bluuebunny/crossref_metadata_2025_split huggingface dataset:
Light-induced Open-circuit Voltage Increase in Amorphous Silicon/Microcrystalline Silicon Tandem Solar Cells
Authors: Zhang Xiaodan , Wang Guanghong , Xu Shengzhi , Xiong Shaozhen , Geng Xinhua , Zhao Ying 
Published: September 2011

ABSTRACTLight-induced metastability of amorphous/microcrystalline (micromorph) silicon tandem solar cell, in which the microcrystalline bottom cell was deposited in a single-chamber system, has been studied under a white light for more than 1000 hours. Two different light-induced metastable behaviors were observed. The first type was the conventional light-induced degradation, where the open-circuit voltage (Voc), fill factor (FF), and short-circuit current density (Jsc) were degraded, hence the efficiency was degraded as well. This phenomenon was observed mainly in the tandem cells with a bottom cell limited current mismatch. The second type was with a light-induced increase in Voc, which sometimes resulted in an increase in efficiency. The second type of light-induced metastability was observed in the tandem cells with a top cell limited current mismatch. The possible mechanisms for these phenomena are discussed.
Primary Photonic Processes in Energy Harvesting: Quantum Dynamical Analysis of Exciton Energy Transfer over Three-Dimensional Dendrimeric Geometries
Authors: Andrews David L. , Jones Garth A. 
Published: September 2011

ABSTRACTIn molecular solar energy harvesting systems, quantum mechanical features may be apparent in the physical processes involved in the acquisition and migration of photon energy. With a sharply declining distance-dependence in transfer efficiency, the excitation energy generally takes a large number of steps en route to the site of its utilization; quantum features are rapidly dissipated in an essentially stochastic process. In the case of engineered dendrimeric polymers, each such step usually takes the form of an inward hop between chromophores in neighboring generation shells. A physically intuitive, structure-determined adjacency matrix formulation of the energy flow affords insights into the key harvesting and inward funneling processes. A numerical method based on this analytic approach has now been developed and is able to deliver results on significantly larger dendrimeric polymers, with the help of large multi-processor computers. Central to this study is the interpretation of key features such as the relevance of a spectroscopic gradient and the presence of traps or irregularities due to conformational changes and folding. With the objective of fine-tune the funneling process, this model now allows the incorporation of parameters derived from quantum chemical calculations, affording new insights into the detailed operation of the harvesting process in a variety of dendrimer systems.
Memristive Switches with Two Switching Polarities in a Forming Free Device Structure
Authors: Bruchhaus Rainer , Hermes Christoph R. , Waser Rainer 
Published: September 2011

ABSTRACTIn this study an electroforming free device structure based on 25nm thin TiO2 thin films is presented. The TiO2 films are deposited on CMOS compatible W plugs. The use of 5nm thick interlayers of Ti and W between the TiO2 and the Pt electrode turn out to be the key step to achieve the forming free performance. In these Pt/Ti/TiO2/W or Pt/W/TiO2/W samples the switching polarity can be repeatedly changed from “eightwise” to “counter-eightwise” in one device by a proper adjustment of the I-V measurement conditions. The most simple explanation for this observation is that the switching interface can be flipped back and forth from the bottom to the top electrode.
Switching speed in Resistive Random Access Memories (RRAMS) based on plastic semiconductor
Authors: Rocha Paulo F. , Gomes Henrique L. , Kiazadeh Asal , Chen Qian , de Leeuw Dago M. , Meskers Stefan C. J. 
Published: September 2011

ABSTRACTThis work addresses non-volatile memories based on metal-oxide polymer diodes. We make a thorough investigation into the static and dynamic behavior. Current-voltage characteristics with varying voltage ramp speed demonstrate that the internal capacitive double-layer structure inhibits the switching at high ramp rates (typical 1000 V/s). This behavior is explained in terms of an equivalent circuit.It is also reported that there is not a particular threshold voltage to induce switching. Voltages below a particular threshold can still induce switching when applied for a long period of time. The time to switch is longer the lower is the applied voltage and follows an exponential behavior. This suggests that for a switching event to occur a certain amount of charge is required.
Vapor-Liquid-Solid Growth of Cadmium Telluride Nanowires by Close-Space-Sublimation for Photovoltaic Applications
Authors: Williams B. L. , Mendis B. , Bowen L. , Halliday D. P. , Durose K. 
Published: September 2011

ABSTRACTArrays of CdTe nanowires have been grown on conductive, flexible Mo substrates by the vapor-liquid-solid technique. A method of forming the arrays on a largely continuous CdTe film is described. For producing nanowire solar cells, this structure provides the advantage of preventing shunts. Nanowires having diameters in the range 100-500 nm and lengths up to 100 μm were generated. The influence of growth temperature, time and pressure on the morphology of deposited layers was investigated, and a mechanism for the generation of layer/nanowire combinations is postulated. Characterization by SEM, TEM and low temperature photoluminescence is presented.
Surface Photovoltage Study of Indium Phosphide Nanowire Networks
Authors: Lohn Andrew J. , Han Jin-Woo , Kobayashi Nobuhiko P. 
Published: September 2011

ABSTRACTSurface photovoltage of three-dimensional networks composed of fused indium phosphide (InP) nanowires is discussed. Particular emphasis is given to the dependence of surface photovoltage on the chopping frequency of light that excites the nanowire network as observed in regions which are laterally separated from the excitation. The nanowire network is modeled as a thin film to simplify numerical solutions to transport equations which aids in the interpretation of diffusion and drift of photo-generated carriers within the nanowire network.
Patterned Polymer Nanofibers Based Biosensors
Authors: Mertz Timothy O. , Kunduru Vindhya , Patra Prabir K. , Vattipalli Krishna , Prasad Shalini 
Published: September 2011

ABSTRACT“Label-free” biomolecule sensors for detection of inflammatory cardiovascular biomarker associated with vulnerable coronary vascular plaque were designed and fabricated using micro and nano-textured polystyrene structures that functioned as sensing elements coupled with electronic measurement equipment. We demonstrated that scaling down the surface texturing from the micro to the nanoscale enhances the amplitude of the measured signal strength. We believe that the nanoscale fiber morphology provides size matched spaces for trapping and immobilizing the protein biomolecules resulting in enhanced detection and signal strength. We selected polystyrene as the model system and demonstrated the detection of human serum C-reactive protein (hs-CRP). We employed these findings in designing a platform “lab-on-a-chip” protein sensor. Comparative studies were performed on two different polystyrene textured surfaces: a polystyrene microsphere mat, and an electrospun polystyrene nanofiber matrix.
Development of New Polymer Systems and Quantum Dots - Polymer Nanocomposites for Low-cost, Flexible OLED Display Applications
Authors: Zhao Lihua , Zhou Zhang-Lin , Guo Zengshan , Pei Jian , Mao Samuel 
Published: September 2011

ABSTRACTRecently, tremendous progress has been made toward application of organic (small molecule/polymer) light-emitting diodes (OLEDs) in full color flat panel displays and other devices. However, with current technologies, OLEDs are still struggling with high manufacturing costs which really limit the size of OLEDs panels and with life time, especially differential aging of colors. To be more cost-effective for fabricating OLEDs, we believe solution-processing would be an attractive path due to its simplicity and highly reduced equipment costs. This proceeding paper discusses our recent progress in development of new polymer systems that are highly solvent-resistant but maintaining their photophysical properties and hybrid quantum-dots (QDs)-polymer nanocomposites for their use in multicolor and multilayer OLEDs pixels through solution-processing. Our new polymer systems are named conductive semi-interpenetrating polymer networks (C-Semi-IPNs) served in different layers of OLEDs devices, containing an inert polymer network and conducting polymer(s) including hole transport and emissive materials. Since these do not require complicated chemical modification or introduction of reactive moieties to OLED materials, many state-of-the-arts emissive polymers can be utilized to achieve RGB and white OLEDs. The research findings on hybrid QDoligomer nanocomposite as a good analogue lead to the successful design and synthesis of QDpolymer nanocomposites which were used to build proof-of-the-concept devices showing a good promise in providing excellent color purity and stability as well as device robustness.
Electronic Excitation Induced Solid-State Amorphization in Ge-Sb-Te Alloy
Authors: Li Xian-Bin , Liu X.Q. , Liu Xin , Han Dong , Zhang Z. , Han X.D. , Zhang S. B. 
Published: September 2011

ABSTRACTOn the basis of ab initio molecular dynamics modeling, we show that Ge-Sb-Te alloy under excitation can realize amorphization without going through a liquid phase. The electronic structure analysis further reveals that the excitation mainly involves the Ge s-like states near the valence band maximum. After the phase transition, the coordination number of Ge is reduced from six to four, while the change in the coordination number for Sb is noticeably less.
Influence of the pH on the Surface and Optical Properties of the Thin Film of Polyaniline / Polyethylene Terephthalate Composite. The AFM and Spectroscopies Studies
Authors: Paschoalin Rafaella T. , Steffens Clarice , Manzoli Alexandra , Hlophe Mhbuti R. , Herrmann Paulo S. P. 
Published: September 2011

ABSTRACTThe effect of pH was investigated on the morphological and spectroscopic properties of PANI thin films on PET. PANI/PET strips were prepared by a pattern-printing technique and coated with a thin film of polyaniline in situ emeraldine oxidation state, doped with HCl (PANI-HCl), obtained by in situ polymerization. AFM, UV-VIS-NIR and FTIR/ATR spectroscopic results showed that pH has a great influence on the polymer layer morphology of the coating layers, while the intensity of vibrational bands decreases with rising pH, increase due to changes in the H-bonded structure in the polymer chain.
Conductive Polymer Bilayers – A Spectroelectrochemical Look at Their Doping Reactions
Authors: Gustafsson Henrik , Kvarnström Carita , Ivaska Ari 
Published: September 2011

ABSTRACTThe doping behavior of bilayers of electropolymerized poly(3,4-ethylenedioxythiophene) doped with hexafluorophosphate and drop-cast poly(benzobisimidazobenzophenanthroline) was studied with cyclic voltammetry, and with in situ ultraviolet-visible and attenuated total reflectance Fourier transform infrared spectroscopy. The spectroelectrochemical characterization of the polymer bilayers provided us with fundamental information of the properties of the materials, information being essential in order to be able to use the conducting polymers in future real-life applications, e.g., as organic semiconducting components.
Development of Si Microliquid Processing using Piezo Actuator
Authors: Akazawa Muneki , Koyanagi Shunki , Higashi Seiichiro 
Published: September 2011

ABSTRACTThe tip of a Si rod was melted by laser diode (LD) irradiation and we succeeded in dropping small Si droplets by vibration of the Si rod using a piezo actuator. We confirmed multiple small Si droplets under a condition of the resonance frequency of 5.8 kHz for the rod length of 6.0 mm. We observed ejection of droplets from a cone edge of molten Si and the minimum width of the solidified Si was ∼ 1 μ m in diameter. The solidified Si show high crystallinity with the Raman scattering TO phonon band of 515.6 cm-1.
Hierarchically Nanostructured Zeolites of Tunable Porosities with Aerogel Templating
Authors: Tao Yousheng , Endo Morinobu , Kaneko Katsumi 
Published: September 2011

ABSTRACTWe present the synthesis of resorcinol-formaldehyde aerogels and carbon aerogels of different nanoporosities, emphasizing on the recent developments in fabrication pathways of lower cost. Recent results showed a simple way to the production of highly nanoporous carbon xerogels. While using an approach combined colloidal silica nanocasting and carbon dioxide supercritical drying, hydrophilicity-controlled carbon aerogels with high mesoporosity were synthesized. Then, we demonstrate the functions of these aerogels for template synthesis of hierarchically nanostructured zeolites having micropores and mesopores.
Optical characterization using ellipsometry of Si nanocrystal thin layers embedded in silicon oxide
Authors: Agocs E. , Petrik P. , Fried M. , Nassiopoulou A. G. 
Published: September 2011

ABSTRACTWe have developed optical models for the characterization of grain size in nanocrystal thin films embedded in SiO2 and fabricated using low pressure chemical vapor deposition of Si from silane on a quartz substrate, followed by thermal oxidation. The as-grown nanocrystals thin film on quartz was composed of a two-dimensional array of Si nanocrystals (Si-NC) showing columnar structure in the z-direction and touching each other in the x-y plane. The nanocrystal size in the z-direction was equal to the Si nanocrystal film thickness, changing by the deposition time, while their x-y size was almost equal in all the samples, with small size dispersion. After high temperature thermal oxidation, a thin silicon oxide film was formed on top of the nanocrystals layer. The aim of this work was to measure the grain size and the nanocrystallinity of the Si nanocrystal thin films, a quantity related to the change of the dielectric function. We used a definition for the nanorcystallinity that is related to the effective medium analysis (EMA) of the material. The optical technique used for the investigations was spectroscopic ellipsometry. To measure the above sample properties the thickness and composition of several layers on a quartz substrate had to be determined by proper modeling of this complex system. We found that the nanocrystallinity (defined as the ratio of nc-Si/(c-Si+nc-Si) decreases systematically with increasing the Si-NC layer thickness. Using this approach we are sensitive to the lifetime broadening of electrons caused by the scattering on the grain boundaries, and not to the shift of the direct interband transition energies due to quantum confinement.
Tailoring of Boehmite-Derived Aluminosilicate Aerogel Structure and Properties: Influence of Ti Addition
Authors: Hurwitz Frances I. , Guo Haiquan , Sheets Erik J. , Miller Derek R. , Newlin Katy N. 
Published: September 2011

ABSTRACTAluminosilicate aerogels offer potential for extremely low thermal conductivities at temperatures greater than 900°C, beyond where silica aerogels reach their upper temperature limits. Aerogels have been synthesized at various Al:Si ratios, including mullite compositions, using Boehmite (AlOOH) as the Al source, and tetraethoxy orthosilicate as the Si precursor. The Boehmite-derived aerogels are found to form by a self-assembly process of AlOOH crystallites, with Si-O groups on the surface of an alumina skeleton. Morphology, surface area and pore size varies with the crystallite size of the starting Boehmite powder, as well as with synthesis parameters.Ternary systems, including Al-Si-Ti aerogels incorporating a soluble Ti precursor, are possible with careful control of pH. The addition of Ti influences sol viscosity, gelation time pore structure and pore size distribution, as well as phase formation on heat treatment.
Reliability of Oxide Thin Film Transistors under the Gate Bias Stress with 400 nm Wavelength Light Illumination
Authors: Lee Soo-Yeon , Kim Sun-Jae , Lee Yongwook , Lee Woo-Geun , Yoon Kap-Soo , Kwon Jang-Yeon , Han Min-Koo 
Published: September 2011

ABSTRACTWe have investigated the reliability of the inverted-staggered etch stopper structure oxide-based TFTs under negative gate bias stress combined with 400 nm wavelength light illumination and the relationship between the carrier concentration at the channel and the extent of Vth shift. It was found that the photo-induced holes cause the severe Vth degradation at the beginning of stress and the hole trapping rate of a single hole is not altered with the increase of the hole concentration. In oxide-based TFTs, the hole concentration at the channel is the determinant factor of the reliability.
Thin-film Photodiode with an a-Si:H/nc-Si:H Absorption Bilayer
Authors: Vygranenko Y. , Vieira M. , Sazonov A. 
Published: September 2011

ABSTRACTWe report on the fabrication and characterization of n+-n-i-δi-p thin-film photodiodes with an active region comprising a hydrogenated nanocrystalline silicon (nc-Si:H) n-layer and a hydrogenated amorphous silicon (a-Si:H) i-layer. The combination of wide- and narrow-gap absorption layers enables the spectral response extending from the near-ultraviolet (NUV) to the near-infrared (NIR) region. Moreover, in the low-bias range, when only the i-layer is depleted, the leakage current is significantly lower than that in the conventional nc-Si:H n+-n-p+ photodiode deposited under the same deposition conditions. Device with the 900nm/400nm thick n-i-layers exhibits a reverse dark current density of 3 nA/cm2 at −1V. In the high-bias range, when the depletion region expands within the n-layer, the magnitude of the leakage current depends on electronic properties of nc-Si:H. The density of shallow and deep states, and diffusion length of holes in the n-layer have been estimated from the capacitance-voltage characteristics and from the bias dependence of the long-wavelength response, respectively. To improve the quantum efficiency in the NIR-region, we have also implemented a Cr / ZnO:Al back reflector. The observed long-wavelength spectral response is about twice as high as that for a reference photodiode without ZnO:Al layer. Results demonstrate the feasibility of the photodiode for low-level light detection in the NUV-to-NIR spectral range.
Influence of Annealing in H2 Atmosphere on the Electrical Properties of Thin Film CdS
Authors: Maticiuc Natalia , Hiie Jaan , Potlog Tamara , Valdna Vello , Gavrilov Aleksei 
Published: September 2011

ABSTRACTChemical bath-deposited (CBD) thin film CdS has been widely used as a buffer and n-type window layer in CdS/CIGS and CdS/CdTe thin film solar cells. Annealing of CBD CdS assigns to the layers required concentration and mobility of electrons, crystallinity, structural stability and perfect Ohmic front contact in TCO/CdS interface. But always annealing reduces band gap (Eg) of solution-deposited CdS and lowers current density of the CdS/CdTe PV device due to optical absorption within the CdS layer.We have studied systematically dynamics of changes in CBD CdS/glass thin film structural, optical and electrical properties in annealing process in H2 ambient at normal pressure in pre-heated ceramic tubular furnace. Here we’ll present electrical, characterization results of annealed CBD CdS/glass thin films, 300 nm thick. The films were deposited with thiourea from ammoniacal 1 mM dilute solution of CdSO4 and 0.001 at. % of NH4Cl relative to Cd for Cl doping.We found high concentration of electrons 1-4 E19 cm-3 in the layers annealed at 200–450 °C, while for 200 °C the long time of annealing over 60 min is needed, but for high temperature region 350–450 °C only for short 10 min annealing this concentration region of electrons was achieved. In the high temperature region rapid decrease of electron concentration and conductivity will go on with increasing annealing temperature and time. Mobility of electrons will decrease from 9 to 5 cm2/V·s in the annealing region 200–350 °C, which is probably connected with disordering of lattice. On the basis of acquired results we propose an hypothesis about substitutional incorporation of OH group on S site in CdS lattice in deposition process and that (OH)s complex defect acts as a donor defect like Cl and we believe that the both defects are responsible for changes of thin film CdS electrical, optical and structural properties in the annealing process. Thermal annealing in hydrogen atmosphere is a convenient and appropriate method for precise control of CdS thin film electrical properties, and also for creation of n/n+ CdS window layers in the substrate configuration of a solar cell.
Zinc Nitride Films by Reactive Sputtering of Zn in N2-Containing Atmosphere
Authors: Jiang Nanke , Georgiev Daniel G. , Jayatissa Ahalapitiya H. , Wen Ting 
Published: September 2011

ABSTRACTFabrication, microstructure, chemical bonding and composition, and optical properties of zinc nitride films are investigated in this work. The films were deposited by reactive magnetron rf sputtering of zinc in N2-Ar ambient. Based on X-ray diffraction data, the as-deposited films are polycrystalline with cubic zinc nitride structure and (400) preferred orientation. Well defined Zn-N, N-N, as well as Zn-O and H-O bonding configurations are revealed by X-ray photoelectron spectroscopy data. The as-deposited films are found to be almost-stoichiometric and contain only a small fraction of oxygen. A direct band gap of 1.5 eV is obtained by using the photon energy dependence of the optical absorption of the films. This result is confirmed independently by spectroscopic ellipsometry.
Characterization of thermal interface resistance in thermoelectric generators
Authors: Koripella C. Ramesh , Bell Lon E. , Crane Doug , Wang Dazhi 
Published: September 2011

Abstract:Thermoelectric generators are actively being pursued to recover waste heat from the auto exhaust gas to improve vehicle fuel economy. Efficiency of a thermoelectric generator is defined as the ratio of electrical power output to the heat input. In a typical thermoelectric generator, a heat exchanger captures the heat from the medium (ex: hot exhaust gas heat) and this heat needs to be transferred to the hot end of the thermoelectric elements with minimum losses. It is important to understand and minimize these thermal losses to improve the efficiency of a thermoelectric generator. Accurate measurement of the thermal interface resistance parameters is also important because they are used in a comprehensive thermoelectric system model to predict the performance of the generator under actual use conditions. To understand the factors influencing the thermal interface resistance, and to determine the effective thermal interface resistance between the heat exchanger and the thermoelectric hot shunts in a prototype generator that is currently being developed for auto exhaust heat recovery application, we have designed and built a test setup to characterize the thermal interface resistance under high heat flux conditions. Measured temperature profiles in the test sample, heat input into the test device and its geometry are fed into a thermal model to extract the thermal conductance parameters. Factors affecting the thermal interface resistance and the influence of different interface materials were evaluated. Suitable solutions with minimum thermal loss were selected for building the prototype thermoelectric generator for waste heat recovery application and validating the system model.