bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theoretical Investigation of The Defect Interactions in Dilute Copper Alloys Intended for Nuclear Waste Containers
Authors: Korzhavyi P. A. , Abriikosov I. A. , Johansson B. 
Published: April 2011

AbstractApplication of pure, oxygen-free copper as a construction material having excllent corrosion resistance is limited because of the effect of intergranular emnibrittleinent at temperatures above 100–150°C. Dilute copper alloys containing S, P, and Ag inpirities and vacancies are studied theoretically on the basis of total energy calculations. The dissolution energies, volunie misfits, and defect interaction energies are calculated and used to study the microscopic miechanisin behind the effect of these impurities on the eiibrittlenieiit of colpper at interinedia temiperatures. A large linding energy of a sulfur-vacancy defect pair (–0.46 eV) is found. The sulfur-vacancy and sulftir-sulftir interactions in the copper matrix seeni to favor precipitation of copper sulphide Cu2S which is the most probable cause of the einhrittleiieiit. The effect of phosphorus and silver ilmpurities on the einbrittlement of sulfiir-contaminated copper can he related to their competition with sulfuir to attract to vacancies as well as to other lattice defects.
Experimental Study of the Nickel Solubility in Groundwater and Cement Water Under Anoxic Conditions
Authors: Carlsson T. , Aalto H. , Vuorinen U. 
Published: April 2011

AbstractThe solubility of nickel under anoxic conditions was investigated in groundwater and in cement-conditioned water. The solubility was studied at 30 °C using the over-saturation method. The nickel concentrations were determined using 63Ni and liquid scintillation counting. The results indicate a nickel solubility of 1–10−4 mol/L in the cement water. The same solubility was also seen in groundwaters that had a pH of 9 or higher. No solubility limit was determined for groundwaters with pH values in the range of 7 to 9.
Problems of Power Feeding in Large Area PECVD of Amorphous Silicon
Authors: Stephan U. , Kuske J. , Grüger H. , Kottwitz A. 
Published: April 2011

AbstractThe production of amorphous silicon, e.g. for solar cells, requires large area, high-deposition rate plasma reactors. Increasing the radio frequency from the conventional 13.56MHz up to VHF has demonstrated higher deposition and etch rates and lower particle generation, a reduced ion bombardement and lower breakdown, process and bias voltages.But otherwise the use of VHF leads to some problems. The non-uniformity of deposition rate increase due to the generation of standing waves (TEM wave) and evanescent waveguide modes (TE waves) at the electrode surface.Increasing the frequency and/or the deposition area the plasma impedance, the capacitic stray impedance of the RF electrode and other parasitic capacitive impedances decrease. Increasing the frequency and/or the RF power, the phase angle of the discharge and of the impedance at every point at the lines between the RF matching network an the RF electrode tends more and more towards -90°. This results in increasing currents and standing waves with extremly high local current maximas. Increasing resistances of lines and contacts due to the skin effect and loss-caused heating up of the lines the power losses increase extremely, up to 90% and more. In spite of the increasing of the coupled power, the plasma power does not increase. Thermal destructions of the lines due to extreme expansion or melting are possible.Some solutions to reduce the non-uniformity of the deposition rate like multipower feeding, central backside power feeding, electrode segmentation, use of load impedances, published in former publications, will be discussed in connection with several reactor types (coaxial, large area, long plasma source) in view of the efficiency of power coupling and the practical realization. Solutions to minimize the power losses at the lines will be presented.
The Role of Vacancies and Dopants in Si Solid-Phase Epitaxial Crystallization
Authors: Chen C. M. , Rassiga S. , Gessmann T. , Petkov M. P. , Weber M. H. , Lynn K. G. , Atwater H. A. 
Published: April 2011

AbstractThe role and interaction of vacancies and dopants in the crystallization of amorphous Si (a-Si) by solid-phase epitaxy (SPE) was investigated. To this end, we studied: (i) the solid-phase epitaxy rate measured by time-resolved reflectivity (TRR), (ii) the dopant and carrier concentrations measured by secondary ion mass spectrometry (SIMS) and spreading resistance (SR) analysis, and (iii) the vacancy concentration measured by positron annihilation spectroscopy (PAS). Phosphorus was implanted into a-Si on Si (001), which was previously amorphized by 29Si+ implantation, to create a nonuniform P doping profile. Phosphorus doped samples compensated with a similar boron profile were also studied. Samples were vacuum annealed for various times so that the amorphous-crystal interface was stopped at various depths providing frozen frames of the SPE process. These samples were then studied with PAS to investigate the vacancy population and to identify the impurity-defect complexes. Using this method, we have observed a population of phosphorus-vacancy complexes in the epitaxial layer.
Possibility of Quasi-Single-Crystalline Semiconductor Films
Authors: Noguchi T. , Usui S. , Gosain D. P. , Ikeda Y. 
Published: April 2011

AbstractThe existence of a novel tetrahedral semiconductor Quasi-Single-Crystalline (QSC) phase is posited. In the QSC semiconductor phase, the films consist of grains with a diamond structure of tetrahedral elements, such as Si, Ge and C, and the grains have a preferred orientation, such as <111> or <100> normal to the film. The lattices perpendicular to the grain boundaries are quasi-matched with neighboring grains. The grains in the films form a regular array, and are distributed more uniformly than in conventional poly-crystalline semiconductor films. Because of the small-angle grain boundaries, a tetrahedral QSC semiconductor such as QSC Si films are expected to have extremely low energy barriers at the grain boundaries.
Medium-Range Order in a-Si:H Below and Above the Onset of Microcrystallinity
Authors: Williamson D.L. 
Published: April 2011

AbstractMedium range order (MRO) and the formation of microcrystallites in a-Si:H prepared by plasma-enhanced chemical vapor deposition (PECVD) and hot-wire chemical vapor deposition (HWCVD) have been probed by systematic x-ray diffraction studies with films as thin as those used in solar cells. Effects of substrate temperature, hydrogen dilution, film thickness, and type of substrate have been examined. High-hydrogen-diluted films of 0.5 μm thickness, using optimized deposition parameters for solar cell efficiency and stability, are found to be partially microcrystalline (μc) if deposited directly on stainless steel (SS) substrates but are fully amorphous provided a thin (20 nm) n-layer of a-Si:H or μc-Si:H is first deposited on the SS. The latter predeposition does not prevent partially microcrystallinity if the films are grown thicker (1.5 to 2.5 μm) and this is consistent with a recently proposed phase diagram of thickness versus hydrogen dilution. Analysis of the first (lowest angle) scattering peak of the a-Si:H phase demonstrates that its width, directly related to MRO, is reduced by heavier hydrogen dilution in PECVD growth or by increased substrate temperature in HWCVD growth. The narrowest width of fully amorphous material correlates with better solar cell stability and this is not likely related to bonded hydrogen content since it is quite different in the optimized PECVD and HWCVD a-Si:H. A wide range of MRO apparently exists in the residual amorphous phase of the mixed a/μc material.
Structural Changes in a-Si:H Films Deposited on the Edge of Crystallinity
Authors: Mahan A.H. , Yang J. , Guha S. , Williamson D.L. 
Published: April 2011

AbstractUsing infrared, H evolution and x-ray diffraction (XRD), the structure of high H dilution, glow discharge deposited a-Si:H films ‘on the edge of crystallinity’ is examined. From the Si-H wag mode peak frequency and the XRD results, we postulate the existence of very small Si crystallites contained within the as-grown amorphous matrix, with the vast majority of the bonded H located on these crystallite surfaces. Upon annealing at ramp rates of 8-15°C/min, a H evolution peak at ~400°C appears, and film crystallization is observed at temperatures as low as 500°C, both of which are far below those observed for a-Si:H films grown without H dilution using similar rates. While the crystallite volume fraction is too small to be detected by XRD in the as-grown films, these crystallites enable the crystallization of the remainder of the amorphous matrix upon moderate annealing, thus explaining the existence of the low temperature H evolution peak.
Interstitial Trapped Hydrogen Molecules in Pecvdamorphous Silicon
Authors: Borzi R. , Mascarenhas F. , Fedders P. A. , Leopold D. J. , Norberg R. E. , Wickboldt P. , Paul W. 
Published: April 2011

AbstractNew NMR measurements show that interstitial T site-trapped molecular hydrogen can amount to more than one third of the contained hydrogen in high quality PECVD amorphous silicon. Microvoid-contained dense molecular hydrogen is negligible in these good films. Experiments on a sequence of hydrogenated and/or deuterated a-Si films have characterized individually-trapped molecular HD and D2 in films deposited from SiD4, and from SiH4+D2. The T site-trapped molecular hydrogen fraction observed here is larger than previously reported because of recent efforts to measure very slowly relaxing molecular components and the employment of radiofrequency pulse sequences to detect ortho-D2 with nuclear spin I=2. The population of interstitially trapped molecular hydrogen increases with increasing photovoltaic quality over a range of an order of magnitude in photoresponse product ημτ. Above 200 K, hopping transport of molecular hydrogen among the amorphous equivalent of interstitial T sites occurs with an activation energy near 50 meV.
Nmr Study of Ortho-Molecular Hydrogen in Hydrogenated Amorphous Silicon
Authors: Su Tining , Taylor P.C. , Chen Shenlin , Crandall R.S. , Mahan A.H. 
Published: April 2011

AbstractA Jeener-Broekaert three-pulse sequence is used to investigate ortho-molecular hydrogen (o-H2) in device quality amorphous silicon films prepared by plasma enhanced chemical vapor deposition (PECVD) and hot wire CVD (HWCVD). For the PECVD sample, the concentration of hydrogen molecules is ~ 11% of the total hydrogen concentration, one order of magnitude larger than that inferred from spin-lattice relaxation time measurements (~1%). Hence, most of the hydrogen molecules do not serve as effective relaxation centers. For HWCVD samples with ~3 to 4% hydrogen and very low void densities, the concentrations of hydrogen molecules are ~1% of the total hydrogen concentration. In these samples, spin-lattice relaxation measurements for bonded hydrogen indicate that the concentration of hydrogen molecules that contribute to spin-lattice relaxation is at most 0.1% of the total hydrogen concentration. Spin-lattice relaxation time (T1) measurements of ortho-molecular hydrogen indicate two very different T1's. The longer T1 is ~ 0.6 s, possibly due to an electric quadrupole-quadrupole (EQQ) interaction between o-H2 molecules and, the shorter T1 is ~ 3 ms, very close to that calculated for a two-phonon Raman process for rotating o-H2.
Anisotropy in Hydrogenated Amorphous Silicon Films as Observed Using Polarized Ftir-Atr Spectroscopy
Authors: Webb J. D. , Gedvilas L. M. , Crandall R. S. , Iwaniczko E. , Nelson B. P. , Mahan A. H. , Reedy R. , Matson R. J. 
Published: April 2011

AbstractWe used polarized attenuated total reflection (ATR) measurements together with Fourier transform infrared (FTIR) spectroscopy to investigate the vibrational spectra of hydrogenated amorphous silicon (a-SiHx) films 0.5-1.0 microns in thickness. We deposited the films using hot-wire or plasma-enhanced chemical vapor deposition methods (HWCVD or PECVD, respectively) on crystalline silicon and cadmium telluride substrates. Our ATR technique gave a spectral range from 2100-400 cm-1, although the Si-H wagging mode absorption band at 640 cm-1 was somewhat distorted in the a-SiHx/Si samples by impurity and lattice absorption in the silicon ATR substrates. We report the identification of a Si-O-C impurity band with maximum intensity at 1240-1230 cm-1. The assignment of this band to a Si-O-C vibration is supported by secondary-ion mass spectrometry (SIMS) measurements. Our polarized FTIR-ATR spectra of HWCVD and PECVD a-SiHx films on <111> Si ATR substrates show that the impurity dipoles are oriented strongly parallel to the film growth direction. The wagging mode absorbance band is more intense in the film plane. This trend is less pronounced for the Si-H stretching vibrations. These observations are consistent with some degree of anisotropy or medium-range order in the films. The anisotropy in the Si-H bands may be related to residual stress in the films. Our scanning electron microscopy (SEM) analyses of the samples offer additional evidence of bulk structural anisotropy in the a-SiHx/Si films. However, the Si-O-C impurity band was not observed in the polarized ATR-FTIR spectra of the a-SiHx/CdTe samples, thus indicating that the Si substrates influence formation of the impurity in the a-SiHx/Si films.
Simulation of Quantum Efficiency Spectroscopy for Amorphous Silicon P-I-N Junctions
Authors: Estwick Rodney , Dalal Vikram L. 
Published: April 2011

AbstractQuantum efficiency(QE) spectroscopy of amorphous silicon and alloy solar cells has been used for many years now to determine the mobility-lifetime products for minority carriers. Similarly, matching of I(V) curves, assuming a linear model for collection as a function of applied voltage, has been used to quantify the effects of degradation on cell performance by estimating changes in the collection length [or range] of holes. In this paper, we do a numerical simulation of these techniques, using the AMPS I-D model developed by Fonash and his coworkers. The simulation shows that neither the lifetime nor the electric field in the devices is constant as a function of position. Nor is the electric field a linear function of applied voltage, particularly when the voltage exceeds about half the built-in voltage. The uniformity of the lifetime depends on the applied bias and on the defect densities in the material. This variation in electric field and lifetime and nonlinearity with applied voltage makes questionable some of the conclusions drawn from fitting device I(V) curves, particularly under forward bias. However, when one uses only a limited range of forward bias, or, preferably, make measurements in cells with thicker i layers under reverse bias, one c.an make reasonable estimates of the hole mobility-lifetime(μτ) product or the collection lengthl The simulations also show that indeed, it is the hole μτ product which is the limiting parameter.
Hydrogen Diffusion in the Hydrogen Collision Model of Amorphous Silicon Metastability
Authors: Branz Howard M. 
Published: April 2011

AbstractThe trap-controlled model of H diffusion that underpins the H collision model of amorphous silicon metastability provides new insight into thermal and light-enhanced H diffusion in a-Si:H. The longstanding puzzle of the linear DB-dependence of diffusion coefficient with doping is resolved. Expressions for the light-induced H diffusion coefficient are derived with and without D-for-H exchange reactions. It is shown that D-for-H exchange does not affect the long-time diffusion coefficient that is measured under illumination.
The Properties of a-SiC:H and a-SiGe:H Films Deposited by 55 kHz PECVD
Authors: Budaguan B.G. , Sherchenkov A.A. , Berdnikov A.E. , Metselaar J.W. , Aivazov A.A. 
Published: April 2011

AbstractThe deposition processes and the properties of a-SiC:H and a-SiGe:H films in 55 kHz glow discharge were investigated. The analysis of deposition rate and RBS measurements showed that the chemical reactions between SiHn spices and CH4 control the incorporation of C in a-SiC:H films. High deposition rates of a-SiC:H and a-SiGe:H films fabricated by 55 kHz PECVD is caused by the increase of radical fluxes to the growth surface. The specific features of a-SiC:H and a-SiGe:H microstructure were revealed by IR and AFM analysis. In a-SiC:H films the islands of low size were distinguished on the surfaces of large islands. The large variation of the total hydrogen content in a-SiGe:H did not affect the optical bandgap, while the hydrogen related microstructure controlled the electronic properties such as dark conductivity, 11p.r product, defect density and Urbach slope.The results of optoelectronic properties and SW effect measurements of 55 kHz a-SiC:H and a-SiGe:H films demonstrated the increased stability in comparison with a-Si:H.
Step Response of a-Si:H Photodiodes
Authors: Mulato M. , Ramón M. , Wagner S. 
Published: April 2011

AbstractWe correlate the dark current-transients of a-Si:H p-i-n photodiodes with solar cell performance and quantum efficiency. For devices with solar cell efficiency varying from 7.2 to 2.2 % subjected to ±1 V and a sampling frequency of 21 kHz: i) the reverse-bias charging time is shorter, with the initial charging time being reduced by ~ 1.5 μs, while the time for final current stabilization is reduced by - 5 μs.; ii) the forward-bias time for the onset of space charge limited current dominated regime is ~ 1 μs faster, the final current limit is achieved also in shorter time (~ 9 μs), and the individual final limit current is diminished by ~ 8 % due to carriers trapping, while the relative final limit current between different diodes is diminished by ~ 50 %.
Optical Transitions in Light-Emitting Nanocrystalline Silicon Thin Films
Authors: Toyama T. , Kotani Y. , Shimode A. , Abo S. , Okamoto H. 
Published: April 2011

AbstractOptical transitions in nanocrystalline Si (nc-Si) thin films with different mean crystal sizes ranging from < 2 nm to ~3 nm have been studied by electroreflectance (ER) spectroscopy. At 293 K, ER signals are observed at 1.20-1.37 eV to be corresponding to fundamental gap in bulk crystalline Si. With a decrease in the mean crystal sizes of nc-Si, the transition energy of the fundamental gap is increased and the ER signal is intensified. The bandgap widening would be due to quantum confinement (QC) in nc-Si, and the increased signal indicates appearance of direct transition nature. The ER signals are also observed at 2.2 eV and at E1 (E0’) direct gap of 3.1-3.4 eV, while photoluminescence (PL) peak energies are located at 1.65-1.75 eV and at 2.3 eV. With the reduced mean crystal size, the 1.7-eV PL peak energy is also increased, suggesting that QC is also responsible for the increased PL peak energy.
Charge Transport in the Transition From Hydrogenated Amorphous Silicon to Microcrystalline Silicon
Authors: Kattwinkel A. , Braunstein R. , Sun G. , Wang Qi 
Published: April 2011

AbstractThe electronic transport properties of a series of samples prepared by hot-wire chemical vapor deposition with a transition from a-Si:H to μc-Si:H were measured applying the photoconductive frequency mixing technique. We found both improved stability against light-soaking and different values for the photomixing electron lifetime and mobility close to the onset of microcrystallinity as compared to the amorphous state. In particular, the mobility-lifetime product of charge carriers in some of the μc-Si:H samples turns out to lie about two orders of magnitude higher than that of a-Si:H films. The mobility on the other hand, is shown rather to decrease in the transition to the μc-region. Additional measurements of the range and the depth of long range potential fluctuations yield a possible explanation for our results in that grain boundaries may serve as scattering centers and barriers against recombination.
Anisotropic Transport in Microcrystalline P-I-N Devices
Authors: Vieira M. , Fantoni A. , Fernandes M. , Maçarico A. , Martins I. , Louro P. , Schwarz R. 
Published: April 2011

AbstractEntirely μc-Si:H p-i-n structures presenting an enhanced sensitivity to the near infrared region and a positive spectral response under forward bias higher than the open circuit voltage are analysed under different external voltage bias and illumination conditions.A two phase model to explain the transport properties is proposed using as input parameters the measured experimental data. The results suggest that the transport is preferentially concentrated inside the crystalline grains. The conduction within the amorphous regions is poor. The percolation path is different for electrons and holes and is determined by the local fields at the boundaries. These local fields are independent of the externally applied condition, and they can be related to the persistence of the small photocurrent observed when a bias voltage higher than the open circuit voltage is applied.
Laser Crystallized Polysilicon TFT'S Using LPCVD, PECVD and PVD Silicon Channel Materials-A Comparative Study
Authors: Fulks R.T. , Boyce J. B. , Ho J. , Davis G. A. , Aebi V. 
Published: April 2011

AbstractIn this work polysilicon TFI's were fabricated by excimer laser crystallization of active channel silicon which was deposited by three different methods: I) LPCVD at 550 °C; 2) PECVD at 225 °C; and 3) PVD at room temperature. CMOS devices were produced with the same low temperature (less than 600 °C) top gate process and the laser anneal condition was optimized for the material type and thickness. For PECVD material a pre-anneal step of 450 °C for 1 hour was required before crystallization to avoid bubbling and ablation due to hydrogen evolution, but no such anneal was required for either LPCVD or PVD material due to their low hydrogen and Ar content. For 50 nm films, laser energy densities were typically in the range of 300-400 miJ/cm2. Excellent device results were obtained for both LPCVD and PECVD material with n-channel field effect mobilities greater than 100 cm2/Vs and on/off ratios greater than 108 at 5 V drain bias. Good results were also obtained for PVD films that can be further improved by optimizing deposition and anneal conditions. In moving toward very low temperature polysilicon processing (less than 230 °C) both PECVD and PVD channel films appear to be viable candidates.
Thin Film Transistors based on Microcrystalline Silicon on Polyimiide Substrates
Authors: Constant A.P. , Witt T. , Bratland K.A. , Shanks H.R. , Landin A.R. 
Published: April 2011

AbstractThis study reports on the fabrication of inverted gate TFT devices and circuits using a low temperature microcrystalline silicon deposition process compatible with polyimide substrates. Results from the electrical and material characterization of μ-Si:H based TFT's are presented. Device performance is compared with that of α-Si:H based TFT's constructed on polyimide. Results indicate that the anticipated improvement in device performance due to an increase in the α-Si:H Hall mobility (~10 cm2/V-sec) over that of α-Si:H (~1 cm2/V-sec) is not realized. Properties of μ-Si:H films are related to deposition parameters.