bluuebunny/crossref_metadata_2025_split huggingface dataset:
Probing Detonation Physics and Chemistry Using Molecular Dynamics and Quantum Chemistry Techniques
Authors: Cook M. D. , Fellows J. , Haskins P. J. 
Published: April 2011

AbstractModem quantum chemistry and molecular dynamics computer codes are powerful tools with which to study the physics and chemistry of energetic materials at the molecular level. Quantum chemistry calculations, on one or two energetic molecules, can give valuable information about the initial steps in their decomposition. Molecular dynamics calculations, even with empirical potentials, can yield important information about the physical processes involved in the initiation and growth of reaction of energetic materials. The combination of Molecular dynamics and quantum chemistry techniques offers the potential to probe energetic material reaction chemistry in real systems, in some detail, in the near future. Such an approach is vital if we are to be able to create new realistic macroscopic models within hydrocodes that can describe the initiation and growth of reaction in explosives. This paper gives an overview of the approach being adopted at DRA Fort Halstead to understanding energetic materials at the molecular level. In particular, the use of quantum chemistry and Molecular dynamics to help construct new macroscopic models will be discussed.
Hot Spots in a Molecular Solid Under Rapid Compression: Energy Sharing Among the T-R-V Degrees of Freedom.
Authors: Tsai D. H. 
Published: April 2011

AbstractSharing of the kinetic energy among the translational-rotational-vibrational (T-R-V) degrees of freedom in a molecular crystal, following excitation of the T degrees of freedom, has been studied by means of molecular dynamics. The model was similar to that employed in [2]. The Tdegrees of freedom were energized by adding a velocity distribution to the (100) molecular lattice planes so as to excite certain normal modes in the [100] direction. The kinetic energy components in TR, V and the rates of energy sharing between T-V and T-R were determined. The results were then compared with those from rapid compression of the same model, with or without defects.
Molecular Dynamics Calculations on the Properties of the Reaction Zone in Liquid Explosive
Authors: Soulard L 
Published: April 2011

AbstractWe present the results of molecular dynamics calculations concerning the structure and the thermodynamic state of the reaction zone in the liquid explosive NO under shock sollicitation.We show that the compression of explosive is due to inertial shock followed by endothermic decomposition. Then exothermic reactions occur and cause a slow decreasing of pressure until the end of the reaction zone. Analysis of particle velocities distribution and interatomic forces shows that only a partial equilibrium is reached in the reaction zone. As the relaxation time of particles velocities is very small compared to the characteristic time of chemical reactions, thermal equilibrium is always reached and the various molecular species are isothermal. It is not the case of interparticle forces and pressure in the usual thermodynamic way cannot be defined: the reaction zone is not isobaric. Our conclusion is that an equation of state cannot be defined in the reaction zone.
Simulations of Ozone Detonation Using a Reactive Empirical Bond Order (REBO) Potential for the Oxygen System
Authors: Barrett J. J. C. , Robertson D. H. , Brenner D. W. , White C. T. 
Published: April 2011

AbstractThe short length and time scales associated with chemical detonations make these processes excellent candidates for study by MD simulation. Potentials used in these simulations must have sufficient flexibility to describe gas-phase properties of isolated reactant and product molecules, high density material generated under shock compression, and allow smooth adjustment of bonding forces during chemical reaction. The REBO formalism has been shown to provide these characteristics and allow the treatment of a sufficient number atoms for sufficiently long times to demonstrate a chemically-sustained shock wave (CSSW). In this paper we present a REBO potential describing the oxygen system for use in MD simulation of detonation in an ozone molecular solid. The potential reproduces spectroscopic properties of isolated gas-phase O2 and O3. It also describes an ozone molecular solid with density and speed of sound within physical norms. We observe detonation characteristics that depend on crystallographic orientation in simulations using a three dimensional ozone molecular crystal.
Vibrational Energy Transfer in High Explosives: Nitromethane
Authors: Hong Xiaoyu , Hill Jeffrey R. , Dlott Dana D. 
Published: April 2011

AbstractTime resolved vibrational spectroscopy with picosecond tunable mid-infrared pulses is used to measure the rates and investigate the detailed mechanisms of multiphonon up-pumping and vibrational cooling in a condensed high explosive, nitromethane. Both processes occur on the ˜100 ps time scale under ambient conditions. The mechanisms involve sequential climbing or descending the ladder of molecular vibrations. Efficient intermolecular vibrational energy transfer from various molecules to the symmetric stretching excitation of NO2 is observed. The implications of these measurements for understanding shock initiation to detonation and the sensitivities of energetic materials to shock initiation are discussed briefly.
Detonation Chemistry Of Glycidyl Azide Polymer
Authors: Ling Ping , Sakata Jill , Wight Charles A. 
Published: April 2011

AbstractThe initial step of chemical reaction initiated by laser-generated shock waves has been observed in glycidyl azide polymer (GAP) in condensed phase. Shocks are generated by pulsed laser vaporization of thin aluminum films and launched into adjacent films of GAP at 77 K. Comparison of FIIR spectra obtained before and after shock passage shows that initial reaction involves elimination of molecular nitrogen from the azide functional groups of the polymer. The shock arrival time has been measured by a velocity interferometer as a function of thickness of GAP and laser fluence. The shock pressure has been calculated by using a universal liquid state Hugoniot. A simple model is proposed to calculate shock velocity and pressure as a function of laser fluence. The results are in agreement with experimental data.
Synthesis of High Density Insensitive Energetic Tetraazapentalene Derivatives
Authors: Trudell M. L. , Subramanian G. , Eck G. , Boyer J. H. 
Published: April 2011

AbstractAn improved nitration procedure has been developed for the synthesis of y-Tacot (3). The synthesis of y-DBBD (8) has been completed in three steps from 3 in 37% yield. y-DBBD (8) was found to be thermally stable up to 274 °C (decomposed) and insensitive to impact (hammer blow). Nitration of z-BDDB (6) and y-DBBD (8) gave carbonyl derivatives resulting from in situ hydroysis/oxidation of the corresponding tetranitro derivatives z-TBBD (7) and y-TBBD (9), respectively.
Dynamic Chemical Processes of Detonations: Underwater Explosion and Combustion Processes With the use of Water as an Oxidant
Authors: Slutsky V. G. , Tsyganov S. A. , Severin E. S. 
Published: April 2011

AbstractThe possibility of producing underwater unconfined explosions with the use of propylcarborane as a fuel and water as an oxidant was demonstrated experimentally. The specific TNT equivalent of the energy release in the explosion reaction between propylcarborane and water was found to be 1.5 times higher than conventional explosives. A possibility of organizing the combustion of initially unmixed propylcarborane and water was experimentally proven as well
Computational Determination of Heats of Formation of Energetic Compounds
Authors: Politzer Peter , Murray Jane S. , Grice M. Edward 
Published: April 2011

AbstractA recently-developed density functional procedure for computing gas phase heats of formation is briefly described and results for several categories of energetic compounds are summarized and discussed. Liquid and solid phase values can be obtained by combining the gas phase data with heats of vaporization and sublimation estimated by means of other relationships. Some observed functional group effects upon heats of formation are noted.
Monte Carlo Simulations of Crystalline TATB
Authors: Sewell Thomas D. 
Published: April 2011

AbstractWe are performing constant-NPT Monte Carlo calculations of the physical properties of crystalline TATB. Our approach is to employ an atomistic model in which the individual molecules are treated as semi-rigid entities. Each molecule is allowed to undergo rigid translations and rotations, and in some cases limited intramolecular flexibility is conferred on the molecules via exocyclic torsions. Additionally, the size and shape of the simulation box is allowed to vary. Our immediate interest is in computing the density, lattice energy, lattice constants, and other structural parameters as a function of temperature. Preliminary results indicate that simulations involving only two molecules suffice for calculations of the energy and density, but that more molecules are required to compute the lattice constants. Intramolecular flexibility is important, particularly at higher temperatures.
Investigation of a-Si:H p-i-n Solar Cell Degradation
Authors: Smole Franc , Groznik Aleč , Topič Marko , Popović Pavle , Furlan Jože 
Published: April 2011

AbstractBased on measured characteristics of degraded p-i-n structures, simulations of degraded structures were performed using our numerical simulator ASPIN in order to fit and explain pronounced hump-shaped voltage-dependent internal collection efficiency (ICE) characteristics under weak short-wavelength illumination. Agreement with measured hump-shaped ICE characteristics was obtained only if in addition to the introduction of light-induced dangling bond defect states, their capture cross-sections were also increased, in particular capture crosssection for the charged defect states. This causes a change in occupancy of defect states at the p-i interface and front part of the i-layer under forward bias. Consequently, it increases the electric field in the front part of the cell, which results in recovery of the ICE.
The Study of Space Charge Effects by Spectral Response, Steady State Charge Collection and Transient Photocurrents in Thick a-Si:H Pin-Diodes
Authors: Zollondz J.-H. , Brüggemann R. , Reynolds S. , Main C. , Gao W. , Bauer G. H. 
Published: April 2011

AbstractCharge collection, transient photocurrents and collection efficiency under additional bias illumination were used to characterize 3–4 micron thick a-Si:H pin-diodes. The wavelength dependent decrease or increase in the spectral response, depending on the bias flux and absorption depth, is related to the distribution of the electric field, recombination and majority carrier diffusion. At higher photon flux an overshoot in the transient photocurrent after switch-on of steady illumination indicates the time scale for the changes in internal variables. Collection efficiencies under large bias monochromatic photon flux well in excess of the maximum value of 100 % for probe beam generated carriers are observed with a large amplification ratio. These efficiencies sensitively depend both on the applied voltage and the defect density. Numerical modelling reveals the influence of internal variables on the transient and steady state photocurrents under the different illumination conditions.
Light-Induced Effects on Fluorinated Amorphous and Microcrystalline Silicon Films
Authors: Choi Hong-Seok , Jang Keun-Ho , Yoo Jhun-Suk , Han Min-Koo 
Published: April 2011

AbstractThe fluorinated amorphous and microcrystalline silicon (a,μc-Si:H;F) films have been prepared by rf plasma enhanced chemical vapor deposition (PECVD) with SiH 4 and SiF 4 gas mixtures. The stretching Si-O (1085 cm-1) and SiH2 (2100 cm-1) bands estimated from infrared (IR) spectroscope data have related to the evolution of crystallinity and the optical band gap was shifted by introducing Si-O bonds. The sub-band gap absorption coefficient in a,μc-Si:H;F films was about one order lower than that in hydrogenated amorphous silicon film (a-Si:H). The subband gap absorption in a-Si:H;F film was comparable to that in tic-Si:H;F films. The lightinduced degradation of a,μc-Si:H;F films were also suppressed.
Improvement in a-Si:H Properties by Inert Gas Plasma Treatment
Authors: Maruyama E. , Hishikawa Y. , Tanaka M. , Kiyama S. , Tsuda S. 
Published: April 2011

AbstractThe modification of surface reactions with an inert gas plasma treatment method has been investigated for the first time in order to improve the properties of a-Si:H for solar cells. The deposition of a thin a-Si:H layer and exposure to inert gas plasma such as He, Ar or Xe were repeated by using RF plasma CVD at a substrate temperature of 200 °C. It has been found that the hydrogen content (CH) can be controlled in a wide range from about 18 atomic% to about 35 atomic%, although it is a hydrogen-free process. Experimental results show that the change in CH of a-Si:H films is mainly determined by the decrease in CH of the treated a-Si:H surface and the increase in CH of the a-Si:H deposited on the treated surface. Furthermore, the plasma treatment probably promotes the surface reaction, which reduces SiH2ISiH and CH. Consequently, wide-gap (1.64 eV by ( a h ν )1/3 versus h ν plots, 1.75 - 1.85 eV by Tauc's plot) a-Si:H films with high stabilized photoconductivity (> 10-5 Ω-1cm-1 under AM-1, 100 mW/cm2 irradiation) have been obtained by the inert gas plasma treatment method.
Pulsed Esr Study of Light-Induced Metastable Defects in 17O and 13C Incorporated a-Si:H
Authors: Yamasaki S. , Umeda T. , Isoya J. , Matsuda A. , Tanaka K. 
Published: April 2011

AbstractHydrogenated amorphous silicon (a-Si:H) samples containing 17O (3 x 1019 cm-3, nuclear spin, I, = 5/2) and 13C (3 - 4 x 1017cm-3, I = 1/2) isotope impurities were used in the detailed pulsed electron spin resonance (ESR) and pulsed electron-nuclear double resonance (ENDOR) measurements to obtain information on the role of O and C impurities in lightinduced metastable dangling bonds in a-Si:H. No hyperfine structure related to 17O and 13C atoms was observed in echo detected ESR, electron spin echo envelope modulation (ESEEM) of pulsed ESR as well as pulsed ENDOR (Davies and Mims sequences), which suggests that O and C impurities are not directly involved in the formation of light-induced dangling bonds.
Ion Energy Distributions in Silane-Hydrogen Plasmas
Authors: Hamers E. A. G. , Van Sark W. G. J. H. M. , Bezemer J. , Van Der Weg W. F. , Goedheer W. J. 
Published: April 2011

AbstractFor the first time ion energy distributions (IED) of different ions from silane-hydrogen (SiH4-H2 ) RF plasmas are presented, i.e. the distributions of SiH3+, SiH2+ and SiH2+. The energy distributions of SiH3+ and SiH3+ ions show peaks, which are caused by a charge exchange process in the sheath. A method is presented by which the net charge density in the sheath is determined from the plasma potential and the energy positions of the charge exchange peaks. Knowing the net charge density in the sheath and the plasma potential, the sheath thickness can be determined and an estimation of the absolute ion fluxes can be made. The flux of ions can, at maximum, account for 10% of the observed deposition rate.
Hydrogen Distribution in High Stability A-Si:H Prepared by the Hot Wire Technique
Authors: Stephen J. Todd , Han Daxing , Mahan A. Harv , Wu Yue 
Published: April 2011

AbstractIn this work the microstructures of 2–3 hydrogen at.% hot-wire CVD a-Si:H films were characterized by 1H nuclear magnetic resonance (NMR). Significant differences were found between the hydrogen distribution in these samples and that in conventional plasma-enhanced CVD samples. Among other things, the broad resonance line in the hot-wire a-Si:H is 50 kHz wide, which is much broader than that observed 25–35 kHz in PECVD a-Si:H films. Moreover, a 0.5 kHz resonance absorption hole width due to intrinsic dipolar interactions is obtained using the hole-burning technique. Surprisingly, approximately 90 percent of the hydrogen atoms give rise to the 50 kHz line and only a very small percentage of the hydrogen atoms give rise to the much narrower resonance line.
Spectroscopic Evidence for Near-Neighbor Bonded H(D) in A-Si:N:H(D) Thin Films
Authors: Lucovsky G. , Santos-Filho P. , Banerjee A. , Jing Z. 
Published: April 2011

AbstractIncreases in the frequency of the silicon monohydride (Si-H) bond-stretching vibration in hydrogenated silicon nitrides, over and above what can be attributed to chemical induction effects, are shown to be generated by a repulsive interaction between the H-atom of the Si-H group, and a near-neighbor SiN-H group. This interaction increases the effective bond-stretching force constant of the H-atom of the Si-H group. This effect has been verified by ab-initio quantum chemistry calculations that have been used to calculate the energy of the H-atom of the Si-H group as a function of the relative separation between near-neighbor Si-H and SiN-H groups. Decreases in the bond-stretching frequencies of SiN-H groups in heavily hydrogenated nitrides are attributed to H-bonding effects associated with near-neighbor pairs of SiN-H groups.
Hydrogen Energetics and Transport Kinetics in Amorphous Silicon Hydride
Authors: Franz A. J. , Gland J. L. 
Published: April 2011

AbstractTo understand the electrical properties and behavior of amorphous silicon, it is imperative to understand the behavior of hydrogen in the amorphous silicon lattice. Although considerable effort has been extended to study hydrogen trapping in a-Si:H, the energetics and populations of the traps remain unresolved. We have developed a reaction diffusion model which includes multiple bulk trapping mechanisms, bulk transport, and realistic surface processes. The model results are compared with existing hydrogen temperature programmed evolution data, isothermal hydrogen evolution experiments, and thermal quenching experiments. We find consistently good fits for all three types of experiments with a shallow trap depth of 1.5 eV and deep trap depth of 1.8–1.9 eV below the mobility level, with 20–30% of hydrogen present in the deep trap. The difference of 0.3–0.4 eV between the two trap depths is similar to the defect formation activation energy and suggests a defect formation mechanism which involves movement of hydrogen from a deep to a shallow trap.
Optically Detected Magnetic Resonance Studies of Undoped a-Si:H
Authors: Schultz N. , Vardeny Z. V. , Taylor P. C. 
Published: April 2011

AbstractPhotogenerated carrier dynamics in undoped a-Si:H have been studied by photoinduced absorption (PA), photoluminescence (PL) and their respective optically detected magnetic resonances: PADMiR and PLDMR. We have detected for the first time the “g = 4” resonance in PADMR, in addition to the previously measured narrow and broad resonances at g≈2. We compare the PADMR and PLDMR resonances over a broad spectral range of detection energies and conclude from the similarities that they share a common underlying mechanism. The PADMIR spectra of the narrow and the broad resonances at g≈2, measured in the spectral range of 0.7 to 1.7 eV, suggest that a correlation exists between the two resonances and PA.
Kinetics of Both Defects and Electron and Hole Diffusion Lengths During Light-Soaking in a-Si:H Films
Authors: Abramov A. S. , Kosarev A. I. , Cabarrocas P. Roca i , Vinogradov A. J. 
Published: April 2011

AbstractConcomitant studies of kinetics of defects ND(t), photoconductivity σph(t), electron and hole diffision lengths Le(t), Lh(t) during light soaking have been carried out. The data have been fitted by stretched exponential expressions and characteristic parameters of kinetics have been determined. Correlation between the kinetics is discussed. In contrast to Nd(t), σph(t) and Le(t), the hole diffusion length Lh(t) was observed to remain constant during initial time (˜ 103s) and then decreased with characteri stic time ˜ 104s.
Thermopower and Conductivity Activation Energies in Hydrogenated Amorphous Silicon
Authors: Dyalsingh H. M. , Kakalios J. 
Published: April 2011

AbstractThe long range fluctuation model has been widely used to account for the difference in activation energies seen experimentally in dark conductivity and thermopower measurements in hydrogenated amorphous silicon. We report on a test of this model using measurements of the conductivity and thermoelectric effects carried out in both open and short circuit configurations. While the thermopower activation energy is less than that of the dark conductivity, the short circuit Seebeck conductivity is found to be nearly identical to the dark conductivity in both activation energy and magnitude, consistent with the long range fluctuation model.
Temperature Dependence of Minority Carrier Lifetimes in a-Si:H
Authors: Cornish J. C. L. , Subaer  , Jennings P. , Hefter G. T. 
Published: April 2011

AbstractChanges in minority carrier lifetimes in a-Si:H, p-i-n photovoltaic cells due to light soaking have been investigated using the open circuit voltage decay (OCVD) method over the temperature range 223 K to 296 K.Using light from a Xenon flash lamp for excitation produced unexpected results: in the light soaked material, band-to-band transitions were evident at a higher temperature than for the asdeposited samples and became increasingly pronounced as the temperature was reduced. Results obtained using red light at 670 nm from a pulsed diode laser to produce relatively uniform- illumination throughout the thickness of the film, however, produced results very similar to those obtained for as-deposited films.Plots of the reciprocal of the trap activation time versus 1000/T for the results for both xenon lamp and laser excitation can be fitted by straight lines. Two distinct sets of lines with activation energies in the ranges 0.07 to 0.20 eV and 0.38 to 0.51 eV are obtained with the activation energy and the exponential prefactors exhibiting a Meyer-Neldel relationship.
Technological Development for Commercialization of Amorphous Silicon Based Multijunction Modules
Authors: Yang Liyou , Bennett M. , Chen L. , Jansen K. , Kessler J. , Li Y. , Newton J. , Rajan K. , Willing F. , Arya R. , Carlson D. 
Published: April 2011

AbstractSome of the significant steps in technological development for large-scale commercialization of amorphous silicon (a-Si:H) based multijunction photovoltaic modules are presented. These developments are establishing a high quality baseline process for manufacturing large-area ( ˜ 8 ft2) a-Si:H/a-SiGe:H tandem junction modules with improved stabilized conversion efficiency, throughput, yield, and reduced materials usage.
Inhibition of Metal Induced Crystallization in the System Ag/ZnO/a-Si:H
Authors: Edelman F. , Brener R. , Cytermann C. , Weil R. , Beneking C. , Beyer W. 
Published: April 2011

AbstractA systematic investigation has been made on the barrier properties of ZnO layer between ndoped a-Si:H and Ag metallization films in the structures (001)Si/SiO2/Ag/ZnO/a-Si:H:P and (001)Si/SiO2/a-Si:H:P/ZnO/Ag. Plasma assisted CVD deposition was used to produce a-Si:H (2500Å thick) highly P-doped films over thermally oxidized Si-wafers at 190 and 270°C. Transparent conductive ZnO:A1 layers, 1000Å and lμm thickness, and Ag films (1000Å thick) were deposited by sputtering. The polycrystalline ZnO layers were textured along the <0001> axis in the as-deposited state. The structures were annealed in vacuum in the temperature range from 300 to 700°C for 1/4 to 16h. X-ray diffraction and transmission electron microscopy studies demonstrated the a-Si:H:P stability against crystallization under ZnO buffer protection up to 700°C (when free a-Si crystallizes itself). The (111) peak position of the Ag reflection was used to show that while the Ag was always strained, the strain was partially relaxed when in contact with the 0. 1 μm ZnO film, it developed additional strain when in contact with the I μm ZnO film.