bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular Configurations and Solvation Forces of Confined i-Tetradecane Jee-Ching Wang
Authors: Fichthorn Kristen A. 
Published: April 2011

ABSTRACTThis work is a molecular-dynamics simulation study of the influence of chain branching on the molecular configuration in confined tetradecane thin films. Simulations of layered interfacial films of n- and i-tetradecane on Pt(111) show, in contrast to experiments, that a side methyl group does not impart sufficient asymmetry to alter the solvation force law from oscillatory to non-oscillatory. Based on previous experimental findings, a novel vertical structure resembling a self-assembled monolayer, is proposed for confined, long-chain iso-alkanes. Simulations show that i-tetradecane in this structure is stableover the time scales that can be probed by molecular dynamics and that vertical films have a lower energy per molecule than layered films. With this structure, many experimental features, including the non-oscillatory solvation forces, of confined iso-alkanes are explainable andwill be discussed in this paper.
Dynamics of Air-Water Contact Lines and Interfaces Near the Pinning Threshold
Authors: Wong Po-Zen , Schäffer Erik , Pengra David B. 
Published: April 2011

ABSTRACTWe report a study of the dynamics of capillary rise of water in glass tubes and glass bead packs. The water column height h is measured as a function of time t byvideo imaging. Analyzing the late time data in terms of critical pinning, dh/dt ∞ (P – Pc)β, we find an anomalously large exponent β for interfaces in bead packs and β ≈ 1 for contact lines in capillary tubes. Repetitive rise and fall experiments in capillary tubes suggests that thinning of the wetting film plays an important role in the dynamics. We discuss these findings in light of recent theories and experiments.
High Electric field effects on the Thermal Generation in Hydrogenated Amorphous Silicon
Authors: Ilie A. , Equer B. 
Published: April 2011

ABSTRACTWe have studied the electric field dependence of the electron-hole thermal generation process in hydrogenated amorphous silicon. A model was developed which takes into account the Poole-Frenkel effect and the thermally assisted tunneling. In order to explain the experimental results it was necessary to consider a strong electron-lattice interaction describing the carrier tunneling mechanism. Deep defects relaxation is also discussed.
Effects of Synchrotron X-Rays on PVD Deposited and Ion Implanted α-Si
Authors: Yu Kin Man , Wang Lei , Walukiewicz W. , Muto S. , McCormick S. , Abelson J. R. 
Published: April 2011

ABSTRACTWe have studied the effects of intense x-ray irradiation on the stucture of amorphous Si films. The films were obtained by either physical vapor deposition or by implantation of high energy ions into crystalline Si. They were exposed to different total doses of synchrotron x-rays. From the EXAFS and EXELFS measurements we find that an exposure to x-rays increases the Si coordination number. Also in the PVD films a prolonged x-ray exposure enlarges, by about 2 %, the Si-Si bond length. Raman spectroscopy shows that Si amorphized with high energy ions contains small residual amounts of crystalline material. Irradiation of such films with x-rays annihilates those crystallites resulting in homogenously amorphous layer with a close to four-fold coordination of Si atoms. This rearangement of the local structure has a pronounced effect on the crystallization process of the amorphous films. Thermal annealing of x-ray irradiated ion amorphized films leads to nearly defect free solid phase epitaxy at 500°C. Also we observe a delay in the onset of the crystallization process in x-ray irradiated PVD films. We associate this with a reduced concentration of nucleation centers in the x-ray treated materials.
Observation of Coulomb Blockade Effect in Silicon Nanocrystallites at room Temperature
Authors: Gu Xiaofeng , Qin Hua , Lu Hai , Xu Jun , Chen Kunji 
Published: April 2011

ABSTRACTWe report the fabrication and electrical characteristics of an ultrathin nanocrystalline-silicon/amorphous silicon oxide double barrier resonant tunneling diode. The cross-section high resolution TEM photographs indicate the layered structure and the crystallinity of nanocrystalline Si with an average grain size of 10 nm. In this prototype device, a series of reproducible conductance peaks have been observed as a function of the applied gate bias at room temperature. The real voltage spacing of 0.38V between the peaks is determined from an equivalent circuit. The results are in agreement with the theory of Coulomb blockade effect using 1.1 aF of capacitance in single Si nanocrystallite. We conclude that the observed behavior results from resonant tunneling, which is strongly influenced by Coulomb blockade effect, through the zero-dimensional states in the well isolated silicon quantum dots.
Microscopic Aspects of the Staebler-Wronski Effect
Authors: Stutzmann Martin 
Published: April 2011

ABSTRACTThe microscopic origin and the creation mechanisms of metastable, light-induced defects in hydrogenated amorphous silicon are reviewed. Based on excitonic electron-hole pair recombination, a consistent quantitative description of defect creation kinetics can be obtained, including the experimentally observed differences between continuous wave and pulsed illumination as well as the effect of competing recombination pathways in compensated material. High resolution spin resonance spectra obtained by low-field spin-dependent transport are used to examine the interaction of metastable defects with hydrogen.
A Novel Method for Fabrication of Hyhdrogenated Amorphous Silicon and High Quality Poly-SI Films on the Same Substrate by Employing Excimer Laser
Authors: Choi Kwon-Young , Lee Jong-Wook , Choi Hyoung-Bae , Jeon Jae-Hong , Han Min-Koo , Kim Yong-Sang 
Published: April 2011

ABSTRACTWe have fabricated the a-Si:H film for pixel region and poly-Si film for driver region on the same glass substrate by a rapid thermal process successfully. By employing the halogen lamp, the considerable amount of hydrogen in the PECVD a-Si:H film, which causes the undesirable film ablation due to hydrogen evolution during excimer laser annealing, could be reduced selectively in the peripheral driver area where the a-Si:H film is recrystallized into poly-Si film in order to obtain the high mobility. After rapid thermal annealing, the hydrogen content in a-Si:H films, of which the inherent hydrogen content was found to be about 10–12 at. %, is successfully reduced to less than 5 at. %. The annealing conditions for dehydrogenation are 500, 550, 600 and 650 °C with various halogen lamp irradiation period which are below the point of the glass shrinkage. It should be noted that after rapid thermal annealing, any physical damage in the glass substrate has not been observed.
Application of Hot Wire Deposited Intrinsic Poly-Silicon Films in N-I-P cells and TFTS
Authors: Rath J. K. , Van Zutphen A.J.M.M. , Meiling H. , Schropp R. E. I. 
Published: April 2011

ABSTRACTPoly-silicon films have been prepared by hot-wire chemical vapour deposition (HWCVD) from hydrogen diluted silane gas at a low temperature (430 °C). The crystalline volume fraction is 95%. The grains have an average size of 70 nm and coalesce completely. The activation energy (0.54 eV) and the low carrier concentration (6.8 × 1010 cm−3) indicate the fully intrinsic nature of the films. The low (<1017 cm−3) defect density, the absence of 2100 cm−1 mode in infrared spectrum, the low activation energy of Hall mobility (0.012 eV) and the ambipolar diffusion length (LD) of 568 nm all indicate that the grain boundaries in the poly-Si:H films are indeed very thin. Preliminary n-i-p cells incorporating a poly-silicon i-layer yielded 3.15% efficiency and a current density of 18.2 mW/cm2 for only a 1.5 μm i-layer. In the solar cell, the conducting path is along the columnar grains ( (220) preferential orientation from XRD) and the carrier transport bypasses the grain boundary defects. This has been confirmed from the c-Si like optical absorption spectrum (measured by Dual Beam Photoconductivity in the cell configuration) at the low energy region. Inverted staggered thin-film transistors incorporating the poly-silicon layers showed transfer and output characteristics similar to those of state of the art a-Si:H TFTs : the saturation mobility is 0.4 cm2/Vs and the off current is approximately 10−11 A. This leads to the conclusion that the silicon near the SiO2 interface (the channel region) is still amorphous. This is illustrated by XTEM.
High-Deposition-Rate a-Si:H Through VHF-CVD of Argon-Diluted Silane
Authors: Meiling H. , Bezemer J. , Schropp R. E. I. , Van Der Weg W. F. 
Published: April 2011

ABSTRACTWe discuss various ways to produce hydrogenated amorphous silicon, a-Si:H, at a high deposition rate. We also present results of our recent study on the structural properties of a-Si:H films deposited at high rates using argon (Ar) dilution of silane in a 50-MHz glow discharge. The results of the depositions with Ar dilution are compared to films deposited from pure silane, SiH4. The deposition rate rd is changed by varying the rf power Prf into the discharge. We focus on the Prf-dependence of the hydrogen (H) bonding configuration and total H content in the film. It is observed that rd saturates at 14 Å/s for pure SiH4, and at 22 Å/s for Ar-diluted SiH4 deposition. Upon increase of Prf the H bonding configuration changes from mostly isolated H to mostly clustered H, and back to mostly isolated H. It is argued that Ar* metastable atoms play an important role in the growth mechanism at intermediate Prf, whereas at high Prf ion bombardment through Ar+ and ions becomes crucial. Two high-rate a-Si:H films are incorporated in thin-film transistors, TFTs. We present their characteristics before and after illumination with calibrated light. It is shown that a-Si:H TFTs with a saturation mobility of 0.7 cm2/Vs can be fabricated, with the complete intrinsic layer deposited at 20 Å/s.
Versatile High Rate Plasma Deposition and Processing with very high Frequency Excitation
Authors: Heintze M. 
Published: April 2011

ABSTRACTThe interest in plasma deposition using very high frequency (VHF) excitation arose after the preparation of a-Si:H at high growth rates was demonstrated. Subsequently the improved process flexibility and the control of material properties offered by the variation of the plasma excitation frequency was recognized. The preparation of amorphous and microcrystalline thin films in a VHF-plasma is described. The increased growth rates have been attributed to an enhancement of film precursor formation at VHF, to the decreased sheath thickness as well as to an enhancement of the surface reactivity by positive ions. Plasma diagnostic investigations show that the parameters mainly affected by the excitation frequency are the ion flux to the electrodes as well as the sheaths potentials and widths, rather than the plasma density.
Study of Microvoids in High-Rate a-Si:H Using Positron Annihilation
Authors: Zou X. , Webb D. P. , Lin S. H. , Lam Y. W. , Chan Y. C. , Hu Y. F. , Beling C. D. , Fung S. 
Published: April 2011

ABSTRACTIn this paper, we have carried out the positron annihilation measurement on high-rate and low-rate a-Si:H thin films deposited by PECVD. By means of the slow positron beam Doppler-broadening technique, the depth profiles of microvoids in a-Si:H have been determined. We have also studied the vacancy-type defect in the surface region in high-rate grown a-Si:H, making comparison between high-rate and low-rate a-Si:H. By plotting S and W parameters in the (S, W) plane, we have shown that the vacancies in all of the high-rate and low-rate deposited intrinsic samples, and in differently doped low-rate samples are of the same nature.
High-Rate PECVD of Low Defect Density a-Si:H on Large Areas
Authors: Röhlecke S. , Steinke O. , Schade F. , Stahr F. , Albert M. , Deltschew R. , Kottwitz A. , Carius R. 
Published: April 2011

ABSTRACTIndustrial production of amorphous silicon solar cells, photoreceptors and several opto-electronic devices requires large area, high-deposition-rate plasma reactors and deposition processes. Non-uniformity of die film thickness and particle generation at high power densities as well as the deposition rate are found to be important limiting factors in large area PECVD.The deposition was performed in a capacitively-coupled coaxial diode rf glow discharge with large areas (1000 cm2 and 2000 cm2) at 13.56 MHz and 27.12 MHz. We studied the particle generation in the plasma reactor over a wide range of silane concentration (20 % to 100 %) in the SiH4/He mixture. We will present the opto-electronic properties of a-Si:H films and the influence of the substrate bias. The films are characterized by dark- and photoconductivity and by PDS.It was confirmed through this study that helium dilution is effective in the suppression of powder growth for high-rate deposition up to 18 μm/hr. Special attention was paid to the optimization of reactor design and plasma conditions for the deposition of low density of states a-Si:H (∼1016 cm−3) at deposition rates of up to 18 μm/hr. Darkconductivity was 10−9 S/cm and photoconductivity was about 5.10−4 S/cm.
Bombardment by Reflection - A Novel Method to Prepare High Quality Hydrogenated Amorphous Germanium by Anodic PCVD
Authors: Diez Annette , Drüsedau Twlo P. 
Published: April 2011

ABSTRACTDeposition of amorphous germanium by anodic PCVD was performed changing the germane/hydrogen dilution ratio from 1/6 to 1/100. Films deposited under high dilution of germane are of a high mechanical density (92.5 % of bulk) and good optoelectronic properties (electrical conductivity at room temperature σ=10−5 (Ω cm)−1, majority carrier mobility-lifetime product at λ=1200 nm ημ=x 10−7 cm2/V). The quality of the films is increased by deposition at increasing pumping speed for hydrogen (lower hydrogen pressure) keeping the other parameters constant. It is suggested that fast atomic hydrogen originating from a backscattering process at the powered electrode bombard the growing film and contribute to the improved quality of the a-Ge:H. Also, the growth kinetics of the films is changed from linear to parabolic dependence on germane flow interchanging deposition from high to low hydrogen pressure. This effect is rationalized in terms of a contribution of energetic atomic hydrogen to the dissociation of germane.
Deposition of Device Quality Amorphous Silicon by Hot-Wire CVD
Authors: Feenstra K. F. , Van Der Werf C. H. M. , Molenbroek E. C. , Schropp R. E. I. 
Published: April 2011

ABSTRACTIn this paper we present the results of the optimization of hydrogenated amorphous silicon films deposited by the hot-wire method in a larger area system. Using a two-wire design, we succeeded in depositing films that exhibit uniform electrical properties over the whole 4” x 4” Corning 7059 glass substrate. At a substrate temperature of 430 °C. and a pressure of 20 μbar we obtained a growth rate of ∼2 nm/s. The temperature of the tungsten filaments was kept at 1850 °C. The values for the photoconductivity and dark conductivity were 8.9×10−6 S/cm and 1.6×10−10 S/cm respectively, whereas the ambipolar diffusion length, as measured with the Steady-State Photocarrier Grating technique (SSPG), amounted to 145 nm. This value is higher than for our device quality glow-discharge (GD) films, which yield devices with efficiencies higher than 10%. The hydrogen content was 9.5%.We report on the density-of-states (DOS) distribution in the films, which was measured with the techniques of Thermally Stimulated Conductivity (TSC) and Constant Photocurrent Method (CPM). Furthermore, we describe the behavior of the electrical properties on light-induced degradation. Finally, we incorporated these films in solar cells, using conventional GD doped layers. Preliminary SS/n-i-p/ITO devices yielded efficiencies in excess of 3% under 100 mW/cm2 AM 1.5 illumination. Further work concerning the optimization of the interfaces is in progress.
Fast Etching of Amorphous and Microcrystalline Silicon by Hot-Filament Generated Atomic Hydrogen
Authors: Wanka H. N. , Schubert M. B. 
Published: April 2011

ABSTRACTA hot tungsten wire effectively dissociates H2 into atomic hydrogen and thereby facilitates etching and hydrognation of silicon. Hot filament generated atomic hydrogen etches amorphous silicon (a-Si:H) at a rate of up to 27 Å/s and microcrystalline (μc) Si at rates up to 20 Å/s. A large laminar gas flow is the key to high etch rates. It provides for a fast transport of the etch products out of the reaction zone and thereby avoids redeposition. The etch rate increases with pressure and with H2 gas flow. Likewise, the etch rate rises with the filament temperature and saturates at a filament temperature of approximately 2150°C when approaching the maximum H2 dissociation probability. The decrease of the etch rate at higher substrate temperatures is attributed to the loss of the surface coverage by atomic hydrogen. The etch selectivity between a-Si:H and μc-Si drops at elevated substrate temperatures. Boron doping decreases the etch rates both for a-Si:H and μc-Si, whereas phosphorous doping does not significantly affect it. This etch selectivity is caused by a catalytic effect of BH3 on the surface hindering the formation of the main etch product silane. Even for highest etch rates no surface roughening of a-Si:H occurs, however, a bond structure modification of the near surfaces arises, an effect which results in the formation of a nanocrystalline surface layer. The increase of the μc-Si etch rate close to the film substrate interface characterizes the film thickness at which the coalescence of the microcrystalline nuclei starts.
Bidimensional Numerical Analysis of A μc-Si:H P-I-N Photodiode under Local Illumination
Authors: Fantoni A. , Vieira M. , Martins R. 
Published: April 2011

ABSTRACTThe behaviour of a inicrocrystalline p-i-n junction locally illuminated with monochromatic radiation (incident power of 50 mW/cm2) is analysed by means of numerical experiences. The model used for the two-dimensional analysis of the transport properties of a μc-Si:H p-i-n photo-detector is based on the simultaneous solution of the continuity equations for holes and electrons together with the Poisson's equation. The solution is found on a rectangular domain, taking into account the dimension perpendicular to the junction plane and one on the parallel plane. The lateral effects occurring wimin the structure, due to the non-uniformity of the illumination, are outlined. The results we present show that the potential profile has a linear variation from the illuminated to the dark neutral region. The lateral components of the electric field and of the current density vectors reveal to be mainly localised inside the doped layers.
VHF Plasma Deposition of μc-Si p-Layer Materials
Authors: Deng X. , Jones S. J. , Liu T. , Izu M. , Ovshinsky S. R. , Hoffman K. 
Published: April 2011

ABSTRACTMicrocrystalline silicon (μc-Si) p-layers have been widely used in amorphous silicon (a-Si) solar cell research and manufacturing to achieve record high solar cell efficiency. In order to further improve the solar cell performance and achieve wider parameter windows for the process conditions, we studied the deposition of high quality μc-Si p-layer material using a very high frequency (VHF) plasma enhanced CVD process. A design of experiment (DOE) approach was used for the exploration and optimization of deposition parameters. The usage of DOE leads to a quick optimization of the deposition process within a short time frame. In addition, by using a modified VHF deposition process, we have improved the solar cell blue response which leads to a 6–10% improvement in the solar cell efficiency. Such an improvement is likely due to an improved microcrystalline formation in the p-layer.
Influence of Front Contact Material on Silicon Heterojunction Solar Cell Performance
Authors: Rizzolp R. , Galloni R , Summonte C. , Pinghin R. , Centurioni E. , Zignan F. , Desalvo A. , Rava P. , Madan A. 
Published: April 2011

ABSTRACTThe emitter of amorphous/crystalline silicon heterojunction (HJ) solar cells is normally very thin. Consequently, the metal used as a front contact can produce a partial or even total depletion of this layer. As a result, the diffusion potential of the p-n junction deviates from its maximum value. In this paper, we report the results concerning HJ in which either metal dots (Au, Al), semitransparent metal layers, or indium tin oxide (ITO) dots or layers were used as front contact on the same HJ structure, namely (p)a-Si:H / (i)a-Si:H / (n)c-Si / Al. We show that, for thin p-layers, the dark and light J-V characteristics of HJ solar cells depend on the material used as front contact. In particular, we found that the dark saturation current increases if a low work function material is used. This increase is interpreted in terms of p-layer depletion, and is shown to directly influence the J-V characteristics under illumination, producing a reduction of the open circuit voltage of solar cells.
Stability of Single and Tandem Junction A-Si:H Solar Cells Grown using the ECR Process
Authors: Dalal Vikram L. , Maxson Tim , Girvan Robert , Haroon Sohail 
Published: April 2011

ABSTRACTWe report on the fabrication and stability tests of single junction a-Si:H, and tandem junction a-Si:H/a-Si:H solar cells using the ECR process under high hydrogen dilution (H-ECR process). We show that devices with high fill factors can be made using the H-ECR process. We also report on the stability studies of the solar cells under 1 and 2-sun illumination conditions. The solar cells show very little degradation even after 500 hours of illumination under 2 x sunlight illumination.
Modeling and Scaling of a-Si:H and Poly-Si Thin Film Transistors
Authors: Shur M. S. , Slade H. C , Ytterdal T. , Wang L. , Xu Z. , Hack M. , Aflatooni K. , Byun Y. , Chen Y , Froggatt M. , Krishnan A. , Mei P. , Meiling H. , Min B.-H. , Nathan A. , Sherman S. , Stewart M. , Theiss S. 
Published: April 2011

ABSTRACTWe have developed analytic SPICE models for hydrogenated amorphous silicon (a-Si:H) and polysilicon (poly-Si) thin film transistors (TFTs) which accurately model all regimes of operation, are temperature dependent to 150°C, and scale with device dimensions. These models have been presented in [1, 2]. In this work, we compare the current-voltage characteristics predicted by our models with the measured characteristics from TFTs fabricated at different foundries. We compare the extracted device parameters in order to evaluate the robustness of our models and to determine a suitable default parameter set. We also use the models to examine the effects of device scaling for short channel TFTs. The models can be accessed using the circuit simulator AIM-Spice [3], which is available at http://nina.ecse.rpi.edu/aimspice.
Prospects for Active Matrix Displays on Plastic
Authors: Gates Stephen M. 
Published: April 2011

ABSTRACTWe review the status of active matrix display fabrication on plastic substrates, specifically active matrix liquid crystal displays (AM LCDs). Research efforts in the U.S. and Europe are surveyed. Currently available transparent plastics, and active programs to improve these materials are described. Our work on thin film transistor (TFT) fabrication at 125°C is then reported, with a comparison of reactive sputtering and plasma enhanced CVD methods.