bluuebunny/crossref_metadata_2025 huggingface dataset:
Step-Controlled Epitaxial Growth of SiC
Authors: Matsunani Hiroyuki , Ueda Tetsuzo , Nishino Hironori
Published: March 2011

Vapor phase epitaxial(VPE) growth of SIC on 6H-SiC substrates has been carried out at 1500°C or below. On well-oriented (0001)Si faces, twin crystalline 3C-SiC with double positioning boundaries was grown, whereas on off-oriented (0001)Si faces, single crystalline 6H-SiC was grown with a very smooth surface. This temperature is more than 300°C lower in comparison with that for 6H-SiC VPE growth reported previously. By the introduction of offorientation, the density of surface steps is increased. Crystal growth occurs through lateral growth from the steps. The surface morphology of grown layers on off-oriented substrates, however, varied with the offdirection and the polarity of substrates. Grown layers are characterized by etch-pits observation, photoluminescence(PL) measurements and reflection high energy electron diffraction. On the basis of these experimental results, the growth mechanism on (0001)Si and (0001)C faces of 6H-SiC is discussed. P-type doping is tried, and electrical and PL properties are examined. Pn junction fabrication is also studied.
Growth of 6H-SiC on CVD-Grown 3C-SiC Substrates
Authors: Yoo Woo Sik , Matsunami Hiroyuki
Published: March 2011

Polytype control and crystal growth on 3C-SIC substrates have been investigated by using a sublimation growth technique. Single crystalline 3C-SiC(100) films (∼10μm thick) grown on Si (100) were used as substrates after removing Si by etching with a HF+HNO3 mixture. Polytypes of crystals grown on 3C-SiC(100) were examined by photoluminescence, Raman scattering, X-ray diffraction and reflection high energy electron diffraction analyses. Polytypes of grown crystals change from cubic 3C-modification to hexagonal 6H-modification with temperature increase. 6H-SiC(0114) was grown on 3C-SiC(100) substrates at high temperatures. For the first time, polytypes of grown crystals were controlled to be 3C- and 6H-modifications, and the reproducibility of polytype control was confirmed through many growth runs. 6H-SiC ingots up to 20mm in diameter and 10mm in length were grown on 3C-SiC for 6 hours. The growth mechanism of 6H-SiC on 3C-SiC was discussed based on experimental study of thermal stability of 3C-SIC. Electrical properties of 6H-SiC ingots were investigated.
Epitaxial Thin Film Growth and Device Development in Monocrystalline Alpha and Beta Silicon Carbide
Authors: Davis Robert F. , Palmour J. W. , Edmond J. A.
Published: March 2011

High purity monocrystalline β-SiC films have been chemically vapor deposited on Si (100) and α-SiC (0001) by numerous groups around the world using SiH4 and C3H8 or C2H4 carried in H2. Films grown on nominal Si (100) contain substantial concentrations of dislocations, stacking faults and inversion domain boundaries; those deposited on α-SiC (0001) contain primarily double positioning boundaries. Both types of boundaries may be eliminated by using off-axis orientations of the respective substrates. However, the films grown on off-axis a substrates were the a(6H) polytype. Schottky diode, p-n junction, MESFET, MOSFET and HBT devices have been fabricated with encouraging results for future commercial applications. The barrier heights and ideality factors of Au Schottky diodes on β-SiC ranged from 0.9—1.15 eV and 1.2—1.6, respectively. However, the reverse leakage currents were much lower and the breakdown voltages considerably higher at all temperatures for the diodes on the α-SiC films. MESFETs fabricated using the diodes in the alpha films were superior to those in beta with the transconductance being more than 15 times greater in the former. Enhancement-and depletion-mode MOSFETs exhibited better behavior in terms of saturation, drain voltage and high temperature operation. All films produced on a-SiC substrates were superior to those produced in beta films grown on Si.
Perspective On Gallium Nitride
Authors: Pankove Jacques I.
Published: March 2011

This paper is a historical review (mostly personal) of some major developments in this wide, direct gap material. It includes key technologies of synthesis, electrical and optical properties and many applications.
Cubic Boron Nitride as a New Semiconductor for Optoelectronics: Luminescence Properties and Potentialities
Authors: Era Koh , Mishima Osamu
Published: March 2011

In cubic boron nitride made by high pressure and high temperature technique in our institute, we have found three luminescence bands in the ultraviolet and the short visible region at room temperature by cathode-ray excitation. They are: a band having vibrational structure and ascribable to undoped state of the crystal, a band ascribable to p-type doping and a band ascribable to n-type doping. Discussion is made on differences between the injection luminescence and the cathodoluminescence. Potentialities and difficulties in realizing the potentialities of cBN for optoelectronic applications are discussed.
Boron Phosphide on Silicon for Radiation Detectors
Authors: Lund J. C. , Olschner F. , Ahmed F. , Shah K. S.
Published: March 2011

We report on radiation detectors fabricated from boron phosphide (BP) layers. These devices were fabricated by growing 1 to 10 μm thick layers of BP by chemical vapor deposition (CVD) on (100) oriented n-type silicon substrates. Ohmic contacts were applied to the Si (Au-Sb). Schottky barrier contacts (also Au-Sb) were applied to the BP layer. The devices were tested as radiation detectors and were found to be capable of detecting individual 5.5 MeV alpha particles. With some improvements we hope to fabricate neutron detectors from these devices, making use of the very high cross-section of boron for thermal neutrons.
Synthesis of Metastable Diamond
Authors: Anthony Thomas R.
Published: March 2011

Diamond can be grown as an equilibrium phase from a liquid metal solution containing carbon at high pressures and high temperatures. Diamond can also be grown as a metastable phase at subatmospheric pressures and moderate temperatures from hydrocarbon gases in the presence of atomic hydrogen. Atomic hydrogen serves several critical roles in CVD diamond growth, namely: 1) stabilization of the diamond surface, 2) reduction of the size of the critical nucleus, 3) “dissolution” of carbon in the gas, 4) production of carbon solubility minimum, 5) generation of condensable carbon radicals in the gas, 6) abstraction of hydrogen from hydrocarbons attached to surface, 7) production of vacant surface sites, 8) etching of graphite, 9) suppression of polycycic aromatic hydrocarbons. A search for substitutes for atomic hydrogen have been unsuccessful to date but several new processes that do not use atomic hydrogen are currently under study.
Thermodynamics and the CVD of Diamond
Authors: Yarbrough Walter A.
Published: March 2011

Bulk diamond is unstable relative to bulk graphite except at high pressure and temperature. In spite of this, well crystallized diamond has been grown using numerous CVD methods, most of which have in common the production of atomic hydrogen and hydrocarbon radicals in regimes where solid carbon is expected to be a stable product. Two fundamentally different points of view have emerged in the effort to explain why well crystallized diamond, and not g”reatcphheitde” obry v aittroemouics hcyadrbroogne, nis aot bas erarvtee dh iignh tehre sthea enx dpiearmimoenndt sa. nTd hhee fnicrset dairagmueosn dth iast gkrinapethiictael liys stable with respect to graphite. If diamond formation is kinetically controlled the deposition mechanism is critical and much debate has centered on the mechanism and species involved. Alternatively it is argued that at the growth interface, diamond surfaces are stabilized by termination with hydrogen. If this is correct, and bulk reorganization ignored, then it is shown that a global understanding of the parameters important to the growth of diamond can be obtained without detailed kinetic analyses. Thus it is argued that single crystal diamond films of arbitrarily high purity and perfection are theoretically possible by CVD in spite of the bulk instability of diamond. It is also suggested that general principles exist which might be applied to the growth of other well crystallized metastable phases - notably cubic boron nitride.
Studies of Diamond Growth Mechanisms in a Hot Filament Reactor
Authors: Chu C. Judith , Bai Benjamin J. , D'Evelyn Mark P. , Hauge Robert H. , Margrave John L.
Published: March 2011

The incorporation of methane into low-pressure CVD diamond thin films has been compared to that of acetylene. 13CH4 and 12C2 H2 were used as the hydrocarbon sources in a heated-filament CVD diamond growth process at a total concentration of 0.5% hydrocarbon in 99.5% hydrogen. Results indicated that methane and/or methyl radical is the dominant carbon source for diamond growth in a hot filament reactor under steady state conditions and that acetylene is rapidly hydrogenated to methane. Results also indicated that diamond surface reactions play an important role in determining the relative methane to acetylene ratios.
Adsorption of Hydrocarbon Radicals on the Hydrogenated Diamond Surface
Authors: Pederson Mark R. , Jackson Koblar A. , Pickett Warren E.
Published: March 2011

In order to gain insight into diamond growth, we have calculated equilibrium geometries for several adsorbates on the hydrogenated diamond <111> surface. While the adsorption height of a single methane radical onto a dangling bond is found to be in excellent agreement with the bulk-diamond bond length, the back bonded hydrogens of adjacent adsorbed methyl radicals repel one another. In contrast, adjacent acetlyinic radicals do not repel one another but lead to the introduction of double carbon bonds, misplaced carbon atoms above the active layer and a bond length which is too short in comparison to that of bulk diamond. Our calculations on the acetylene molecule near a dangling bond indicate that the resulting adsorbate bond length is substantially too large and that the carbon atom is unlikely to be stable directly above the surface carbon atom. Of the adsorbates studied, geometrical arguments suggest that the methyl radical is likely to be the most ideal adsorbate.
Optical Properties of II-VI Semiconductor Doped Glass
Authors: Persans P. D. , Tu An , Lewis M. , Driscoll T. , Redwing R.
Published: March 2011

We review structural and optical properties of CdSxSe1−x semiconductor nanoparticles embedded in an insulating glass matrix. Vibrational Raman scattering and x-ray diffraction can be used to determine the composition of the crystallites for all X and sizes. Debye-Scherrer broadening of x-ray diffraction peaks from the crystallites yields an average grain size in the semiconductor crystallites of 60Å for the series studied here. Small angle x-ray scattering reveals that the average particle diameter is close to 120Å. Optical absorption, photoluminescence, and photomodulated absorption spectra are interpreted within a spherical quantum well model. Electron-phonon coupling and size distribution effects on the spectra are also discussed.
Opto-Electronic Properties of μc-Si Grown from SiF4 and H2 by PECVD
Authors: Okada Y. , Campbell I. H. , Fauchet P. M. , Wagner S.
Published: March 2011

Microcrystalline Si was grown from SiF4 and H2 by plasma-enhanced chemical vapor deposition. The films are almost completely crystalline with a crystallite size (determined from Raman spectra) of about 60 Å. The optical absorption and the electrical conductivity of these films were studied. With increasing hydrogen content in the films, the dark conductivity decreases strongly and the activation of the conductivity increases. We explain the conductivity qualitatively in terms of a grain boundary model.
The Role of Hydrogen in Silicon Microcrystallization
Authors: Wagner S. , Wolff S.H. , Gibson J.M.
Published: March 2011

We report and interpret two groups of experiments on the role that hydrogen plays in the formation of silicon microcrystals. We show that the growth of singlecrystal Si by molecular beam epitaxy at 475°C is disrupted by H2, which induces the formation of microcrystals. In crystallization experiments of non-hydrogenated a-Si and of hydrogenated a-Si:H on a hot stage in a transmission electron microscope, hydrogen facilitates the nucleation of crystallites. We explain our observations with a substantial reduction of the grain boundary energy by hydrogen.
Effects of Hydrogen Atoms on Passivation and Growth of Microcrystalline Si
Authors: Ito Toshimichi , Yasumatsu Tatsuro , Watabe Hirokuni , Iwami Motohiro , Hiraki Akio
Published: March 2011

Effects of hydrogen atoms bonded to silicon atoms on microcrystalline surfaces in a μc-Si:H and anodized porous silicon have been investigated using infrared spectroscopic technique and a semi-empirical molecular-orbital calculation (AM1 method). Experimental results on thermal stability of the Si-H bonds and oxidation of H-covered Si can be explained consistently in terms of system total energies and heats of formation of various clusters constructed by 13–18 Si and 18–24 H atoms (with an additional 0 atom). Possible role of H on the growth of μ c-Si:H is discussed in relation to stable Si-H bonds.
A Discussion of Electronic Optical Absorption Spectra of Nanocrystalline Silicon thin Films
Authors: Bustarret Etienne , Hachicha M.A.
Published: March 2011

Both fully crystallized nanocrystalline as-deposited silicon layers with an average grain size ranging between 6 and 80 nm and mixed-phase hydrogenated doped and undoped silicon films are studied at room temperature by Photothermal Deflection Spectroscopy (PDS), Transmission Spectroscopy and Spectroscopic Ellipsometry. The differences with regard to similar data obtained on monocrystalline and hydrogenated amorphous silicon are discussed, with an emphasis on the low-energy part of the 0.6-5.6 eV explored range.
Critical Review of Raman Spectroscopy as a Diagnostic Tool for Semiconductor Microcrystals
Authors: Fauchet P.M , Campbell I.H.
Published: March 2011

Raman scattering is becoming a widely used tool for the characterization of semiconductor microcrystals due to its sensitivity to crystal sizes below a few hundred angstroms. Through detailed analysis of the first order Raman spectrum it is possible to determine the size and shape of microcrystalline grains. First order spectra must be examined with care however, since they are sensitive to other factors including: stress/strain, surface vibrations, mixed amorphous/microcrystalline phases and intragrain defects. Second order Raman spectra are more sensitive to microcrystalline effects than first order spectra. They offer the potential to measure crystal sizes greater than a few hundred angstroms but much work remains to be done to quantify the size dependence of the second order spectra.
Optoelectronics and Photovoltaic Applications of Microcrystalline Sic
Authors: Hamakawa Y. , Matsumoto Y. , Hirata G. , Okamoto H.
Published: March 2011

A review is given of the electrical and optical properties of hydrogenated microcrystalline silicon carbide (μc-SiC:H) films prepared by ECR (Electron Cyclotron Resonance) plasma chemical vapor deposition. The material produced with the ECR plasma technology has a very wide energy gap from 2 to 2.8 eV with good valency electron controllability, e.g., a dark conductivity as high as 10 Scmg− which is more than seven orders of magnitude larger than that of amorphous SiC:H.

Employing this material as a wide gap heterojunction window, 15.4% and 12.0% conversion efficiencies have been achieved with the structures of ITO/p type μc-SiC:H/n type poly-Si and p type vc-SiC:H/i type a-Si:H/n type Pc-Si:H heterojunction solar cells, respectively. The successful development of a visible light thin film light emitting diode show the promise of microcrystalline materials for optoelectronic applications.
Dopant Segregation at Polycrystalline Silicon Grain Boundaries in Device Fabrication Processes
Authors: Itoh M. , Aikawa I. , Hirashita N. , Ajioka T.
Published: March 2011

The dopant segregation at the polycrystalline silicon grain boundaries in device fabrication processes has been studied with a new approach using spreading resistance(SR) measurement, SIMS and cross-sectional TEM(XTEM). Phosphorus implanted LPCVD poly-Si films were annealed at 900°C-1000°C in N2 for 30min. Electrically active dopant concentrations obtained from SR measurements are constant in depth within the poly-Si films. On the other hand, the phosphorus concentration measured by SIMS is found to increase with increasing depth and to have linear relationships to reciprocal grain sizes observed by XTEM for all poly-Si films. The linear relationship indicates that the number of segregated phosphorus atoms per unit grain surface area at the grain boundaries is uniform throughout poly-Si films. Both phosphorus concentrations in the grains and at the grain boundaries are evaluated. The heat of segregation of 1.7eV is obtained from the annealing temperature dependence of the segregation ratio. Our results indicate that carrier concentration in the poly-Si film is more sensitive to annealing temperature in device fabrication processes. The carries concentration is determined by kinetics rather than by equilibrium segregation of dopants.
Correlations Between Optical, Electrical, and Structural Properties of In-Situ Phosphorus-Doped Hydrogenated Microcrystalline Silicon - Effects of Rapid Thermal Annealing on Material Properties
Authors: Kotecki David E. , Jeng Shwu J. , Kanicki Jerzy , Parks Christopher C. , Rausch Werner , Seshan Krishna , Tien Jean
Published: March 2011

Films of in-situ phosphorus-doped hydrogenated microcrystalline silicon (n--μc-Si:H) were deposited by plasma enhanced chemical vapor deposition (PECVD) on Si(100) and fused quartz substrates over a range of substrate temperatures (100 - 500°C) and reactant gas dilutions (I - 100% of 1% PH3/SiH4 in H2) while maintaining a constant RF power density (0.1 W-cm−2) and total gas pressure (1 Torr). Some of the films were subjected to a rapid thermal anneal (RTA) at temperatures between 600- 1000°C for a duration of 10 seconds. The μ-Mc-Si:H films were characterized, before and after RTA, in terms of their microstructure, optical band-gap, electrical conductivity, and hydrogen and phosphorus content. The deposition rate was determined to be insensitive to substrate temperature and to decrease with increasing H2 gas dilution indicating that deposition kinetics are dominated by plasma chemistry and are not thermally activated. For pre-annealed films, cross-sectional TEM confirmed the presence of a mixed phase material at all deposition temperatures with gas dilutions ≤10%. The surfaces of thick films (>0.15 μm) were rough, giving them a hazy appearance, while thin μic-Si:H films (<0.15 μm) were smooth and mirror-like. The rough surfaces were correlated with voids and microcracks in the μuc-Si:H films observed by TEM. The optical band-gap of all pre-annealed films was 11.8eV and the electrical conductivity varied between 1 and 20 (Δ-cm)−l. The H content was found to be independent of gas dilution but decreased with increasing substrate temperature; the P content depended on both the gas dilution and substrate temperature, decreasing at high deposition temperatures. RTA was observed to significantly alter film morphology and microstructure, increase electrical conductivity, and decrease the optical band-gap.
Crystal-Axis-Rotation of Laser-Recrystallized Silicon on Insulator
Authors: Sugahara K. , Ippóshi T. , Inoue Y. , Nishimura T. , Akasaka Y.
Published: March 2011

The relation between the seed pitch and defect density of the laserrecrystallized SOI film was investigated. It was found that the defect density of the SOI increases as the seed pitch increases. The dependences of the laser scan speed and laser power on rotation angle of the SOI film were experimentally and numerically investigated. The crystal-axisrotation of the SOI film was considered to be due to the difference of the temperature between the top and bottom surface of the SOI film near the liquid-solid interface. A polysilicon heat sink structure with high thermal conductivity was newly proposed and was found to reduce the rotation in a small angle.
Electrical Properties of Sipos Films Deposited on Crystalline Silicon
Authors: Chuang Tien-Min , Rose Kenneth , Gutmann Ronald J.
Published: March 2011

Transport and trapping effects on undoped and phosphorus-doped SIPOS films on n-type and p-type Si have been characterized by C-V-ω, I-V, DLTS and photo-induced microwave reflection techniques. Our C-V and DLTS data on undoped SIPOS indicate that interface traps with a density of 2 × 1012cm−2 eV−1 and a response time between 1 and 10 μsec exist near the midgap of the SIPOS. Photo-induced microwave reflection transient-waveforms show an order of magnitude increase in photoconductivity decay time with doped SIPOS films. Our data shows that trapping effects exist in doped SIPOS and that these traps could reduce the cutoff frequency of SIPOS emitter transistors.
Chemistry and Solid State Physics of Microcrystalline Silicon
Authors: Vepřek Stan
Published: March 2011

Various methods for the preparation of microcrystalline (nanocrystalline) silicon are summarized and compared with respect to the possibility of the control of the materials quality and scaling of the deposition process to large area applications. It is shown that the deposition of a pure microcrystalline material is achieved under conditions close to partial chemical equilibrium. The mechanism of the crystallization during the growth will be briefly discussed.

The second part of the paper deals with the physical properties of pure microcrystalline silicon which is free of any amorphous phase detectable by X-ray diffraction, i.e. less than about 1 vol%. Several aspects of electric conductivity, optical absorption and Raman scattering which have been frequently misinterpreted in the literature will be reviewed.
Electrodeposition of 3-D Size-Quantized Cds and CdSe Films
Authors: Hodes G. , Engelhard T. , Albu-Yaron A. , Pettford-Long A.
Published: March 2011

CdS and CdSe films electrodeposited from chalcogen-containing non-aqueous electrolytes are shown to possess a nanocrystalline structure and exhibit 3-D quantum size effects. A large variation in optical transmission spectra, due for the most part to this sizequantization, is shown. Photoelectrochemical activity of the as-deposited films is discussed in terms of their nano-structure. Extension of the crystallite size effects to a metalinsulator transition in MoO2 deposited from a similar electrolyte is mentioned.
A Study of the Pressure-Induced Phase Transition in Bulk and Nanocrystalline Cadmium Sulfide
Authors: Zhao Xue-Shu , Schroeder John , Persans Peter D. , Lu Enlian
Published: March 2011

We have used Resonant Raman scattering induced by pressure tuning to study the phase transition and electronic states of bulk and 60±20 Å colloidal microcrystallite CdS. The experimental results show that bulk CdS undergoes a well-defined first order phase transition at 27 kbar and that the intensity of the Raman scattering increases sharply when the level of the intermediate state (bound exciton I2) is close to the photon energy. After the phase transition no Raman scattering and photoluminescence can be observed. However, the phase transition in the colloidal CdS is quite different from the bulk CdS and the complete phase transition occurs above 60 kbar. Both bulk and colloidal CdS reverse to the original wurtzite phase after releasing the pressure.
RF Power Dependence of the Material Properties of PECVD Silicon Dioxide
Authors: Chapple-Sokol J. D. , Tiemey E. , Batey J.
Published: March 2011

Silicon dioxide films deposited from the PECVD reaction of silane and nitrous oxide in the presence of helium were studied to determine the effects of RF power on the deposition process. Increased RF power density yielded oxides which were structurally and chemically more homogeneous. The combination of elevated power density with increased silane concentration resulted in the deposition of films of high electrical and physical integrity at high deposition rates.
High Rate Deposition of Hydrogenated Amorphous Silicon Films by ECR Plasma CVD
Authors: Ozaki S. , Akahori T. , Tani T. , Nakayama S.
Published: March 2011

A new electron cyclotron resonance (ECR) plasma CVD system has been developed in order to obtain high deposition rates. By using this system, hydrogenated amorphous silicon (a-Si:H) films have been prepared at a deposition rate of 1.0. μ m/min. The utilization efficiency of SiH4 gas is 16% under such conditions. Films prepared at 1.0 μ m/min have high photoconductivity (σ ph) of 10-6 S/cm and low dark conductivity (σ d) of 10-12 S/cm, leading to a high photosensitivity of σ ph/σ d=106. Both high microwave power and high SiH4 gas flow rates are essential to the high rate deposition of sufficiently photosensitive a-Si:H films. Annealing at 300° C improves the photosensitivity up to σ ph/σ d=107.
Formation of Multilayer SiO2- SiOx Heterostructures by Control of Reaction Pathways in Remote PECVD
Authors: Tsu D. V. , Kim S. S. , Theil J. A. , Wang Cheng , Lucovsky G.
Published: March 2011

We have deposited thin films of silicon dioxide, SiO2, and amorphous silicon, a- Si, by remote Plasma-Enhanced Chemical-Vapor Deposition (Remote PECVD), and have extended this process to the deposition of silicon suboxides, SiOx, 0<x<2. Heterostructures, comprised of alternating layers of SiO 2, and SiOx, x∼1, have been deposited by electronically controlling the flow of charged particles from the plasmageneration region into the deposition chamber, without interrupting the flow of process gases. We discuss the electrical properties of these heterojunction structures.
Low Temperature Cleaning of Ge and GaAs Surfaces Using Hydrogen Dissociated with a Remote Noble-Gas Discharge
Authors: Hatitangady S. V , Rudder R. A. , Mantini M. J. , Fountain G. G. , Posthill J. B. , Markunas R. J.
Published: March 2011

The native oxides of Ge and GaAs have long been known to preclude the formation of suitable MIS structures. In situ cleaning of Ge and GaAs surfaces has been achieved at 300–375 °C using a novel technique employing hydrogen that is dissociated using a remote Ar discharge. Such a technique circumvents the problems of cross contamination introduced from a directly excited hydrogen discharge due to erosion of the quartz tube walls by the active hydrogen. Reconstructed surfaces characteristic of clean Ge and GaAs surfaces have been observed with Reflection High Energy Electron Diffraction (RHEED) following such a treatment. Auger and X-ray Photoelectron Spectroscopy (XPS) analyses show that such a treatment removes both oxygen and carbon contamination from the surface. XPS window scans on the Ga-3d and the As-3d peaks show that the treatment is successful in removing oxygen bonded to both Ga and As on the GaAs surface.

Following the in situ cleaning, excellent MIS structures on Ge and GaAs have been realized with a novel structure that utilizes an ultra-thin Si interlayer (1.5 nm) between the insulator-oxide and the clean semicondutor surface. The Si interlayer prevents any sub-cutaneous oxidation of the underlying semiconductor while exploiting the advantages of the excellent Si-SiO2 interface. The entire structure is fabricated in a single-chamber remote plasma CVD unit.
Structure and Morphology of Vitreous Chalcogenide Thin Films Obtained by Plasma-Enhanced CVD
Authors: Ribes Michel , Cros Bernard , Peytavin Serge , Camon Henri , Balladore Jean-Louis
Published: March 2011

Thin films of chalcogenide glasses GeSeywere prepared by PECVD for lithographic applications. Their structure and morphology were characterized by EXAFS and electron microscopy. EXAFS studies enabled comparison of the structures of thin films and those of homologous bulk glasses. Morphology studies by SEM and TEM revealed an heterogeneous structure explained by a phase separation: these glasses consist of microdomains whose size varies with the overall GeSey composition.
Direct Kinetic Studies of Silicon Hydride Radicals
Authors: Jasinski Joseph M.
Published: March 2011

Laser-based techniques have been developed to directly study the kinetics of the reactions of the mono-silicon hydride radicals SiH, SiH2 and SiH3. A summary of rate constants obtained from these studies is presented along with a discussion of the implications of these results for present mechanistic models of the PECVD of amorphous hydrogenated silicon from silane.
Interdiffusion of Cadmium Arachidate in Langmuir-Blodgett Films
Authors: Stroeve Pieter , Rabolt John F. , Hilleke Russ O. , Felcher Gian P. , Chen Sow-Hsin
Published: March 2011

The interdiffusion of Cadmium Arachidate (CdA) in Langmuir-Blodgett films has been studied by neutron reflection at the Intense Pulsed Neutron Source of Argonne National Laboratory. One of the samples consisted of a few layers of perhydro H-CdA deposited on a silicon support, overlayered with a few layers of deuterated D-CdA, for a total thickness of ∼300 Angstroms. In a second sample the layers of perhydro-and deuterated- CdA were separated by two monolayers of Hn-octadecene/co-maleic acid copolymer. When heated for 15 minutes at 70°C, well below the disorder temperature [1], approximately 25% of the D-CdA molecules were replaced by H-CdA molecules, although the overall Langmuir-Blodgett film structure is known to remain unchanged [1]. The presence of copolymer layers limited the interdiffusion process to about 5%.
Neutron Diffraction Studies of Cd1−xMnxSe Epilayers and ZnSe/MnSe Multilayers
Authors: Giebultowicz T. M. , Klosowski P. , Rhyne J. J. , Samarth N. , Luo H. , Furdyna J.K.
Published: March 2011

Neutron diffraction patterns of MBE-grown single crystal zinc-blende epilayers of Cd1−xMnxSe with x=0.70 and 0.75 reveal the onset of long-range Type-III AF ordering at low T, in sharp contrast with earlier studies of bulk II-VI diluted magnetic semiconductors, where only short-range Type III correlations are observed. Results of first neutron diffraction studies of magnetic ordering in MBE-grown ZnSe/MnSe superlattices are also reported.
Local Environmental Effects in Magnetic Alloys and Multilayers: Calculations of the Static Response Functions
Authors: Johnson D. D. , Staunton J. B. , Györffy B. L. , Pinski F. J. , Stocks G. M.
Published: March 2011

We have developed an ab-initio method for calculating the static response functions in substitutional alloys. For magnetic alloys, in addition to the nuclear diffuse scattering, a contribution to the alloy diffuse scattering intensities results from the response of the local moments to changes in the ‘local’ chemical environment (i.e. ∂μi/∂cj). We present results of firstprinciples calculations of these ‘local’ response functions in magnetic alloys. These response functions, which may be directly compared to neutron-scattering and Mößbauer experiments, are derived via a mean-field statistical mechanical description of compositional fluctuations in alloys. The statistical averages are performed via the Korringa-Kohn-Rostoker coherent potential approximation, which incorporates the electronic structure of the high-temperature, chemically disordered state. As a first application of the theory, we have investigated the environmental dependence of the moments in NiFe alloys and FeV alloys and multilayers. We compare our results with experiments on bulk alloys and multilayers. Also, a comparison is made to a set of first-principle ‘supercell’ calculations. Although preliminary, the results demonstrate the utility of these response functions for investigating the effects of changes in the chemical environment on the alloy moments and for aiding experimental interpretation in other multilayer systems that are less experimentally amenable than FeV.
Determination of Hydrogen(Deuterium) Density Profiles in Thin Metal Films and Multilayers by Neutron Reflection
Authors: Majkrzak C. F. , Satija S. , Neumann O. A. , Rush J. J. , Lashmore D. , Johnson C. , Bradshaw J. , Passell L. , Dinardo R.
Published: March 2011

The density of hydrogen in thin films or multilayers of metal hydrides can be inferred from an expansion of the host lattice as measured by conventional x-ray diffraction techniques. However, because hydrogen and deuterium have scattering lengths for neutrons that are comparable to those of most metal nuclei, unlike the corresponding case for x-ray atomic scattering amplitudes, the hydrogen density profile normal to the surface of a flat, thin film can be determined directly from neutron reflectivity measurements. The hydrogen (deuterium) density modulation in an artificial superlattice along the growth direction can also be determined in this manner. The thin film or multilayer host metal material need not even be crystalline. Furthermore, because relatively large, flat single crystal substrates such as Si or quartz are nearly transparent to neutrons, the substrate can serve as the incident medium and the reflectivities of films or multilayers in contact with liquid solutions can be obtained. Thus, in situ studies employing active electrochemical cells, for example, can be performed. In addition to discussing the sensitivity of the method, the results of some neutron reflectivity experiments on metal multilayers and films, electrolytically loaded in situ with deuterium, are reported in this paper.
Phase Diagrams and Diffuse Neutron Scattering
Authors: Caudron Rene , Sarfati Maurice , Finel Alphonse , Solal Francine
Published: March 2011

The order or segregation properties of compounds or solid solutions are important ingredients of the phase diagrams. If the order can be described as an atomic distribution on an underlying lattice, and if the interactions can be expressed in terms of pairs and other multiplet potentials between the atomic species, phase diagrams should be deducible from these potentials, along with other properties, such as antiphase boundaries, core structures of the dislocations in ordered compounds&; This approach, i.e. the very existence of the potentials, is legitimated by electronic structure calculations for or alloys of normal [1] and transition metals [2]. The G.P.M. (General perturbation Method) allows indeed to develop the order energy in terms of interatomic potentials, the reference state, namely the random alloy, being calculated within the C.P.A. (Coherent Potential Approximation).
Diffuse Neutron Scattering Study of Short-Range Order in Fe0.8Al0.2Alloy
Authors: Sciiweika Werner
Published: March 2011

Diffuse neutron scattering experiments have been performed on a single crystal Fe0.8Al0.2at T-1013K. The data are analysed in terms of short-range order and lattice displacements. Effective pair-interactions have been determined by the inverse Monte Carlo method.Further measurements of the temperature dependence of the diffuse scattering reveal a long-range ordered phase with the B32 structure belowT∼ 650K.This new phase is related to the influence of the magnetism on the chemical ordering in the, iron-aluminum alloys.
Residual Stress Analysis with Neutrons
Authors: Krawitz Aaron D.
Published: March 2011

The use of neutrons for the measurement of stress is complementary to and extends traditional x-ray diffraction methods to new types of problems. This is due to the lower absorption of neutrons compared to x-rays by most engineering materials, which increases the sampling depth from microns to millimeters. It is particularly suitable for triaxial macrostress gradients through the depth of engineering components and volumetric microstresses in composites. In addition, applied stress studies may also be performed. This paper briefly describes the nature of residual stresses, the use of diffraction for stress measurements, experimental aspects of the use of neutrons, and illustrative applications.
Neutron Measurement of Residual Stresses in a Used Railway Rail
Authors: Webster P.J. , Low K.S. , Mills G. , Webster G.A.
Published: March 2011

The high resolution neutron diffraction technique has been applied to determine, non-destructively, the residual stress distribution developed in the head of a railway rail after normal service.

Measurements were made, using the neutron strain scanner at the Institut Laue Langevin, Grenoble, on a transverse slice of rail 12mm thick taken from a section of straight track. The rail head was scanned in the three principal orientations in a series of parallel traverses sufficiently close to enable a two- dimensional matrix of data to be accumulated and vertical, transverse and longitudinal residual stress contours to be drawn.

Substantial residual compressive and tensile stresses and steep stress gradients were observed related to the depth below the top surface, distance from the running line and shape of the rail head. The highest stresses and stress gradients were observed in transverse and vertical directions but significant stresses were also retained in the longitudinal (12mm thick) direction of the rail.

The results demonstrate the effectiveness and unique characteristics of the neutron technique to determine non- destructively and continuously the residual stresses inside engineering components.
TOF Measurements of Pulsed Neutrons for Texture Analysis of Low Symmetry Materials
Authors: Larson Allen C. , Vergamini Phillip J. , Wenk Hans-Rudolf
Published: March 2011

The single crystal diffractometer at LANSCE, SCD, provides an ideal ca- pability for the study of preferred orientation in geological samples by time-of flight(TOF) measurement of pulsed neutrons. The 2-d position sensitive neutron detector with the large wave length range allows one to measure the complete dis- tribution of intensities for several poles very quickly. Each histogram covers about πt2/16 radians of reciprocal space and contains information from all possible poles visible with the wave length range used, usually about 0.5 to 5.OÅ. With this method complete pole figures of many lattice planes can be constructed from only 12 to 20 sample orientations as compared to over 1000 sample settings per lattice plane using conventional diffractometers.

Pole figures from measurements of experimentally deformed standard samples of calcite and quartzite with a known history of deformation provide in- formation about deformation mechanisms and their temperature/strain history. This information can be applied to interpret preferred orientation of naturally de- formed rocks.
Characterization of Sol-Clay Composites by Small-Angle Neutron Scattering
Authors: Moini Ahmad , Pinnavaia Thomas J. , Thiyagarajan P.
Published: March 2011

Silica-clay composites were prepared by reacting a 40 Å silica sol with aqueous clay suspensions. The clays which were studied included Na+-montmorillonite, fluorohectorite, and the synthetic clay Laponite. The aggregation mechanism of the sol particles and the degree of dispersion of the clay layers were monitored by small-angle neutron scattering. The data for powdered silica-montmorillonite products showed the presence of highly dispersed clay platelets and spherical sol particles. The results suggest that the interaction between these two components inhibits the sol aggregation process. Studies on the products prepared from other types of clays, however, showed that this interaction is highly dependent on the morphology and charge density of the clay platelets.
A Sans Study of Capillary Condensation in Porous Media
Authors: Lin M.Y. , Sinha S.K. , Huang J.S. , Abeles B. , Johnson J.W. , Drake J.M. , Glinka C.J.
Published: March 2011

We use small angle neutron scattering (SANS) to study the microstructure of porous Vycor glass and the capillary condensation of fluids in the medium. Using a chord distribution model, we can predict the structure factor measured by SANS. Excellent agreement with the data is obtained. The fitted parameters characterize quantitatively the porous structure before and during the process of condensation, and are in good agreement with isotherm measurements. However, at the latest stages of the process, when all the pores are nearly filled, the model can no longer describe the system.
Real Space Method of Powder Diffraction for Non-Periodic and Nearly Periodic Materials
Authors: Egami T. , Toby B. H. , Dmowski W. , Janot Chr. , Jorgensen J. D.
Published: March 2011

The use of high-energy neutrons from pulsed or hot sources allows the method of atomic pair distribution analysis to be applied to the structural determination of crystalline as well as amorphous solids. This method complements the standard crystallographic methods in studying non-periodic aspects of solids with or without long range order.
Neutron Rietveld Analysis of Anion and Cation Disorder in the Fast-Ion Conducting Pyrochlore System Y2(ZrxTi1−x)2O7
Authors: Haile Sossina M. , Wuensch B. J. , Prince E.
Published: March 2011

All information on the site occupancies and atomic displacements which relate a pyrochlore superstructure to the parent fluorite-type subcell is contained in the normally-weak superstructure diffraction intensities. As Ti has a negative scattering length, the supercell maxima in the present phases are up to three times as intense as the fluorite-like reflections, and neutron diffraction provides an especially sensitive probe of the state of disorder. Y2Ti2O7 is found to have a fullyordered anion array and slight disorder, Y0.984Ti0.015, among the cations. In Y2(Zro.6TiO.4)2O7 the oxygen site normally vacant in pyrochlore is half filled and on the order of 15% exchange between cation sites has occurred.
Gas Phase Characterization in LP CVD Processes by a Performant Raman Equipment: Gas Temperature in the Vicinity of the Substrate
Authors: Gaufres R. , Huguet P. , Boya D. , Lafforet J.
Published: March 2011

Using a performant spontaneous Raman equipment, with intracavity laser excitation, the temperatures of tungsten hexafluoride and hydrogen have been measured in a cell reproducing the industrial conditions of C.V.D. tungsten deposition, in the vicinity of a heated graphite substrate. For tungsten hexafluoride, a vibrational temperature, much lower than that of the substrate, is determined. For hydrogen, rotational temperatures much higher than that of the substrate are found. After a discussion of the sources of experimental errors, possible interpretations of the results are given.
Characterization of Silicide Formation of LPCVD-W By Means of Rutherford Backscatrering Spectrometry and X-Ray Diffractometry
Authors: Zhang S.-L. , Buchta R. , Östling M.
Published: March 2011

Tungsten disilicide (WSi2 ) was formed by annealing 185 nm and 750 nm thick LPCVD-W films deposited on <100>-Si substrates. The thickness of the formed WSi2 was observed by Rutherford backscattering measurements (RBS) to increase parabolically with the annealing time. This agrees with the behavior reported in the literature for sputter deposited or evaporated W films. However, a higher stlicide growth rate was found in this work. An activation energy of 2.6 eV/atom was measured, which is smaller than those for sputter deposited or evaporated W films. The crystal structures of the formed WSi2 and the unreacted W films were analyzed using X-ray diffraction (XRD) technique. The thermal history of the samples was found to play an important role for the crystal structure of the unreacted W and formed WSi2. The as-deposited W films became more oriented to the <100> direction with increasing film thickness, while the unreacted W films on top of the formed WSi2, from the samples annealed at temperatures from 700 to 800°C, became more <100> direction dominated with decreasing W film thickness. The preferred orientation of the grown WSi2 films also varied with the silicidation conditions. These observations indicate that the simple method of determining W film thickness by comparing the W diffraction peak heights of the remaining W films after heat treatment to a reference sample will unavoidably introduce large errors. A compensation technique was suggested where both the W and WSi2 diffraction signals were used. A parameter x, a function of reacted W thickness, was introduced to fit the compensation procedure. The conclusion of this study is that attention should be paid to the orientation change of W and WSi2 films during heat treatment if XRD is employed to study the kinetics of WSi2 formation.
Influence of Impurities and Microstructure on the Resistivity of LPCVD Titanium Nitride Films
Authors: Buiting M. J. , Reader A. H.
Published: March 2011

The electrical resistivity of LPCVD TiN films deposited at temperatures between 450 and 700°C has been found to vary from about 900 to 150 μ Ωcm. The elemental composition (Ti:N), impurity content and the microstructure of the films have been investigated in order to explain the resistivity variation. It appears that this variation is directly related to the chlorine (impurity) content of the films. Films deposited at 700°C have both the lowest chlorine content and the lowest value of resistivity. Additionally the difference between the resistivity of this latter film and the (lower) value for bulk TiN is discussed.
Influence of Substrate and Process Parameters on The Properties of CVD-SiC
Authors: Parretta A. , Giunta G. , Cappelli E. , Adoncecchi V. , Vittori V.
Published: March 2011

The microstructure and mechanical properties (adhesion, hardness) of beta-SiC coatings, prepared in a cold wall reactor, were studied by examining different substrates and deposition process conditions. Hard (3500 HK), fine grained beta-SiC coatings were deposited onto graphite at relatively high deposition terperatures (1473–1673 K) using SiC14,C3H8,H2 gas mixtures. The thermal decomposition of methyltrichlorosilane (MTS) in hydrogen and argon allowed the production of beta-SiC coatings onto a variety of substrate materials in the temperature range 1173–1373 K. The growth mechanisms of SiC deposited from MTS/H2/Ar system onto graphite and polycrystalline alfa-SiC substrates were studied. At low (40 kPa) and atmospheric pressure, the growth kinetics is limited by surface reactions. Also, a strong dependence of the microstructure and crystallographic orientation on the deposition parameters was observed. Hard metals (WC/Co) were succesfully coated with beta-SiC using the MTS/H2/Ar system. Problems of chemical compatibility between the substrate and the beta-SiC coating were minimized by deposition of an intermediate layer of TiN.
Oxidation Resistant Coatings Produced by Chemical Vapor Deposition :Iridium and Aluminum Oxynitride Coatings
Authors: Netter P. , Campros Ph.
Published: March 2011

Oxidation resistant coatings of iridium on graphite, carbon/ carbon or molybdenum and of aluminum oxynitride on graphite and carbon/carbon have been produced by low pressure CVD from halide starting compounds (IrF6 and AlCl3). The resulting deposits are adherent, non porous and have proved to be impervious to oxygen in subsequent heating to 2000° C in air for more than 30 minutes (no evidence of deterioration).

These coatings materials are promising for effective protection against oxidation in rocket engines, gas turbines and thermal protection tiles space shuttles or against corrosion in the glass industry (iridium).
Reactive Chemical Vapor Deposition (R.C.V.D.) as a Method for Coating Carbon Fibre with Carbides
Authors: Bouix J. , Vincent C. , Vincent H. , Favre R.
Published: March 2011

Carbon fibre is an ideal material for reinforcing inorganic matrix composites, especially for high temperatures. Its main drawback is its susceptibility to oxidation and to reaction with metals.

Our challenge was to perfect a method of producing a carbon fibre in which each elementary filament is covered and protected by a very thin and adherent layer of a refractory carbide such as SiC, B4C, etc…

For this purpose, we use reactive chemical vapor deposition (R.C.V.D.) in which only the M element of the M C carbide is carried by the gas phase, carbon being supplied by the fibre itself. The growth rate is self regulated by the solid state diffusion.

This method has been developed in a continuous reactor with ex-PAN (6K) or ex-PITCH (2K) fibres.

The mechanical behaviour of the coated fibres is very near that of the initial ones, but their oxidation rate at 600°C is 100 times lower.