bluuebunny/crossref_metadata_2025 huggingface dataset:
MOCVD of Wide Bandgap III-V Semiconductors by using Novel Precursors
Authors: Ho Kwok-L. , Jensen Klavs F. , Hanson Scott A. , Evans John F. , Boyd David C. , Gladfelter Wayne L.
Published: March 2011

Thin films of aluminum nitride have been grown by metalorganic chemical vapor deposition (MOCVD) from diethylaluminum azide. Growth rates of AIN on Si(111) were monitored in-situ with laser interferometry. The growth rate was linear in the partial pressure of the reactant at high temperatures and sublinear at low temperatures. A simple surface reaction mechanism consistent with these observations has been proposed. Surface reaction kinetics and mechanism were further investigated by steady-state kinetic mass spectrometry. Parameters in the growth rate expression were determined by a nonlinear regression of growth rate data. A typical sample of AIN on B-plane sapphire showed a bandgap of about 5.2eV which was increased to 5.9eV upon annealing in nitrogen at atmosphere pressure.
Room Temperature Excitonic Absorption in Small Cds Crystallites
Authors: Rai D.K. , Kumar Binod
Published: March 2011

The absorption characteristics of commercial CdS-containing yellow glass which shows constant transmitted intensity over a range of incident CW laser intensity have been studied at room temperature. Although the thick specimen (t>0.6 mm) shows only a broad step-like feature near λ>460 nm, a thin (t-0.09 mm) specimen shows two absorption features which can be interpreted as the first two quantum-confined exciton absorption features corresponding to a crystallite size of -45 Å. The absorption spectrum of a sample (t∼O.6 mm) heated for 15 min. at 700°C shows two new absorption features at 450 nm and 380 nm, which correspond to a much smaller crystallite size of -25 Å. This reduction in size is not inconsistent with estimates made from a well-known model for crystallite growth. Some consequences of these changes in the absorption features on the optical nonlinearities of the glass will be discussed.
Hydrogen Passivation of Doped and Undoped Microcrystalline Silicon
Authors: Stutzmann M. , Herrero C.P. , Ingels M. , Breitschwerdt A.
Published: March 2011

The effect of hydrogen plasma treatment on the properties of undoped and doped microcrystalline silicon are investigated by Raman and infrared spectroscopy, conductivity measurements, hydrogen effusion, and subgap absorption. It is found that hydrogen causes a passivation of dopant atoms similar to that seen in crystalline silicon. However, the efficiency of the dopant passivation appears to be smaller in μc-Si, and the vibrational spectra of dopants and hydrogen show distinct broadening due to local disorder. It is suggested that intergrain regions may efficiently getter atomic hydrogen introduced from the plasma and also provide the origin for a weakly bound hydrogen phase observed in the effusion experiments.
Control of Chemical Reactions for Growth of Crystalline Si at Low Substrate Temperature
Authors: Shimizu Isamu , Hanna Jun-Ichi , Shirai Hajime
Published: March 2011

A systematic study has been made on the formation of Si-network of amorphous(a-), microcrystalline(μc-) and epitaxial (epi)-Si prepared by Plasma-Enhaced (PE-) CVD under control of flow of atomic hydrogen. The control of the Si-network structures requires a deliberate selection of the precursor, i.e., SiHn (n≤53) and SiFnHm (n+m≤53), as well as an intentional acceleration of the chemical reactions for the propagation of Si-network in the vicinity of the growing surface by impinging of atomic hydrogen. A plausible interpretation was given to the growing mechanism of c-Si at low temperature.
Enhanced Nonlinear Optical Response of Coated Nanoparticles
Authors: Kalyaniwalla N. , Haus J.W. , Birnboim M.H. , Inguva R. , Ma W.P.
Published: March 2011

We study coated, nanometer-size, ellipsoidal particles that have a semiconductor or polymer core surrounded by a metal coating. We predict that composite materials containing these particles will have much larger enhancement of the nonlinear optical response than had previously been found by using semiconductor colloid suspensions or semiconductor - doped glasses. The enhancement is due to the surface plasmon resonance from the metal dielectric constant that increases the local field in the core material. The frequency of the resonance and the enhancement depend upon the particle shape and the coating thickness, as well as on the specific materials.

Also, we predict intrinsic optical bistability in these new materials and show that the threshold intensity for optical bistability can be greatly reduced by using the coated particles. We predict a switching intensity of silver coated GaAs particles below 100W/cm2
Power Density Effects in the Physical and Chemical Properties of Sputiered Diamond-Like Carbon thin Films
Authors: Cho N.-H. , Krishnan K.M. , Veirs D.K. , Rubin M.D. , Hopper C.B. , Bhushan B. , Bogy D.B.
Published: March 2011

Thin films of diamond-like amorphous carbon were prepared by dc magnetron sputtering. A systematic variation in the physical properties of the films (mass density and electrical resistivity) was found as a function of sputtering power density. Chemical bonding and microstructure of the carbon thin films were investigated using electron energy loss spectroscopy (EELS) and Raman spectroscopy. Films grown at a lower power density were found to have more sp3 -bonded atomic sites and larger graphite microcrystals than films produced at higher sputtering power densities.
Composition Determination of Microcrystalline Two-Phase Silicon Rich Oxides
Authors: Bouldin D.H. , Lam C.H. , Rose K.
Published: March 2011

HRTEM measurements of silicon rich oxides (SRO) show silicon microcrystals in an oxide matrix [1]. Simple, reliable characterization of this two phase material has been a problem. Ellipsometric measurement of the refractive index is a convenient method for characterizing SRO films. Film composition can be related to the refractive index by Bruggeman's effective medium approximation. In this paper we demonstrate correlation of film compositions obtained by this technique with those obtained by Auger electron spectroscopy (AES)and Rutherford back scattering (RBS). We further demonstrate regimes of LPCVD growth where simple correlation of film composition with [N2 0]/[SiH4] gas ratios is not reliable.
Selective Growth of Si Crystals over Amorphous Substrates Seeded by Solid-State Agglomeration of Patterned Si
Authors: Yamagata K. , Yonehara T.
Published: March 2011

Selective growth of Si crystals over amorphous substrates, seeded by agglomerated single domained Si crystals is demonstrated. In this method, Si crystal seeds are periodically placed and selectively overgrown until impingement upon adjacent crystals, resulting in a matrix of large Si islands with controlled grain boundary locations. Si seeds are formed over amorphous SiO2 by the solid-state agglomeration phenomenon, and grown selectively up to 100 μm by CVD selective epitaxial growth technique. The grown crystals are classified in three crystalline forms of single crystals, primary twins, and multiple twins. However, most are single crystals with a specific orientation of (110) normal to the substrate surface.
A New Model for the Poly-Silicon thin Film Transistor for Use with Spice
Authors: M.J. Izzard , P. Migliorato , W.I. Milne
Published: March 2011

A set of analytical equations that accurately model the large-signal current-voltage and charge-storage characteristics of the poly-silicon thin film transistor (TFT) have been developed. The model is based on theories of conduction in materials with a bulkdistribution of gap states[l]. The equations are suitable for incorporation into a circuit simulator capable of transient-analysis of circuits, such as SPICE.
The Formation of Silicon Clusters in Plasma-Enhanced Chemically Vapour Deposited Si:O:H:F Alloys
Authors: Dias A. G. , Figueiredo J.
Published: March 2011

The structural and optoelectronic properties of a new plasma-enhanced chemically vapour deposited Si:O:H:F alloy are reported taking into account respectively the results from X-ray diffraction, Raman and infrared absorption spectroscopy analysis and from dark and photo conductivity and optical absorption measurements. Films produced with a F2/SiH4 gas ratio (r) lower or equal than 0.4 are amorphous semiconducting Si:O:H:F alloys, whereas films deposited with r≤0.5 exhibit a multiphase structure consisting of silicon clusters embedded in an amorphous insulating fluorine doped silicon oxide tissue. The formation of silicon clusters is the result of a segregation process of the fluorine and oxygen atoms in the amorphous Si:O:H:F matrix.
Evidence for Strongly Enhanced Paramagnetic Defect Creation in Low Temperature Pecvd SiO2 Films
Authors: Devine R. A. B. , Pfeffer R. L.
Published: March 2011

Amorphous SiO2 films have been deposited by plasma enhanced chemical vapor deposition (N2O:SiH4 flow rate ratio of 40:1) then 60Co gamma irradiated. We observe paramagnetic defects similar to oxygen vacancy centers which are created at least 100 times more efficiently in as-deposited oxide than in the same oxide annealed for 1 hr in Ar at 950°C. Positive fixed oxide charge creation in samples irradiated in the unbiased mode has a fractional yield of 0.018 defects per electron-hole pair. No enhancement of the positive fixed oxide charge creation is observed when comparing as-deposited and annealed films suggesting that the paramagnetic and electric defects do not have the same physical origin. Comments are made about the potential hazards of using such deposited oxide near a semiconductor surface where surface inversion may occur.
The Electrical and Optical Properties of Amorphous Silicon Alloys by Plasma-Enhanced CVD Method
Authors: Lin G. H. , Kapur M. , Bockris J. O'M.
Published: March 2011

High and low bandgap amorphous silicon thin film alloys (a-Si:Al, a-Si:Se, a-Si:S, and a-Si:Ga) were prepared by plasma-enhanced chemical vapor deposition. It was found that Al and Ga amorphous silicon alloys are low bandgap materials whereas a:SiS and a:SiSe are high bandgap semiconductors. The optical band gap of these systems could be changed from 1.0 eV to 2.0 eV, depending on the alloying element and its concentration in the film. The dark to light conductivity ratio was measured. The elemental content and distribution was analyzed by the SIMS and EPMA techniques. The results show that some of the amorphous silicon alloys studied are promising materials for multi-bandgap photovoltaic devices.
Ftir Investigations of Plasma Modified Polymer Surfaces and Their Interfaces with Plasma Deposited Tungsten
Authors: Leu Jihperng , Dalvie Manoj , Jensen Klavs F.
Published: March 2011

Surface modifications of thin polyimide films (100–2000 A˚) in downstream microwave CF4/NF3/Ar plasmas and radio-frequency (RF) CF4 plasmas have been studied in situ by Fourier transform infrared (FTIR) reflection-absorption spectroscopy. The downstream microwave plasma treatment produced significant surface fluorination in terms of polyfluorinated alkyl and aryl compounds as well as acyl and benzoyl fluorides. The depth of fluorination was approximately 500 Å. Similar changes in polymer surface functionalities were observed for RF plasma surface modifications, but the depth of fluorination was reduced to 30Å because of ion-bombardment. The interface between the tungsten film and polyimide surfaces has been characterized by ex situ FTIR reflection-absorption technique through the silicon side of Si/polymer/W structures. The observed spectral changes relative to polyimide-gold interfaces were interpreted in terms of interactions of tungsten with functionalities of the polyimde backbone. Tungsten deposited by both sputtering and plasma enhanced chemical vapor deposition (PECVD) showed significant chemical interactions, strongest for PECVD tungsten.
Laser-Induced Fluorescence of Silicon and Silicon Monoxide in a Glow Discharge
Authors: Hynes Anthony J.
Published: March 2011

Si atoms and SiO radicals have been monitored in DC ulow discharges via laser-induced fluorescence on the Si 4s 3P0-3P2−3P and SiO A1 π-x1Σ+ (0−0), (1−0) and (1−1) transitions. Production of Si 4s 3P0 in the 193 and 251 nm multiphoton dissociation of silanes has been observed and the implications for Si atom diagnostics discussed.
Spatial Generation Profiles of Active Radicals in Plasma-Enhanced CVD Of a-Si:H
Authors: Mataras D. , Cavadias S. , Rapakoulias D.
Published: March 2011

Spatially resolved Laser Induced Fluorescence and Optical Emission Spectroscopy were applied in an rf silane discharge, for the simultaneous detection of both ground and excited states of SiH radicals. Axial intensity profiles of these radicals were recorded under various conditions. The experimental observations indicate that the two radicals have different generation paths. LIF profiles are considered to represent the generation profile of all the ground state radicals and they were used as such in kinetic calculations.
Nitrogen Incorporation in a-Si,N:H Alloy Films Produced by Remote PECVD
Authors: Parsons G. N. , Lucovsky G.
Published: March 2011

We have produced a-Si,N:H alloy films using remote PECVD at a substrate temperature of 200°C with Si/N ratios between 0 (a-Si:H) and 3/4 (Si3N4). Films were prepared using nitrogen or ammonia source-gases, introduced downstream from a helium rf plasma. Nitrogen and hydrogen bonding environments were investigated using infrared absorbance. For films produced from N2, [N] and [H] concentrations were determined by SIMS. A random bonding model is used for a quantitative analysis of Si-H and Si-N bonding distributions, and to estimate the N/Si ratio in films produced from NH3. A comparison of N2 and NH3 source gases for nitrogen incorporation is also presented.
The Morphology of Symietric Diblock Copolymers as Revealed by Neutron Reflectivity
Authors: Satija S. K. , Majkrzak C. F. , Anastasiadis S. H. , Russell T. P.
Published: March 2011

The specular reflectivity of neutrons has been used to characterize quantitatively the microphase separated morphology of symmetric, diblock copolymers of polystyrene, PS and polymethylmethacrylate, PMMA, as a function of the total molecular weight of the copolymer where either block is perdeuterated. It is shown that the hyperbolic tangent function, as opposed to a linear or cosine squared function, most closely describes the concentration gradient at the interface between the lamellar copolymer microdomains. The effective width of the interface is found to be independent of the molecular weight of the copolymer blocks and has a value of 50 ± 3Å. This interface is also found to be identical to that of PS and PMMA, homopolymers. However, using measured values of the Flory-Huggins interaction parameter for PS and PMMA current theoretical treatments cannot describe the observed widths of the interface.
Structure of ErBa2Cu3Ox in the Composition Range 6.1 < x < 7.0
Authors: Pörschke E. , Meuffels P. , Rupp B.
Published: March 2011

The structure of a series of homogeneous ErBa2Cu3Ox powder samples (6.1 < x < 7.0) has been determined by elastic neutron scattering using the Rietveld method of profile refinement. All samples were prepared in the same way using a defined absorption-desorption method.

By removing oxygen the c axis expands, whilst the Cu2–Cu2 and the Ba–Ba distances contract. Accordingly, the most significant changes in atomic distances occur between the Cu2–O2,3 planes and the Cul–O4–Cul chains. With decreasing oxygen content the distance between the Cu–O planes and the Cu–O–Cu chains increases and the oxygen (0, 0, z) apex atom O1 moves closer to the Cu–O–Cu chains withdrawing from the Cu–O planes. The O1–plane and O1–chain distances are monotonic functions of the oxygen content, but the x dependence of these bonding lengths seems to be much stronger below x < 6.5. The change of the interatomic distances can be correlated to the suppression of superconductivity which clearly occurs within the orthorhombic phase.
Short-Range Order in α-Brass
Authors: Reinhard L. , Schoenfeld B. , Kostorz G. , Buehrer W.
Published: March 2011

Quenched equilibrium states of Cu–31.1 at.% Zn and Cu–22.4 at.% Zn single crystals (prepared with the Cu-65 isotope) were investigated by elastic diffuse neutron scattering. The diffuse intensity showed maxima which are attributed to the flat portions of the Fermi surface in the <110> directions. Short–range order parameters and linear displacement parameters were obtained from a fit to the measured data. Pair interaction energies were determined based on the inverse Monte–Carlo method. An ordered low-temperature phase Cu3Zn with the DO23 structure is suggested.
A First-Principles Study of Short Range Order in Cu-Zn
Authors: Sluiter M. , Turchi P.E.A. , Johnson D.D. , Pinski F.J. , Nicholson D.M. , Stocks G.M.
Published: March 2011

Recently, measurements of short-range order (SRO) diffuse neutron scattering intensity have been performed on quenched Cu-Zn alloys with 22.4 to 31.1 atomic percent (a/o) Zn, and pair interactions were obtained by Inverse Monte Carlo simulation [1]. These results are compared to SRO intensities and effective pair interactions obtained from first-principles electronic structure calculations. The theoretical SRO intensities were calculated with the Cluster Variation Method (CVM) in the tetrahedron-octahedron approximation with first-principles pair interactions as input. More generally, phase stability in the Cu-Zn alloy system is discussed, using ab-initio energetic properties.
Ordering Mechanism in Ni-Cr Alloys: Theory and Experiment
Authors: Turchi P.E.A. , Pinski F.J. , Howell R. H. , Wachs A.L. , Fluss M.J. , Johnson D.D. , Stocks G.M. , Nicholson D. M. , Schweika W.
Published: March 2011

Recently, short range order (SRO) parameters have been extracted from the neutron diffuse scattering intensities on Ni-Cr alloys with 11 to 25 at. pct. chromium. These data were analyzed using inverse-Monte Carlo simulations to extract atomic interactions and the results suggested the existence of a well defined, flat sheet of Fermi surface normal to the [110] direction. In this paper, this suggestion is investigated with a series of calculations which are based on the first-principles Korringa-Kohn-Rostoker-coherent-potential-approximation (KKRCPA). We calculate the electronic structure and the Bloch spectral function at the Fermi energy. We then proceed to calculate the effective cluster interactions using the generalized perturbation method (GPM) and compare them with the above-mentioned experimentally deduced interactions. In addition, we present preliminary results of two-dimensional angular correlation of positron annihilation radiation (2D-ACPAR) measurements, which probe the fermiology of this alloy system. The positron experiments demonstrate the existence of well-defined features in the Fermi surface of Ni89Cr11 but our calculations still have not yet established the origin of SRO in this system.
Phonon Dispersion and Kohn Anomaues in the Alloy Cu0.84Al0.16
Authors: Chou Henry , Shapiro S. M. , Moss S. C. , Mostoller Mark
Published: March 2011

We have made detailed measurements of phonon frequencies along all high-symmetry directions on a large single crystal of Cu0.84Al0.16 at room temperature. Phonon frequencies were ascertained to better than ±0.03 meV. Inter-atomic force constants and vibrational density of states were calculated by performing a Born-von Karman analysis on the complete set of phonon dispersion curves. In contrast to the case of pure Cu, no evident Kohn anomaly (neither in the phonon dispersion itself nor in the derivatives) was observed near the expected wave vector q=2kF. The absence of Kohn anomalies in the present system could be due either to a smeared out Fermi surface or to the possibility that the electron-electron interaction which screens the inter-ionic potential is not the dominant interaction in the system; i.e. the existence of Kohn anomalies in these alloys may depend mainly on the details of the electron-phonon interaction.
Influence of Interstitial Oxygen on the Lattice Parameters of Solution-Treated and Aged Ti-8.6 wt% Al Alloys
Authors: Gray G. T. , Lawson A. C.
Published: March 2011

Neutron powder diffraction data have been obtained on Ti-8.6wt.% Al alloys with three different oxygen contents ( 500, 1000, and 2000 ppm) in the solution-treated and aged condition ( containing α2) to investigate possible oxygen and aluminum ordering and lattice parameter variations. The lattice parameters “a” and “c” were found to depend on the oxygen content and heat-treatment condition. Consistent with the literature lattice parameter data on pure Ti, the “a” lattice parameter of the solution-treated Ti-8.6Al material is relatively insensitive to the oxygen content while the “c” parameter increases with increasing oxygen. Following aging to precipitate the ordered α2, the “c” lattice parameter in the Ti-8.6Al alloys still exhibits a positive dependence on oxygen content with aging and a slight “c” increase over the solution-treated condition. The “a” lattice parameter following aging is observed to be lower than the solution-treated value, particularly for the 1000 and 2000ppm alloys. The diffraction data will be discussed in light of parallel electron microscopy results and literature data.
Sans Measurement of Deuterium-Dislocation Correlation in Palladium
Authors: Heuser Brent J. , Summerfield G.C. , King J.S. , Epperson J.E.
Published: March 2011

Small angle neutron scattering (SANS) measurements have been made on deformed polycrystal palladium samples with and without deuterium dissolved in the solution phase (a) at room temperature. Concentrations were held constant during SANS experiments by an equilibrium gas pressure cell. The difference scattering cross section for the same sample with and without deuterium loading has a 1/Q behavior (Q=4Φ/λsinθ/2) at intermediate values of Q. At very low values of Q the dependence is much stronger than 1/Q. The 1/Q behavior is attributed to deuterium trapping close to long dislocation cores forming rod-like scattering structures.
Residual Stress Measurements by Means of Neutron Diffraction
Authors: Prask H. J. , Choi C. S.
Published: March 2011

Energy-dispersive neutron diffraction has been developed at the NIST reactor as a probe of sub- and near-surface residual stresses in technological samples. Application of the technique has been made to a variety of metallurgical specimens which includes the determination of tri-axial stresses as a function of depth in a number of uranium-3/4wt%Ti samples with different thermo-mechanical histories, and in two types of 7075-T6 aluminum “ogives”- of interest to the Army. Preliminary results have been obtained for an induction-hardened steel shaft, a fatigue lifetime test specimen for the SAE.
Neutron Diffraction Measurement of the Stress Field During Fatigue Cycling of a Cracked Test Specimen
Authors: Hutchings M.T. , Hippsley C.A. , Rainey V.
Published: March 2011

The triaxial stress field has been measured along the centre line of a compact tension specimen in the direction of cracking. The specimen had been subjected to ∼60,000 cycles at δK=31 and Kmax = 34 MPa mm½ and was bolted open at maximum stress. The field was remeasured after the stress had been fully relaxed. The results are discussed in terms of expectations from fracture mechanics calculations.
Diffuse Neutron Scattering from Excess Oxygen in UO2.13
Authors: Goff J.P. , Hutchings M.T. , Brown K. , Hayes W. , Godfrin H.
Published: March 2011

Coherent diffuse neutron scattering from single crystal UO2.13 has been investigated at temperatures up to 2100K. Above 850K the crystal as a single phase and the excess anions give rise to a characteristic pattern of elastic diffuse scattering. This can be interpreted in terms of uncorrelated simple clusters of defective anions first postulated by Willis. The intensity distribution changes with temperature increase but no quasielastic scattering has yet been resolved. On cooling to 293K a strong hysteresis is exhibited.
Observation of Micellar Formation in the Cavity of Porous Silica Glass
Authors: Bradley K.F. , Chen S-H , Thiyagarajan P.
Published: March 2011

The small angle neutron scattering intensity distribution from the empty pores of the silica glass Vycor can be satisfactorily interpreted using a simplified late stage spinodal decomposition model, due to Cahn', if one allows for a distribution of wave numbers in the material's density function. The result confirms that the porosity of the glass is 28% and gives the mean wave number of the density wave to be k0 = 0.0285 Å-−1 with a dispersion, δk / k0, of about 0.29. Small angle neutron scattering measurements of the anionic surfactant SDS in the Vycor pores indicate that when the surfactant is introduced into the pores at 80 × CMC in bulk solution, the surfactant forms micelles with the same average micelle separation distance as in the bulk solution, but the distribution of micelle separations is much greater in the glass pores.
Characterization of Chemically Modified Pore Surfaces by Small Angle Neutron Scattering
Authors: Glinka C. J. , Sandert L. C. , Wiset S. A. , Berk N. F.
Published: March 2011

Small angle neutron scattering has been used to characterize the structure of linear hydrocarbon chains chemically grafted to the internal pore surfaces of microporous silica particles. The aim of this work has been to relate the structure of the bonded adsorbate layers in these particles to their performance in, for example, reverse-phase liquid chromatography. By filling the pore space in the modified silica with a solution that matches the scattering density of the silica framework, the scattering from the adsorbate layers is enhanced and provides a sensitive probe of the effective thickness, uniformity and degree of solvent penetration in the layers. Results are presented for both monomeric and polymeric phases of alkyl chains ranging from C8 to C30 bonded to silica particles with a mean pore size of 100 nm.
Small Angle Neutron Scattering and Small Angle X-Ray Scattering from Bulk Microporous Silica
Authors: Long G. G. , Krueger S. , Black D. R. , Cline J. P. , Jemian P. R. , Gerhardt R. A.
Published: March 2011

The microstructure of low-density porous silica precursor (unsintered) bodies was studied as a function of starting chemistry. The ratio of colloidal silica sol to potassium silicate is known to have a marked effect on the size distribution of pores in this material, which in turn have a major impact on the resultant physical properties of the sintered product. In the present research, the sizes and the size distributions of particles underlying the pore microstructure was investigated, and it was found that the lower the amount of colloidal silica, the greater the size distribution of particle aggregates.
Small Angle Neutron Scatitering Study of Sol-Gel Glasses
Authors: Wiltzius P. , Dierker S. B.
Published: March 2011

We present small angle neutron scattering data of porous glasses. Analysis of the structure factor shows that the morphology on length scales between 30 A and 800 A depends on fabrication procedures. Fast gelation leads to a clumpy glass, whereas slow gelation produces a random smooth internal interface.
Dynamics of Star-Branched Polymers in Solution
Authors: Huangi J. S. , Fetters L. J. , Richter D. , Farago B. , Ewen B.
Published: March 2011

We have studied star-branched polymers in solution under various labelling and contrast matching conditions by small angle neutron scattering and neutron spin echo spectroscopy. We have investigated the relation between the static and dynamic partial structure factors of the variously labeled star polymers. The system of interest is a set of solutions containing 12-arm star branched polyisoprene of arm-molecular weight of 8000, and two polystyrene 12-arm stars, one fully labelled, the other with one arm labelled. The polyisoprene star polymer arms consisted of diblock copolymers, half-deuterated, and half-protonated. Measurements were performed on a center-deuterated star in a contrasted matching deuterated solvent (shell contrast), and on a reverse labelled star with core contrast. We have also studied a solution with the solvent matched the average star scattering length density and solutions containing identical stars with protonated homopolymers. It is found that in the frame-work of the random phase approximations, the initial relaxation rate of the partial dynamic structure factors can be quantitatively accounted for by a function of the eigenmodes of the mobility matrix weighted by an appropriate combinations of the various partial static structure factors.
Surface Enrichment and Evaporation in a Polymer Mixture of Long and Short Chains
Authors: Composto Russell J. , Stein Richard S. , Felcher Gian P. , Mansour Abdelkader , Karim Alamgir
Published: March 2011

Neutron reflectivity has been used to determine the concentration profile at the vacuum-polymer interface for a two polymer blend. To quantify surface enrichment and evaporation due to differences in chain length, we have measured the reflectivity of a mixture of short deuterated and long protonated polystyrene chains (DPS & PS), with a weight fraction of 0.5. When a mixture of DPS and PS chains of molecular weight 720 and 910k respectively were annealed, a small but measurable increase in asymptotic reflectivity occured, coupled with a decrease of film thickness and scattering length density. This is indicative of surface enrichment and evaporation of the light chains (DPS). Ellipsometry studies confirmed that the short chains evaporated and its rate was established as a function of the temperature. Upon increasing the DPS molecular weight to 9600, the enrichment becomes considerably greater whilst the evaporation becomes negligible.
Multiple Small Angle Neutron Scattering Characterization of the Densification of Alumina
Authors: Krueger S. , Long G.C. , Page R.A.
Published: March 2011

Multiple small angle neutron scattering (MSANS) was used to follow the evolution of the pore size distribution in α-Al2O3through the intermediate and final stages of sintering. This technique makes it possible to determine microstructure morphology in the 0.08 to 10 μm size regime under conditions where the total scattering cross-section is dominated by elastic incoherent multiple scattering, as is often the case for ceramics. The MSANS results indicate an initial decrease in the effective pore radius from 0.19 μm at 57% of theoretical density (TD) to 0.17 μm at 79% TD. As the sample density further increased, there was a transition region after which the effective pore radius grew rapidly to ≤0.5 μm at 98% TD. Standard Porod analysis on scattering by the same samples also indicates a transition between the intermediate and final stages of processing. Both sets of results support a topological model of sintering in which the interconnected pore network in the intermediate stage of sintering decays in a stable manner. The pores become fewer, while retaining the same diameter, as densification proceeds. In the final stage, isolated pores remain.
In Situ Reflectometry During LPCVD Tungsten Growth.
Authors: Holleman Jisk , Hasper Albert , Middelhoek Jan
Published: March 2011

The formation of LPCVD tungsten by means of the reduction of WF6 with Si, H2 and SiH4 is monitored in situ using a wavelength adjustable reflectometer. The initial self stopping growth of W by Si reduction is strongly dependant on surface status [1]. SEM observations together with Auger depth profiling and weight measurements support a growth model of islands that grow laterally and vertically until islands touch. After the self stopping Si reduction the W layer was increased in thickness by either the h or SiH4 reduction. The surface roughness calculated from the reflectance appears to increase linearly with thickness in the case of H2 reduction. Typical rms roughness was found to be 7% of layer thickness in the H2 reduction case. The reflectance of H2 reduced W layers could be improved by interrupting the growth process with a renucleation step using SiH4. Selective deposition and in situ growth rate measurements can be monitored when the deposition is carried out on a grating of SiO2 as a mask. Precleaning of the reactor with an NF3 plasma results in a strong retardation of the H2 reduction reaction.
Gas Phase Reactions Relevant to Chemical Vapor Deposition: Optical Diagnostics
Authors: Burgess D.
Published: March 2011

Laser photolysis, optical emission, and laser-induced fluorescence (LIF) were used to investigate laser driven decomposition processes in the gas phase pertaining to the systems: SiH4 → Si (s) and SiH4 → NH3 → Si3N4 (s). These processes are important to silicon/ silicon-nitride chemical vapor deposition, flame-driven gas phase silicon-particle nucleation, and laser-induced processes for materials fabrication. UV laser photolysis was used to generate SiHx and NHx species from silane and ammonia. A number of photofragments were identified by emission from excited states. The rate of reaction of NH2 with silane was measured using LIF to detect NH2 as a function of time following photolysis of ammonia
Chemical Vapor Deposition of Silicon Borides
Authors: Goto T. , Mukaida M. , Hirai T.
Published: March 2011

Monolithic SiB4±x and SIB6 plates about 1 nm in thickness were prepared by CVD using SiCl4, B2H6 and H2 gases as source materials. The CVD-SiB4±x, plates have nonstoichiometric compositions between B/Si=3.1 and 5.0. The lattice parameters of the CVD-SiB4±x, plates are a=0.633 nm and c=1.262 to 1.271 nm. The density of the CVD-SiB4±x ranges from 2.39 to 2.45 g/cm3. The CVD-SiB6 plates have a constant composition of B/Si=6.0. The lattice parameters of the CVD-SiB6plates are a=1.444 nm, b=1.828 nm, c=0.9915 nm, and their density Is 2.42 g/cm3. These measured densities are both almost in agreement with theoretical values. The electrical conductivity, Seebeck coefficient, Hall mobility and thermal conductivity of the CVD-SiB4±x and CVD-SiB6 plates were examined in the temperature range from 300 to 1000K. The conduction mechanism Is discussed and their figure of merit values for thermoelectric materials are evaluated.
Adhesion of Diamond Films on Various Substrates
Authors: Yen Tyan-Ywan , Kuo Cheng-Tzu , Hsu S. E.
Published: March 2011

The adhesion as determined by indentation of diamond films deposited by microwave plasma-assisted CVD on various substrates was investigated. The critical loads for crack initiation and the propagation of the lateral crack under different loads were measured. The effects of the coating conditions and surface pretreatment of the substrate on the adhesion were examined.
Interaction of Titanium with SiC Coated Boron Fiber
Authors: Hwan Luchen , Tan Beng Jit , Suib Steven L. , Galasso Francis S.
Published: March 2011

SICABO fiber, which is one of the silicon carbide coated fibers, has been found to be more stable than BORSIC fiber in titanium matrix composites because SICABO fiber has excess carbon in the SiC layer which was determined by an AES depth profile study. Tensile strength data also show that the SICABO fiber has a higher tensile strength after heating in titanium during hot pressing and chemical vapor deposition processing. Ti5Si3 and TiSi phases were identified from XRD studies on titanium coated BORSIC, but there was no TiSi phase identified in the titanium coated SICABO fiber. AES depth profile results have shown that the BORSIC-Ti has a broad interdiffusion zone.
The Emergence Of Plasma Enhanced Chemical Vapor Deposition (PECVD) As A Viable Industrial Coating Process
Authors: Engle George , Warren James W.
Published: March 2011

The potential of Chemical Vapor Deposition, as a process for applying erosion and corrosion resistant ceramic and metal coatings to ferrous and non-ferrous alloys has long been recognized. Unfortunately, the high deposition temperatures (900°-1000°C) cause deleterious and generally nonreversible metallurgical changes in the coated parts. Corresponding shape stability and dimensional tolerances are also lost. For more than twelve years, Plasma Enhanced Chemical Vapor Deposition (PECVD) technology has evolved from the laboratory into production operations within the semiconductor industry.

This acceptance is primarily due to the low PECVD deposition temperatures (<450 ° C). The PECVD processes have recently demonstrated an adaptability to coating alloy components and carbon/ceramic fibers with a wide range of carbide, boride, nitride, oxide and metal coatings to render them corrosion and erosion resistant. Typical Knoop hardness control of sili on carbide coatings can be controlled from about 2300 to more than 7000 kgfmn−2 at 10% penetration of the indenter while coating thickness and uniformity can be controlled from 300A ± 5%. Selected coating applications and performance are described.
Laser Induced Photochemical Vapor Deposition of Tungsten on Silicon
Authors: Maaren A. J. P. van , Sinke W. C.
Published: March 2011

An ArF excimer laser (193 nm) aligned parallel to the substrate has been used to initiate photo-activation of the W-CVD process. W was deposited on silicon and SIMOX at a 310 °C substrate temperature using WF6 as a W precursor, together with H2. The samples were analyzed after deposition with SEM and 2 MeV He+ RBS, to obtain information about the reaction between WF6 and Si in laser-induced CVD of W. The data indicate that the reaction between WF6 and Si is suppressed upon laser irradiation. The suppression increases with increasing laser-pulse frequency. An explanation for this phenomenon is given in terms of atomic Hformation after (partial) photodissociation of WF6.
Silicon Nitride Synthesis by Laser Pyrolysis of an Aerosol-Dispersed Precursor
Authors: Xiao Tongsan D. , Strutt Peter R. , Gonsalves Kenneth E.
Published: March 2011

Surface layers of ultrafine Si3N4 particles (30–100 nm. diameter) have been synthesized by laser-pyrolysis of a liquid precursor, dispersed as an aerosol. This aerosol was formed in a nitrogen environment (at near ambient pressure) using an ultrasonically activated nozzle. The organosilazane precursor, which was specially designed for CO2 laser pyrolysis, was of the type (CH3SiHNH)x, with x = 3 or 4. In the current experiments deposition was performed on Ni substrates using a (i) 7 cm/s. substrate translational velocity, and (ii) ˜2.8 × 102 w/cm2 power density.
Titanium Nitride Thin Films: Properties and Apcvd Synthesis Using Organometallic Precursors
Authors: Fix Renaud M. , Gordon Roy G. , Hoffman David M.
Published: March 2011

A novel process for the low temperature synthesis of titanium nitride thin films by APCVD is described. TiN coatings containing less than one atom percent of carbon and oxygen were deposited at 200 °C on silicon, vitreous carbon, glass, stainless steel and plastic substrates using Ti(Nme2)4 and ammonia gas as precursors. The films were characterized by Rutherford backscattering spectrometry and X-ray photoelectron spectroscopy.
The Effect of Metal Impregnation on the Microstructure of Porous Vycor Glass
Authors: Sunil D. , Sokolov J. , Rafailovich M. H. , Mendoza E. , Wolkow E. , Gafney H. D.
Published: March 2011

It has recently been demonstrated that highly resolved images can be produced by photochemical deposition of metal oxides in porous Vycor glass. This process has potential applications to the development of integrated optics in glass since it enables one to deposit in the same material refractive index patterns of optically and electro-magnetically active adsorbates. In order to learn in more detail about the interaction of the metal oxides with the glass, we impregnated porous Vycor glass (PVC) with tin or iron oxides and analyzed the samples with electron microscopy, x-ray microprobe analysis, and small angle x-ray scattering (SAXS). The results indicate that even though both oxides produce images of comparable resolution (approx 1μ), the interaction with the glass surface and particulate distribution is different for the two oxides. In particular, the Sn oxide appears to chemically modify the glass surface and prevents its consolidation.
Calculation of Transport-Shifted CVD Phase Diagrams
Authors: Rosner Daniel E. , Collins Joshua
Published: March 2011

A non-iterative method is presented for constructing CVD phase diagrams which include the systematic effects of chemical element segregation in mass-transfer controlled flow reactors. Element segregation is shown to substantially shift predicted deposit phase boundaries when the vapor/deposit interface equilibrium is calculated using the local element fractions instead of the feed gas elemental composition, as is usually done. The mass transfer analysis developed here accounts for both Fick and Soret multicomponent diffusion acting across a non-isothermal boundary layer. The gas phase is assumed to be chemically frozen, with local thermochemical equilibrium imposed only at the vapor/deposit interface (as in a cold wall reactor with a hot substrate). As a specific example, this model is applied to the chemical vapor deposition of titanium diboride from TiCl4(g), BC13(g) and H2(g) in an Ar(g) carrier gas for ceramic composite material applications. These calculations, which account for boron and titanium transport via 17 chemical species, are illustrated for a long cylindrical reactor with a resistively heated coaxial fiber deposition substrate and coaxial annular flow. However, the method presented here is general in that both the chemical system and CVD reactor geometry can be changed to any other system of interest, provided: i) adequate themochemical and thermophysical data are available, ii) the deposition rate is vapor transport controlled, and iii) convective-diffusion heat and mass transfer coefficients are estimable.
Light-Scattering Measurements of CVD Silicon Carbide
Authors: Sheldon B. W. , Besmann T. M.
Published: March 2011

Surface morphologies created by the chemical vapor deposition (CVD) of silicon carbide were examined with light scattering. Silicon carbide was deposited from methyltrichlorosilane under various conditions to create different surfaces. A helium neon laser was used, and the scattered light was measured over a range of scattering angles. These measurements are compared with scanning electron microscopy (SEM) observations and profilometer measurements of the same surfaces. In theory the scattered light contains all of the information needed to provide a statistical description of a given surface; however, a complete vector theory for the scattering phenomena is too complex to provide any simple basis for experimental analysis. The application and limits of existing descriptions of scattering from a rough surface are discussed.
Raman Measurements of Epitaxial YBa2Cu3O7–δ Films
Authors: Burns G. , Dacol F. H. , Feild C. A. , Gupta A. , Holtzberg F. , Koren G. , Laibowitz R. , McGuire T. R. , Segmuller A. P. , Worthington T. K.
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.
Magnetic and 119-Sn Mössbauer Effect Study of Sn-Doped Pb2Sr2Eu.5Cu3-xSnxO8+z (x = 0.0, 0.1) Superconductors
Authors: Vaishnava P. P. , Nelson C. D. , Pratt W. P.
Published: March 2011

X-ray diffraction, magnetic susceptibility and 119-Sn Mössbauer effect measurements have been performed on Pb2Sr2Eu.5Cu3-xSnx08+z (x = 0.0, 0.1) superconductors. The x-ray diffraction pattern indicated that the samples are single phase materials. The diamagnetic shielding and the Meissner fraction increase with the introduction of Sn in the lattice. The 119-Sn Mössbauer effect measurements have been used to determine the site symmetry and valence state of Sn atom in the superconductor.
Superconductivity and Stoichiometry in Tl2Ca2Ba2Cu3Ox Single Crystals
Authors: Venturini E. L. , Tigges C. P. , Baughman R. J. , Ginley D. S. , Morosin B.
Published: March 2011

Magnetization and resistivity data are presented which show a substantial difference in superconducting transitions for nominal Tl2Ca2Ba2Cu3Ox plates with identical crystal structures grown from two different “melt” compositions. A Tl-O and CuO-rich flux yielded approximately stoichiometric plates which have sharp transitions beginning near 111 K, while a second Tl-O-rich flux produced plates containing more Tl and less Ba with very broad transitions starting near 96 K. These data demonstrate the extreme sensitivity of superconductivity to cation site disorder in the Tl-Ca-Ba-Cu-O system.
Magnetic Properties of Pb2Sr2Eu1-xCaxCu308+z Superconductors
Authors: Nelson C.D. , Pratt W.P. , Vaishnava P.P.
Published: March 2011

X-ray diffraction and magnetic measurements using a SQUID magnetometer have been performed on the title compounds for 0 ≤ x ≤ 0.9. For 0 ≤ x ≤ 0.5, we have single phase materials. However, a small percentage of an impurity phase is noticed in the x = 0.7 sample, and the x = 0.9 sample is clearly not a single phase material. The transition temperature, the diamagnetic-shielding effect, and the Meissner-effect increase as x becomes larger. We have obtained, approximately, Hc1 ≤ 700 oe and Hc2 ≥ 800 k0e.
Certain Novel Aspects of Thallium and Bismuth Cuprate Superconductors
Authors: Rao C. N. R.
Published: March 2011

Novel superconducting thallium cuprates of the type T1Ca1‐X LnX Sr2 Cu2O6+δ (Ln = Y or rare earth), T1Srn+1‐x Lnx Cun OY and Tl1‐x PbX Srn+1Cun08+δ are described. These cuprates as well as Bi2Ca1‐x Lnx Sr2Cu2O8+δ and TICa1‐xYxBa2 Cu2 O6+δ . show maximum T around a specific composition or oxygen content. They also show interesting changes in the sign and magnitude of the thermopower with the composition. Specially noteworthy is the negative slope of the thermopower‐temperature plots. The thermopower behaviour in these two‐band systems can be understood in terms of entropie and quasiparticle contributions. It appears that Tl1‐x Pbx CaSr2Cu2O6+δ is a genuine high T electron superconductor.
Ibad Diffusion Barriers Between YBaCuO and Si
Authors: Greenwald Anton , Hirvonen James , Jaggi Narendra , Allen John
Published: March 2011

Different materials were investigated for use as diffusion barriers between silicon and yttrium barium copper oxide (YBCO). Ion beam assisted deposition (IBAD) of 300nm zirconia films at room temperature prevented interdiffusion at sintering temperatures over 800°C. Similar MgO and indium-tin oxide films did not prevent degradation at elevated temperatures. All films deposited on top of YBCO reduced the effects of extended atmospheric exposure.
The Influence of Tte Substrate Surface on the Nucleation and Growth of Superconducting Thin Films
Authors: Basu S. N. , Bordes N. , Rollett A. , Cohen M. , Nastasi M.
Published: March 2011

The quality of epitaxially grown superconducting thin films is dependent on the nature of the substrate surface. In this study, the surface of <100> oriented SrTiO3 single crystals was modified by mechanical polishing, thermal annealing and chemical etching. A study of the YBa2Cu3O7-x thin films grown on these substrates showed that high quality superconducting films were obtained when the substrate surface was highly oriented in the <100> direction and was also microscopically smooth.
Electric-field modulation of a Bi-Sr-Ca-Cu-O film with a polymer film as an insulator
Authors: Morohashi Shin'ichi , Suzuki Hideo , Gotoh Kohtaroh , Fujimaki Norio , Hasuo Shinya
Published: March 2011

We fabricated the multi layered structure with Au gate electrode/polymer film/Bi-Sr-Ca-Cu-O film to study the electric-field control of high Tc superconductor. A Bi-Sr-Ca-Cu-O(BSCCO) film was fabricated using an ion beam sputtering technique. The plasma polymerization using trif luoroethane gas was used to make the gate insulator. The patterning of the BSCCO film was carried out using an ion beam etching technique. The supercurrent of the structure decreased when the gate voltage was applied to the gate electrode.