bluuebunny/crossref_metadata_2025 huggingface dataset:
From Proposal To Product: Scaling Up The Chemical Synthesis of MOCVD Oxide Precursors
Authors: Leedham T J
Published: April 2011

An essential step in the commercialisation of the MOCVD technique is the prompt availability of reliable precursors such as volatile alkoxides and diketonates for oxide deposition. Synthesis methods must be scaled by three orders of magnitude from grams to kilos to manufacture precursors for commercial devices. Impurities determine whether an identified method is viable due to the way in which they affect yield, shelf life and performance. Deleterious contaminants include free radicals, moisture damage and raw material remnants. Such considerations dominate multi-kilo synthesis but their impact may not have been perceived at an earlier stage. By particular examples we show attention to methodology can overcome these problems.
Barium bis(β-Diketonate)•tetraglyme Complexes as Potential CVD Precursors for Electronic Materials
Authors: Luten Henry A. , Otway David J. , Rees William S.
Published: April 2011

MOCVD, one preferred technique of the present electronics industry, has not yet emerged as the thin film method of choice for group 2 element containing materials due to the demonstrable shortcomings of the available source compounds. Most specifically, the challenge presented by the group 2 element charge/ionic radius ratio must be overcome to meet the vapor pressure requirements for CVD. To date, development of group 2 precursors suitable for MOCVD has focused mainly on the use of substituted acetylacetonate (acac) complexes. Earlier, several series of somewhat volatile precursors were developed by the use of acetylacetonate complexes containing fluorinated sidegroups. These precursors, while elegantly designed for the thermal deposition of BaF2, are not ideal for the preparation of oxide thin films. This arises from their propensity to initially form MF2, which must be reacted further in situ, or in a post-deposition treatment to yield the ultimately sought metal oxide. It is of interest, therefore, to develop stable, volatile precursors lacking fluorinated ligands.
Optical Properties of Diamond-Like Carbon Films Deposited by Laser Ablation
Authors: Seager C. H. , Friedmann T. A. , Bliss D. E.
Published: April 2011

Various optical techniques, including Photothermal Deflection Spectroscopy (PDS), ellipsometry, and transmission measurements, have been used to examine the optical properties of diamond like C films deposited at various laser power densities on Si and fused quartz. The absorption coefficients of these films are typically above 5 × 104 cm−1 throughout the visible part of the spectrum, decreasing quasi-exponentially in the infra-red. Larger sp2/sp3 bonding ratios caused by deposition at lower laser power settings noticeably increase film absorption coefficients. While Tauc plots of our absorption data yield bandgaps of 1.5-1.0 eV, the quality of these fits is unimpressive and the slopes are unphysically low. Rather than modelling these materials as narrow gap semiconductors, we have pursued another avenue: treating the films as a mixture of small graphitic particles embedded in a diamond, sp3-like matrix. We will discuss the results of this approach as well as the evolution of the optical properties after thermal anneals.
About Homogeneity of CVD Diamond Nuclear Particles Detectors
Authors: Manfredotti C. , Fizzotti F. , Polesello P. , Vittone E. , Jaksic M. , Bogdanovic I. , Fazinic S.
Published: April 2011

CVD diamond films show both at optical microscope and at SEM a quasi-columnar structure, not homogeneously distributed in the bulk which is agreed to be responsible for the relatively large charge collection lengths measured in the material. In this work, we present the first data on charge collection efficiency distributions as measured directly in the bulk by a 3 Meν proton microbeam. The results indicate that the material is really non-homogeneous, that only few columns are really connecting both electrodes and that, finally, a real connection exists between the morphological structure and the maps of collection efficiency distribution.
Measurement and Modeling of Optical Constants for Rough Surface Diamond Thin Films
Authors: Yin Z. , Tan H. S. , Smith F. W.
Published: April 2011

The measurement of the optical constants for a rough surface thin film is needed for CVD polycrystalline diamond films which typically have surface roughnesses of the order of tens to hundreds of nm. In this paper, we present a method for determining the optical constants n and k as well as the surface roughness σ for a rough surface diamond thin film. By using the theory of optical reflectance (R) and transmittance (T) for a thin film with incorporation of rough surface scattering factors which are functions of the surface roughness a, the following function can be obtained: R=R(n,k,σ,λ,d), T=T(n,k,σ,λ,d), and Rp=Rp(n,k,σ,λ,d), where λ and d are the incident wavelength and film thickness, respectively. Rp is the reflectance from the smooth back surface of the thin film. From the experimental data for R, T, and Rp in a range of wavelengths, the optical constants n, k, and σ can be extracted by solving the above non-linear equations using a three-dimensional Newton-Raphson technique. Examples of experimental results on diamond films and other examples of simulated results are presented to illustrate the usefulness and validity of this technique.
Bonding Silicon Devices on Diamond Heat Spreaders
Authors: Fan W. D. , Jagannadham K. , Narayan J.
Published: April 2011

We have developed diamond heat spreaders and bonding technology to silicon device structure. Diamond films were grown on molybdenum and Si substrates using hot filament chemical vapor deposition. Tin or gold-tin solders were used for bonding. Bonding of silicon on diamond was carried out at 20 Torr with hydrogen ambient and a temperature between 300 to 400°C for half hour. The diamond films were characterized by Raman spectroscopy and scanning electron microscopy. Interfaces between silicon and diamond films Were examined by scanning electron microscopy and energy dispersive spectroscopy. Pull-tests were used to determine the strength of the bonding between the silicon substrate and the diamond film. Bonding is improved with special metallization procedure using Ti and Cu films on the silicon substrate and Ti and Au or Cu films on the diamond film. Mechanisms of improvement of bonding due to metallization layers are discussed.
High Quality Homoepitaxial Diamond Films Grown in End-Launch Type Reactors
Authors: Hayashi Kazushi , Yamanaka Sadanori , Okushi Hideyo , Kajimura Koji
Published: April 2011

High quality diamond films have been successfully grown, by step-flow, on (001) diamond substrates using an end-launch type chemical vapor deposition reactor. Electrical properties of as-deposited diamond films as well as the surface morphology and the film crystallinity were investigated. Optical and atomic-force microscope images indicated that diamond films consisted of atomically flat terraces and macroscopic steps running parallel to [110×l and 1×2 double-domain structure. The currentvoltage characteristics of Al-Schottky contacts to these step-flow grown diamond films showed excellent rectification properties, indicating the potential of this material for electronic applications.
Towards Large Area Diamond Substrates: The Mosaic Process
Authors: Janssen Ger , Schermer John J. , Giling L. J.
Published: April 2011

A method has been developed for producing large area single-crystal diamond plates, suitable for optical and electronic applications. It starts with orienting and closely packing a set of diamond seed crystals with (001) top faces. This assembly, or mosaic, is then joined by a single-crystal overgrowth using a CVD process. A number of assembling techniques have been tested for compatibility with homoepitaxial diamond growth by hot filament assisted CVD and/or growth and etching by the acetylene-oxygen combustion flame. Furthermore a two-step process is described. First an initial layer (20-50/μm) is deposited by hot filament assisted CVD at a low growth rate in order to bridge the gap between the seeds. Subsequently the fast growth rate of the acetylene-oxygen combustion flame is employed to increase the layer thickness (>250,μm). It was found that both the basic mosaic process as well as the two step process can produce a single-crystal diamond layer on top of mosaics consisting of seed crystals with well aligned crystallographic directions. The width of the gaps between the seed crystals (up to 25 μm) was found to be less critical, while the orientation of the side faces and the direction of the misorientation (i.e. the step flow direction) seem not to effect the successful overgrowth. Apart from the alignment of the seed crystals the most severe problem, which has to be overcome in order to obtain one single-crystal overgrowth, is the occurrence of penetration twins in the joint regions. The largest mosaic structure -up to now- overgrown by CVD consists of seven seed crystals and has a surface area slightly in excess of 1 cm2
Correlation of Electrical Properties With Defects in A Homoepitaxial Chemical-Vapor-Deposited Diamond
Authors: Han S. , Rodriguez G. , Taylori A. , Plano M. A. , Moyer M. D. , Moreno M. A. , Pan L. S. , Black D. B. , Burdette H. , Ager J. W. , Chen A.
Published: April 2011

A high-quality, low-stress 200 gim epitaxial diamond film has been grown on a 400 μm thick high-temperature-high-pressure Ila diamond. X-ray diffraction images of the film indicate that a large region of the film is fairly defect free and individual dislocations have been imaged in this region. Depth-resolved Raman results indicate that the region of the film with a low density of defects also has lower stress than in the higher defect density region. Transient photoconductivity measurements were performed on the high and low line defect density regions of the homoepitaxial diamond film to determine the effects of the stress and defect density on the combined electron-hole mobility and carrier lifetime. The correlation between the electrical properties and the x-ray diffraction imaging suggests that line defects may not be the limiting factor in the carrier transport at the present film quality
Polycrystalline Diamond, Boron Nitride and Carbon Nitride Thin Film Cold Cathodes
Authors: Pryor R. W.
Published: April 2011

Recent observations are presented on the emission of electrons from n-type polycrystalline diamond and from two new families of nitride-based cold cathode films, n-type boron nitride (BN) and n-type carbon nitride (CN). The n-type polycrystalline diamond films were synthesized by MPECVD. The BN and CN n-type films (∼150 nm) were synthesized by reactive laser ablation on n-type polycrystalline diamond (∼24 μm) on (100)Si.

Emission current densities have been measured as high as 119 ma cm−2. Extraction fields have been observed to range from ∼0 V μm−1 up. The diamond films show a field activated thermionic behavior. Both the BN and the CN films show a power-law current density / applied field response implying a negative electron affinity (NEA) type behavior.
Theory of Electron Emission and Transport Properties of Diamond
Authors: Miskovsky N. M. , Cutler P. H. , Huang Z.-H. , D'Ambrosio P. , Lerner P.
Published: April 2011

Electron field emission from diamond films was calculated using a model consisting of the projection of the energy-band surfaces in the <111>, <110> and <100> emission directions. It is found that the tunneling from bulk conduction and valance bands is negligible in p-type diamond, while emission from n-type doped diamond, surface states located near the conduction band edge, and hypothesized defect bands in the energy gap all have sufficient transmission probabilities to produce the low power-high current observed in experiments. To understand the mechanism for supplying electrons to these tunneling states, we analyze charge transport in diamond with internal fields. In particular, a Monte Carlo simulation was performed for electrons in the conduction band as a function of field and film thickness. The results predict hot electron behavior at lower fields with a transition to ballistic-like behavior for high fields (≥ 10 V/μm) and thin samples (≤0.1 μm). It is suggested that if a viable electron injection mechanism into the conduction band of a diamond-metal or diamond-semiconductor interface could be found for those faces of diamond exhibiting NEA, then a copious cold cathode electron emitter with field tunable energies is feasible.
Homoepitaxial Mosaic Growth and Liftoff of Diamond Films
Authors: Pehrsson Pehr E. , Mccormick Terri , Alexander W. Brock , Marchywka Mike , Black David , Butler James E. , Prawer Steven
Published: April 2011

Growth of large area, single or almost single crystal diamond is of great importance to the electronics industry. In this work, single crystal diamonds were implanted with C+ ions, inducing a subsurface damage layer in the diamond lattice. Homoepitiaxial diamond films were then grown on the implanted crystals using a microwave plasma CVD reactor. Films grown on on-axis substrates were dominated by large numbers of hillocks, renucleation and penetration twins, while miscut substrates exhibited stepflow growth. The homoepitaxial layers were separated from the substrate by a water-based etch which selectively attacks the subsurface damage layer of the diamond lattice. The films were analyzed by Raman scattering, scanning electron microscopy (SEM), optical microscopy, photo- and cathodoluminescence, and x-ray diffraction. CVD growth on adjacent, oriented substrates formed a single, continuous diamond layer. The resulting homoepitaxial film quality, orientation, defect density and it's relationship to the underlying substrates were compared at various points on the surface, particularly the region which overgrew the gap between different substrates.
Defects and Morphology of Homoepitaxial Diamond Films on Natural Nonplanar and Isotopically Pure Planar Substrates
Authors: McCauley Thomas S. , Vohra Yogesh K.
Published: April 2011

We have carried out diamond deposition by microwave plasma-assisted chemical vapor deposition (MPCVD) on planar and nonplanar diamond substrates at temperatures between 850° and 2000° C. The nonplanar and planar substrates were the polished (100) surfaces of type Ia natural diamond anvils and isotopically pure (99.95% 12C) type Ila synthetic crystals, respectively. The extremely low level of lattice and optical defects in the isopure substrates relative to natural crystals makes them ideal for optical characterization and defect studies, as well as high performance optical and electronic applications [1's (1) geometry, (2) type (defect density), and (3) temperature. The phase purity and defect structure of the films were analyzed by micro-Raman and low temperature photoluminescence (PL) spectroscopy. Optical and atomic force microscopy (AFM) were used to examine the surface morphology of the films. High temperature growth on the nonplanar anvil tip was anisotropic and extremely rapid (50-400 μm/hr), with significant incorporation of optically active defects. A possible model for the observed rapid growth is discussed. The films grown at lower temperatures on planar isopure substrates showed a dense array of oriented, stepped, square growth hillocks with penetration twins at their tops, while those grown at higher temperatures exhibited reasonably smooth, <110> oriented macrosteps. The higher temperature planar films showed a larger variety of incorporated optical centers than the lower temperature films.
Heteroepitaxial Nucleation of Diamond
Authors: Stoner B. R. , Ellis P. J. , Mcclure M. T. , Wolter S. D.
Published: April 2011

The heteroepitaxial nucleation and eventual growth of large area single crystal diamond films has long eluded researchers interested in tapping it's many enabling properties, specifically in the field of active electronics. The uncertainty surrounding the diamond nucleation mechanism(s) and corresponding inability to carefully control this process are often blamed for the difficulty in achieving true heteroepitaxial growth. Biasenhanced nucleation (BEN) has been shown to provide in-situ control of the nucleation process. Subsequent advancements in both nucleation and deposition stages has resulted in highly oriented diamond films, approaching single crystal quality yet still plagued by arrays of medium to low angle grain boundaries that can degrade the electronic transport properties. To further improve upon these results and achieve large area, single crystal films it is believed that development must focus on the more fundamental problems of diamond nucleation. This paper presents a review of recent progress pertaining to the bias-enhanced process and focuses on data specific to the epitaxial nucleation dilemma.
Free Radicals from Photolysis of (NTO) 5-Nitro-2,4-Dihydro-3H-1,2,4-Triazol-3-One Studied by EPR Spin Trapping
Authors: Pace M. D. , Fan L. , Burkey T.
Published: April 2011

NTO (5-Nitro-2,4-dihydro-3H-1,2,4-triazol-3-one)is shown to form aphotochemical free radical in alkaline aqueous solution containing nitromethane (CH3NO2). The NTO free radical can also be produced by chemical reduction of NTO with hydroquinone in alkaline solution. Details of radical formation and assignment of the NTO radical to a nitro anion radical, having the NTO ring intact, are presented.
Effect of Structure of Energetic Materials on Burning Rate
Authors: Fogelzang A. E. , Sinditskii V. P. , Egorshev V. Y. , Serushkin V. V.
Published: April 2011

Data on the steady-state combustion in a constant-pressure bomb at 0.1–40 MPa are presented for energetic materials from the following classes: metal salts of organic explosive acids, salts of organic bases with inorganic oxidizing acids, explosive coordination compounds, and endothermic polynitrogen compounds.

For combustion of salts of organic bases with oxidizing acids it has been found that an increase in the oxidant redox potential, whose value serves as an estimate of the oxidizer reactivity, causes the burning rate value to increase. The same tendency has been disclosed for explosive coordination compounds which can formally be considered as metal-containing analogs of the salts of organic bases with oxidizing acids.

The introduction of a metal atom in an organic explosive acid has been shown to result generally in an enhancement of the burning rate, with the effectiveness of the metal as the combustion catalyst being dependent not only on the nature of the metal but on its position in the molecule as well.

Neither the nature of the metal, nor the nature and structure of the ligand really affects the combustion of coordination compounds of metal azides, whose combustion occurs at the expense of the heat produced in the decomposition process. All the coordination azides seem to have the same rate-limiting stage, namely, the decomposition of the intermediate HN3 and differ from one another by their burning temperatures. The similar behavior is also characteristic of metalless analogs of the coordination azides: salts of HN3 with amines.
Toward Quantitative Thermodynamics and Kinetics of Pyrolysis of Bulk Materials at High Temperature and Pressure
Authors: Williams G. K. , Brill T. B.
Published: April 2011

An evaluation was made of whether T-jump/FTIR spectroscopy could be used to determine the decomposition kinetics (Ea and ln A) and thermochemical (ΔHd) constants of an energetic material at high temperature and high heating rate. Polystyrene peroxide was chosen because of its known, simple, decomposition process. The kinetic constants are reasonable for O-O bond homolysis as the rate determining step: Ea = 39 kcal/mol, ln (A, s−1 ) = 21.5. Significant uncertainty exists, however, in the estimation of ΔHd.
Self-Affinity of Combustion-Generated Aggregates
Authors: Neimark A. V. , Köylü Ü. Ö. , Rosner D. E.
Published: April 2011

A large population of combustion-generated soot aggregates (more than 3,000 samples) was thermophoretically extracted from a variety of laminar and turbulent flames and analyzed using transmission electron microscopy (TEM). It was shown that the scaling structural properties of these fractal aggregates cannot be exclusively characterized by a single mass fractal dimension. Asymmetric properties of the aggregates were considered here by first assuming and then demonstrating their self-affinity via. an affinity exponent reflecting scaling with respect to the length and width of the aggregate projections. In addition to the conventional fractal dimension, Df, determined by using the geometrical mean of the longitudinal and transverse sizes as the characteristic length, the affinity exponent, H, and two complementary fractal dimensions, one longitudinal, DL =[(1+H)/2 ]Df, and one transverse, DW =[(1+H)/2H]Df, were introduced. By fitting TEM data for the entire population of aggregates, the values Df = 1.75 and H = 0.91 were obtained. This more complete description of aggregate morphologies in terms of the self-affine scaling is expected to lead to a better understanding of the transport properties and restructuring kinetics of flame-generated aggregates.
Nitric Oxide Interactions with C2 Hydrocarbon Species
Authors: Williams B. A. , Pasternack L.
Published: April 2011

We have investigated the combustion chemistry of nitric oxide doped into premixed 10 Torr flames of CH4/O2/N2, C2H6/O2/N2, C2H2/O2/N2, and C2H2O2N2 which had similar peak temperatures. Profiles of OH, CH, 3C2, CN, NCO, NH, and NO were recorded by laser-induced fluorescence and compared among the different fuels, indicating differences in hydrocarbon flame structure and NO reactivity in these environments. Concentrations of nitrogen intermediates are comparable for the methane, ethane, and ethylene flames, but are approximately a factor of three higher with acetylene, indicating much greater NO reactivity in this flame.
Products and Kinetics of Flash Pyrolysis of Peg: A Minimum Smoke Binder
Authors: Arisawa H. , Brill T. B.
Published: April 2011

Flash pyrolysis of polyethyleneglycol by T-Jump/FTIR spectroscopy to temperatures of the surface during combustion reveals that volatile products arise from approximately equal amounts of C-O and C-C homolysis. Nine volatile products are discussed. The average number of repeating units in the volatile oligomers is 2.5. A shift in product distribution occurs at 420–480°C resulting from a change in the polymer structure. Below 420°C, di- and mono-ether oligomers and diethyleneglycol dominate. Above 480°C, the mono-ethers and ethyleneglycol dominate. The Arrhenius constants for decomposition reflect this difference: Ea=8.8 kcal mol−1, In (A, s−1) =2.0 at 370–420°C and Ea=19 kcal mol−1, In (A, s−1)=10 at 480–550°C.
Combustion Chemistry of Energetic Materials Studied by Probing Mass Spectrometry
Authors: Korobeinichev O. P. , Kuibida L. V. , Paletsky A. A. , Shmakov A. G.
Published: April 2011

The methods of probing mass spectrometry (PMS) for diagnostic of flames and for the study of kinetics and mechanism of the thermal decomposition products of energetic materials (EM) are described. Several types of instruments based on microprobe and molecular beam mass spectrometric sampling have been developed. Time of flight mass spectrometer has been used. Apparatuses for high (10 atm) and low (<1 atm) pressure have been developed for the study of combustion and decomposition of EM by PMS “in situ”. Several examples are presented to demonstrate application of PMS method for the study of EM flame structure, thermal decomposition and dynamic of ignition. Experimental data on decomposition of double base propellants ammonium dinitramide, ammonium perchlorate are presented.
Effects of Nanoscale Voids on the Sensitivity of Model Energetic Materials
Authors: Whitea C. T , Barretta J. J. C. , Mintmirea J. W. , Elert M. L. , Robertson D. H.
Published: April 2011

Because of its importance in designing safer, more reliable explosives the shock to detonation transition in condensed phase energetic materials has long been a subject of experimental and theoretical study. This transition is thought to involve local hot-spots which represent regions in the material which couple efficiently to the shock wave leading to a locally higher temperature and ultimately initiation. However, how at the atomic scale energy is transferred from the shock front into these local “hot spots” remains a key question to be answered in studies of the predetonation process. In this paper we report results of molecular dynamics simulations that suggest that even nanometer scale defects can play an important role in the shock to detonation transition.
Molecular Dynamics Study of the Effect of Varying Exothermicity on the Properties of Condensed-Phase Detonation
Authors: Elert M. L. , Robertson D. H. , White C. T.
Published: April 2011

To investigate the role of exothermicity on the properties of a chemically sustained shock waves, a series of two-dimensional molecular dynamics simulations was carried out in which the exothermicity was systematically varied. The simulations were based on a model diatomic system which has been previously shown to produce reasonable values for shock wave properties. A decrease of 33% in the amount of energy released in the reaction produced a significant decrease in detonation front velocity and an increase in the impact energy necessary to initiate a sustained shock wave. Redistribution of energy between the reaction products at constant total exothermicity had a much smaller effect on the properties of the detonation front.
Ultrafast Dynamics of Shock Waves and Shocked Energetic Materials
Authors: Hare David E. , Lee I-Y. Sandy , Hill Jeffrey R. , Franken Jens , Suzuki Honoh , Baer Bruce J. , Chronister Eric L. , Dlott Dana D
Published: April 2011

Experimental measurements of material effects induced by the passage of sharp shock fronts require techniques which provide high temporal resolution and high spatial resolution. Since typical shock velocities are a few microns per nanosecond, sub-nanosecond probing requires sub-micron spatial resolution. In our experiments, the required temporal resolution is furnished using picosecond laser generated shock waves and picosecond spectroscopy. The spatial resolution is furnished by engineering nanometer scale structures into our shock target arrays. In one technique, absorption transients in the spectrum of a thin layer of molecules, termed an optical nanogauge, are investigated. Shock-induced molecular energy transfer processes are observed in condensed matter for the first time. In a second technique, sub-micron particles of an energetic material are shocked and probed using ps coherent Raman spectroscopy. This probing technique permits the instantaneous measurement of the temperature, pressure and composition of an energetic material under dynamic shock loading.
Heterogeneous Reaction of Boron in CHNO and CHNOF Environments Using High-Pressure Matrix Isolation
Authors: Rice Jane K. , Russell Thomas P.
Published: April 2011

We have developed a technique in which the decomposition of energetic materials can be initiated under high pressure conditions which resemble the pressures reached in the non-ideal detonation process. A gem anvil cell is cooled to cryogenic temperatures, 50 K, and remains in thermal contact with the cooling element throughout the experiment. Following initiation, the reaction products are rapidly cooled and quenched on the microsecond time scale and detected using FTIR spectroscopy. In the present study, binary mixtures of boron with energetic materials containing (CHNOF) and lacking fluorine (CHNO) are compared. The differences in the reaction products suggest that the presence of the fluorine substituent leads to a complete combustion of boron to B2O3. In the decomposition of binary mixtures lacking the fluorine substituent, the boron in appears to be unchanged following the reaction of the oxidizer. The observed products are compared to predict the affect of fluorine on the formation of boron combustion products in the two environments.
Explosive Thermal Decomposition Mechanism of NTO
Authors: Beardall David J. , Botcher Tod R. , Wight Charles A.
Published: April 2011

The initial step of the thermal decomposition of NTO (5-nitro-2,4-dihydro-3H-1,2,4- triazol-3-one) is determined by pulsed infrared laser pyrolysis of thin films. Rapid heating of the film and quenching to 77 K allows one to trap the initial decomposition products in the condensed phase and analyze them using transmission Fourier-transform infrared spectroscopy. The initial decomposition product is CO2; NO2 and HONO are not observed. We propose a new mechanism for NTO decomposition in which CO2 is formed.
Time Resolved Emission Studies of Aluminum and Water High Pressure Reactions
Authors: Brown C. A. , Russell T. P.
Published: April 2011

The detonation of underwater explosives is a complex problem involving a temporally dependent heterogeneous reaction regime of oxidizer reactions and high pressure metal combustion. For simplicity, underwater explosions may be described as a two stage reaction process. First, the oxidizing material detonates to produce species under extreme conditions of temperature (up to 5000 K) and pressure (up to 10 GPa). The chemical energy produced from this reaction is transferred to the bulk water as three forms of work: (I) shock, (2) heat, and (3) initial bubble formation. Second, the species produced by the oxidizer detonation form a high pressure and high temperature reactive fluid that surrounds the solid particles. The solid particles are primarily consumed while the pressure is decreasing from 10 GPa to 0.1 GPa at a reaction temperature in excess of 3200 K. The secondary reaction of the solid particles produces a lower energy shock and a pressure response that reinforces the initial energy delivered to the bulk water medium. The ability to tailor this late energy release between shock and bubble formation is dependent on the reaction time and chemistry of the solid particle under extreme conditions. We present a series of single-shot time resolved emission experiments that probe the reaction of aluminum particles under extreme conditions. The temporal behavior of the observed species is used to gain insight into the chemical reaction mechanism that leads to the formation of A1203 during underwater detonations.
High Pressure Equation of State for Fe2O3
Authors: Zerilli Frank J. , Jones Hermenzo D.
Published: April 2011

A Debye-Gruneisen equation of state for hematite (Fe2O3) was developed for use in studying the high pressure solid state reaction Al + Fe2O3 → Fe + A12O3. A simple, single Curie temperature Curie-Weiss ferromagnetic term was used to account for the complex antiferromagnetic contributions to the entropy and specific heat. In the absence of information on the variation of Curie temperature with pressure, it is taken to be constant, so that the antiferromagnetism makes no contribution to the pressure-volume equation of state.
Charge Densities and Electrostatic Potentials for Energetic Materials
Authors: Pinkerton A. A. , Martin A.
Published: April 2011

High resolution (sinθ/λ < 1.34 Å−1), low temperature (85 K) X-ray diffraction data has been used to map the deformation density and the derived electrostatic potential for three dinitramide salts. The traditional presentation of contour maps has been replaced with 3D views of the molecule. A comparison of the dinitramide ions from each salt is presented.
Optical Properties of RDX and HMX
Authors: Isbell R. A. , Brewster M. Q.
Published: April 2011

Optical properties of RDX (cyclotrimethylene-trinitramine) and HMX (cyclotetramethylenetetranitramine) were obtained from 2.5 to 18 gtm using scattering-corrected KBr pellet-FTIR transmission spectrometry. Absorption index (k) was measured directly and refractive index (n) was deduced using dispersion theory. At 10.6 μm the absorption coefficients were RDX, 2800 cm−1 and HMX, 5670 cm−1.
Three Color Detection in the Charge Integration Regime by ATCD for Large Area Applications
Authors: Irrera F. , Lemmi F. , Palma F.
Published: April 2011

Large area color image scanners are currently being widely investigated. The a-Si:H/a-SiC:H Adjustable Threshold Color Detector (ATCD) recently presented by the authors is suitable for greatly simplifying the structure of the arrays since ATCDs have just two external electrical connections. This makes possible to use the row-column addressing of pixels.

In this work, the transient operation of ATCDs in the charge integration regime is discussed. Charge integration is operated by photocurrent discharging the three series connected capacitances which compose the device structure. The penetration depth of the incident radiation depends on the wavelength and determines which of the three capacitances is discharged. The applied bias voltage determines the polarization of the three junctions and the three capacitance actually sensed. Correct blue, green and red light detection is shown in the read-out transients and the read-out and saturation times are presented. Finally design rules of the device and read-out system are given in order to achieve a correct detection of the three colors.
A New Type of Cylindrical a-Si:H X-Ray Detector
Authors: Link D. , Keppner H. , Chabloz P. , Shah A. , Germond J.-F. , Haefliger J.- M. , Pochon Y. , Frosio G.
Published: April 2011

The present paper describes a new type of cylindrical X-ray detector based on thick amorphous silicon diodes. The authors report on the successful development of these detectors that have diameters as small as 3mm. The effect of silane dilution in hydrogen on deposition rate, powder formation, layer adhesion and detector performance is discussed. A set of deposition parameters is presented, that allows a reasonable compromise between the mentioned effects. First prototypes of this type of dosimeter have been characterised with the radiation from a 60Co source in a hospital. The corresponding results and interpretation are given in this paper.
Progress Towards a High-Resolution X-Ray Photon Counter
Authors: Apte R. B. , Nickel N. , Street R. A. , Weisfield R. , Wu J. X.-D. , Ready S. , Nguyen M. , Nylen P.
Published: April 2011

Progress towards x-ray shot-noise limited imaging with resolution superior to film is reported for a large format amorphous silicon imaging system containing 1536x 1920 pixels. Improvements over previous work include the development of a complete system, the use of charge-sensitive amplifiers, and careful control of extrinsic noise. A charge-sensitive amplifier with 1000:1 dynamic range is used to detect the signal in the presence of a large parasitic capacitance, 95pF, which both increases the intrinsic noise in the amplifier and technical noise coupled from other sources. The RMS noise level, 4200 e, is within two octaves of single x-ray counting.
Amorphous Silicon-Carbon Thin Film P-I-N Structures for Liquid-Crystal Spatial Light Modulators
Authors: Feoktistov N. A. , Ivanova N. L. , Morozova L. E. , Nikulin Yu. A. , Onokhov A. P. , Pevtsov A. B. , Schwarz R.
Published: April 2011

Photoaddressed spatial light modulators (PSLM) based on nematic liquid crystals using hydrogenated amorphous silicon-carbon films (a-Si1-xCx,:H) and p-i-n structures as photosensitive layers are designed and studied. It is shown that an application of a-Si1-xCx:H p-i-n diodes greatly improved the operation speed of a PSLM, increased the film transparency and decreased the absorption of the red readout light. As a result, the readout light intensity could become ≈ 20 times larger. The maximum diffraction efficiency of the PSLM was achieved for a write-in light intensity of 40μLW/cm2, with a resolution (FWHM) of the diffraction efficiency of 54 mm-1. The optical response of the PSLM was observed in the frequency range from 1 Hz to 100 Hz.
Probe of Field Collapse in a-Si:H Solar Cells
Authors: Wang Qi , Crandall Richard S.
Published: April 2011

We study the effect of illumination intensity on solar cell performance in a-Si:H solar cells. We find that the fill factor strongly depends on light intensity. As we increase the illumination intensity from low levels to one sun we observe a decrease in fill factor of approximately 15% in as grown cells. We attribute this effect to electric field collapse inside the cell. We propose that photogenerated space charge (free and trapped charge) increases with light intensity and causes field collapse. We describe the origin of space charge and the associated capacitance - photocapacitance. We measure the photocapacitance as a barometer to probe the collapsed field. We obtain a good agreement between photocapacitance experiments and theory. We also explore the light intensity dependence of photocapacitance and explain the decrease of FF with the increasing light intensity.
Electrical Transport Mechanisms in p+a-SiC:H/n c-Si Heterojunctions: dark J-V-T Characteristics
Authors: van Cleef M. W. M , Philippens M. W. H. , Rubinelli F. A. , Kolter M. , Schropp R. E. I.
Published: April 2011

In the present paper we show results of dark current-voltage measurements performed on p+ a- SiC:H/n c-Si heterojunction diodes at various temperatures (100–400K). We investigated the voltage derivative of these J-V curves in order to the distinguish possible current transport mechanisms. It was found that for low temperatures (<300K), the current is determined by recombination of carriers in the crystalline silicon, whereas at high temperature (>300 K), by a tunnelling mechanism. At room temperature, both mechanisms contribute to the current. By using an equivalent circuit model and detailed numerical simulations we have interpreted our experimental characteristics. The simulations done at room temperature, show that at low forward bias voltage the current is controlled by recombination in the crystalline silicon and that at high forward bias voltage by a combination of multi-step tunnelling and a-SiC:H series resistance. For interface state densities equal to or higher than 1012 cm−2, the recombination was found to be dominated by the states at the amorphous-crystalline silicon interface.
Defect Density-of-states in a-Si:H TFTs
Authors: Globus T. , Gelmont B. , Mattauch R. J. , Sun L. Q.
Published: April 2011

The novel version of the field effect conductivity method for the direct density-of-states (DOS) determination has been developed. The combination of both, a new analytical solution, in the form of integral equation which relates the surface potential to the gate voltage, and new data-analysis algorithms allows one to solve the problem by using the results of measurements of TFT quasi-static transfer characteristics. This sensitive, and easy to use, method provides the detailed information on the defect density in the gap of hydrogenated Si. The ability of this technique to extract parameters of the TFT, including the flat band voltage, from the dependence of the surface potential on the gate voltage, and to resolve fine-scale features in the midgap DOS of a-Si:H has been demonstrated.

We have shown that the dependence of the DOS on the energy in the range 0–0.15 eV from the conduction band is close to the exponent, while deeper in the gap, the DOS can be described as a series of localized defect bands with amplitude values in the range 1016 cm−3 eV−1-2×1018 cm−3 eV−1.

The integrated charge density and the surface potential as functions of gate voltage have been investigated. The difference between the surface potential and activation energy from temperature dependence of drain current has been discussed. The short-time current relaxation and metastable defect transformations have been studied and analyzed.
Highly Conductive p-type Microcrystalline Silicon Thin Films
Authors: Heintze M. , Schmitt M.
Published: April 2011

The plasma deposition of boron doped microcrystalline films was optimized with respect to crystallinity and doping efficiency. High room temperature conductivities up to 39 Scm−1 were achieved under condition when the energy of positive ions impinging on the growth surface is minimized.
New Results of nc-Si:H Films Prepared by Hydrogen-Diluted Silane in a Triode Pecvd System
Authors: Qin Hua , Chen Kunji , Huang Xinfan , Li Wei , Ikuta Kazuyuki , Matsuda Akihisa , Tanaka Kazunobu
Published: April 2011

We report new results on microstructures and electronic properties of nanocrystalline silicon (nc-Si:H) films prepared by a triode PECVD method with a hydrogen diluted silane plasma. The transition from a-Si:H to nc-Si:H was obtained by varying the ratio of H2 to SiH4 while the bias of the grid electrode was fixed at 100.V with respect to the substrate. The threshold value of [H2]/[H2 ]+[SiH4] is about 93.3%. With increasing value of [H2]/[H2]+[SiH4], the volume fraction of crystallinity in nc-Si:H films increased from 12% to 50%, while the average grain size remaind constant. This is quite different from the structures of samples prepared by the conventional diode PECVD with H2 dilution. The traveling-wave technique was applied to study the transport properties of nc-Si:H films, and experimental results confirmed percolation transport in nc-Si:H films.
STM Observation on the Initial growth of Amorphous and Microcrystalline Silicon Films
Authors: Ikuta K. , Toyoshima Y. , Yamasaki S. , Matsuda A. , Tanaka K.
Published: April 2011

Direct nanoscale observation on the nucleation and growth of hydrogenated amorphous and microcrystalline silicon on graphite substrates was made using scanning tunneling microscopy, atomic force microscopy, and Raman scattering spectroscopy. Nucleation of hydrogenated silicon clusters is initiated through the nucleation sites created by reactive hydrogen species coming from the source gas plasma. The difference in spatial distribution of nucleated clusters at the initial stage of deposition between a-Si:H and μc-Si:H is ascribed to the difference in the number density of nucleation sites which results in difference in the diffusion length of a SiH3 radical at the initial stage of deposition on the graphite substrate. The RMS roughness of μc-Si:H films is larger than that of a-Si:H when the film thickness is larger than 10 Å, which is opposite to the behavior at the initial nucleation stage on the graphite substrate.
Chemical Properties of A-Si:H Interface Layers on Oxide-Covered and Hydrogen-Terminated Silicon
Authors: Knobloch Jürgen , Hess Peter
Published: April 2011

High quality a-Si:H films were deposited by pulsed VUV (157nm) laser CVD, allowing digital control of the deposition process. Nucleation and growth on native oxide-covered Si (100) and on H-terminated Si (111) surfaces were studied in situ by FTIR transmission spectroscopy with sub-monolayer sensitivity. The film thickness was monitored simultaneously using a quartz crystal microbalance (QCM) with comparable resolution. The in situ spectra reveal that the nature of the substrate surface significantly influences the hydrogen bonding configuration in the interface region. In both cases the assumed cluster growth during the initial stage is characterized by a band around 2100cm−1, which is assigned to SiHX (x = 1 – 3) surface modes. This band broadens until the clusters coalesce and band saturation occurs. At this time a second band starts to grow at 2000cm−1, which is attributed to bulk SiH bonds. Difference spectra calculated for layers at different depths with definite thickness and the deconvolution of the broad feature observed during the very first stage of film growth indicate the existence of a hydrogen-rich layer at the substrate surface whose composition and thickness depend on the properties of the substrate surface.
Tritium in Amorphous Silicon
Authors: Sidhu L. S. , Kosteski T. , O'Leary S. K. , Gaspari F. , Zukotynski S. , Kherani N. P. , Shmadya W.
Published: April 2011

Preliminary results on infrared and luminescence measurements of tritium incorporated amorphous silicon are reported. Tritium is an unstable isotope that readily substitutes hydrogen in the amorphous silicon network. Due to its greater mass, bonded tritium is found to introduce new stretching modes in the infrared spectrum. Inelastic collisions between the beta particles, produced as a result of tritium decay, and the amorphous silicon network, results in the generation of excess electron-hole pairs. Radiative recombination of these carriers is observed.
Hydrogen Density of States and Defects Densities in a-Si:H
Authors: Deane S C , Powell M J , Robertson J
Published: April 2011

Further details are given of a unified model of the hydrogen density of states and defect pool of a-Si:H. The model is compared to other defect models and extended to describe a-Si alloys and the creation of valence band tail states during growth.
Plasma Induced Changes to TCO/a-Si:H Interfaces
Authors: Wallinga J. , Knoesen D. , Hamers E. A. G. , Sark W. G. J. H. M. Van , Weg W. F. Van Der , Schropp R. E. I.
Published: April 2011

The effect of ion bombardment on the plasma enhanced chemical vapor deposition of a-Si:H and on TCO/a-Si:H interface reactions has been studied. An external DC-bias voltage is applied to the deposition plasma in order to change the ion flux and ion energy. The deposition rate increases with the applied bias-voltage i.e. with the plasma potential. Hydrogenated amorphous silicon is grown on natively rough transparent conductive oxide. With cross-sectional transmission electron microscopy lower density regions can be observed in the a-Si:H in all sharp valleys of the TCO. The appearance of the lower density regions changes under influence of the ion bombardment. The observed changes are in agreement with the changes observed when no ion bombardment is present at all, like in a hot wire chemical vapor deposition process. The increased ion bombardment did not give rise to observable chemical reactions at the TCO/a-Si:H interface.
Nonlinear Dependence of μeτe on Subgap Absorption in Pulse and cw Light-Soaked a-Si:H
Authors: Hata Nobuhiro , Ikeda Toru , Matsuda Akihisa
Published: April 2011

We report new results from subgap absorption and transport measurements on pulse and continuous (cw) light-soaked a-Si:H which include that (1) the mobility-lifetime product of electrons (μeτe) shows the same dependence on defect subgap absorption irrespective of whether the sample was soaked by pulse or continuous lights, but that (2) the dependence of μeτe on defect subgap absorption is not linear. These results are compared with annealing energy distribution of light-induced defects, and discussed in terms of (1) annealing energy (Eann) distribution of light-induced defects (LIDs), and of (2) photo-induced structural change.
Bonding Defects in Hydrogenated Amorphous Silicon
Authors: Lucovsky G. , Yang H.
Published: April 2011

A mechanism for charged-carrier-trapping-inducedde fect metastability in hydrogenated amorphous silicon (a-Si:H) and in hydrogenated amorphous silicon alloys containing relatively high concentrations of oxygen and/or nitrogen atoms (a-Si:X:H, X = O or N) is described. The experimental results that identified this defect metastability mechanism were i) differences in the Staebler-Wronski effect in a-Si:H and a-Si:N:H alloys prepared from N2 and NH3 source gases by remote plasma-enhanced chemical-vapor deposition, and ii) differences in defect generation at N-atom terminated Si-SiO2 interfaces prepared from NH3 and N2O.