bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electron Beam Activated Diamond Devices
Authors: Lin Shiow-Hwa , Sverdrup Lawrence H. 
Published: April 2011

ABSTRACTDiamond's unique properties are ideally suited for high power and high frequency electronic applications. Natural type Ila diamond wafers of various thicknesses and active areas were used to construct several electron beam activated diamond devices. Average voltage gradients in the diamond target on the order of a mega-volt per centimeter were obtained. Possibilities of improving the attainable average voltage gradient are discussed. Electron activation avoids the necessity of semiconducting doping of the active diamond devices. The electron bombardment on diamonds yields a current-voltage characteristics very similar to that of a bipolar transistor. In the experiments discussed here, the diamond conduction to bombarding current gain ranged from 1,000 to 3,000 depending upon the diamond thickness and the bombarding electron energy. The bombarded diamond on-state resistance is consistent with a simple carrier drift and space charge model. Maximum conduction current density achieved in diamond is 19kA/cm2. High power switching of greater than 25kW with less than 100ns risetime is demonstrated. An electron beam bombarded millimeter wave diamond device has generated more than one watt of power.
Auger Electron Spectroscopy of The CVD Diamond Surface Under Electron Exposure
Authors: Krainsky I. L. , Mearini G. T. , Asnin V. M. , Sun H. , Foygel M. , Petukhov A. G. 
Published: April 2011

ABSTRACTA simultaneous study of Auger spectra and secondary electron emission from the chemical vapor deposited diamond films under extended electron beam exposure is presented. Up to a 1.2 eV increase in energy of the carbon Auger peak accompanied by the decrease of the total secondary electron yield has been found. Exposure to hydrogen has resulted in recovery of the both Auger peak position and secondary yield. First-principles electronic structure calculations have been carried out to interpret the Auger peak shift. The effect is shown to be due to a change in the surface upper-valence band local density of states of the diamond crystal which is dependent on the extent of hydrogen coverage of the surface.
Electron Field Emission Properties of Diamond
Authors: Zhu W. , Kochanski G. P. , Jin S. 
Published: April 2011

ABSTRACTWe have developed both experimental and numerical methods to collect and analyze field emission data from diamond samples. The diamond emitters are either films prepared by low pressure chemical vapor deposition (CVD) or powders synthesized by traditional high pressure high temperature (HPHT) processes. We established a strong correlation between the electric field required for emission and the defect densities in undoped or p-type doped diamond. We further found that ultrafine diamond particulate emitters offer substantially enhanced electron field emission properties at low electric fields compared to CVD diamond emitters. When subject to appropriate processing schemes, the particulate diamond emitters exhibit extremely low emission fields, typically 1-5 V/μm for a current density of 10 mA/cm2. These are believed to be the lowest-voltage field emitters ever reported.
Secondary Electron Emission Studies of Diamond Surfaces
Authors: Shih A. , Yater J. , Pehrsson P. , Butler J. , Hor C. , Abrams R. 
Published: April 2011

ABSTRACTDiamond exhibits high secondary-electron yields which vary strongly with sample preparation and sample treatment. In this study, we identify some of the factors that govern the secondary-electron emission yield of diamond. Comparative studies are made with polycrystalline diamond films having different dopants (boron or nitrogen), dopant concentrations and surface conditions (hydrogen-terminated or oxidized). In these studies, the total electron yield as a function of the incident-electron energy and the energy distribution of the secondary emitted electrons are measured. The results show that both electrical conductivity and hydrogen-termination play essential roles in the secondary-electron emission process. For hydrogen-terminated samples, the energy distribution shows a large and narrow peak at the onset of electron emission. The long mean-free path of the secondary electrons and the low or negative electron affinity are essential to the exceedingly high electron yield of diamond.
Measurement of Thermal Diffusivity of Cvd diamond films using modified ac calorimetry
Authors: Maesono Akikazu , Tye Ronald. P. 
Published: April 2011

ABSTRACTMany applications of thin films, especially for electronics devices, require that these materials, which are often anisotropic, have a very high thermal conductivity as well as uniform areal properties to ensure that reproducible performance be attained. These factors necessitate that measurements of thermal transport properties are required both to provide absolute application values for different heat flow directions as well as to evaluate uniformity and homogeneity of a wafer. For diamond, the combination of a very high thermal conductivity with limited size and form of available specimen presents unique challenges to the experimentalist. As a result, a modification of the ac calorimeter method has been developed to evaluate the thermal diffusivity of thin films.Details of the technique will be provided together with examples of its use to evaluate thermal diffusivity and thermal conductivity of different CVD diamond film composites having thicknesses from 10µm to 600µm and free-standing films. In addition, results using this method will be compared. with those obtained by other techniques involved in a recent international round-robin measurements program designed to evaluate a potential standard method(s).
Kinetic Analysis of Solid-State Reactions: An Improved Analysis Method
Authors: Smith D. P. , Chaudhri M. M. 
Published: April 2011

AbstractMany reactions of interest occur in the solid state, or with low mobility of the reactants or products, with the result that the physical mechanisms operative during the reaction determine the shape of the reaction rate-time profile; i.e. topochemistry is important. However, often improper account is taken of the physical mechanisms, resulting in erroneous values for the activation energy and kinetic constants.An improved method of analysis is suggested, allowing the mechanisms of reaction to be determined explicitly. This thus allows the activation energy and kinetic constants to be determined with good theoretical justification. The method has been verified by studying the thermal decomposition of barium azide, where the activation energy was determined to better than 1%. The operative mechanisms so determined are in agreement with visual observations and the literature.
A Theoretical Study of BF + OH and BO + HF Reactions
Authors: Soto M. R. 
Published: April 2011

AbstractThe reactions of BF + OH and BO + HF are critical reactions in the reaction mechanism of fluorine-enriched boron combustion.1 In this study, ab initio multiconfigurational methods have been used to calculate energies, optimized geometries, harmonic vibrational frequencies and zero-point energies for reactants, products and intermediates of these reactions. Results for the following reactive pathways will be discussed:
High Pressure Ignition of Boron in Reduced Oxygen Atmospheres
Authors: Foelsche R. O. , Spalding M. J. , Burton R. L. , Krier H. 
Published: April 2011

AbstractBoron ignition delay times for 24 μm diameter particles have been measured behind the reflected shock at a shock tube endwall in reduced oxygen atmospheres and in a combustion bomb at higher pressures in the products of a hydrogen/oxygen/nitrogen reaction. The shock tube study independently varies temperature (1400 – 3200 K), pressure (8.5, 34 atm), and ignition-enhancer additives (water vapor, fluorine compounds). A combustion chamber is used at a peak pressure of 157 atm and temperature in excess of 2800 K to study ignition delays at higher pressures than are possible in the shock tube.
Reaction Rate Modeling in the Deflagration to Detonation Transition of Granular Energetic Materials
Authors: Son S. F. , ASAY B. W , Bdzil J. B. , Kober E. M. 
Published: April 2011

AbstractThe problem of accidental initiation of detonation in granular material has been the initial focus of the Los Alamos explosives safety program. Preexisting models of deflagration-to-detonation transition (DDT) in granular explosives, especially the Baer & Nunziato (BN) model, have been examined. The main focus of this paper is the reaction rate model. Comparison with experiments are made using the BN rate model. Many features are replicated by the simulations. However, some qualitative features, such as inert plug formation in DDT tube-test experiments and other trends, are not produced in the simulations. By modifying the reaction rate model we show inert plug formation that more closely replicates the qualitative features of experimental observations. Additional improvements to the rate modeling are suggested.
Detonation and Deflagration Properties of Pyrotechnic Mixtures
Authors: Tanaka Katsumi 
Published: April 2011

AbstractTheroretical calculation of detonation and deflagration properties of pyrotechnic mixtures have been performed including report charges and display charges. Calculation were performed with the KHT (Kihara-Hikta-Tanaka) code[l]. KHT results are compared with a modified version of the TIGER code[2] which allows calculation with 900 gaseous and 600 condensed product species at high pressure. Detonation properties computed by KHT and BKWS (Becker-Kistiakowskii-Wilson) give favorable agreement with experimental results of detonation velocity measurements. Hydrodynamic computation by one dimensional Lagrangian hydrodynamic code using the isentrope given by KHT constant volume explosion, indicated that experimental results for blast wave measurement for 30kg and 50kg of report charge were an incomplete reaction. Underwater detonation experiments with explosive charge of 25g, however, indicates a more energetic nature than the KHT prediction. This scale effect indicates complicated slow reactions and a number of condensed phase deflagration products of powder mixtures such as aluminum or titanium with oxidizers such as potassium perchlorate or nitrate salts as suggested by Hobbs et al[3].
Crystal Growth of Energetic Materials During High Acceleration
Authors: Lanzerotti M. Y. D. , Autera J. , Borne L. , Sharma J. 
Published: April 2011

AbstractStudies of the growth of crystals of energetic materials under conditions of high acceleration in an ultracentrifuge are reported. When a saturated solution is accelerated in an ultracentrifuge, the solute molecules move individually through the solvent molecules to form a crystal at the outer edge of the tube if the solute is more dense than the solvent. Since there is no evaporation or temperature variation, convection currents caused by simultaneous movement of solvent and solute are minimized and crystal defects are potentially minimized. Crystal growth is controlled by the g-level of the acceleration. In addition, solution inclusions and bubbles migrate out of the saturated solution as a result of the pressure gradient induced by the g-force. We present results of TNT, RDX, and TNAZ grown at high g from various solutions.
Improved Monolithic Photovoltaic-Electrochromic Devices Incorporating an a-SiC:H Solar Cell
Authors: Bullock John N. , Bechinger Clemens , Xu Yueqin , Benson David K. , Branz Howard M. 
Published: April 2011

AbstractIn the tandem photovoltaic-electrochromic (PV-EC) device, a wide-gap, semitransparent, amorphous silicon-carbon alloy (a-SiC:H) photovoltaic device and an electrochromic optical transmittance modulator (EC device) are deposited sequentially to form a monolithic device on a single substrate. This device can be used as a “smart” window for active control of daylighting and building cooling load without an external electrical connection.Last year we reported preliminary results on our development of a semi-transparent PV cell incorporating an a-SiC:H i-layer. Here we report our recent progress on the semitransparent PV component of a PV-EC device and development of a Li-based EC device that colors at voltages below 0.9 V. Finally, we discuss both recent progress and difficulties in integrating the two devices on one substrate.
Two-layer Model for Electroabsorption and Built-in Potential Measurements on a-Si:H pin Solar Cells
Authors: Jiang Lin , Schiff E. A. 
Published: April 2011

AbstractModulated Electroabsorption (EA) measurements have been widely used to estimate built-in potentials (Vbi) in semiconductor devices. The method is particularly simple in devices for which the built-in potential is dropped in a single layer of the device. However, experimental results in amorphous silicon and organic devices can involve at least 2 layers. In the present paper we consider the information which can be obtained about 2-layer semiconductor devices from electroabsorption measurements. In particular we describe a 2-layer EA model appropriate to a-Si:H based pin solar cells, for which both the p+ and i layers contribute to the EA signal. We present an analysis of capacitance and second harmonic measurements which yields the EA coefficient for the p+ layer of the device, and we present measurements on a-Si:H pin devices which appear consistent with this analysis. Wavelength dependent EA then yields the built-in potential across the 2-layer device.
Effects of Laser Annealing on the Furnace Annealed Amorphous Silicon Thin Films
Authors: Choi Kwon-Young , Jeon Jae-Hong , Han Min-Koo , Kim Yong-Sang 
Published: April 2011

AbstractThe performance of polysilicon thin film transistors fabricated by two-step annealing, which consists of furnace annealing and subsequent excimer laser annealing, is described. It was found that the average grain size of low temperature furnace annealed polysilicon films was several times larger than that of excimer laser annealed polysilicon films while the density of in-grain defect in low temperature furnace annealed films was much higher than that of excimer laser annealed film. The device characteristics of the low temperature furnace annealed polysilicon thin film transistors were improved significantly by postannealing, such as high temperature furnace annealing and excimer laser annealing, due to the effective elimination of in-grain defects. The density of trap states, which was extracted from the transfer curves of polysilicon thin film transistors, was used to demonstrate the effects of modifying the deep and tail trap levels by two-step annealing.
Wide-Gap a-Si:H Fabricated by Controlling Voids
Authors: Yoshino K. , Futako W. , Wasai Y. , Shimizu I. 
Published: April 2011

AbstractHigh quality wide gap hydrogenated amorphous silicon has been prepared using the chemical annealing technique. It was possible to prepare materials with band gaps ranging 1.8 to 2.1 eV by varying the preparation parameters. Low defect densities less than (3–8) x 1015 cm-3 could be maintained over the entire band gap range. Improved stability for light soaking was also observed in the wide gap materials.
The Influence of Hydrogen Dilution and Substrate Temperature in Hot-Wire Deposition of Amorphous and Microcrystalline Silicon With Filament Temperatures Between 1900 And 2500 °C
Authors: Conde J. P. , Brogueira P. , Castanha R. , Chu V. 
Published: April 2011

AbstractThe effect of hydrogen dilution and substrate temperature on the optoelectronic and structural properties of thin films deposited by hot-wire chemical vapor deposition with filament temperatures between 1900 and 2500 °C from silane and hydrogen are studied. Amorphous silicon films are obtained at high deposition rates for hydrogen dilutions below 90%. The deposition rate scales approximately linearly with the filament temperature in this regime. Microcrystalline films are obtained for hydrogen dilution above 90%, independently of the filament temperature and substrate temperature, with much lower growth rates. The Raman spectrum of these films shows high crystalline fraction and small grain size. High conductivity films, typical of microcrystalline silicon, with high growth rates were achieved by either increasing the substrate temperature at low hydrogen dilution, or by using a hydrogen dilution just at the amorphous to microcrystalline transition point.
The Electronic Properties of a-Si:H Deposited With Hydrogen or Helium Dilution
Authors: Zhong F. , Hong W. S. , Perez-Mendez V. , Chen C. C. , Cohen J. D. 
Published: April 2011

AbstractWe have applied the Drive-Level Capacitance Profiling (DLCP) method to n-i-p a-Si:H diodes to characterize the mid-gap defect densities in the i layer. Our results show that there are no significant changes in the drive-level densities, Ndl, in n-i-p diodes and p+-i-m as well as n-i-m Schottky diodes, which indicates that DLCP can directly provide reliable energy distribution and spatial distribution of the mid-gap defects in the n-i-p device. We have found that the ratio of Ndl to ND*, the ionized defect density determined by hole onset measurement, is changed with the deposition conditions; it is 3 for standard samples, 2 for helium diluted samples and 6 for hydrogen diluted samples. These results indicate that there may be different defect distributions in these materials, which suggest the ratio of charged (D-) density to the neutral defect (D0) density may be altered when growth conditions are varied.
Mechanical and Electrical properties of Hydrogen or Helium Diluted a-Si:H Prepared at Low Temperatures
Authors: Hong Wan-Shick , Zhong Fan , Perez-Mendez Victor 
Published: April 2011

AbstractHydrogen or helium dilution of silane has been used to improve charge transport characteristics or deposition rate for thick amorphous silicon layers. In both cases, mechanical instability, such as peeling-off, due to high strain energy stored in the a-Si:H film is one of the major concerns. Growing the a-Si:H film at temperatures below 150°C brought the residual stress in the film to a level low enough to prevent delamination. The defect density increased at the same time, but it could be recovered by annealing at 160°C for 100 hours without affecting the stress state. In the hydrogen-diluted material, the deposition condition for optimum mobility and defect density values corresponded to the onset of the microcrystalline formation, and this relationship was confirmed by Transmission Electron Microscopy (TEM). Existence of a small amount of an ordered phase in the helium-diluted material, which was hardly observed by the TEM, was revealed by IR absorption spectra and supported by the change in ratio of photo-todark conductivity compared to that of undiluted material.
Study of a-Si:H / c-Si Heterojunctions for PV Applications
Authors: Zignani F. , Galloni R. , Rizzoli R. , Ruth M. , Summonte C. , Pinghini R. , Zini Q. , Rava P. , Madan A. , Tsuo Y. S. 
Published: April 2011

Abstracta-Si:H / c-Si heterojunction diodes were produced by PECVD with varying amorphous silicon layer thickness and hydrogen dilution of the gas phase. An accurate determination of the growth rate also in the initial stages of the deposition was made possible by an original chemical method based on the dissolution of the films followed by spectroscopical analysis of the obtained solution.The electrical characterization of the diodes confirms the generation - recombination - multitunneling nature of the transport. Although H2 dilution is important, however, beyond a certain level it is detrimental for the junction quality, probably due to the transition to a microcrystalline phase deposition. Solar cells were also produced, the best results being an open circuit voltage of 610 mV and an intrinsic efficiency of 14.2%.
A Study of Local and Extended Migration of H and Defects in a-Si by Molecular Dynamics Simulations
Authors: Fedders Peter A. 
Published: April 2011

AbstractWe report on extensive molecular dynamics (MD) simulations on a-Si:H for up to 5 Ps using the ab initio code of Sankey and Drabold. The supercells contain about 70 atoms and only one defect in order to minimize defect-defect interaction. Simulations on supercell samples that originally contain one bond centered (BC) H in an otherwise defect free sample exhibit BC to BC diffusion as in c-Si. However, we also observe localized motion of defects and H atoms on a very fast time scale that probably has been observed in several experiments.
Defect Formation During Deposition of Undoped a-Si:H BY PE-CVD
Authors: Maeda Keiji , Umezu Ikurou 
Published: April 2011

AbstractDependence of the as-grown defect concentration in PECVD undoped a-Si:H on the deposition parameters, i.e., substrate temperature and precursor density in the plasma produced by H2 dilution of SiH4 gas, is investigated. It is found that the defect density behaves similarly to the concentration of SiH2 configuration in the films deposited at substrate temperatures below 300 °C. The defect concentration, however, varies proportionally to about the 3rd to 4th power of the SiH2 concentration depending on the deposition condition. Based on the surface reaction mechanism proposed in our previous paper, a large enthalpy change is expected to accompany the bimolecular reaction of the adsorbed SiH3 radicals, which incorporates the SiH2 configuration into the network. Characteristics of the defect formation caused by tile breaking Si-Si bond near the growing surface owing to this energy is compared with those of the Staebler-Wronski effect. Both similarity in dependence on II atom concentration and difference in annealing temperature are discussed. It is concluded that the as-grown defects are most likely formed during deposition owing to the large enthalpy change accompanying the bimolecular surface reaction.
Photoluminescence in Hydrogenated Amorphous Silicon with Sulfur
Authors: Chen S. , Taylor P. C. , Wang S. L. , Viner J. M. 
Published: April 2011

AbstractPhotoluminescence (PL) has been measured at 80 K in a series of samples of sulfur doped a- Si:H using above- and below-bandgap excitation energies (2.4 and 1.38 eV). In addition, the absorption coefficients at room temperature have been obtained using photothermal deflection spectroscopy (PDS). At light sulfur doping levels (S/Si < 10-2), the Urbach slopes of the absorption coefficients on a semilog plot and the optical energy gaps, as measured by the points at which ca =104 cm-1, are independent of sulfur concentration. The slopes decrease and optical gaps increase with increasing doping level for doping levels above 10-2. At light sulfur doping levels the PL spectra excited with both above- and below-gap light are independent of sulfur concentration. For larger sulfur concentrations the shapes of the PL spectra vary. In particular, for S/Si > 10-2the peak of the PL spectrum shifts to below 0.8 eV using below-gap excitation at 1.38 eV, and the defect PL band dominates. Comparing the PL spectra of sulfur- and phosphorus-doped samples, the PL spectra change for sulfur doping above 10-2 and for phosphorus doping above 1 ppm. This trend is consistent with inefficient sulfur doping.
Interdiffusion and Carrier Recombination in High Intensity Transient Gratings
Authors: Schwarz R. , Grebner S. , Nebel C. E. , Lanz M. , Stutzmann M. 
Published: April 2011

AbstractTransient grating (TG) experiments were performed to study carrier diffusion and recombination in amorphous silicon films (a-Si:H) at high light intensities using 8 ns pulses from a frequency-doubled Nd:YAG laser. The ambipolar diffusion coefficients reached about 10−2cm2/s, which is 2 orders of magnitude larger than the steady-state value. Similar results were obtained in intrinsic, p-, and n-doped a-Si:H films, indicating that the diffusion coefficients in all cases reflect the near band edge mobility of the slower carriers, that is holes. In particular, the p-type sample shows an initially fast, then a slow grating efficiency decay, consistent with dispersive transport.