3.24
A Novel Hybrid Based on σ-Conjugated Hyperbranched polymethylphenylsilane-co-methylsilane (PMPS-co-MS) and fullerene (C60): PMPS-co-MS-C60
Jiang Yu 1 , Weijian Xu 1 , Zhenghua Zhang 1 , Yu Ni 1 , Yanbing Lu 1 , Yuanqin Xiong 1 Show Abstract
1 College of chemistry and chemical engineering, Hunan University, Changsha, Hunan, China
9:00 PM - O3.25
The Effect of Interfaces on Performance of MEH-PPV/CdS Blend Solar Cells
Chanchana Thanachayanont 1 , Kroekchai Inpor 2 , Somboon Sahasithiwat 1 , Chanipat Euvanannont 1 , Laongdao Menbangpung 1 , Vissanu Meeyoo 2 , Peerapol Yuvapoositano 2 Show Abstract
1 Nanomaterials, National Metal and Materials Technology Center, Pathumthani Thailand, 2 Department of Electrical Engineering, Faculty of Engineering, Mahanakorn University of Technology, Bangkok Thailand
9:00 PM - O3.27
Connecting Curable Siloxanes to Luminescent Organic Semiconductors - Monomers for Functional Hybrid Materials
Heiner Detert 1 Show Abstract
1 Organic Chemistry, Universitaet Mainz, Mainz Germany
9:00 PM - O3.28
Hybrid Organic Oxide/Al Composite Cathode for Efficient Polymer LEDs.
Tzung-Fang Guo 1 , Fuh-Shun Yang 1 , Zen-Jay Tsai 1 , Ten-Chin Wen 2 , Sung-Nien Hsieh 2 , Yaw-Shyan Fu 3 , Chia-Tin Chung 4 Show Abstract
1 Institute of Electro-Optical Science and Engineering, National Cheng Kung University, Tainan Taiwan, 2 Department of Chemical Engineering, National Cheng Kung University, Tainan Taiwan, 3 Department of Environment and Energy, National University of Tainan, Tainan Taiwan, 4 , Chi Mei Optoelectronics Corporation, Tainan Taiwan
This work reports on the fabrication of efficient polymer light-emitting diodes (PLEDs) by thermally evaporating a salt-free, neutral, organic-oxide buffer layer between electroluminescence (EL) film with relatively stable Al as the hybrid organic oxide/Al composite cathode instead of using low work function metals, such as Ca or Ba. EL efficiencies of phenyl-substituted poly(para-phenylene vinylene) copolymer based PLEDs with the hybrid organic oxide/Al composite cathode reach 8.86 cd/A, significantly higher than that of 5.26 cd/A and 0.11 cd/A for devices with Ca/Al and Al cathodes, respectively. The enhanced device performance is due to the formation of specific organic oxide/Al complex at cathode interface during the deposition of Al, facilitating the injection of electrons and preventing the metal-induced quenching sites of luminescence in EL layer near the recombination region. The interfacial reaction between the cathode with EL layer was investigated by X-ray photoelectron spectroscopy. In addition, by varying the thickness, the functional groups of the organic buffer layer and the metal electrodes with different work functions, we have verified the multiple functions of hybrid organic oxide/Al composite cathode for the significant increase of device performance.
9:00 PM - O3.29
Phosphonate Monolayers on Hafnium Modified Gold
Michael Jespersen 1 , Christina Inman 1 , Gregory Kearns 1 , Evan Foster 1 , James Hutchison 1 Show Abstract
1 Chemistry, University of Oregon, Eugene, Oregon, United States
Control over the surface and interfacial properties of materials is essential to their integration into a wide range of applications, and a variety of surface functionalities are required to meet the needs of current and future materials modification. Self-assembled monolayers (SAMs) are particularly attractive candidates for materials modification because they produce well-defined surfaces that may incorporate a wide range of functionalities without significantly modifying the bulk properties of the underlying material. While thiol monolayers have been extensively studied for the surface modification of coinage metals, here we report the first modification of gold substrates with an alkylphosphonate using a hafnium linker.Alkylphosphonate monolayers have been previously investigated for use in the functionalization of metal oxides as well as hafnium-modified silicon dioxide. In previous work from this lab, hafnium (IV) modified silicon dioxide has also been used to create patterned, two dimensional gold nanoparticle arrays. Here we report how hafnium oxychloride can be used to modify gold surfaces, and how the resulting film can be employed as a substrate for alkylphosphonate monolayer assembly. Forming phosphonate monolayers on a conductive metal substrate has a number of benefits. This chemistry opens up the possibility of patterning gold surfaces with rigid domains. The hafnium/phosphonate chemistry should allow the creation of well-defined boundaries between two different surface functionalities. It could be used as either an interdiffusion barrier between patterned thiol regions, or to pattern a region on a gold surface, which can be subsequently backfilled with a thiol adsorbate. The gold/hafnium/alkylphosphonate chemistry also can be used to modify metal and metal oxide surfaces concurrently, making it ideal for use in the homogeneous functionalization of interdigitated arrays for numerous electronics applications.Here we report the initial discovery and subsequent characterization of alkylphosphonate monolayer assemblies on hafnium-modified gold. We also demonstrate how hafnium patterned gold surfaces can be used in tandem with 2-mercaptoethylphosphonic acid to create a patterned surface.
9:00 PM - O3.3
CdS Thin-film Transistors Fabricated by Chemical Deposition and PDMS Shadow Mask.
Ju Won Yoon 1 , Jong Hyeon Lee 1 , Hye Jin Nam 1 , Duk Young Jung 1 Show Abstract
1 Chemistry, Sungkyunkwan university , Suwon Korea (the Republic of)
We report the fabrication and analysis of the CdS thin-film transistors. The PDMS shadow masks were fabricated by using micro molding of laser patterned metal shadow masks. The patterned channel layer of CdS were deposited by chemical solution deposition(CSD) in aqueous solution with solution-tight PDMS shadow mask on SiO2/Si(n-type) substrates. The source and drain electrodes of Au/Ti were prepared by electron-beam evaporation with other PDMS shadow mask on CdS patterns. The gate electrode is produced using indium metal. Utilization of PDMS shadow mask offers facile cleaning of surface to allow low size tolerance and edge-sharpness of patterned thin films. The scanning electron micrograph, atomic force microscope and current-voltage measurements present formation of CdS and Au/Ti patterns on the substrates and these materials demonstrate electrical characteristics for TFTs.
9:00 PM - O3.30
Hybrid (CnH2n+1NH3)2CuCl4 Self-Assembled Films as Potential UV Emitters for LED Applications
Andrea Zappettini 1 , Maura Pavesi 1 , Fabio Chiarella 2 , Francesca Licci 1 , Patrizia Ferro 1 , Tullo Besagni 1 , Roberto Mosca 1 Show Abstract
1 , IMEM-CNR, Parma Italy, 2 Dip. di Scienze Fisiche, Univ. of Napoli, Napoli Italy
The organic inorganic (CnH2n+1NH3)2MX4 perovskites (where M is a metal and X a halide) are presently attracting much attention, due to their unique electronic properties as well as to the excellent film processability. These self-assembling structures contain 2D semiconductor layers ((MX6)= octahedra) alternately stacked with organic ammonium layers. The excitons resulting from the low dimensionality of the semiconductor sheets have binding energy of several hundred meV, and are expected to strongly emit, even at room temperature.In view of exploiting such a potentiality and of finding new materials for UV-LED applications, we are performing systematic studies on the (CnH2n+1NH3)2MX4 hybrids, in form of thin films. In this communication we present our recent results on the optical characterization of (CnH2n+1NH3)2CuCl4 (1<n<4) compounds and the dependence of the physical properties on the film preparation technology.The films were obtained by either, a single source thermal ablation (SSTA) technique, and by spin-coating from alcoholic solutions. X-ray diffraction proves that in both cases the as-prepared films are single phase, well crystallized and with a dominant c-axis grain orientation.A sharp, intense photoluminescence (PL) emission at about 384 nm has been observed in ablated films, after exciting at 326 nm, at room temperature. The peak position is almost independent on the organic chain length (n), while shifts at higher wavelengths by decreasing temperature. The PL intensity significantly increases when decreasing temperature. The optical absorption of films deposited on quartz was measured at several temperatures. At room temperature three absorption peaks were observed, centered at 280, 375, and 384 nm, respectively. Spin-coated films had less resolved optical features. The ultraviolet-visible absorption is dominated by a single broad band centered at about 380 nm. Also PL spectra show a broad band centered at about 400 nm. These last results are in agreement with what reported in literature.A band structure description of these systems seems often appropriate, besides a molecular orbital spectroscopic analysis is sometimes used. We intend to investigate the degree of optical confinement of the CuCl4 complex by comparing the temperature dependent absorption and PL spectra of evaporated and spinned samples. In addition we will examine the links between these two description models. The application of hybrid perovskites for the realization of electroluminescent devices will be evaluated and discussed.
9:00 PM - O3.31
Growth of Lying Columns of Large Disklike Moleculesin Edge-on Position on a Surface.
Luc Piot 1 , Alexandr Marchenko 1 , Jishan Wu 2 , Klaus Muellen 2 , Denis Fichou 1 Show Abstract
1 LRC Nanostructures et Semi-Conducteurs Organiques (CNRS-CEA-UPMC), SPCSI/DRECAM, CEA-Saclay, Gif sur Yvette France, 2 , Max-Planck-Institute for Polymer Research, Mainz Germany
The design of modern electronic devices requires organic materials with anisotropic mobility of charge carriers. Discotic liquid crystal molecules by stacking one on top of the other can form columns and the large overlapping of cores within the columns enables the delocalisation of π-electrons parallel to the main columnar axis. Moreover the inter-columnar space is occupied by highly disordered “liquid-like” insulating aliphatic side chains. These observations suggest the concept of columnar disc-shaped systems as charge-transport channels in devices acting as “coaxial cables”. We will describe here the self-assembly properties of a family of functionalized hexa-peri-hexabenzocoronenes (HBC) deposited on highly ordered pyrolitic graphite (HOPG) and Au(111) substrates. We characterised these systems in situ by mean of scanning tunnelling microscopy at the liquid-solid interface using n-tetradecane as a solvent.Functionalized HBC-molecules were found to form long range ordered monolayers on HOPG (up to 1 μm) with molecules lying flat on the surface (“face-on” orientation), while on Au(111) the size of ordered domains does not exceed 50 nm. Furthermore, on HOPG, we show the possibility to induce an “edge-on” orientation of HBC- molecules with the STM tip. The edge-on oriented molecules then self assemble into horizontal columns adsorbing as a second layer on top of the former “face-on” monolayer. This method enables us also to grow multilayers of columns with a fine control on the number of multilayers.
9:00 PM - O3.32
Nano-crystalline TiO2-Semiconducting Polymer Solar Cells
David Taylor 1 , Hmoud Al-Dmour 1 Show Abstract
1 School of Informatics, University of Wales, Bangor United Kingdom
An investigation will be reported into the photovoltaic properties of nanocrystalline TiO2/poly(3-hexylthiophene) (P3HT) heterojunction solar cells. The porous TiO2 layer was prepared from a thermally-cured sol-gel layer prepared on a tin oxide coated glass slide. The semiconducting polymer, P3HT, was spin-coated over the layer and the device completed by evaporation of a gold top electrode. Current-voltage (I-V) characteristics of the device have been obtained in the dark and under illumination, both in air and under vacuum, for a range of light intensities and temperatures. Under white light illumination from a 50 W halogen lamp in air at room temperature, the cell produces an open-circuit voltage, Voc, of ~ 0.55 V with a fill factor of 27%. Short circuit currents of ~ 0.1 mA/cm2 are consistent with the low intensity of the illumination. Increasing the device temperature in air resulted in a significant reduction in Voc. A reduction also occurred when the device was tested under vacuum, pointing to the role of oxygen in defining Voc: it is well known that oxygen dopes P3HT and interacts with the surface of nanocrystalline TiO2. Capacitance-voltage measurements suggest that the reduction in Voc seen under vacuum is allied to the collapse of the depletion which is supposed to exist at the TiO2-polymer interface. Scanning Kelvin Probe measurements are being undertaken to confirm this. In our latest study in which P3HT is replaced by a polyarylamine, Voc is found to be higher, ~0.8 V, and less sensitive to temperature.
9:00 PM - O3.33
The Preparation and Characterization of A Novolac Cured Epoxy-Clay Nanocomposites
Tsung-Yen* Tsai 1 , Shau-Tai Lu 1 , Chin-Jei Huang 1 , Jia-Xiang Liu 1 , Chih-Hung Li 1 Show Abstract
1 Department of Chemistry & Center for Nanotechnology, Chung Yuan Christian University, Chung Li, Taoyuan, Taiwan
Intercalated or exfoliated nanocomposites were composed by the novolac cured epoxy and one of three different kinds of layered silicates, montmorillonite (PK-802), saponite (Semecton-SA) and nontronite (PK-805). The bi-functional modifiers with different ratio, which contained one of the promoters (2-phenylimidazole and 2-methylimidazole) of epoxy and benzalkonium chloride (BEN), were intercalated into the interlayer regions of pure clays and followed by a crosslinking reaction. The properties of novolac cured epoxy/clay nanocomposites were characterized by wild-angle X-ray diffraction (WAXRD), thermal analysis (TGA/DSC), coefficiency of thermal expansion (TMA), mechanical properties (DMA), and transmission electron microscopy (TEM). According to the measurement, these novolac cured epoxy-clay nanocomposites have shown the significant improvement in the thermal, mechanical and barrier properties
9:00 PM - O3.34
Laser Direct-Write of Hybrid Sol-Gel Films for Optical Waveguides
Rodrigo Ruizpalacios 1 , Joseph Beaman 1 , Kristin Wood 1 , Richard Crawford 1 , David Bourell 1 Show Abstract
1 Mechanical Engineering, University of Texas at Austin, Austin, Texas, United States
Research in manufacturing techniques for novel and cost effective optical components has focused on versatile new materials and low temperature processing. The laser direct-write of hybrid organic-inorganic sol-gel optical films has the potential addressing these two needs for the fabrication of photonic components for rapid prototyping purposes. The combination of Solid Freeform Fabrication (SFF) and Direct-Write (DW) approaches to manufacturing, along with the use of high optical quality materials prepared by the sol-gel process, can result in optical components produced with maskless techniques and the potential of being used as real products.The fundamental approach in this research consisted in four steps. Initially the sol is synthesized under controlled atmospheric conditions. This is followed by the deposition of the sol-gel thin films by spin coating. After deposition the film is thermally and in some cases chemically treated. The final step involved the use of a laser source for photophysical processing of the film, translating the sample through an XY stage. This research provides results of the preparation procedures of hybrid organic-inorganic sol-gel materials, with the goal of developing a repeatable and reliable process of high optical quality films. The main experimental aspects explored were the synthesis, deposition, thermal and laser processing of the sol-gel materials. It also presents experimental results that demonstrate light propagation through a straight ridge waveguide made by the proposed process.The results of this research set the groundwork for the development of a fully automated directwrite SFF machine with the capability of depositing high optical quality solgel films, thermally treating the films, and laser direct-write the structures on inorganic or hybrid organic/inorganic glassy matrices. Applications for large area patterning and multi-layer films are envisioned.
9:00 PM - O3.4
Towards Nanowire-Based Thermocouple Arrays.
Megan Bourg 1 , Reginald Penner 1 Show Abstract
1 Chemistry, University of CA Irvine, Irvine, California, United States
A thermocouple consists of a junction between any two dissimilar metals. The ability for a thermocouple to act as a temperature sensor is based upon the Seebeck effect, which is the conversion of temperature differences into electromotive force. Over 50% of all industrial temperature measurements are made using thermocouples, and this is a highly mature technology, the miniaturization of thermocouples has not yet reached the nanometer-scale. The objective of miniaturization is three-fold: First, to increase the utility of thermocouples for the measurement of temperatures in small volumes, second, to decrease the response time for thermocouples, and finally to investigate the effect on temperature sensitivity of miniaturization into the nanometer-scale regime.We have prepared two types of thermocouples based on metal nanowires: Nanowire-Thin Film junctions, consisting of a junction between a metal nanowire and a metal film, and nanowire-nanowire junctions, consisting of a junction between two nanowires. The nanowires were fabricated on Highly Oriented Pyrolytic Graphite (HOPG) utilizing the Electrochemical Step Edge Decoration method1 (ESED). Once the nanowires were transferred to an insulator the film was evaporated to form the junction and appropriate extension wires were attached to turn the device into a working thermocouple. Thermal measurements were perfomed and revealed that these devices have a slight enhancement (increased sensitivity) in the Seebeck coefficient. These devices measure temperature accurately and reproducibly, and have a response time faster than 7ms.Nanowire-Nanowire junctions have also been fabricated utilizing a modified version of the ESED method2 in order to try to improve upon the enhancements shown by the Nanowire-Thin Film thermocouples. The characterization of these thermocouple arrays by SEM, EDS, and thermal measurements will be discussed in this presentation. (1)E.C. Walter, B.J. Murray, F. Favier, G. Kaltenpoth, M. Grunze, R.M. Penner*, Noble and Coinage Metal Nanowires by Electrochemical Step Edge Decoration, J. Phys. Chem. B 106 (2002) 11407. (2)E.C. Walter, B.J. Murray, F. Favier, R.M. Penner*, Beaded Bimetallic Nanowires: Wiring Nanoparticles of Metal 1 Using Nanowires of Metal 2**, Adv. Mat. 15 (2003) 396.
9:00 PM - O3.5
Investigation of the Effect of Refractive Index Modifier Species on the Thermal and Optical Properties of an Organic/inorganic Hybrid Material for Waveguiding Applications.
Shane O'Brien 1 , Mehmet Copuroglu 1 , Gabriel Crean 1 2 Show Abstract
1 MMP Group, Tyndall Institute, Cork Ireland, 2 Dept. of Microelectronic Engineering, NUI- University College Cork, Cork Ireland
9:00 PM - O3.6
Blended TiO2:CuPc Solar Cells Deposited Using SuSMBE
Alex Mayer 1 , Nicola Coppede' 2 , Tulio Toccoli 2 , Fabrizio Siviero 2 , Marco Nardi 2 , Salvatore Iannotta 2 Show Abstract
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 , IFN-CNR, Trento Italy
Photovoltaic cells comprised of a bulk heterojunction of titanium dioxide and copper phthalocyanine sandwiched between ITO-coated glass and aluminum have been fabricated from the vapor phase in-situ. The ability to create this blend requires in-situ creation of 5 nm TiO2 particles that can be co-deposited with the CuPc. The nanoparticles are realized through the use of a pulsed microplasma cluster source (PMCS) while the CuPc portion of the film is deposited using super sonic molecular beam epitaxy (SuSMBE). Preliminary results are presented.
9:00 PM - O3.7
A WORM Memory Device Based on PVK Containing Gold Nano-Particles
Yan Song 1 , Q.D Ling 2 , E.Y.H Teo 1 , Y.P Tan 1 , S.L Lim 2 , Chunxiang Zhu 1 , D.S.H Chan 1 , E.T Kang 2 , D.-L Kwong 3 Show Abstract
1 Electrical and Computer Engineering, National University of Singapore, Singapore Singapore, 2 Chemical and Biomolecular Engineering, National University of Singapore, Singapore Singapore, 3 , Institute of Microelectronics, Singapore Singapore
Organic materials have been aggressively explored for semiconductor device applications. Very recently, organic memories have received a great attention due to their simple structure, good scalability, CMOS compatibility, and most importantly, low cost. Several kinds of organic molecular materials were found to exhibit memory effects. Polymer memory devices are potentially far less expensive to make than those based on organic molecular materials. In this paper, we report memory characteristics of poly(N-vinylcarbazole) (or PVK) containing gold nano-particle (or GNP). The device uses a MIM (metal-insulator-metal) structure on SiO2 capped silicon substrate, with TaN as the bottom electrode, PVK containging GNP as the active layer and Al as the top electrode. The toluene solution of PVK-GNP was spin-coated on the TaN, followed by solvent removal in a vacuum chamber. Finally, Al was thermally evaporated to the polymer film. The memory effect of PVK was observed in the I-V characteristics of the sandwich device. For the as-fabricated device, the device is in its OFF state. A transition from the OFF state (low conductivity) to ON state (high conductivity) occurs at a threshold bias. After the device reached the high conductivity state, it cannot be reversed to the low conductivity state by applying a reverse bias. The memory effect of the device may be due to the containing GNP as trapping centers. A simple model is given to explain the memory effect. The device shows a high ON/OFF current ratio of about 1E5. The effect of continuous read pulse on the ON- and OFF-states was evaluated and no resistance degradation is observed for both ON- and OFF-state after 1E6 read cycles. The stability of both states under ambient conditions with a constant stress was also characterized and the device showed a quite few degradation after 10 hours test. Thus, the device shows a high potential as a low power and high density Writer-Once-Read-Many Times (or WORM) memory device
9:00 PM - O3.8
Evidence of Gap State Formed by Heat Treatment in C60/Cu Interface Studied by Ultraviolet and X-ray Photoelectron Spectroscopy.
Sang Wan Cho 1 , Jung Hwa Seo 1 , Kwanghee Cho 1 , Kyul Han 1 , Chung Yi Kim 1 , Kwangho Jeong 1 , Chung-Nam Whang 1 Show Abstract
1 Institute of Physics and Applied Physics, Yonsei University , Seoul Korea (the Republic of)
9:00 PM - O3.9
Blends of Organic Dye Molecules and II-VI Semiconductor Matrices
Eric Mankel 1 , Yvonne Gassenbauer 1 , Thomas Mayer 1 , Wolfram Jaegermann 1 Show Abstract
1 Surface and Solar Energy Research, University of Technology Darmstadt, Darmstadt Germany
We report on the growth of hybrid organic dye / inorganic semiconductor film blends in the context of sensitization of wide gap semiconductors to multi-band photo-absorption for photovoltaic applications. Organic dyes offer a broad variety in tailoring the energetic position of electronic states versus the inorganic semiconductor bands for optimizing charge transfer processes. Substituted zinc phthalocyanines with different numbers of F atoms have been incorporated into ZnSe and ZnTe. Composites of varied dye fractions have been grown by codeposition from separate effusion cells onto SnO2 coated glass substrates at room temperature. Only minor changes are observed in the dye RAMAN spectra when incorporated into inorganic semiconductor matrices, indicating the stability of the organic molecules versus the growth process. The composites show optical absorbance features clearly related to the dye guest and the host matrix. In situ analysis of the electronic state line up using UPS and XPS shows a dependence of the HOMO line up on the number of F substitute atoms and dye concentration. Luminescence spectra show additional features beyond linear superposition.
Vladimir Bulovic Massachusetts Institute of Technology
Seth Coe-Sullivan QD Vision, Inc.
Peter Peumans Stanford University
O4: Hybrid Materials for Light Emission and Memory
Wednesday AM, April 19, 2006
Room 3005 (Moscone West)
9:15 AM - **O4.1
All-Inorganic, “Hybrid” Approaches to Nanocrystal-Based Light-Emitting Devices.
Victor Klimov 1 Show Abstract
1 Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
A significant challenge for realizing applications of semiconductor nanocrystals (NCs) in optolelectronic devices is associated with difficulties in achieving injection or extraction of charge carriers. Recently, we explored two novel, all-inorganic approaches for the “nonoptical” injection of charges into nanocrystals using either nonradiative energy transfer (ET) from an epitaxial quantum well  or direct electrical injection from p- and n-layers of wide-gap semiconductors . In the ET approach, we combine nanocrystal mono- and multi-layers with traditional epitaxial quantum wells. In these hybrid structures, the rate of nonradiative exciton transfer exceeds that of carrier recombination in the quantum well, which results in high (greater than 50%) transfer efficiencies. In a p-i-n device, nanocrystals are incorporated as an i-layer in the GaN p-n junction using novel, room-temperature, epitaxial technique that employs a beam of neutral energetic atoms. The latter approach demonstrates >1% injection efficiencies. Both types of hybrid nanocrystal/epitaxial structures show stable, multi-hour operation under ambient conditions and long shelf lifetimes. The analysis of injection/recombination mechanisms in these devices indicates the feasibility of a significant increase in the efficiency for both ET and direct-injection structures.1. M. Achermann, M. A. Petruska, S. Kos, D. Smith, D. D. Koleske, and V. I. Klimov, "Energy-transfer pumping of semiconductor nanocrystals via nonradiative energy transfer using a quantum well," Nature 429, 642 (2004).2. A. H. Mueller, M. A. Petruska, M. Achermann, D. J. Werder, E. A. Akhadov, D. D. Koleske, M. A. Hoffbauer, and V. I. Klimov, “Multicolor light-emitting diodes based on semiconductor nanocrystals encapsulated in GaN charge injection layers,” Nano Letters 5, 1039 (2005).
9:45 AM - O4.2
Hybrid Nanocomposite Materials for Electrochromic Device Applications.
Manoj Namboothiry 1 , Tyler Zimmerman 1 , Jiwen Liu 1 , Faith Coldren 1 , David Carroll 1 Show Abstract
1 Physics, The Center for Nanotechnology and Molecular Materials , Wake Forest University, Winston Salem, North Carolina, United States
Electrochromic thiophene host polymers, were blended with a variety of metal nanoparticles and used in making flexible electrochromic devices. Using atomic force microscopy and transmission electron microscopy, we have been able to determine the meso-phase structure induced by blending, as a function of loading and size of the nano-material. Meso-phase formation as well as the local nano-scale morphology, has been studied for a variety of nanoparticle compositions including: Ag, Au, Cu, etc, and and correlated to the dielectric shift of the host, ionic conductivities, and overall spectral response of the device. We further demonstrate surprising control over the electrochromic contrast and color without significantly affecting device lifetimes or performance. Through this work, we show that metal nano-particle - polymer blends might represent a powerful tool in broadening the applicability of electrochromic device technologies
10:00 AM - **O4.3
Saturated Color RGB Quantum Dot/Organic Hybrid Light Emitting Devices for Display Applications
Jonathan Steckel 1 , Seth Coe-Sullivan 1 , Vladimir Bulovic 2 1 Show Abstract
1 , QD Vision, Inc., Watertown, Massachusetts, United States, 2 Dept of Electrical Engineering & Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Organic light emitting diodes have undergone rapid advancement over the course of the past decade. Similarly, quantum dot synthesis has progressed to the point that room temperature highly efficient photoluminescence can be realized. We have shown that it is possible to utilize the beneficial properties of these two material sets in a robust light emitting device. Efficient, reliable manufacturing techniques that are compatible with known device fabrication methods are necessary to make QD organic hybrids a commercial reality. We have learned that the creation of efficient and saturated color quantum dot light emitting devices (QD-LEDs) is dependent on the development of robust manufacturing methods for the QD layer. We demonstrate pixilated, saturated color QD-LEDs with good external quantum efficiencies in the red, green, and blue, making QD-LEDs a viable alternative display technology, which is being commercialized by QD Vision, Inc.
10:30 AM - O4.4
Nanoscale Probing of Optical Properties of Materials by Decay Rate Coupling in Electrically Pumped Organic Heterostructures
Kwang Hyup An 1 , Yiying Zhao 2 , Kevin Pipe 1 , Max Shtein 2 Show Abstract
1 Department of Mechanical Engineering, University of Michigan, Ann Arbor, Ann Arbor, Michigan, United States, 2 Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Ann Arbor, Michigan, United States
In OLEDs, the decay rate of a molecular exciton near a metal-organic interface is affected strongly by optical feedback through microcavity effects, as well as resonant energy transfer to surface plasmon polaritons (SPPs) in the electrodes. Using a classical electromagnetic model which takes into account these effects, a change is predicted in the total decay rate of excitons within a typical OLED heterostructure when the permittivity of the layers external to the electrodes is varied. Electrical measurements on vacuum-deposited OLEDs with organic caps show a systematic variation of the device steady-state current in forward bias with varying cathode thickness and organic coverage, independent of device degradation kinetics. The change in current is consistent with predicted change in the exciton decay rate, suggesting that there may be a feedback mechanism in which the steady-state exciton density in an OLED measurably alters the density of transport states. Based on these results, a high resolution probe mechanism is considered, wherein current change in a small OLED can be used to sense the distance from the cathode to a sample, as well as surface and subsurface variations in the dielectric constant of the sample.
11:15 AM - **O4.5
Polymer-nanoparticle Blends for Memory Applications.
Luisa Bozano 1 , Sally Swanson 1 , Gary McClelland 1 , Richard DiPietro 1 , Kerem Unal 1 , Delia Milliron 1 , Jane Frommer 1 , J. Scott 1 , Scott Sills 2 1 , Katsuhiko Fujita 3 1 Show Abstract
1 Almaden Research Center, IBM, San Jose, California, United States, 2 CPIMA, Stanford, Palo Alto, California, United States, 3 , Kyushu University, Kyushu Japan
11:45 AM - O4.6
Impedance Spectra and Equivalent-Circuit Analysis of Polymer-Nanoparticle Organic Memory Devices
Daniel Simon 1 , Michael Griffo 1 , Sue Carter 1 Show Abstract
1 Physics, University of California, Santa Cruz, Santa Cruz, California, United States
Conducting polymers have received recent attention as a candidate for organic-based memory devices. The ease of processing, resiliency to defects, and commercial availability of these materials indeed make them ideal for the next-generation of memory hardware. We report here on polymer/nanoparticle based memory devices fabricated using standard spin-casting and metal-evaporation techniques. The devices consist of triphenyl-phosphine protected gold nanoparticles (∼10 nm diameter) embedded in the cross-linkable polymer poly[(4-N-hexyltriphenyl)amine] (xHTPA), sandwiched between electron-, or hole-, transport layers (e.g. PEDOT-PSS), and a variety of evaporated metal electrodes. The memory effect is observed using read, write, and erase voltages of single polarity, with typical on-off ratios of 2–4 orders of magnitude at a read-voltage of 1 V. The threshold (write) voltage and erase voltage are 2.5–4 V and 5.5–6.5 V, respectively. Impedance spectra is obtained by monitoring the phase shift of the current using a lock-in amplifier, and a transition into and out of a parallel resistor/capacitor equivalent circuit is observed which is related to the on/off memory state of the device. We discuss the relevancy of such equivalent circuit models in the analysis of polymer/nanoparticle memory elements and their relationship to the dielectric properties of isolated nanoparticles.
12:00 PM - O4.7
Polymer/Nanoparticles Memory Devices with Asymmetrical Electronic Switching Behavior.
Jianyong Ouyang 1 , Yang Yang 1 Show Abstract
1 Department of Materials Science and Engineering, University of California, Los Angeles (UCLA), Los Angeles, California, United States
Electrical bistable behavior has been observed on polymer film containing gold nanoparticles and small organic conjugated compounds. [1, 2] This device can be used as a nonvolatile memory device. This device exhibited symmetrical switching behavior, that is, the device can be switched from the low to high conductance state at either polarities.Recently, we demonstrated a novel polymer/nanoparticles memory device which exhibited asymmetrical switching behavior. Switching from the low to high conductance state was observed only at one polarity, while switching from the high to low conductance state was observed only at another polarity. This behavior indicates that this device can be used as a nonvolatile memory device and have unique advantages, such as to avoid the connection to a rectified diode in the practical application. The effect of materials and electrode/polymer film interface will be presented. The switching mechanism will be presented as well.References: J. Ouyang, C.-W. Chu, C. Szmanda, L. Ma, and Y. Yang, Nat. Mater. 3, 918 (2004). J. Ouyang, C.-W. Chu, R. J.-H. Tseng, A. Prakash, and Y. Yang, Proc. of IEEE, 93, 1287 (2005).
12:15 PM - **O4.8
Hybrid Organic/Inorganic Semiconductor Write Once Read Many Times Memory Elements
Stephen Forrest 1 Show Abstract
1 Electrical Engineering and Computer Science, and Physics, University of Michigan, Ann Arbor, Michigan, United States
We discuss a non-volatile, write-once-read-many-times (WORM) memory element employing a thin film silicon p/n junction diode on a flexible substrate integrated in series with a conductive polymer fuse. The nonlinearity of the silicon diode enables a large scale passive matrix memory configuration, while the conductive polyethylenedioxythiophene:polystyrene sulfonic acid (PEDT:PSS) polymer acts as a switch with fuse-like behavior for data storage. The polymer can be switched within a few hundred nanoseconds, resulting in a permanent increase of resistivity of the memory pixel up to a factor of 100,000. The switching performance is reliable in its operation, and the fuses do not degrade after many thousand read cycles in ambient at room temperature. More recently, we have found that similar memory effects can be observed using the polymer directly layered onto a bare Si or GaAs substrate, considerably simplifying device design. We investigate the energetics and chemistry of this apparently general effect, and find that rectification at the organic/inorganic heterojunction is understood in terms of previous work on small molecular weight organic/inorganic semiconductor junctions. Given these results, very high performance, low cost, lightweight archival hybrid inorganic/organic WORM memories for video image and other archival storage applications are feasible.S. Möller, C. Perlov, W. Jackson, C. Taussig, and S. R. Forrest, "Dramatic Conductivity Switching in an Electrochromic Polymer Used in a Write Once Read Many Times (WORM) Organic/Inorganic Memory Element," Nature, vol. 426, pp. 166, 2003.S. E. Smith and S. R. Forrest, "A Low Switching Voltage Organic-on-Inorganic Heterojunction Memory Element Utilizing a Conductive Polymer Fuse on a Doped Silicon Substrate," Appl. Phys. Lett., vol. in press, 2004.Q. D. Ling, Y. Song, S. J. Ding, C. X. Zhu, D. S. H. Chan, D. L. Kwong, and E. T. Kang, "Non-volatile polymer memory device based on a novel copolymer of N-vinylcarbazole and Eu-complexed vinylbenzoate," Adv. Mater., vol. 17, pp. 455, 2005.
12:45 PM - O4.9
Conductance Requirements for Arrays of Organic Programmable-Resistance Memory Devices
Troy Graves-Abe 1 2 , Tse-Jen Ku 1 , J. Sturm 1 2 Show Abstract
1 Department of Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 2 Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey, United States
Recent work on two-terminal organic programmable-resistance devices has attracted interest because of their potential for use in high-performance, low-cost memory arrays . For example, these devices are compatible with very simple and high-density “cross-point” arrays where the organic layer is sandwiched between two perpendicular sets of metal column and row lines (so that a device is defined at each column/row intersection) . In this work, we study integration of memory elements into both cross-point arrays (corresponding to a passive-matrix architecture) and more traditional active-matrix arrays (in which a transistor is used to access each device). We determine the device characteristics that are needed for application in high-speed memory arrays of different sizes. A key result is that for a reasonably competitive technology (1 Gb memory, 50 x 50 nm2 device area, and 100 ns access time), devices must have a very large conductance/area of >104 S/cm2 to minimize resistance-capacitance (RC) delays during read operations.To read the state (resistance) of a memory element, a voltage must be applied to the device and the current (ie, the voltage across the impedance of a sense amplifier in series with the device) measured. In an array, the row and column lines used to access individual devices have finite capacitance due to nearby metal lines. The duration of the read operation is determined by the time needed to charge this capacitance through the device resistance. To determine the read time, we have performed circuit simulations for a variety of array sizes (in bits), device areas, and device conductance/area. Because the line capacitance/length stays constant (or increases) for decreasing device area while device resistance increases (for constant conductance/area), RC delays increase dramatically in highly-scaled memory arrays with large numbers of bits (which require long row and column lines). To minimize these times, a large conductance is required. For example, a device with a conductance of ~1 S/cm2 in the low-resistance state (which is traditional for an organic programmable-resistance device) would be limited to relatively large device sizes of 250 x 250 nm2 in a very small array (103 bits). The relatively low conductance of most organic devices may thus limit their compatibility with dense and high-speed memory arrays, although recently organic devices with conductance of up to 106 S/cm2 have been reported .In summary, we have performed circuit simulations of organic programmable-resistance memory devices integrated into passive- and active-matrix arrays. We have found that for application in high-speed (100 ns access time) and high-density (1 Gb, 50 x 50 nm2 device area) memories, devices with very large conductance > 104 S/cm2 are desirable. Y. Yang et al, MRS Bull. 29, 833 (2004). J. C. Scott, Science 304, 62 (2004). T. Graves-Abe and J. C. Sturm, App. Phys. Lett. 87, 133502 (2005).
O5: Hybrid Materials for Transistor Applications
Wednesday PM, April 19, 2006
Room 3005 (Moscone West)
2:30 PM - O5.1
Low Voltage Pentacene Thin Film Transistors Using an Organic Monolayer as Gate Insulator.
Kang Dae Kim 1 , Chung Kun Song 1 Show Abstract
1 Electronics Eng., Dong-A University, Busan Korea (the Republic of)
The organic thin film transistors(OTFT) were sufficiently developed to be applied to flexible display and organic RFID. However, the operation voltage is still too large for the portable applications. Although the high k materials have been adopted for the gate, the inorganic materials may not be appropriate for the flexible applications.In this work we employed the organic monolayer of molecules with the properties of high insulation and low surface energy for pentacene thin film growth as the gate dielectric. The molecule of (Benzyloxy)alkyltrichlorosilane was self-assembled on Si and Al gate electrode and (Benzylthio)alkanethiol on Au gate electrode. Pentacene was used for the active layer and Au for source and drain electrode.All of the OTFTs operated at the voltages less than 2 V for VGS as well as VDS. The OTFTs using Si gate electrode produced the mobility of 0.2 cm^2/V.sec and the on/off current ratio of 10^2 to 10^4 depending on the chain length. In the case of the OTFTs with Au and Al gate electrode the mobility was 0.056 cm^2/V.sec and the on/off current ratio 10^2 smaller than Si gate OTFTs. The reason of the inferior performance is estimated that the self-assembly (SA) is well processed on Si rather than on Al and Au electrode because the natural oxide of Si provide the more uniform platform for SA than Al2O3and Au. However, in order to implement integrated circuits based on the low voltages OTFTs the SA process for Al and Au gate should be well developed because the gate electrode must be patterned.
2:45 PM - O5.2
Pentacene Thin Film Transistors Prepared by Micro Contact Printing and Selective Surface Wetting.
Amare Benor 1 , Veit Wagner 1 , Dietmar Knipp 1 Show Abstract
1 , International University Bremen, Bremen Germany
Micro Contact Printing (μCP) of self-assembled monolayer (SAMs) in combination with selective surface wetting was used to realize radio frequency micro coils and pentacene thin film transistors for radio frequency information tags (RFID tags). The combination of micro contact printing and selective wetting/dewetting provides an universal route to pattern a variety of different materials including polymers and metal films. In our study we used the self-assembled monolayers (Octadecyltrichlorosilane (OTS), CH3(CH2)17SiCl3, which was printed on cleaned silicon or glass substrate. The printed monolayer leads to the formation of hydrophilic and hydrophobic regions, which facilitates the selective deposition of polymers or resists like Poly (methyl methacrylate), PMMA, on the hydrophilic regions. Following the selective deposition of a resist, a lift-off process was used to pattern gold or titanium metal films. This technique was applied to realize radio frequency (RF) coils and electrodes for pentacene thin film transistors. The techniques allows for patterning of electrodes down to 2μm. However, the patterning process depends on several parameters like the geometry of the structures, the chemistry of the heterogeneous substrate, the selective wetting process itself and the resist. Therefore, the influence of the printing parameters on the patterned structures was investigated. Furthermore, the printing process was studied in terms of fundamental printing limits. A simple model describing the limiting factors will be presented. Finally, the pentacene transistors will be compared with transistors prepared by optical lithography.
3:00 PM - **O5.3
Synthesis and Use of Soluble Pentacene Precursors in Organic Thin Film Transistors.
Cherie Kagan 1 , Ali Afzali 1 Show Abstract
1 Molecular Assembly & Devices, IBM Research, Yorktown Heights, New York, United States
Among organic semiconductors, pentacene has emerged as the most promising material for use in electronic devices such as field effect transistors. In orde to exploit the advantages of organic materials, fabrication of integrated circuits must entail solution-based process. In this talk a simple, one-step synthesis of variety of soluble pentacene precursors are described and relationship between physical properties and structure of precursors presented. Solution processed fabrication of OFET using pentacene precursors and environmental stability of pentacene devices are also described in detail.
3:30 PM - O5.4
Degradation of Pentacene Thin Film Transistors Under Current Stress.
Tae Ho Kim 1 , Chung Kun Song 1 , Jin-Seong Park 2 , Min Chul Suh 2 Show Abstract
1 Electronics Eng., Dong-A University, Busan Korea (the Republic of), 2 , Samsung SDI, Yongin Korea (the Republic of)
Recently, the technology of organic thin film transistors(OTFT) became mature enough for the flexible applications such as flexible display and organic RFID. However, the stability of OTFTs is not sufficiently addressed yet.In this study the various materials such as SiO2, SiO2/OTS, PVP, PVP/OTS, and Al2O3 were adopted for the gate of pentacene TFTs in order to investigate the origin of performance degradations such as threshold voltage shift, the decrease of mobility, and increase of off-state current and sub-threshold voltage under the various current stress conditions and environment. The stress effects were quite sensitive depending on the materials of gates and the surface conditions of gates. The OTFTs with SiO2 and SiO2/OTS exhibited the negative shift of threshold voltage meanwhile PVP and PVP/OTS gates the positive shift with stress time. And also the shifts were partially recovered after a few days in vacuum. The facts indicated that the origin of threshold voltage shift was the ionic charges in the gate, which were migrated to the gate surface near channel when stressed by the applied gate voltage. And the OTFTs stressed in vacuum were much more stable comparing with them in air. Therefore the charges in the gates as the origin of the shift were estimated to be the hydroxyl radicals induced from the air.In addition the OTFTs stressed by a high current level such as 20uA the mobility was also degraded. We estimated that the causes of degradation might be the gap states in pentacene or the modification of electric field on traps at grain boundaries by trapping of hydroxyl radicals.We are going to address the stability of pentacene TFTs under the various stress conditions and environments, and then the possible mechanism of degradation will be presented.
3:45 PM - O5.5
Combining Silicon and Organic/Polymer Semiconductors in a New Class of Sensor Devices
Deepak Sharma 1 , Daniel Fine 1 , Ananth Dodabalapur 1 Show Abstract
1 Electrical Engineering, University of Texas at Austin, Austin, Texas, United States
There is currently a great need to develop new and improved solid-state device based chemical sensors. We report the characteristics of a new sensor device that combines the functional properties of silicon field-effect devices with unique properties of organic semiconductors. The novel four-terminal field effect device has two channels: one formed in an organic semiconductor (p) and the second in silicon (n). Both the channels are coupled so that one channel gates the other. The organic channel is exposed to air and interacts with the chemical vapor present in the ambient. The device can operate as a traditional CHEMFET as well as an organic TFT based sensor. Another sensing mode, which is most sensitive, is designated as the chemical memory mode. In this unique mode of operation, the device operates in a manner akin to a non-volatile memory in which the write function is provided by the chemical analyte. The erase is done electrically by reverse biasing the device. In the chemical memory sensor mode, the n-channel is biased on while keeping the p-channel off and the n-channel current is measured with time. Subsequently, both the channels are biased on and conducting and analyte is delivered to the exposed pentacene layer. Following this, the n-channel current is measured again at the biasing condition prior to analyte delivery. The current increases by as much as a factor of 65. This indicates a decrease in the threshold voltage (VT) due to the hole trapping in the organic channel after the interaction with analyte. From the VG Vs IDS curve, this 65X improvement corresponds to a 3V decrease in VT. Thus, trapped charge density, that is the amount of charge imparted to the device during the write cycle of the memory, can be estimated as (change in VT)*Cox/q which, for the oxide thickness of 40nm, is equal to 1.6x1012 cm-2. In our sensor we are essentially using trapped charges as the “non-volatile” gate charge. The charge retention requirements of the sensor are much less than that of a normal non-volatile memory. The reset mechanism is very similar as well – electrical reverse bias based resetting. The chief difference with established silicon CHEMFET technology is that CHEMFETs use channel charge modulation by dipoles (which have a net charge of zero) whereas in our device we use trapped positive charges which will obviously produce a much greater conductivity and capacitance modulation. This results in a performance improvement of a factor of 10-100 in comparison with existing technology (CHEMFETs). In order to increase the selectivity and sensitivity of the device, receptors having affinity to particular analytes can be deposited with the organic semiconductor. We also report on the sensitivity of this device and detection levels of 50 PPB (part-per-billion) have been obtained for some analytes.
4:30 PM - O5.6
Solution-processed High-performance Zinc Oxide Field-effect Transistors Based on Self-assembly of Colloidal Nanorods.
Baoquan Sun 1 , Henning Sirringhaus 1 Show Abstract
1 Cavendish Laboratory, University of Cambridge, Cambridge United Kingdom
Colloidal zinc oxide (ZnO) nanocrystals are an attractive candidate for a low-temperature and solution-processible semiconductor for high-performance thin-film field effect transistors (TFTs). To obtain reproducible TFTs performance the formation of high-quality films by techniques such as spin-coating is very important. We have found that high-quality nanocrystal films can be obtained from high concentration solutions, which can be achieved by choosing the proper ligand on the ZnO surface. The shape of ZnO can be tuned from nanosphere to nanorods by increasing the reaction time. Here we show that by controlling the shape of the nanocrystals from spheres to rods the device performance can be much improved as a result of increasing particle size, and self-alignment of the nanorods along the substrate. In the as-spun films the interactions between the colloidal nanorods during solution growth lead to the formation of small liquid-crystalline domains with a size on the order of 100 nm in which the nanorods are oriented parallel to each other. And the nanorods are preferentially oriented with their long-axis in the substrate plane. We believe that this oriented in-plane self-assembly of the colloidal nanorods is an important factor contributing to the enhanced mobility of the as-deposited nanorod films compared to nanosphere films. Post-deposition hydrothermal growth in an aqueous zinc ion solution has been found to further enhance grain size and connectivity, and improve device performance. During post-deposition hydrothermal growth, the nanorods grow further along their c-axis forming longer rods. And an increase in the diameter of the nanorods was observed, which appears to be mainly occurring due to fusing of several nanorods. TFT devices made from 65 nm long and 10 nm wide nanorods deposited by spin coating have been fabricated at moderate temperatures 230 oC with mobilities of 0.61 cm2V-1s-1 and on/off ratios of 3×105, which is comparable to the characteristics of a TFT fabricated by traditional sputtering methods
4:45 PM - O5.7
Inorganic Oxide Core Polymer Shell Nanoparticle Films for Use as High K Gate Dielectric in Thin Film Field Effect Transistor Applications.
Ashok Maliakal 1 , Howard Katz 1 2 , Pat Cotts 3 , Shehkar Subramoney 3 , Peter Mirau 4 Show Abstract
1 Department of Materials Research, Bell Laboratories, Murray Hill , New Jersey, United States, 2 Department of Material Science and Engineering, John Hopkins University, Baltimore , Maryland, United States, 3 , Dupont, Wilmington , Delaware, United States, 4 , Air Force Research Labs, Wright Patterson AFB, Ohio, United States
Organic/inorganic core shell nanoparticles have been synthesized using both high K TiO2 and BaTiO3 as the core nanoparticle, and polystyrene as the shell. These materials are easy to process and forms transparent continuous thin films, which exhibit dielectric constant enhancements of over three times that of bulk polystyrene. These new dielectric materials has been incorporated into capacitors and thin film transistors (TFTs). Mobilities approaching 0.2 cm2/Vs have been measured for pentacene TFTs incorporating the new TiO2 polystyrene nanostructured gate dielectric, indicating good surface properties for pentacene film growth. This novel strategy for generating high K flexible gate dielectrics would be expected to be of value in improving organic and flexible electronic device performance.
5:00 PM - O5.8
Improvement of Electrical Characteristics of Pt Schottky Contacts to n-type ZnO using KrF Excimer Laser Tempering.
Min-suk Oh 1 , Dae-kue Hwang 1 , Jae-Hong Leem 1 , Seong-ju Park 1 Show Abstract
1 Department of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of)
5:15 PM - O5.9
Fabrication of Printable SiO2 Insulator Thin Film and (Metal / Printed SiO2 / Organic Semiconductor) Thin Film Transistor
Takehito Kodzasa 1 , Manabu Yoshida 1 , Sei Uemura 1 , Satoshi Hoshino 1 , Toshihide Kamata 1 Show Abstract
1 Photonic Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan
Organic thin film transistors (OTFTs) are very promising for the development of printing electronics technology, which bring us the future low-cost ubiquitous society. In order to take such advantage of OTFTs devices, many researches into the use of the gate insulator prepared by printing process have been performed by using polymeric dielectric materials. However, it is supposed that most polymeric materials are not applicable to the gate insulator of TFT devices because of their poor dielectric strength and instability. Now we succeeded to fabricate superior silicon dioxide (SiO2) insulator thin film from the silazane compound by the low temperature (below 150C) printing process. The important key technique is an irradiation of ultraviolet light. The radius of mean-square values of the SiO2 thin film is estimated at 0.15 nm by the atomic force microscopy measurement, indicating that this printed SiO2 insulator thin film has an extremely smooth surface. The current-voltage measurement of the obtained SiO2 thin film showed a high resistivity in the order of 10 to 13 ohm*cm with well flat characteristic curve until about 7MV/cm of electric field. OTFT device with the printed SiO2 thin film were fabricated using pentacene or poly (3-hexyl thiophene) thin film as organic semiconductor layer. The field effect mobility of the OTFT with pentacene thin film as the organic semiconductor layer was estimated to 0.36 cm2/Vs. The field effect mobility of pentacene OFET using thermally oxidized SiO2 as a gate dielectric was estimated to 0.30 cm2/Vs from the similar measurement. These results demonstrated that the printed SiO2 thin film prepared by this technique excellently useful for the gate insulator of printable OTFTs devices.
5:30 PM - O5.10
Nanocrystalline Barium Strontium Titanate (Ba0.7Sr0.3TiO3) for Ultra Thin Dielectrics
Samar Kalita 1 , Vikas Somani 1 Show Abstract
1 MMAE, University of Central Florida, Orlando, Florida, United States
Nanograin Barium Titanate based ceramics are of interest for applications in ultra thin dielectric layers. In this work, we have successfully synthesized nanocrystalline Barium Strontium Titanate (Ba0.7Sr0.3TiO3 powder in the range of 15 – 20 nm using a simple sol-gel processing route. Barium acetate, strontium acetate and titanium isopropoxide were used as precursors. The BST gel obtained was dried at 200 oC to form powder and subsequently calcined in the temperature range of 400 oC to 700 oC for crystallization. X-Ray Diffraction (XRD) was used to study phase evolution and particle size of the powder. XRD patterns showed increase in peak intensity with increase in calcination temperature. pH of the solution played a major role obtaining pure single phase Ba0.7Sr0.3TiO3 powder. High Resolution Transmission Electron Microscopy (HR-TEM) results showed that Ba0.7Sr0.3TiO3 powder calcined at 700oC had particle size in the range 15-20 nm. Uniaxially pressed powder pellets were used for densification study in the temperature range 950oC to 1150oC. Sintering at 1000oC resulted in highest density. The density at 1000oC increased with the increase in sintering time and reached a maximum at 6 h. XRD patterns showed presence of Ba4Ti13O30 and Sr2Ti5O30 phases with increase in sintering temperature. Electrical properties of nanostructured BST were also studied. This presentation will discuss our work on synthesis, processing and characterization of nanocrystalline Ba0.7Sr0.3TiO3 ceramics.