bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear Optical Properties of Structured Nanoparticle Composites
Authors: Birnboim Meyer H. , Ma Wei Ping
Published: March 2011

The effective nonlinear susceptibility X( 3 ) for a composite that consists of a dilute suspension of structured nanoparticles that utilizes the surface mediated plasmon resonance can be enhanced by orders of magnitude compared to the intrinsic X(3) for a film of the same neat material. Here we report calculations for various multilayer spherical nanoparticle models in a host dielectric: i) polymeric core and metallic shell, ii) semiconductor core and metallic shell, iii) metallic core, polymeric shell and metallic second shell, and iv) metallic core, semiconductor shell and metallic second shell. The polymer is polydiacetylene, FDA, the semiconductor is Si, the metal is Ag, and the host is water, a GaAs2 glass or Si. Enhancements as great as 104 can be obtained in both x(3) and the figure of merit with no degradation in the intrinsic speed of the nonlinearity. The choice of geometrical parameters and of component materials permit tailoring of the wavelength dependence and bandwidth characteristics of the nonlinear response. However, fabrication of these structured nanoparticle suspensions remians the key challenge.
The Effect of Hydrogen on the Structure and Electrical and Optical Properties of Silicon-Germanium Alloys
Authors: Fortmann C.M. , Albright D.E. , Campbell I.H. , Fauchet P.M.
Published: March 2011

The transport properties of intrinsic micro-crystalline and amorphous SiGe films are investigated. In the amorphous system it is found that the electron lifetime is relatively independent of band gag while the electron mobility of a-Ge:H is a factor of ten less than that of a-Si:H. Micro-crystalline silicon films have greater excess photo-conductivity as compared to a-Si:H predominantly due to longer effective lifetimes. Films containing micro-crystalline silicon in a matrix of a-SiGe:H have been prepared and are found to have comparatively poor transport.
Raman Studies of Microstructural Changes in Amorphous Silicon-Boron Alloys Due to Annealing
Authors: Yang G. , Bai P. , Wu Y.-J , Tong B. Y. , Wong S. K. , Du J. , Hill I.
Published: March 2011

Crystallization of amorphous Sil−x.Bx alloy films by annealing is studied. Amorphous Sil−xBx. alloy films with composition of boron x ranging from 0.01 to 0.5 are deposited on Si substrates at a temperature of 480° in a low pressure chemical vapor deposition (LPCVD) system. Three films with the boron contents, 1%, 7% and 45%, are used in this study. The films are annealed in a nitrogen ambient for 30 minutes at temperatures between 600°C and 900°C. Raman spectra of the silicon vibrational mode serve as a indicator for the microstructure of the Sil−xBx, alloy films. Quantitative estimates of the volume fraction of the crystalline silicon component in respect to the amorphous silicon component in the films are calculated based on the silicon TO mode. The results show that while for the film with the boron content of 1% crystallization occurs at the annealing temperature of 500°C, the annealing temperature of 7000C is required to observe crystallization in the films with the boron contents of 7% and 45%. As the annealing temperature increases, the volume fraction of the crystalline component increases. For a given annealing temperature, the rate of crystallization depends inversely on the boron content in the films.
Characteristics of μc-Si:H for Si Heterojunction Bipolar Transistors
Authors: Fujioka H. , Ito M. , Takasaki K.
Published: March 2011

To improve the thermal stability of the Si heterojunction bipolar transistors (HBTs), we studied the effect of carbon and fluorine doping on μc-Si:H characteristics. We found that carbon doping suppresses crystalline growth and increases the hydrogen concentration in the film, and that fluorine atoms are more thermally stable than hydrogen atoms. We confirmed that carbon or fluorine doping is promising for use with the μc-Si:H HBT.
Electronic and Structural Characterization of the Near Surface Layer and the Bulk in νc-Si:H Prepared with Hydrogen dilution
Authors: Aljishi Samer , Jin Shu , Stutzmann Martin , Ley Lothar
Published: March 2011

The near surface layer and the bulk of νc-Si:H prepared with hydrogen dilution are investigated by Raman, optical absorption, and total yield photoelectron spectroscopies. The results show that for low hydrogen dilution ratios, microcrystallites appear in the bulk while the growing surface layer remains amorphous, indicating that microcrystallite formation takes place primarily in the sub-surface layer. At high hydrogen dilution ratios, microcrystallites are detected at both the bulk and the near surface layer. The defect density and hydrogen bonding configurations at various hydrogen dilution levels are presented.
Preparation of Crystalline Si thin Films by Spontaneous Chemical Deposition
Authors: Komiya Tohru , Kamo Akira , Kujirai Hiroshi , Shimizut Isamu , Hanna Jun-Ichi
Published: March 2011

The novel technique for the preparation of crystalline Si thin films termed “Spontaneous Chemical Deposition” has been proposed, in which silane decomposes spontaneously by gas phase reactions with fluorine at reduced pressure. The technique provided us the crystalline films in a wide range of the preparation conditions by a choice of the external parameters for the reactions. The films exhibited unique characteristics in the chemical structure and the optical and electrical properties, different from the conventional uc-Si:H thin films by the silane plasma processes.

The technique have been successfully applied for the homoepitaxial growth of Si thin films.
The Graphitization of Amorphous Hydrogenated Carbon Films During Thermal Annealing
Authors: Lin Sam Shuhan , Chen Shuguang , Mo Dang
Published: March 2011

Effects of thermal annealing on the properties of amorphous hydrogenated carbon films have been studied with spectroscopic ellipsometry, electrical conductivity, and infrared and Raman spectroscopy. The results show that not only the optical and electrical properties, but also the infrared and Raman spectra, change significantly after annealing above 400°C. We suggest that thermal annealing makes amorphous hydrogenated carbon films more graphite-like, and the observed changes in the microstructure cause the changes in the optical and electrical properties.
The Role of Low-Energy Ion/Surface Interactions During Crystal Growth from the Vapor Phase: Effects on Microchemistry and Microstructure
Authors: Greene J. E. , Sundgren J.-E.
Published: March 2011

Low-energy (≤ 200 eV) ion irradiation during crystal growth from the vapor phase can be used to provide new chemical reaction pathways, modify film-growth kinetics, and, hence, controllably alter the physical properties of films deposited by a variety of techniques. The latter includes sputter deposition, ion plating, plasma-assisted chemical vapor deposition (PA-CVD), primary-ion deposition (PID), and molecular-beam epitaxy (MBE) using accelerated beam sources. Ion/surface interaction effects such as ion-induced chemistry, trapping, recoil implantation, preferential sputtering, collisional mixing, enhanced diffusion, and alteration in segregation behavior are used to interpret and model experimental results concerning the effects of low-energy particle bombardment on nucleation and growth kinetics, elemental incorporation probabilities, compositional depth distributions, and the growth of metastable phases.
Remote Plasma-Enhanced Chemical Vapor Deposition of Epitaxial Silicon on Silicon (100) at 150°C
Authors: Hsu T. , Anthony B. , Breaux L. , Banerjee S. , Tasch A.
Published: March 2011

Low temperature processing will be an essential requirement for the device sizes, structures, and materials being considered for future integrated circuit applications. In particular, low temperature silicon epitaxy will be required for new devices and technologies utilizing three-dimensional epitaxial structures and silicon-based heterostructures. A novel technique, Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD), has achieved epitaxial silicon films at a temperature as low as 150°C which is believed to be the lowest temperature to date for silicon epitaxy. The process relies on a stringent ex-situ preparation procedure, a controlled wafer loading sequence, and an in-situ remote hydrogen plasma clean of the sample surface, all of which provide a surface free of carbon, oxygen, and other contaminants. The system is constructed using ultra-high vacuum technology (10-10 Torr) to achieve and maintain contaminantion-free surfaces and films. Plasma excitation of argon is used in lieu of thermal energy to provide energetic species that dissociate silane and affect surface chemical processes. Excellent crystallinity is observed from the thin films grown at 150°C using the analytical techniques of Transmission Electron Microscopy (TEM) and Nomarski interference contrast microscopy after defect etching.
Reaction Kinetics of Epitaxial Silicon Deposition at 220-400°C Using Remote Plasma-Enhanced Chemical Vapor Deposition
Authors: Anthony B. , Hsu T. , Breaux L. , Banerjee S. , Tasch A.
Published: March 2011

In this paper the reaction kinetics of Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD) are investigated. Growth rate characterization has been performed for substrate temperatures of 220 – 400°C, r-f powers from 4 – 8 W, and silane flow rates of 10 – 30 sccm. Growth rate has been found to increase exponentially with r-f power, which is, as yet, unexplained. An approximate square root dependence of growth rate on silane partial pressure agrees with the theory of Claasen et. Al for Chemical Vapor Deposition (CVD) of silicon from silane with an inert carrier gas. From an Arrhenius plot of the temperature dependence of growth rate, we note a change of slope at ∼300°C which we have attributed to the behavior of hydrogen at the silicon surface.
Development of Remote Plasma Enhanced Ohemical Vapor Deposition Processes Through the use of in Vacuo Electron Diffraction and Electron Spectroscopy
Authors: Rulder R. A. , Fountain G. G. , Hattangady S. V. , Posthill J. B. , Markunas R. J.
Published: March 2011

Remote plasma enhancecd chemical vapor deposition techniques have been developed for a wide variety of processes. These include SiO2, Si3N4, Si, Ge, GaN, GaAs, and a-Si:H depositions. This development has been enabled through the use of electron diffraction and electron spectroscopy techniques. These techniques have been used to qualify cleaning procedures prior to epitaxial or dielectric depositions. They have beeii used to qualify epitaxial deposition conditions by defining suitable.temperature and rate conditions. And, they have been used to evaluate cross-contamination issues.In situtechniques have been used in conjunction withex situcharacterizations to identify and correct problems in wafer cleaning, epitaxy, and process integration.
Low-Temperature Pecvd Si3N4 Films for GaAs Encapsulation and Passivation.
Authors: Pfeffer R. L. , Gerardi G. J. , Lux R. A. , Jones K. A. , Poindexter E. H. , Chang W. H. , Devine R. A. B.
Published: March 2011

We have begun a detailed study of the physical properties of Si3 N4 films deposited at low temperatures using a PECVD process based on dilution of reactive gases with inert carrier gas [1] in order to investigate their feasibility for use as post-implant encapsulants and/or device passivation layers for GaAs. The films and substrates are analyzed by ion channeling, ellipsometry, IR spectrometry, ESR, RBS, and SEM to evaluate implantationinduced substrate and interface damage as well as the films’ optical properties, surface morphology, stoichiometry, uniformity, stress, and electrical trapping characteristics. Following furnace or RTA annealing they are recharacterized, adding SIMS to evaluate As diffusion into the films. Both Schottky and ohmic contacts are then formed and used to measure Hall mobility, trap density and 1/f noise. Preliminary results of these studies are presented and compared with those obtained using other techniques such as wafer-to-wafer As entrapment, arsine overpressure, or conventional CVD.
Pecvd RF Discharge Models Review
Authors: Garscadden Alan
Published: March 2011

This paper presents a concise and subjective summary of the rapid progress that has been made in the understanding of the essential features of RF discharges. The paper concentrates on introducing the important concepts used in modeling the rf discharge. The discharges have been modeled from several distinctly different approaches. These include circuit, beamdiffusion, plasma fluid or continuum, and particle kinetic models. The treatments have their usefulness depending on the application. The circuit models give easily parameterized results, power deposition, and phase angles between voltage and current, however, they do not describe the important plasma chemistry and the source terms for deposition and etching. The newer continuum models efficiently give self-consistent plasma parameters for higher pressure discharges but synergistic ion and neutral interactions with surfaces are difficult to include. The particle kinetic models can include many effects without approximations, however they need extensive data sets and long computer run times. The coupling of improved diagnostics and the different theories has resulted in a convergence of their conclusions. There are four distinct energy-gain mechanisms in the RF discharge : a bulk plasma excitation; electron beam excitation resulting from secondary emission from ion collisions with the electrodes; wave-riding acceleration on the sheath oscillation (collisional: Kushner); and a noncollisional plasma electron-sheath boundary interaction (Godyak). The relative contributions are sensitive functions of the gas mixture, pressure, frequency and RF voltage.
Radical and Molecular Product Concentration Measurements in CH4 RF Plasmas by Infrared Tunable Diode Laser Absorption
Authors: Wormhoudt J.
Published: March 2011

Infrared tunable diode laser absorption studies of radicals and stable molecules formed in radio frequency plasmas are being carried out in a laboratory reactor which allows a long absorption path. In this paper we describe studies of CH4 RF plasmas. We report absolute concentration measurements as functions of total pressure and RF power for CH3 and C2H2 in CH4 plasmas, as well as measurements of the CH4 rotational temperature and dissociation fraction.
Plasma Deposition of SiNxHy: Process Chemistry vs Film Properties
Authors: Smith Donald L.
Published: March 2011

The chemistry of silicon nitride deposition from ammonia-silane and nitrogensilane mixtures in a glow-discharge plasma was analyzed using special mass spectrometric techniques involving line-of-sight sampling through an orifice in the wafer plane of a parallel-plate reactor. It was found that high rf power is needed to activate the nitrogen source sufficiently, and that silane flow must be held below a certain critical value to ensure an excess of activated nitrogen. This critical value is detectable by the appearance of disilane in the plasma, which is indicative of silane reacting with itself. At low power, silane reacts only with itself, and disilane is the dominant gaseous product. Conversely, disilane-free plasmas in either gas mixture result in films that are nitrogen-rich and free of the Si-H bonding that has been correlated with poor dielectric behavior. Utilization of silane to form SiNxHy is near unity. The aminosilanes, SiH4-n(NH2)n, are the sole gas-phase Si-N products of the ammonia mixture, and the triaminosilane radical, Si(NH2)3, is the key deposition precursor. The precursor is transformed into SiNxHy by way of a temperature-driven chemical condensation reaction at the surface, with the evolution of ammonia. The nitrogen mixture produces no gas-phase Si-N products, and deposition proceeds by the reaction of SiHn radicals and N atoms at the surface. These basic differences in deposition mechanism result in significant and logical differences in the physical and electrical properties of films deposited from the two mixtures.
Plasma Deposited Silicon Nitride Film Chemistry
Authors: Chiang Justin N. , Hess Dennis W.
Published: March 2011

The structure and composition of plasma deposited (PD) silicon nitride thin films formed using NH3/SiH4, N2/SiH4, and N2/SiH4/H2, discharges are compared. The effect of introducing a DC grounded stainless steel mesh between the parallel electrodes is also discussed. Chemical structure and composition of these films are measured using X-ray Photoelectron Spectroscopy and Fourier Transform Infrared Spectroscopy. Significant changes in film composition are observed with changes in gas composition and with utilization of the screen. When the screen is invoked, variations in film composition are more pronounced for PD silicon nitride films formed using N2 as the nitrogen source. An increase in the N:Si ratio occurs for all films deposited using the screen. This compositional change is reflected in increased N-H and decreased Si-H bonding. Similar changes are also observed in films deposited from a N2/SiH4/H2 discharge compared to films formed using a N2/SiH4 discharge.
Temperature Dependence of the Morphology of Thin Diblock Copolymer Films as Revealed by Neutron Reflectivity
Authors: Russell T. P. , Anastasiadis S. H. , Satija S. K. , Majkrzak C. F.
Published: March 2011

The order-disorder transition in thin films of symmetric diblock copolymers of polystyrene and polymethylmethacrylate has been investigated by neutron reflectivity. At temperatures above the order-disorder temperature, TMST, a surface induced oscillatory segment density profile with an exponential decay length, χ, is observed. The inverse of decay length 1/≤ TMST a lamellar morphology oriented parallel to the surface propagates through the entire specimen.
Phonons at Martensitic Phase Transitions of bcc-Ti, bcc-Zr and bcc-Hf
Authors: Petry W. , Heiming A. , Trampenaux J.
Published: March 2011

Inelastic neutron scattering on in situ grown bcc single crystals of the group 4 metals Ti, Zr and Hf show a band of low energy and strongly damped phonons. Geometrical considerations show how these damped lattice vibrations achieve the displacements necessary for the two martensitic phase transitions from bcc to ω(under pressure) and from bcc to hcp (upon lowering the temperature). The low energy and temperature dependent phonons are precursor fluctuations of the hcp or ω phase within the bcc phase.
Use of Neutron Diffraction in Determining Strains in High-Temperature Superconducting Composites
Authors: Kupperman D. S. , Singh J. P. , Majumdar S. , Faber J.
Published: March 2011

The Argonne Intense Pulsed Neutron Source and General Purpose Powder Diffractometer have been used to study high Tc metal oxide composites composed of yttrium barium copper oxide and silver. Neutron diffraction techniques were applied to composites with 15, 20 and 30% silver content by volume. We have observed that after hot pressing, the 30% Ag specimens contained both orthorhombic high Tc and tetragonal, non-superconducting phases near the center of the specimens but only tetragonal near the surface. The relationship of shifts in Bragg peaks to strains of the constituents is discussed.
High Resolution Neutron Powder Diffraction Studies of the Ferroelastic Phase Transition in LaNbO4
Authors: David W I F
Published: March 2011

Analysis of high resolution neutron powder diffraction data of ferroelastic LaNbO4 indicates a monoclinic to tetragonal structural phase transition that is accompanied by anomalous line broadening. The origins of this line broadening have been investigated using a novel modification of the Rietveld technique. The results show that strain broadening is associated with the ferroelastic phase transition both above and below the transition temperature. This anomalous ‘microstrain’ is well-described by a second rank strain tensor, the principal axes of which are collinear with the spontaneous lattice strain. This phenomenon may be a general feature of proper ferroelastic phase transitions.
Neutron Scattering from Lattice Defects
Authors: Peisl Johann , Dosch Helmut , Kirchner Stefan
Published: March 2011

For O in Nb the experimental scattering distribution can be described by a so-called 3-force model. The scattering pattern exhibits close similarity to the one observed for the ω-phase in some bcc alloys. It is shown that the lattice distortion calculated from the proposed 3-force model contains static fluctuation of the ω-phase. The ω-phase is closely related to the minimum in the LA 2/3 (111) phonon dispersion branch. With decreasing temperature the frequency of this phonon decreases, whereas the elastic diffuse scattering at the same position increases. This “softening” of the lattice, together with an increasing “central peak”, gives an equivalent description of the situation.
Lattice Misfit and Decomposition in Ni-Al-Mo Alloys
Authors: Calderon Hector , Kostorz Gernot
Published: March 2011

The effect of lattice mismatch δ between the γ-matrix and γ'-precipitates on the decomposition process of Ni-Al-Mo alloys has been investigated. The results show that for δ = 0 spherical precipitates are formed without any orientational correlation. For δ > 0 non-spherical particles, aligned along <100>, are produced. The kinetics of the γ-γ' decomposition becomes slower as δ is reduced to zero.
Non-Destructive Measurement of Residual Stresses in U-0.8 WT% Ti by Neutron Diffraction
Authors: Salinas-Rodriguez A. , Root J.H. , Holden T.M. , Macewen S.R. , Ludtka G.M.
Published: March 2011

The macroscopic residual stress distribution in γ-quenched and stress levelled U-0.8wt% Ti alloy tubes was studied using neutron diffraction techniques. Residual strains were evaluated from the difference in d-spacings measured in the tubes and in small reference samples machined from each tube. Residual stresses were calculated with the isotropic bulk values of the elastic constants for polycrystalline α-U. Quenching from the γ field resulted in a nearly equi-biaxial stress state at every point across the wall thickness of the tube. The magnitude of the radial stress was very small compared with that of the axial and hoop stresses which were compressive at the surfaces and tensile in the interior. Stress levelling relieved almost completely the hoop residual stress without affecting the radial stress. The axial residual stress becomes tensile through the wall thickness and remains constant at about 20% of its magnitude in the as-quenched condition.
The Measurement of Boron at Silicon Wafer Surfaces by Neutron Depth Profiling
Authors: Downing R.G. , Lavine J.P. , Hossain T.Z. , Russell J.B. , Zenner G.P.
Published: March 2011

The thermal neutron reaction 10B(n,α)7Li is used to measure the boron concentration on the surface of silicon wafers. The technique, referred to as neutron depth profiling (NDP), requires no special sample preparation. Boron is determined on the as- received wafers at a level of 1012 to 1013 atoms/cm2. A boron level of about 2×1012 atoms/cm2 is found at the wafer surface after oxidation, epitaxial, or polycrystalline silicon deposition. Additional measurements are given from SIMS measurements of multilayer structures on silicon also showing the presence of boron. Ambient air appears to be a significant source of the boron.
Structure and Dynamics of Glasses and Liquids
Authors: Price David L.
Published: March 2011

Neutron scattering has proved to be a powerful tool in the study of glasses and liquids: structures are investigated by neutron diffraction, and dynamics by inelastic neutron scattering. Evidence of current interest in this field is provided by the new instruments for diffraction from amorphous systems being constructed at IPNS, ISIS and the R2-reactor at Studsvik, in addition to existing instruments such as the D4B diffractometer at ILL.
Dynamics of Weakly Connected Solids: Sintering of Polymeric Aerogels
Authors: Schaefer D. W. , Richter D. , Farago B. , Brinker C. J. , Ashley C. S. , Olivier B. J. , Seeger P.
Published: March 2011

A combination of small angle scattering (SAS) and neutron spin-echo (NSE) spectroscopy is used to characterize the structure and dynamics of polymeric silica aerogels during sintering. The SAS data indicate that densification at short length scales precedes the densification at longer scales (comparable to that of the pore structure). Interpreted within the fracton model, the NSE data are consistent with an initial decrease in connectivity during relatively early stages of densification.
Inelastic Neutron Scattering Studies of Nonlinear Optical Materials: p-Nitroaniline Adsorbed in Alpo-5
Authors: Nicol Jacqueline M. , Udovic Terrence J. , Rush J.J. , Cox Sherman D. , Stucky Galen D.
Published: March 2011

Inelastic neutron scattering has been used to characterize the vibrational spectroscopy below 220 meV of para-nitroaniline adsorbed in the molecular sieve ALPO-5. Samples at loadings of both 3 and 13 weight %, which represent the onset of and the maximum in the nonlinear optical properties respectively, were studied. The torsional vibration of the amino (NH2) group has been identified at ca. 50 meV. The splitting and structure of this mode is sensitive to the loading level. This can be related to differences in the nature of the hydrogen bonding in these materials.
Thermal Expansion of Graphite and HNO3-Graphite Intercalation Compounds, a Neutron Diffraction Study
Authors: Pinto Haim , Melamud Mordechai , Shaked Hagai
Published: March 2011

The temperature dependent lattice parameter, c(T), was determined for samples of graphite, and HNO3 -graphite intercalates stage 3 and stage 4, using neutron diffraction. The temperature range studied is 12 to 300 K. The stage 3 and stage 4 intercalates exhibit a strong two-step discontinuity at the temperature of their structural phase transition (≈260 K). A stage-independent, temperature-dependent lattice parameter for the intercalant layer is extracted from the observed lattice parameters for graphite, stage 3, and stage 4 intercalates. The graphite and the intercalant lattice parameters are calculated using one-dimensional Debye theory in the framework of the Grüneisen relation. The Debye temperatures that yield best fits to the observed lattice parameters of the graphite and the intercalant are 500 K and 421 K, respectively. Using these values, thermal expansion coefficients for graphite, the intercalates and the intercalant are derived.
Neutron Powder Diffraction: A Powerful Materials Research Technique
Authors: David W I F
Published: March 2011

Neutron powder diffraction is a powerful technique that provides a detailed description of moderately complex crystal structures. This is nowhere more apparent than in the area of high temperature superconductors where neutron powder diffraction has provided precise structural and magnetic information, not only under ambient conditions but also at high and low temperatures and high pressures. Outside superconductor research, the variety of materials studied by neutron powder diffraction is equally impressive including zeolites, fast ionic conductors, permanent magnets and materials undergoing phase transitions. Recent advances that include high resolution studies and real-time crystallography will be presented. Future possibilities of neutron powder diffraction will be discussed.
Small Angle Neutron Scattering Study of Critical Binary Fluids in Porous Glasses
Authors: Dierker S. B. , Wiltzius P.
Published: March 2011

We present small angle neutron scattering measurements of the static structure factor S(q) of the binary fluid mixture water-lutidine imbibed into the porous glass Vycor as a function of temperature and composition. S(q) changes from a Lorentzian in the one phase region to a Lorentzian squared at the random field transition. The correlation length increases from ∼ 20 A in the one phase region to to ∼ 52 Å (≈ pore diameter) in the frozen domain state.
Neutron Irradiated Uranium Silicides Studied by Neutron Diffraction and Rietveld Analysis
Authors: Birtcher R. C. , Mueller M. H. , Richardson J. W. , Faber J.
Published: March 2011

Uranium silicides have been considered for use as reactor fuels in both high power and low enrichment applications. However, U3 Si was found to become amorphous under irradiation [1] and to become mechanically unstable to rapid growth by plastic flow [2,3]. U3Si2 appears to be stable against amorphization at low displacement rates, but the extent of this stability is uncertain. Although the mechanisms responsible for plastic flow in U3Si and other amorphous systems are unknown, as is the importance of crystal structure for amorphization, it may not be surprising that these materials amorphize, in light of the fact that many radioactive nuclide - containing minerals are known to metaminctize (lose crystallinity) under irradiation [4]. The present experiment follows the detailed changes in the crystal structures of U3Si and U3Si2 introduced by neutron bombardment and subsequent uranium fission at room temperature. U-Si seems the ideal system for a neutron diffraction investigation- since the crystallographic and amorphous forms can be studied simultaneously by combining conventional Rietveld refinement of the crystallographic phases with Fourier-filtering analysis [5] of the non-crystalline scattering component.
Gas Density in Helium Bubbles in Nickel and Iron Determined by Small Angle Neutron Scattering
Authors: Schwahn D.
Published: March 2011

A general discussion of the gas density determination of He bubbles in Ni and Fe with neutron scattering using the contrast variation method is given. One finds, that best results are obtained using isotope combinations for Ni, and magnetic and nuclear scattering for Fe. An experiment to determine the density of He in Ni demonstrates the applicability of this method.
Microstructure and Isotopic Labeling Effects on the Miscibility of Polybutadiene Blends Studied by the Small-Angle Neutron Scattering Technique
Authors: Han Charles C. , Hasegawa Hirokazu , Hashimoto Takeji , Hargis I. Glen , Aggarwal S. L.
Published: March 2011

Deuterated polybutadiene and protonated polybutadiene (PBD/PBH) blends with various microstructures have been studied by the small-angle neutron scattering experiments. Correlation length, ξ, zero-wavenumber structure factor, S(q=o), and interaction parameter, Xblend have been obtained. All PBD/PBH blends exhibit UCST behavior. With the use of random copolymer theory, the interaction parameter, Xblend, has been successfully separated into X1, X2 and X3 which are interaction parameters between the same isotope labeled 1,2-unit and 1,4-unit, opposite isotope labeled 1,2-unit and 1,4- unit, and opposite isotope labeled 1,2-unit with 1,2-unit or 1,4-unit with 1,4-unit, respectively.
The Application of Neutron Topography to the Study of X-ray Sensitive Organic Crystals - a Possible Alternative to X-ray Topography.
Authors: Dudley M.
Published: March 2011

Neutron topography has been carried out on organic single crystals of varying Xray sensitivity, in order to test the feasibility of the technique as an alternative to X-ray topography for the study of the influence of defects on the solid state reactivity of X-ray sensitive single crystals. Specimens studied include the diacetylene PTS, and Pyrene. A comparison of the strain sensitivity and spatial resolution of the neutron and X-ray based techniques is made. Preliminary results of dynamic neutron topographic studies of the UV induced polymerization in PTS are presented. These results are compared to those obtained from similar X-ray topographic studies.

Results indicate that the neutron technique can be a useful ally technique to the analogous X-ray techniques in studies of the influence of defects on reactivity in specimens of moderate X-ray sensitivity. In cases of extreme sensitivity, the neutron technique is the only one available for studies of this nature.
A Small Angle Neuitron Scattering Investigation of Compacted Nanophase TiO2 and Pd
Authors: Epperson J. E. , Siegel R. W. , White J. W. , Eastman J. A. , Liao Y. X. , Narayanasamy A.
Published: March 2011

Nanocrystalline compacts of TiO2 and Pd were prepared by first condensing the Ti or Pd vapors in an inert gas atmosphere. The Ti was oxidized in situ to TiO2. Samples were prepared by scraping off and compacting the nanophase materials into thin disks. The small angle neutron scattering was measured in the as-prepared condition and after isothermal anneals of up to 23 hrs at 550°C for the TiO2 and up to 3.3 hrs at 300°C for the Pd. Scattering data were obtained in absolute cross sections. Integrated small angle scattering and maximum entropy methods were used in estimating the structural parameters. The results are interpreted in terms of a model which consists of nanometer sized grains of the materials separated by boundary regions which are, on average, much less dense than the respective bulk materials; 21% for the TiO2 and about 56% for Pd. However, the boundary regions contain voids or pores, which contribute to these density decrements. Possible sources of error are discussed.
Surface Investigation by Neutron Reflection
Authors: Farnoux B.
Published: March 2011

Several phenomena analogous to those observed in classical optics, such as reflection, refraction and interference, are also observed with slow neutrons. Information on surface properties, described by a refractive index profile, can be extracted from reflection experiments. This information is similar to that obtained by X-ray reflection. However, there are some instances where the new neutron method provides a distinct advantage. The refractive index is related to the scattering length density, a parameter which describes the neutron-matter interaction. Owing to the magnetic interaction, magnetic materials have a neutron spin dependent refractive index, and a critical reflection of polarized neutrons is a particularly sensitive probe of surface magnetism. On the other hand, in contrast to X-rays, neutron scattering length values vary randomly from element to element. Isotopic substitution can then produce a contrast in the scattering length density. Of particular importance is the large difference between hydrogen and deuterium. This is a distinct advantage for studiyng many problems in surface chemistry, particularly in the polymer field.
Initial Stages in the Growth of Oxide Thin Films by CVD
Authors: Tietz Lisa A. , Summerfelt Scott R. , English Gerald R. , Carter C. Barry
Published: March 2011

A technique has been developed for studying the early stages of heteroepitactic nucleation and growth of oxide thin films by TEM using direct deposition onto electron-transparent ceramic substrates. Observations of α-Fe2O3 island growth on four orientations of α-Al2O3 – (0001), {1102}, {1010}, and {1120} – are reported. Moir6 fringes and selected-area diffraction are used to show heteroepitactic growth. Island morphology is compared to known growth habits of hematite crystals. Preferential nucleation of islands at low-energy sites (e.g. surface steps) is also demonstrated.
Predicting The Chemistry In Cvd Systems
Authors: Spear Karl E. , Dirkx Ryan R.
Published: March 2011

Tailoring the chemical and physical nature of CVD deposits for specific applications requires understanding and controlling the chemical processes occurring in a deposition reactor. This implies understanding the combined equilibrium, kinetic, and transport processes. The occurring processes produce composition gradients in the reactor which can cause variations in the deposition chemistry. Derived physical and mathematical models of possible mechanisms provide critical tools for manipulating and controlling the chemical and physical nature of CVD deposits. Examples of silicon boride deposition from SiH4, BC13, and H2 mixtures are used to illustrate thermochemical modeling techniques which utilize the concept of partial equilibrium. Predictions of limits on the chemical behavior, and comparison of these limits with experimental observations are used to hypotheses deposition mechanisms.
Internal Stresses In Amorphous Mocvd SiO2 Films
Authors: Desu Seshu B.
Published: March 2011

Amorphous SiO2 films were deposited by the low pressure pyrolysis of organometallic precursors at temperatures of 350 to 500°C. Films were deposited on both single crystal silicon and fused quartz substrates. Intrinsic stresses in the films were measured by a curvature method as a function of deposition conditions and thermal processing conditions. As–deposited films showed significant tensile stress of the order of 400 MPa. The intrinsic stresses in the films increased as the deposition temperature decreased and deposition pressure increased. Small concentrations of dopants like B2O3 and P2O5 significantly decreased the intrinsic stress of as–deposited films. Stress reduction was also achieved by post deposition annealing. SiO2 film stress is correlated to the Si-O-Si bond angle distribution in the structure of the resultant film.
Morphological Evolution Of Titanium Carbide Whiskers
Authors: Mathur R. , Gallois B. M.
Published: March 2011

The early growth of titanium carbide whiskers from mixtures of TiCl4-CH4-H2 was investigated. Fine nickel particles were the catalytic agent in a hot-wall CVD reactor. It was confirmed that whisker growth is initiated by the vapor-liquid-solid mechanism at the growth temperature of 1423 K. The initial growth proceeds by the diffusion of the constituent species through a Ni-Ti liquid droplet and is characterized by a rapid increase in whisker length, the diameter remaining essentially constant. In the later stage, the whiskers grow primarily in the axial direction at a reduced rate with a gradual increase in the diameter. The whisker diameter (D) and its rate of increase are independent of the nickel particle sizes, but increased proportionately to the reactant supersaturations. The whisker length (L) also increased with increasing nickel particle size and reactant supersaturation, resulting in large aspect ratios (L/D = 12.5). The whiskers exhibited extensive branching and kinking and a <100> primary growth direction.
Characterization Of Ceramic Matrix Composites Fabricated By Chemical Vapor Infiltration
Authors: Stinton D. P. , Hembree D. M. , More K. L. , Sheldon B. W. , Besmann T. M.
Published: March 2011

A process for the preparation of fiber-reinforced SiC composites by chemical vapor deposition has been developed at Oak Ridge National Laboratory. Composites are prepared by infiltrating fibrous preforms with reactant gases that decompose at elevated temperatures to deposit silicon carbide between and around the fibers. Because the infiltration process utilizes both temperature and pressure gradients, SiC is deposited under conditions that vary considerably from the hot face to the cool face of the composite. Matrix characterization of composite samples by transmission electron microscopy and Raman spectroscopy are described.
Benefits and limits of the thermodynamic approach to C.V.D. Processes
Authors: Bernard C. , Madar R.
Published: March 2011

This paper intends to develop and illustrate by a few examples the principles of thermodynamic analysis which can be applied at an early stage to assist in selecting the following:

• the material to be deposited for a well-defined application,

• the nature of reactants

• the range of experimental parameters.

Specific emphasis will be given to the main problems relating to data selection: assessments, availability of coherent data, sensitivity of results to data accuracy, etc.

Finally, the validity of a thermodynamic approach at equilibrium will be discussed with a view to optimizing a dynamic non-equilibrium process.
Gas Phase Reactions Relevant to Chemical Vapor Deposition: Numerical Modeling
Authors: Burgess D. , Zachariah M. R.
Published: March 2011

Numerical modeling of gas phase chemical kinetics was used to investigate reactions following silane decomposition to suggest experimental conditions and to interpret concentrations measurements. The effects of concentration and temperature gradients on kinetic pathways and reactive intermediates were studied. These processes are relevant to silicon-based chemical vapor deposition (CVD), to flame-driven gas phase particle nucleation, and to laser-induced processes for materials fabrication.
Structure, Composition, and Properties of Mocvd ZrO2 Thin Films
Authors: Desu Seshu B. , Shi Tian , Kwok Chi K.
Published: March 2011

ZrO2 films were deposited on silicon substrates at temperatures from 350 to 550 °C by metallorganic chemical vapor deposition (MOCVD) using zirconium acetylacetonates. Depositions were carried out at both atmospheric and low pressures. The optical properties, structure, microstructure, and composition of these films were characterized by Ellipsometer, X-ray diffraction, scanning electron microscopy (SEM), and electron spectroscopy for chemical analysis (ESCA), respectively. The deposition was kinetically controlled at low temperatures and mass transfer controlled at high temperatures. Use of zirconium (IV) acetylacetonate resulted in cubic ZrO2 with some carbon contamination whereas, tetragonal pure ZrO2 were obtained with the precursor zirconium (IV) trifluroacetylacetonate. The tetragonal ZrO2 films are fine grained and showed preferential orientation. The measured values of dielectric constant, refractive index, and electrical resistivity of ZrO2 films are 18, 2.0, and 5E13 Ohm.cm, respectively.
Chemical Vapor Deposition of Niobium Carbide using a Novel Organometallic Precursor.
Authors: Stupik Paul D. , Cheatham Linda K. , Graham John J. , Barron Andrew R.
Published: March 2011

Chemical vapor deposition from (MeCp)2Nb(allyl) at atmospheric pressure yields niobium carbide films at temperatures as low as 300°C. X-ray photoelectron spectroscopy (XPS) studies indicate that the bulk films contain a carbide phase and a nearly stoichiometric ratio of niobium to carbon. The morphology of the films has been examined by scanning electron microscopy (SEM).
Transport Properties of CVI Preforms and Composites
Authors: Freeman G. B. , Starr T. L. , Elston T. C.
Published: March 2011

A simple model, based on physical microstructure, that predicts the anisotropic transport properties of cloth lay-up composites is discussed. This anisotropic material is modeled as a layer structure consisting of two, or more, isotropic components. Composite transport coefficients perpendicular and parallel to the layers are given by “series” and “parallel” combining laws involving the isotropic coefficients of these component materials and their volume fractions. These component material properties are determined using microstructural information and fundamental material properties. Model calculations are compared to experimental measurements for gas permeability.
3-D Modeling of Forced-Flow Thermal-Gradient CVI for Ceramic Composite Fabrication
Authors: Starr Thomas L. , Smith Arlynn W.
Published: March 2011

Forced-flow thermal-gradient chemical vapor infiltration (FCVI) has demonstrated excellent potential for fabrication of high strength, high toughness ceramic composites. Extension of this process to large and complex shapes is facilitated by use of a computer model to optimize process conditions and hardware for rapid, uniform infiltration.

A 3-D model has been developed using a “finite volume” formulation. A steady-state solution for heat conduction and Darcy's law permeation produces temperature and gas flow distributions within the fiber preform. These are used to generated matrix deposition rates within each volume element. By “marching” through time, a complete simulation of the densification process can be obtained.

The model is demonstrated for a FCVI system with cylindrical symmetry and compared to experimental results obtained at the Oak Ridge National Laboratory. The model results suggest a self-optimizing feature of the force flow/thermal gradient CVI process that produces uniform density in the final composite over a range of infiltration conditions. This matches experimental observation where good uniformity has been achieved over a wide range of gas flows, pressure and temperature.
Infrared and Raman Spectroscopy of Phonons in n-Type High Tc Superconductors
Authors: Crawford M. K. , Burns G. , Chandrashekhar G. V. , Dacol F. H. , Farneth W. E. , Carrón, III E. M. Mc , Smalley R. J.
Published: March 2011

We have measured the infrared (IR) reflectance and Raman spectra of electron doped and undoped Nd2CuO4 and Pr2CuO4. Utilizing the results from doped ceramics and undoped ab plane oriented single crystals, we observe and assign all the IR active phonons (3A2u + 4Eu) predicted by group theory. We have also observed the Raman active modes involving atom motion along the c axis. We compare our results to those found in the related hole superconductors based upon La2CuO4.
The Upper Critical Magnetic Field of Superconducting YBa2(Cu1-xNix)3O7
Authors: Xu Youwen , Moodenbaugh A. R. , Suenaga M.
Published: March 2011

The upper critical magnetic field of a series samples of YBa2(Cu1-xNix)3O7 is measured. Other related parameters, such as the lower critical magnetic field Hc1, the Ginsberg-Landau parameter k, the jump in the specific heat ∆C/Tc, the superconducting coherence length ξ, and the penetration depth λ, are calculated from Tc, dHc2/dT and dM/dH. The results show that Hc2(0), and consequently ξ(0), are essentially constant, but Hc and ∆C/Tc decrease with increasing Ni content.
Magnetic Phase Diagram of YBa2(Cu1–xFex)30y and YBa2 (Cu1–xCox)30y
Authors: Doyama Masao , Matsui Masaaki , Matsuoka Hiroshi , Ishikawa Kazuhito , Hayashi Eiji , Nishiyama K. , Nagamine K.
Published: March 2011

Magnetic phase diagrams of YBa2 (Cu1–xFex)30y and YBa2 (Cu1–xCox)30y were determined by measuring positive muon spin relaxation and magnetic susceptibility (SQUID).
Fe Doping Effects in Aerosol Processed YBa2 (Cu1-xFex)307–δ Submicrocrystalline Grains
Authors: Boolchand P. , Biswas P. , Zhou D. , McDaniel D. , Huff W. , Oostens J. , Farrell D.
Published: March 2011

Magnetization and Mössbauer spectroscopy results on aerosol processed YBa2 (Cu1-xFex)307–δ samples are presented. Systematics of Tc(x), x(x) and Fe dopant site occupancies In/I(x) as a function of dopant concentration ‘x’ are deduced and compared to those established on analogous solid-state- reacted samples. The absence of twinning in the aerosol processed grains leads to a random replacement of Cu for Fe in chains and planes of the host structure.
The Effects of Transition Metal Substitutions for Copper in the Bi-Sr-Ca-Cu-O Superconducting System
Authors: Bennett J.C. , Boswell F.W. , Corbett J.M. , Kohara S. , Razavi F.S.
Published: March 2011

The effects of transition metal dopants on superconductivity in samples of nominal composition Bi2CaSr2(Cu1-xMx)208+δ with M = Co, Fe, Ni and Zn have been investigated for 0 ≤ x ≤ 1. Co and Fe additions progressively suppress the ? of the doped material and result in semiconducting behaviour for x ≤ 0.2. In the ranges 0 ≤ x ≤ .07 and near x = 1.0, x-ray diffraction reveals the samples are essentially single phase but are multiphase otherwise. Ni and Zn dopants have only a very slight effect on Tc; however, EDX analysis reveals these elements are not significantly Incorporated into the superconducting phase.