bluuebunny/crossref_metadata_2025_split huggingface dataset:
Light Trapping effects in Thin Film Silicon Solar Cells
Authors: Haug Franz-Josef , Söderström Thomas , Dominé Didier , Ballif Christophe 
Published: August 2010

AbstractWe present advanced light trapping concepts for thin film silicon solar cells. When an amorphous and a microcrystalline absorber layers are combined into a micromorph tandem cell, light trapping becomes a challenge because it should combine the spectral region from 600 to 750 nm for the amorphous top cell and from 800 to 1100 for the microcrystalline bottom cell. Because light trapping is typically achieved by growing on textured substrates, the effect of interface textures on the material and electric properties has to be taken into account, and importantly, how the surface textures evolve with the thickness of the overgrowing layers. We present different scenarios for the n-i-p configuration on flexible polymer substrates and p-i-n cells on glass substrate, and we present our latest stabilized efficiencies of 9.8% and 11.1%, respectively.
Defect Study of Polycrystalline–silicon Seed Layers made by Aluminum Induced Crystallization
Authors: Venkatachalam Srisaran , Van Gestel Dries , Gordon Ivan 
Published: August 2010

AbstractA polycrystalline silicon (pc-Si) thin film with large grains on a low-cost non-Si substrate is a promising material for thin-film solar cells. One possibility to grow such a pc-Si layer is by aluminum-induced crystallization (AIC) followed by epitaxial thickening. The best cell efficiency we have achieved so far with such an AIC approach is 8%. The main factor that limits the efficiency of our pc-Si solar cells at present is the presence of many intra-grain defects. These intra-grain defects originate within the AIC seed layer. The defect density of the layers can be determined by chemical defect etching. This technique is well suited for our epitaxial layers but relatively hard to execute directly on the seed layers. This paper presents a way to reveal the defects present in thin and highly-aluminum-doped AIC seed layers by using defect etching. We used diluted Schimmel and diluted Wright etching solutions. SEM pictures show the presence of intra-grain defects and grain boundaries in seed layers after defect etching, as verified by EBSD analyses. The SEM images of diluted Wright etched pc-Si seed layer shows that grain boundaries become much better visible than with diluted Schimmel etch.
First-principles Modeling of Structure, Vibrations, Electronic Properties and Bond Dynamics in Hydrogenated Amorphous Silicon: Theory versus Experiment
Authors: Shkrebtii Anatoli , Kupchak Ihor , Gaspari Franco 
Published: August 2010

AbstractWe carried out extensive first-principles modeling of microscopic structural, vibrational, electronic properties and chemical bonding in hydrogenated amorphous silicon (a-Si:H) in a wide range of hydrogen concentration and preparation conditions. The theory has been compared with experimental results to comprehensively characterize this semiconductor material. The computer modeling includes ab-initio Molecular Dynamics (MD), atomic structure optimization, advanced signal processing and computer visualization of dynamics. We extracted parameters of hydrogen and silicon bonding, electron charge density and calculated electron density of states (EDOS) and hydrogen diffusion. A good agreement of the theory with various experiments allowed us to correlate microscopic processes at the atomic level with macroscopic properties. Here we focus on correlation of the amorphous structure of the material, atom dynamics and electronic properties. These results are of increasing interest due to extensive application of a-Si:H in modern research and technology and to the significance of detailed understanding of the material structure, bonding, disordering mechanisms and stability.
Single and Mixed Self-Assembled Monolayers of Phenyl Species on SiO2 with Various Ring to Ring Interactions
Authors: Gadenne Virginie , Desbief Simon , Patrone Lionel 
Published: August 2010

AbstractWe studied the formation of phenylalkyltrichlorosilane self-assembled monolayers on native oxide covered silicon. After a first chemisorption step in the monolayer growth, the presence of the short alkyl chain (3-4 carbon atoms) is responsible for a second growth step which corresponds to the arrangement between molecules. We found that this packing step is accelerated by replacing phenyl by pentafluoro-phenyl rings, possibly due to quadrupolar interactions between fluorinated cycles. Furthermore we demonstrate that mixing phenyl and pentafluoro-phenyl molecules leads to an even faster packing step which is accounted for by hydrogen bonding CH...FC in a face to face phenyl/pentafluoro-phenyl arrangement. We believe these results allow improving charge delocalization over conjugated molecular domains. In a second part, we studied the phase separation between phenyl-alkyltrichlorosilane and octadecyltrichlorosilane (OTS) molecules. Improving the phase separation was studied using ring to ring interactions afore-analyzed. We show phase separation is improved and OTS islands are smaller with phenyl species that involve stronger ring to ring interactions. The best case is obtained with mixing phenyl and pentafluoro-phenyl rings using hydrogen bonds for packing together the aromatic species. These results demonstrate improved control of SAM composition and morphology essential to further use the obtained islands for building molecular devices.
Towards Greatly Improved Efficiency of Polymer LED
Authors: Zhou Zhang-Lin , Sheng Xia , Zhao Lihua , Gibson Gary , Lam Sity , Nauka K. , Brug James 
Published: August 2010

AbstractPolymer light-emitting diodes (PLEDs) show great promise of revolutionizing display technologies. The archetypical multilayer PLED heterostructure introduces numerous chemical and physical challenges to the develoment of efficient and robust devices. These layered structure are formed from solution based spin-casting or printing with subsequesnt removal of the solvent. However, solvent from the freshly deposited film may dissolve or partially dissolve the underlying layer resulting in loss of the desired structure and corresponding device functionality. Undesirable changes in the morphology and interfaces of the polymer films are another detrimental effect associated with solvent removal. Herein, we demonstrated that by embedding hole transporting materials (HTLs) in a cross-linked polymer matrix, the total luminance and external quantum efficiency were greatly improved over devices without this HTL layer.
Degradation of Ir(ppy)2(dtb-bpy)PF6 iTMC OLEDs
Authors: Goldberg Velda , Kaplan Michael D. , Soltzberg Leonard , Armira Dolly , Bigelow Megan , Bitzas Stephanie , Brady Rachel , Browne Shannon , Dichiaro Bianca , Foley Heather , Hutchinson Lauren , Inglis Alison , Kawamoto Nicole , McLaughlin Amanda , Millett Caitlin , Nasri Hanah , Newsky Sarah , Pham Tram , Saikin Cassandra , Scharpf Mary , Trieu Melissa , Malliaras George G. , Bernhard Stefan 
Published: August 2010

AbstractSimplicity of construction and operation are advantages of iTMC (ionic transition metal complex) OLEDs compared with multi-layer OLED devices. Unfortunately, lifetimes do not compare favorably with the best multi-layer devices. We have previously shown for Ru(bpy)3(PF6)2 based iTMC OLEDs that electrical drive produces emission-quenching dimers of the active species. We report evidence here that a chemical process may also be implicated in degradation of devices based on Ir(ppy)2(dtb-bpy)PF6 albeit by a very different mechanism. It appears that degradation of operating devices made with this Ir-based complex is related to current-induced heating of the organic layer, resulting in loss of the dtb-bpy ligand. (The dtb-bpy ligand is labile compared with the cyclometallated ppy ligands.) Morphological changes observed in electrically driven Ir(ppy)2(dtb-bpy)PF6 OLEDs provide evidence of substantial heating during device operation. Evidence from UV-vis spectra in the presence of an electric field as well as MALDI-TOF mass spectra of the OLED materials before and after electrical drive add support for this model of the degradation process.
Stress Gradients Observed in Cu Thin Films Induced by Capping Layers
Authors: Murray Conal E. , Besser Paul R. , Witt Christian , Jordan-Sweet Jean L. 
Published: August 2010

AbstractGlancing-incidence X-ray diffraction (GIXRD) has been applied to the investigation of depth-dependent stress distributions within electroplated Cu films due to overlying capping layers. 0.65 μm thick Cu films plated on conventional barrier and seed layers received a CVD SiCxNyHz cap, an electrolessly-deposited CoWP layer, or a CoWP layer followed by a SiCxNyHz cap. GIXRD and conventional X-ray diffraction measurements revealed that strain gradients were created in Cu films possessing a SiCxNyHz cap, where a greater in-plane tensile stress was generated near the film / cap interface. The constraint imposed by the SiCxNyHz layer during cooling from the cap deposition temperature led to an increase in the in-plane stress of approximately 180 MPa from the value measured in the bulk Cu. However, Cu films possessing a CoWP cap without a SiCxNyHz layer did not exhibit depth-dependent stress distributions. Because the CoWP capping deposition temperature was much lower than that employed in SiCxNyHz deposition, the Cu experienced elastic deformation during the capping process. Cross-sectional transmission electron microscopy indicated that the top surface of the Cu films exhibited extrusions near grain boundaries for the samples undergoing the thermal excursion during SiCxNyHz deposition. The conformal nature of these caps confirmed that the morphological changes of the Cu film surface occurred prior to capping and are a consequence of the thermal excursions associated with cap deposition.
Research Progress in the Resistance Switching of Transition Metal Oxides for RRAM Application: Switching Mechanism and Properties Optimization
Authors: Wang Qun , Li Xiaomin , Chen Lidong , Cao Xun , Yang Rui , Yu Weidong 
Published: August 2010

AbstractElectric-induced resistance switching (EIRS) effect based on transition metal (TM) oxides, such as perovskite manganites (Pr1-xCaxMnO3, La1-xCaxMnO3) and binary oxides (NiO, TiO2 and CoO) etc, has attracted great interest for potential applications in next generation nonvolatile memory known as resistance random access memory (RRAM). Compared with other nonvolatile memories, RRAM has several advantages, such as fast erasing times, high storage densities, and low operating consumption. Up to date, the switching mechanism, property improvement and new materials exploitation are still the hotspots in RRAM research.In this report, the main results of resistance switching of two kinds of TM oxides including La0.7Ca0.3MnO3 and TiO2 were presented. Based on the I-V characteristics, the field-direction dependence of resistance switching (RS) behavior, and the conduction process analysis, the EIRS mechanisms were studied in detail. For the La0.7Ca0.3MnO3 film, the EIRS mechanism was related to the carrier injected space charge limited current (SCLC) conduction controlled by the traps existing at the interface between top electrode and La0.7Ca0.3MnO3 film. The RS behavior is produced by the trapping/detrapping process of carriers under different voltages. For the TiO2 film, both unipolar and bipolar RS behavior can be obtained in our experiments. The interface controlled filamentary mechanism was proposed to explain the unipolar EIRS in nanocrystalline TiO2 thin films, while the bipolar RS behavior may be related to the charge trapping or detrapping effect. In addition, it was confirmed that the I-V sweeps in vacuum environment, the applying of asymmetry pulse pairs and the oxygen annealing of films can improve the endurance of the EIRS devices. Our researches will provide some meaningful clues to understanding the EIRS mechanism and some useful pathways for the development of RRAM devices.
Investigation of Resistance Switching Properties in Undoped and Indium Doped SrTiO3 Thin Films Prepared by Pulsed Laser Deposition
Authors: Li Xiaomin 
Published: August 2010

AbstractIn this paper, the undoped SrTiO3 (STO) and Indium doped STO (SrTi1-xInxO3: STIO) thin films were grown on Pt/Ti/SiO2/Si substrates by pulsed laser deposition with low substrate temperature. For undoped STO film, the influences of the forming processes on their resistive switching properties were studied by current and voltage controlled I-V sweeps, respectively. An obvious current controlled negative differential conductance phenomenon was found in both polarities of the electrical field. However, for low Indium doped STIO (x=0.1), the filament related resistance switching was observed in both the current and voltage I-V sweeps. And for high Indium doped STIO (x=0.2), a resistance switching with a reverse direction change to that in undoped STO can be obtained by a proper forming process. Based on these results, the reversible change of the Schottky like barrier at the grain boundary by the migration of oxygen vacancies were proposed to interpret the mechanism of the resistance switching.
Growth of Epitaxial ZnO:Mn/ZnO:V Heterostructures and Ferroelectric-ferromagnetic Characterization
Authors: Mukherjee Devajyoti , Dhakal Tara , Srikanth Hariharan , Mukherjee Pritish , Witanachchi Sarath 
Published: August 2010

AbstractThe wide band gap semiconductor ZnO is well known for its multifunctionality in the form of ferromagnetism (FM), piezoelectricity, and magneto optics. ZnO has been found to grow with intrinsic oxygen deficiencies which in turn are believed to give ferromagnetism and high conductivity in this material. Doping Zn2+ sites by V5+ ions creates a mixed valency as well as strain in the original ZnO hexagonal structure because of the reduced ionic size of vanadium. The mixed valency creates charge polarity between Zn-O and V-O bonds. This charge polarity and the rotation of the nonlinear V-O bonds with respect to Zn-O bonds under electric field have been shown to produce ferroelectricity. Furthermore, Mn doping of ZnO has also shown enhancement in ferromagnetic properties in ZnO. For this material to be a viable ferromagnetic material the magnetic properties should not be from segregated phases. In the present study we have grown undoped, Mn, and V doped ZnO thin films using pulsed laser deposition (PLD). ZnO target with 2% atomic Mn doping and a target with 0.5% atomic V doping were prepared by solid state reactions and sintering. Films were grown both epitaxially on sapphire substrates and in polycrystalline form on silicon substrates. Magnetization measurements by the PPMS showed M vs. H hysteresis loops with saturation for all ZnO: Mn films. V doped films showed high saturation polarization for film deposited at high pressures. We have also fabricated epitaxial bilayers of ZnO:V/ZnO:Mn on sapphire substrates. Ferroelectric and ferromagnetic properties of these heterostructures are presented.
Fabrication and Magneto-Capacitance Measurements of PbNb0.02Zr0.2Ti0.8O3/La0.7Sr0.3MnO3/SiO2/Si Structure Grown by Chemical Solution Deposition
Authors: Kotru Sushma , Nampoori Harshan V. 
Published: August 2010

AbstractMultiferroic composite thin films consisting of PbNb0.02Zr0.2Ti0.8O3 (PNZT) and La0.7 Sr0.3 MnO3 (LSMO) were deposited on SiO2/Si substrates. SiO2 films were deposited by pulsed electron deposition and LSMO and PNZT films were prepared using chemical solution deposition process using a metal organic deposition route. Individual films and the test structure PNZT/LSMO/ SiO2/Si were characterized using various characterizing techniques. Preliminary results of magnetic field dependent capacitance (magneto-capacitance) on the test structure are reported. A change in capacitance from 18.92 pf to 5.49 pf is observed as frequency changes from 50 KHz to 1 MHz, when no external magnetic field is applied. When a magnetic field of 330 Oe (positive or negative) is applied, the change in magneto-capacitance is appreciable, with a maximum change of 37 % being observed at a frequency of 1 MHz.
Photonic Crystals: Shaping the Flow of Thermal Radiation
Authors: Čelanović Ivan , Ghebrebrhan Michael , Yeng Yi Xiang , Kassakian John , Soljačić Marin , Joannopoulos John 
Published: August 2010

AbstractIn this paper we explore theory, design, and fabrication of photonic crystal (PhC) based selective thermal emitters. In particular, we focus on tailoring spectral and spatial properties by means of resonant enhancement in PhC's. Firstly, we explore narrow-band resonant thermal emission in photonic crystals exhibiting strong spectral and directional selectivity. We demonstrate two interesting designs based on resonant Q-matching: a vertical cavity enhanced resonant thermal emitter and 2D silicon PhC slab Fano-resonance based thermal emitter. Secondly, we examine the design of 2D tungsten PhC as a broad-band selective emitter. Indeed, based on the resonant cavity coupled resonant modes we demonstrate a highly selective, highly-spectrally efficient thermal emitter. We show that an emitter with a photonic cut-off anywhere from 1.8 μm to 2.5 μm can be designed.
High Temperature Plasmonic Photonic Crystal MEMS Emitter
Authors: Puscasu Irina , Johnson Edward , Taylor Andrew , Schell Brent , Schaich William , Biswas Rana 
Published: August 2010

AbstractWe describe a new class of plasmonic photonic crystal emitters integrated into a MEMS platform for high temperature-intensity, high speed, and high efficiency tuned emitting and sensing applications in the infrared. We exploit 2D organized metallo-dielectric surface structures for angular and spectral control of reflection, absorption and emission from surfaces in the infrared. We have built a FDTD model that incorporates complex frequency dependent properties and provides quantitative agreement with measured spectral data. High temperature materials and special fabrication techniques allow high temperature operation. This technology offers new solutions for spectral control with application in thermophotovoltaic (TPV) energy conversion. Built on a MEMS platform, for thermal isolation from the environment, these devices also modulate at high speed, opening new applications in spectroscopy, infrared imaging, and signaling. Demonstrated wafer-level vacuum sealing improves the wall plug efficiency dramatically. We describe device architecture and fabrication considerations for plasmonic photonic crystal structures which simultaneously act as emitters and sensors in a defined narrow waveband radiation. In particular, this combined capability opens new avenues for research for vital commercial applications such as environmental protection, household safety, bio-hazardous material identification, meteorology and industrial environments.
Radiation Heat Transfer in Porous Materials
Authors: Shklover Valery , Braginsky Leonid , Mishrikey Matthew , Hafner Christian 
Published: August 2010

AbstractThe effect of porosity on the radiation component of the thermal conductivity of the thermal barrier coatings is studied. Heat transfer in the disordered porous structures as well as the porous photonic band-gap structures is investigated. The pores, which size is comparable with the characteristic radiation wavelength λmax=2897.8/T μm, were found to be most efficient obstacles for the heat radiation.
Origins of Twinned Microstructures in B12As2 Epilayers Grown on (0001) 6H-SiC and Their Influence on Physical Properties
Authors: Zhang Yu , Chen Hui , Zhang Ning , Dudley Michael , Gong Yinyan , Kuball Martin , Xu Zhou , Zhang Yi , Edgar James , Zhang Lihua , Zhu Yimei 
Published: August 2010

AbstractThe defect structure in B12As2 epitaxial layers grown at two different temperatures on (0001) 6H-SiC by chemical vapor deposition (CVD) was studied using synchrotron white beam x-ray topography (SWBXT) and high resolution transmission electron microscopy (HRTEM). The observed differences in microstructures were correlated with the differences in nucleation at the two growth temperatures. The effect of the difference in microstructure on macroscopic properties of the B12As2 was illustrated using the example of thermal conductivity which was measured using the 3-ω technique. The relationship between the measured thermal conductivity and observed microstructures is discussed.
Accelerating Laboratory Thin Film Photovoltaic Innovation into Commercial Production
Authors: Seymour Fred H. 
Published: August 2010

AbstractAlternative energy sources such as thin film photovoltaics can be accelerated by improving the rapid and successful transition from laboratory research innovation to commercial production. Most laboratory research and development is on a small scale and its production is in small volumes. It focuses on exploration, discovery, and understanding. When the successful innovation is commercialized, both the scale and the volume increase dramatically and the focus shifts to performance, reliability, yield and cost. This transformation can be accelerated by closely managing risk and by integrating the equipment design and the process development. Also, the cadmium telluride photovoltaic technology has properties that make it more amenable to rapid scale up to low cost and high volume manufacturing.
A CdTe Thin Film Module Factory with a Novel Process
Authors: Romeo Nicola , Bosio Alessio , Romeo Alessandro , Mazzamuto Samantha 
Published: August 2010

AbstractThe CdTe thin film module technology can be considered mature for large scale application.First Solar is now capable of producing more than 400MW/year of CdTe modules and it is still increasing its production. First Solar also announced that they can get a production cost close to 1$/W. A further cost reduction will render this kind of energy production competitive with the energy obtained from fossil fuels.In our laboratory we developed a novel dry process that could further reduce the production cost.This process is now being used by a new company (Arendi Spa) in a line that will produce ∼15-18MW/year. Half of the line has been already built and the complete line should be ready in July 2009. The module production will start at the end of 2009.
The Influence of CuCl Treatment on the PL Spectra of CdTe Thin Film, Component of CdS/CdTe Heterojunctions
Authors: Vatavu Sergiu A , Zhao Hehong , Caraman Iuliana M , Gasin Petru A , Morel Don L , Ferekides Chris S 
Published: August 2010

AbstractTechnology variations involving Cu and Cl impurities are among the major performance influencing factors for CdS/CdTe thin film solar cells. CuCl and CdCl2 influence on the energetic diagram of impurity levels with respect to variation of deposition parameters has been investigated. A comparative analysis has been carried out by using low temperature photoluminescence (PL) studies (17-98K) of CdTe thin films in the device configuration (from CdS/CdTe inteface and CdTe sides). To study the effect of CuCl influence, as-deposited, annealed heterojunctions, with CuCl treatment of CdS have been investigated.
Growth Conditions Effect on the Structure and Optical Properties of ZnO Thin Films Synthesized by rf magnetron Sputtering
Authors: Angelats-Silva Luis , Tomar Maharaj S. , Perales-Perez Oscar , Singh S. P. , Jauregui-Rosas Segundo R. 
Published: August 2010

AbstractWe report a systematic study of the influence of the target-substrate distance and rf power on the structural and optical properties of ZnO thin films grown by rf magnetron sputtering in Ar atmosphere from ZnO sputtering target. Sharp (002) peak showed by XRD indicates a c-axis crystalline growth of ZnO films. Growth rate remained almost constant for short target-substrate distances. However, the grain size increases with the rf power decreasing the compressive stress in ZnO films. As-grown ZnO films have average transmittance more than 80% in the visible region. Optical bandgap (Eg) increases from 3.18 to 3.27 eV as increase the target-substrate distance probably due to low stress compression in ZnO films. In addition, when rf power is above 100 W, the optical band gap increases as increase of the stress compression.