bluuebunny/crossref_metadata_2025_split huggingface dataset:
An original flexible structure for Organic Photovoltaic Devices
Authors: Sanna Ornella , Cossu Mario , Pilia Tomas , Bonfiglio Annalisa 
Published: April 2011

ABSTRACTA simple idea is proposed for the realization of organic photovoltaic devices on flexible substrates. According to this, a poly(ethylene terephtalate) layer (Mylar), transparent, a few micrometers thick and completely flexible, works as mechanical support. It is an insulating material, which has good mechanical and dielectric properties and, most important, it is completely transparent to ultraviolet light. For this reason it could be suitable for being used as transparent supporting layer for large area photovoltaic devices. Furthermore, its mechanical properties allow to employ it in a roll-to-roll lamination procedure that could give rise to low cost extended films carrying solar cells on the surface.
Electrical Hysteresis of PEDOT/PSS-Metal Contact Devices
Authors: Liu Zhengchun , Su Yi , Varahramyan Kody 
Published: April 2011

AbstractPEDOT/PSS is an air-stable and solution-processable semiconductor polymer with great potential for electronic applications. In this research, we investigated the PEDOT/PSS-metal contacts using Al-PEDOT/PSS-Au as a test device. Abnormal electrical hysteresis phenomena were observed in both the current-voltage and capacitance-voltage characteristics of the device. A model in terms of metal-polymer interfacial MIS structure and ion motion in the polymer is proposed for explanation of the ‘hysteresis’ phenomena.
Electron-Transporting Thiophene-Based Semiconductors Exhibiting Very High Field Effect Mobilities
Authors: Facchetti Antonio , Yoon Myung-Han , Marks Tobin J. 
Published: April 2011

AbstractOrganic semiconductors exhibiting complementary n-type carrier mobility are the key components for the development of the field of “plastic electronics”. We present here a novel series of oligothiophenes designed to improve performance and stability under electron- transporting conditions. Furthermore, the key structural features of these compounds allows additional modifications of the n-type conducting core to achieve material solubility and processability. Thin film transistor (TFT) devices were fabricated employing both vacuum- and solution-deposited semiconducting layers. Field-effect transistor measurements indicate that all the members of this new series are n-type semiconductors with mobilities and Ion:Ioff ratios approaching 1 cm2/(Vs) and 107, respectively. This family represents a key milestone in the design, understanding, and development of the next generation of highly efficient n-type OTFT components.
Temperature Dependent Carrier Transport in Single-Crystalline Si TFTs inside a Location-Controlled Grain
Authors: Rana V. , Ishihara R. , Hiroshima Y. , Abe D. , Inoue S. , Shimoda T. , Metselaar J.W. , Beenakker C. I.M 
Published: April 2011

AbstractTemperature dependant I-V characteristics were measured on single-crystalline Si (c-Si) TFTs fabricated inside a location-controlled grain by [.proportional]-Czochralski process using an excimer-laser. At ON-state, temperature the activation energy (Ea) of the drain current drops to a negative value. The field effect mobility ([.proportional]FE) also decreases with temperature with a power of -1.86, which indicates that, the carriers transport are governed by acoustic phonon scattering. At OFF state with a small gate bias, leakage current is dominated by thermal generation, however the Ea was 0.9eV, i.e., near the band gap value of Si. This suggests that the carrier generation centers are not located at the mid-gap states. These distinctive results from a typical poly-Si TFTs are systematically investigated for c-Si TFTs having ECR- PECVD and LPCVD SiO2 gate insulator.
Organic field-effect transistors with bending radius down to 1 mm
Authors: Sekitani Tsuyoshi , Kawaguchi Hiroshi , Sakurai Takayasu , Someya Takao 
Published: April 2011

AbstractWe have investigated the allowed bending radius of high-quality pentacene field-effect transistors (OFETs) manufactured on a plastic substrate of a polyethylenenaphthalate (PEN) film with a polyimide gate dielectric layer. It is found that the reduction of mobility due to the application of an expansive stress with a radius of curvature (R) smaller than about 1 mm, was only 20 %. Furthermore, the mobility increase by 7 % to 0.28 cm2/Vs on a compressive stress with R=4.6 mm. We also studied the recovery performance after stressing OFETs. No significant change and residual effect in performance has been found after the removal of the compressive bending the device down to a radius of 4.6 mm (1.4 ± 0.1 % in strain). In the analysis of the mechanical flexibility, we demonstrated that our OFETs electrical properties were fairly stable during the application of an expansive and compressive stress down to several mm in bending radius.
Flexible PLED displays and related technologies
Authors: Nisato G. , Mutsaers C. , Buijk H. , Duineveld P. , Janssen E. , Goede J. de , Bouten P. , Zuidema H. 
Published: April 2011

AbstractFlexible, free shape displays are the enabling technology for new robust, lightweight, extremely thin, portable electronic devices. Polymer Light Emitting Diodes (PLED) are especially suited for these applications, due to their fast response time, low voltage, high luminous efficiency and viewing angle performance. On the other hand, PLED displays are extremely sensitive to moisture and oxygen. Substrate materials provided with high performance hermetic and conducting layers are therefore an essential component for manufacturing these flexible devices. Polymer based substrates provide the necessary mechanical flexibility; they also require several thin, brittle, functional inorganic layers such diffusion barriers and transparent electrodes. The structural integrity, dimensional stability and thermal properties of the substrate stack are crucial to insure device functionality and reliability. For polymer-based substrate several effects lead to dimensional variation of the substrates, such as solvent uptake, physical ageing of the polymer base, thermal expansion and stress induced deformations. These effects must be taken into account to successfully perform classic photolithographic steps.Ink-jet printing is a critical enabling technology for flexible PLED displays, providing a customizable means to dispense solution-based polymers onto a flexible substrate, allowing for multi-color devices. On the other hand, IJP must meet several challenges, especially to comply with industrial applications. For example, accurate landing position of the droplets to form homogeneous hole-transport and electroluminescent layers as well as good wetting characteristic of the substrates must be obtained with reliable high throughput techniques.
Mechanical Performance of Thin Films in Flexible Displays
Authors: Lewis Jay , Grego Sonia , Vick Erik , Chalamala Babu , Temple Dorota 
Published: April 2011

AbstractThe use of brittle materials in flexible displays requires the understanding of the mechanical limitations of the materials and the various display architectures. We discuss various approaches to mechanical bend tests for components of flexible displays and describe a new test method based on a three-axis motion. We discuss the mechanical limitations of indium tin oxide (ITO) as a transparent conductor, and present results for a more mechanically robust multilayer transparent conductor made of an ITO-metal-ITO (IMI) stack. The IMI structures showed dramatically improved mechanical properties when subjected to bending both as a function of radius of curvature as well as number of cycles to a fixed radius. Organic light emitting devices fabricated on IMI anodes showed improved performance compared with those made on ITO anodes at current densities greater than 1 mA/cm2 due to the improved conductivity of the anode. We discuss the difficulties in analysis of the mechanical failure of transparent thin film permeation barriers. We present a novel approach for etching barrier-coated polymer substrates such that film cracking is readily visible. We report on the bend test results for sputter- deposited SiOxNy films.
Technique for Monitoring the Etching Rate of Alumina
Authors: Deb B. , Altay A. , Gilliss S. R. , Munoz N.E. , Carter C. B. 
Published: April 2011

AbstractThe effect of chemical and thermal treatments on the grains and grain boundaries of polycrystalline μ-Al2O3has been examined using a combination of microscopy techniques. Commercially available alumina samples (Lucalox™) were chemically etched in phosphoric acid at 200°C in increments of 15 min. Thermal treatments were carried out at 1650°C before chemical treatments. Using maps obtained by visible-light microscopy (VLM) as a guide, the same regions were re-examined using atomic force microscopy (AFM) after subsequent treatments. Variations in the dissolution rates of different grains and grain boundaries could then be studied using AFM. The geometry of the grain-boundary grooves was compared after thermal and chemical treatments. Electron backscattered diffraction (EBSD) patterns recorded in the scanning electron microscope (SEM) were used to obtain crystallographic orientations of the grains which enabled variations in dissolution rates between grains to be correlated to orientation.
Grain Boundary Engineering of Copper Shaped-Charge Liners
Authors: Blobaum Kerri J.M. , Stölken James S. , Kumar Mukul 
Published: April 2011

SummaryGrain boundary engineering technology has been successfully transferred from rolling and forging to back-extrusion, and back- extruded copper shaped-charge liners with engineered microstructures have been produced. The grain-boundary engineered SCLs have special boundary fractions of 0.60 and 0.66, compared to 0.48 in a conventionally processed SCL. It is hoped that these engineered SCLs will perform better through a combination of a delayed onset of plastic instability and an improved resistance to void nucleation and coalescence.Previous work demonstrates that SCL performance is affected by microstructure, and there is significant evidence which shows that microstructure influences both the fracture and constitutive responses of a material. For SCLs, constitutive properties which affect both the strength and stability of a material are important to performance. In the work described here, the focus is on improving stability properties such as strain-hardening rate and strain-rate sensitivity through grain boundary engineering.Initial mechanical tests of grain boundary engineered copper indicate that its yield strength is nearly the same as conventionally processed material, even though the engineered sample has a larger grain size. Yield strength certainly affects the strength of an SCL, but its effect on stability, in terms of delaying the onset of plastic instability in a jet, is still under investigation. Although we can measure constitutive properties such as yield strength and strain to failure in the laboratory, the true effects of grain boundary engineering on SCL performance can only be measured in actual tests of the liners. Therefore, conventionally processed and grain boundary engineered SCLs will be fielded in real shaped-charges.
Modeling and Simulation of the Percolation Problem in High-Tc Superconductors: Role of Crystallographic Constraints on Grain Boundary Connectivity
Authors: Frary Megan , Schuh Christopher A. 
Published: April 2011

AbstractSuperconductivity in high-Tc materials is often modeled as a percolation problem in which grain boundaries are classified as strong or weak-links for current transmission based on their disorientation angle. Using Monte Carlo simulations, we have explored the topology and percolation thresholds for grain boundary networks in orthorhombic and tetragonal polycrystals where the grain boundary disorientations are assigned in a crystallographically consistent manner. We find that the networks are highly nonrandom, and that the percolation thresholds differ from those found with standard percolation theory. For biaxially textured materials, we have also developed an analytical model that illustrates the role of local crystallographic constraint on the observed nonrandom behavior.
The Er3+ and Yb3+-related emission from Er, Yb co-implanted Al0.70Ga0.30As/GaAs substrates prepared MOCVD method
Authors: Arai Tomoyuki , Uekusa Shin-ichiro 
Published: April 2011

ABSTRACTYtterbium (Yb) ions were co-implanted into Al0.70Ga0.30As:Er substrates at room temperature. The photoluminescence (PL) and PL lifetime were characterized. Co-implanted Yb3+ enhanced PL intensity of Er3+-related emission. Er3+-related main peak (1538.2 nm), in addition to Yb3+ dose, was enhanced approximately twice. The energy transfers from 2F5/2 (the first excited state) → 2F7/2 (the grand excited state) of Yb3+ to 4I11/2 (the second excited state) → 4I15/2 (the grand excited state) and 4I15/2 → (the first excited state) 4I15/2 of Er3+ was observed.
First-principles Calculation of Electron Mobilities in Ultrathin SOI MOSFETs
Authors: Evans Matthew H. , Zhang Xiaoguang , Joannopoulos John D. , Pantelides Sokrates T. 
Published: April 2011

ABSTRACTUltrathin silicon-on-insulator (UTSOI) technology1 has emerged as a key candidate for sub-100nm gate length CMOS devices. Recent experiments have characterized MOSFETs with silicon channels as thin as 1nm (four atomic layers of silicon),2,3 and found them to be well-behaved electrically. Quantum effects are important to the electron transport in such devices, and the penetration of the electron wavefunction into the gate oxide introduces new scattering mechanisms. We introduce here a novel method for first-principles calculation of electron mobilities in ultrathin SOI channels, including surface roughness and defect scattering. The electronic structure and scattering potentials are calculated with Density Functional Theory in the Local Density Approximation (DFT-LDA), and the mobility is calculated through Green's functions. The method requires little computational effort beyond that of the DFT-LDA calculations, and allows the calculation of temperature- and carrier concentration-dependent mobilities. Since the silicon-oxide interface is treated at the atomic-scale, the mobility contributions of different defects (e.g. suboxide bonds, oxide protrusions) and impurities (e.g. nitrogen, hydrogen) can be calculated separately, giving a precise physical picture of channel electron transport.
High Quality MPCVD Epitaxial Diamond Film for Power Device Application
Authors: Yang Jie , Huang Weixiao , Chow T. P. , Butler James E. 
Published: April 2011

ABSTRACTAs a wide bandgap (5.47 eV) semiconductor material, single crystal diamond has high electron mobility (reportedly between 2000 and 4400 cm2V-1s-1), high electron saturation velocity (2×107 cms-1), high breakdown voltage (>107 Vcm-1), and high thermal conductivity (>21 Wcm-1K-1). Diamond-based semiconductor devices offer the potential of operation at high voltages, power levels, temperatures and under extreme radiation conditions. In this work, we present our effort to grow high quality homo-epitaxial diamond films on (100)-single crystal diamond substrates by microwave plasma chemical vapor deposition (MPCVD). The growth rate can vary from 0.01 to 100 micrometers per hour, depending on growth conditions, doping, and quality; and using a “lift-off” process, free-standing homo-epi films with remarkably low p-type doping (1×1014–1×1017 cm-3) and exceptionally low compensation ∼ 1×1013 cm-3 have been made. Vertical and lateral structure high voltage diamond Schottky rectifiers have been built for frequency dependent capacitance-voltage (C-V), and current-voltage (I-V) measurements. A breakdown voltage of 8 kV at 100 μm distance and 12.4 kV at 300 μm distance is recorded for lateral structure devices without Ohmic contact (back to back Schottky contacts), while an un-optimized vertical device with an back-side Ohmic contact has demonstrated a forward voltage drop of 7 V at 18 A/cm2 in a device that can only block 600 V. New test results show 3.7 kV blocking voltage vertical devices on 20 μm freestanding MPCVD diamond film. This data shows that the quality of diamond film extremely affect the electrical properties of the built devices.
Metal-oxide Semiconductor Field-effect Transistors using Single ZnO Nanowire
Authors: Heo Young-Woo , Kang B. S. , Tien L. C. , Kwon Y. , La Roche J. R. , Gila B. P. , Ren F. , Pearton S. J. , Norton D. P. 
Published: April 2011

ABSTRACTSingle ZnO nanowire metal-oxide semiconductor field effect transistors (MOSFETs) were fabricated using nanowires grown by site selective Molecular Beam Epitaxy. When measured in the dark at 25°C, the depletion-mode transistors exhibit good saturation behavior, a threshold voltage of ∼-3V and a maximum transconductance of order 0.3 mS/mm. Under ultra-violet (366nm) illumination, the drain-source current increase by approximately a factor of 5 and the maximum transconductance is ∼ 5 mS/mm. The channel mobility is estimated to be ∼3 cm2 /V.s, which is comparable to that reported for thin film ZnO enhancement mode MOSFETs and the on/off ratio was ∼25 in the dark and ∼125 under UV illumination.
Beam Induced Lateral Epitaxy of GaAs on a GaAs/Si Template
Authors: Naritsuka Shigeya , Saitoh Koji , Kondo Toshiyuki , Maruyama Takahiro 
Published: April 2011

ABSTRACTBeam induced lateral epitaxy (BILE) on truncated ridges was applied to the heteroepitaxial growth of GaAs on a Si substrate. A GaAs buffer layer was formed on the Si substrate, and then this GaAs/Si template was used as a substrate for the BILE process. As a result, overgrown regions of GaAs of widths as large as 6.5 μm were grown laterally from the sides of the truncated ridges. The growth regions had a flat, smooth top surface consisting of a (111) facet. Although stacking faults from the GaAs/Si template remained in the growth region, which are unfavorable for device applications, the lateral grown region has no dislocations. Thus, the BILE method is useful for reducing dislocations in heteroepitaxy.
Sublimation growth of AlN bulk crystals by seeded and spontaneous nucleation methods
Authors: Balakrishnan Krishnan , Banno Masao , Nakano Kiyotaka , Narita Go , Tsuchiya Noritaka , Imura Masataka , Iwaya Motoaki , Kamiyama Satoshi , Shimono Kenji , Noro Tadashi , Takagi Takashi , Amano Hiroshi , Akasaki Isamu 
Published: April 2011

ABSTRACTSingle crystals of AlN have been grown by seeded (on SiC substrates) and unseeded (spontaneous nucleation) sublimation techniques. Tantalum carbide coated graphite crucibles were used. Temperature gradient and source-substrate distance have been found to be the most influencing parameters of crystal growth. AlN crystals of maximum dimension 12 mm (length) × 10 mm (width) × 300 μm (thickness) were grown on 6H-SiC substrates and the best (0002) oriented crystal showed an XRD omega rocking curve FWHM of 4.81 arcmin. AlN nucleated as independent hexagonal islands and coalesced as growth progressed on. Growth rate of AlN grown on C-face SiC has been found to be higher than that on Si-face SiC. Tantalum carbide coated crucibles have been found to be better suited for AlN growth as the impurity incorporation in to the crystals due to crucible was very less. Spontaneously nucleated crystals exhibited an incompleted pyramid-like structure with (1010) and (1100) as their prominent faces.
Extended X-ray Absorption Fine Structure Studies of InGaN Epilayers
Authors: Katchkanov V. , O'Donnell K.P. , Mosselmans J.F.W. , Hernandez S. , Martin R.W. , Nanishi Y. , Kurouchi M. , Watson I. , Van der Stricht W. , Calleja E. 
Published: April 2011

ABSTRACTThe local structure around In atoms in InGaN epilayers grown by Molecular Beam Epitaxy (MBE) and by Metal-Organic Chemical Vapour Deposition (MOCVD) was studied by means of Extended X-ray Absorption Fine Structure (EXAFS). The averaged In fraction of MOCVD grown samples ranged from 10% to 40% as estimated by Electron Probe Microanalysis (EPMA). The In fraction of MBE grown samples spanned the range from 13% to 96%. The In–N bond length was found to vary slightly with composition, both for MBE and MOCVD grown samples. Moreover, for the same In content, the In-N bond lengths in MOCVD samples were longer than those in MBE grown samples. In contrast, the In-In radial separations in MOCVD and MBE samples were found to be indistinguishable for the same In molar fraction. The In-Ga bond length was observed to deviate fromaveragecation-cation distance predicted by Vegard's law for MBE grown samples which indicates alloy compositional fluctuations.
Reduction of Threading Dislocations in GaN grown on ‘c’ plane sapphire by MOVPE
Authors: Datta R. , Kappers M. J. , Barnard J. S. , Humphreys C. J. 
Published: April 2011

ABSTRACTThe reduction of threading dislocations (TDs) in GaN is very important as TDs act as non-radiative recombination centres and generally reduce the luminescence efficiency of GaN-based optoelectronic devices, particularly UV emitting devices. In order to reduce the density of TDs, we have used an in-situ ELO technique by depositing a non-uniform SiNx mask (as revealed by STEM-EDX) using simultaneous flow of silane and ammonia gas, either on a sapphire substrate or on a GaN pseudo-substrate. The effect of several growth parameters, such as V/III ratio, duration of Si/N treatment, pressure and temperature, on the morphology, structural quality and reduction mechanisms of TDs in GaN have been investigated and the effects of the first two parameters are reported here. To start the epilayer growth with a low V/III ratio gives rise to predominantly 3D growth, forming islands with multiple inclined facets and a vanishing top (0001) facet. A high V/III ratio enhances the lateral growth, and islands with inclined {-2112} facets together with wide flat top (0001) facets are formed. The duration of the Si/N treatment and the low V/III ratio growth regime are optimised in order to reduce the TD density down to 8×107 cm−2, as measured from plan-view TEM images. It is observed that TDs bend through 90° at inclined side facets. The role of atomic ledges moving across inclined facets which are responsible for bending the line direction of the TDs is briefly discussed.
Spintronics in Nitrides
Authors: Dietl Tomasz 
Published: April 2011

ABSTRACTThe report of progress in studies of magnetism in the group III nitrides doped with transition metals and rare earth elements is described taking into account conclusions stemming from the recent advances in understanding of Ga1−xMnxAs, GaAs:MnAs, and related systems. The actual position of magnetic impurities in the host lattice as well as a possible role of structural, atomic, and electronic phase separation is described. The question whether the hole introduced by the Mn impurities is localized tightly on the Mn d-levels or rather on the hybridized p-d bonding states is addressed. The nature of spin-spin interactions and magnetic phases, as provided by theoretical and experimental findings, is outlined, and possible origins of high and low temperature ferromagnetism observed in these systems is discussed. Finally, the suitability of nitrides for single spin manipulation is analyzed considering linear in k spin splitting.
Improved Optoelectronic Characteristics of Nanocrystalline Porous Silicon by High-Pressure Water Vapor Annealing
Authors: Gelloz Bernard , Kojima Akira , Koshida Nobuyoshi 
Published: April 2011

ABSTRACTA high-pressure H2O vapor annealing technique has been applied to nanocrystalline porous silicon (PS). The effects on the photoluminescence (PL) are reported here for PS samples of different initial porosities, in different conditions of the annealing pressure. A drastic enhancement of the PL intensity has been achieved, while both the emission band and the peak wavelength remain almost unchanged. The best results have been obtained with an initial PS porosity of about 68 %. The resulting layers consist of Si nanocrystals embedded into an SiO2tissue. The high external quantum efficiency obtained in treated PS (23%) may be attributed mainly to a very high surface passivation by high quality oxide and an enhancement in the localization of photoexcited carriers.