bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Preparation and Economics of Silicon Carbide Matrix Composites by Chemical Vapor Infiltration
Authors: Roman Yvette G. , Stinton David P. 
Published: April 2011

ABSTRACTThis paper describes a number of processing techniques that are currently in use for the development and production of continuous fiber reinforced ceramic composite materials. The limited number of available processing routes are compared with respect to the resulting material properties.As it appears, the Chemical Vapor Infiltration technique is one of the most extensively developed methods. During the last decade, at least five different modifications of the isobaric isothermal CVI principle have been developed; each route having its own benefits. CVI techniques have now been developed to the extent that industrial commercialization is being realized. Projected cost aspects of the various CVI manufacturing techniques have been examined and compared.
Resistivity Control by Solid-State Reaction of Perovskite-Type Oxides
Authors: Nagamoto H. , Tanaka H. , Koya T. 
Published: April 2011

ABSTRACTResistivity control has been conducted by solid–state reaction of two different perovskite–type oxides. One is La0.5Ba0.5CoO3−δ (LBC) which showed metallic conduction, and its resistivity, ρ was 10−3 Ω.cm at 20 °C. The other is Ba0.998Sb0.002TiO3 (BT) which showed positive temperature coefficient of resistivity (PTCR) effect. The sintered body of the mixiure of the two oxides did not show PTCR effect. The logarithm of the resistivity of the sintered body, log ρmix was expressed using the resistivity of LBC, ρLBC, the molar ratio of BT, x, and temperature dependent constant, α(T) aslog ρmix = (l–x) log PLBC + xα(T)which holds for 0 ≤ x ≤ 0.8 at the temperature ranging from 20 to 240° C ρmix changed by about 8 orders of magnitude at room temperature. X–ray diffraction analysis suggested that metal ions at the A–site move from one perovskite–type oxide to another and that the sintered body consisted of two perovskite–type oxides different from starting ones.
Correlation Between Changes in Microhardness and Phosphorus Segregation During Post-Irradiation Annealing
Authors: Kameda J. , Gold C. R. , Bloomer T. E. 
Published: April 2011

AbstractThis paper describes the effect of post-irradiation annealing (PIA: 573-873K for 10 h) on the microhardness and intergranular P segregation in P doped and Cu-P doped iron alloys containing residual S. Hardening and softening occurred during PIA at lower and higher temperatures, respectively. PIA-induced hardening was more profoundly observed in the Cu-P doped alloy. Intergranular P enrichment was achieved by lower temperature PIA and P desegregation associated with S segregation dominated at higher PIA temperatures in both the alloys. Changes in the microhardness and intergranular P segregation induced by the PIA were found to be correlated with each other although the Cu-P doped alloy showed more scatter. The dynamic interaction between solute and defects in the grain interior and near grain boundaries during the PIA is discussed in order to explain the experimental observation.
Irradiation Effects on Fe Distributions in Zircaloy-2 and Zr-2.5Nb
Authors: Zou Heilong , Hood G.M. , Roy J.A. , Packwood R.H. 
Published: April 2011

AbstractIrradiation of large-grained Zircaloy-2 (Zy) and Zr-2.5Nb (ZN) with 1.5 MeV Ar+ ions to fluences of ≈ 1020/m2 (= 10-30 dpa) at 50, 300 and 420 °C, leads to enhanced ∝-phase Fe dissolution. Electron microprobe analyses showed ∝-phase Fe levels of 250-1500 ppma, compared to equivalent, non-irradiated state values of ≈ 70 ppma. In ZN the β-phase Fe levels fell from about 6000 to 3500 ppma: this result accords, qualitatively, with the loss of Fe from the β-phase following in-service neutron irradiation. Concentration vs depth measurements for Zy showed higher Fe levels towards the surface. Limited data for Ni in Zy show similar behaviour.
The Observations of Paramagnetic Centers in Tellurite Glasses
Authors: Prohaska J.D. , Li J. , Kannan S. , Snitzer E. , Wang J.S. , Bartram R.H. 
Published: April 2011

AbstractThis is the first report of ESR observations of three distinct paramagnetic centers in TeO29 glasses. One center is intrinsic to the glass and the other two are induced by KrFexcimer-laser radiation. The intrinsic center with a broad ESR spectrum is tentatively identified as an oxygen-associated hole center. One radiation-induced center fades slowly at room temperature; its proposed structure is that of an electron trapped in a diffuse orbital associated with a modifier ion. The other radiation-induced center is stable at room temperature and corresponds to the Vo· center observed in crystalline paratellurite.
Computer Simulation of Thermal Annealing Effects on Self Implanted Silicon
Authors: Sandre G. DE , Colombo L. , Maric D. 
Published: April 2011

AbstractWe investigate the effects of thermal annealing on the structural, elastic and electronic properties of self implanted silicon by tight binding molecular dynamics. The irradiated samples, after a careful relaxation at room temperature, are annealed at different temperatures and for different times and, finally, their properties are carefully monitored during constant temperature simulations. We further provide a characterization of the chemical bonding in the amorphous network and show the evolution of the point defect distribution against maximum annealing temperature.
Molecular dynamics studies of Radiation Effects in Silicon Carbide
Authors: de la Rubia T. Diaz , Caturla M.-J. , Tobin M. 
Published: April 2011

AbstractWe discuss results of molecular dynamics computer simulation studies of 3 keV and 5 keV displacement cascades in β-SiC, and compare them to results of 5 keV cascades in pure silicon. The SiC simulations are performed with the Tersoff potential. For silicon we use the Stillinger-Weber potential. Simulations were carried out for Si recoils in 3 dimensional cubic computational cells with periodic boundary conditions and up to 175,616 atoms. The cascade lifetime in SiC is found to be extremely short. This, combined with the high melting temperature of SiC, precludes direct lattice amorphization during the cascade. Although large disordered regions result, these retain their basic crystalline structure. These results are in contrast with observations in pure silicon where direct-impact amorphization from the cascade is seen to take place. The SiC results also show anisotropy in the number of Si and C recoils as well as in the number of replacements in each sublattice. Details of the damage configurations obtained will be discussed.
Nucleation with Radiation Dissolution and Resolution
Authors: Russell K.C. 
Published: April 2011

AbstractEnergetic particle irradiation may induce athermal processes in addition to the thermallyactivated single atom addition or subtraction events considered by classical nucleation theory. Displacement cascades could destroy sub-critical precipitates. Similarly, either displacement cascades or energetic knock-on atoms could remove single atoms or groups of atoms from subcritical clusters.Cluster destruction becomes significant in nucleation when the probability of destruction is comparable to the probability of growth by single atom capture. The model is applied to the nucleation of embrittling precipitates in pressure vessel steels. The scaling of accelerated embrittlement tests on the basis of displacements per atom is found only sometimes to be applicable. Athermal single atom loss, as in ion mixing, may appreciably reduce the nucleation if the rate of loss approaches or exceeds the rate of solute atom capture.
Solution Chemistry Effects on the Nonlinear Optical Properties of Phosphazenes
Authors: Ferris Kim F. , Samuels W. D. , Morita Y. , Exarhos G. J. 
Published: April 2011

AbstractUsing the combination of experimental (DFWM) measurements and electronic structure calculations, ligand electron donating power and explicit solvent interactions were shown to have critical roles in enhancing the χ3 yields for phosphonitrilic materials. Experimental measurements have shown that decreasing solution pH to 1.0 can significantly increase the χ3 yield for P3N3(NHCH3)6 and P3N3(N(CH3)2)6. Corresponding electronic structure calculations indicate replacement of amino by thiomethyl groups will also significantly enhance these yields. Comparison of electrostatic-based solvation effects and explicit water molecules indicates that dielectric stabilization from the solvent plays a minor influence on χ3 in comparison to strategies which affect the strong P-N bond polarity.
Towards a Structure-Rsa Relationship for Non-Linear Optical Materials.
Authors: Bahra G. S. , Griffiths J. , Healy W. , Millar V. , Till S. J. , Till J. 
Published: April 2011

AbstractMeasurements on the reverse saturable absorption (RSA) properties of some polyene dyes are presented. For a series of linear dyes, a correlation is observed between the symmetry of a molecule and its ability to exhibit RSA. To our knowledge, this is the first structure-RSA relationship discovered to date.Certain of these materials have been studied with semi-empirical quantum chemical techniques and the observed structure-RSA relationship is rationalised in terms of the calculated electronic structures. In this paper, we report primarily on some studies we have carried out on the linear dye systems.
Electro-Optic Power Limiter: Broadband, Self-Actuating Optical Limiter for Visible and Infrared Radiation
Authors: Chang Tallis Y. , McMichael Ian , Hong John H. , Khoshnevisan Monte 
Published: April 2011

AbstractWe present studies of an optical power limiter that uses a combination of the photoconductive and linear electro-optic effects. The electro-optic power limiter (EOPL), first demonstrated using CdTe in the near IR, possesses many desirable qualities including broadband wavelength responsivity, self-actuation, and low threshold power. One unique capability of EOPL, not found in any other nonlinear optical power limiter, is the fact that any light - coherent or incoherent - can be used. Our studies in CdTe, GaAs, and BSO crystals resulted in extending the wavelength range from the visible to MWIR wavelengths.
Deposition of Si Thin Films by Reactive CVD
Authors: Hanna Jun-Ichi 
Published: April 2011

ABSTRACTA new concept of Reactive CVD is proposed for the low-temperature growth of thin films by CVD and discussed in terms of general features of such film growth. One demonstrated example of the reactive CVD, called Spontaneous Chemical Deposition, features gas phase reactions of silane with fluorine is outlined in terms of the general characteristics of the film growth and properties.In addition, a second example of reactive CVD, called Reactive Thermal CVD and involving thermal CVD of poly-SiGe from germanium fluoride and disilane, is discussed and low-temperature growth using this method is reviewed.
Growth and Nucleation of Hydrogenated Amorphous Silicon on Silicon (100) Surfaces
Authors: Tanenbaum D. M. , Laracuente A. , Gallagher A. C. 
Published: April 2011

ABSTRACTA scanning tunneling microscope (STM) has been used to study the topology of the surfaces of a series of thin hydrogenated amorphous silicon (a-Si:H) films deposited by rf discharge from pure silane. The substrates were atomically flat, oxide-free, single-crystal Si (100). Films were grown in our laboratory and transferred to the STM with no air exposure between growth and measurement. A series of thin films between 1 and 50 nm in thickness reveals the initial growth stage of a-Si:H on Si (100). Initial nucleation and islanding can be seen on these films. The surface has a distribution of island sizes. The rms roughness and a surface lateral correlation length were measured as functions of film thickness. The rms roughness grows sublinearly with thickness from 0.3–0.5 nm as the film thickness is raised from 1 to 50 nm. The lateral size of the surface features also grows with film thickness. The growth of the roughness and correlation length can be compared with the dynamic scaling model. In addition, the topographs reveal occasional structures of larger size and low density on the film surface. These structures are nanoparticles of silicon deposited from the plasma during film growth. The frequency of these features scales with film thickness, and represents 10−510−4 of the total film volume.
Below Gap Excitation of Photoluminescence in a-Si:H
Authors: Yin X. , Raikh M. E. , Taylor P. C. 
Published: April 2011

ABSTRACTPL measurements on device-quality samples of a-Si:H (dark ESR bulk signal, Ns < 3 × 1015spins/cm3) and on a sample with Ng = 1016 spins/cm3 have been performed using excitation energies, E×, from approximately 1.3 to 2.4 eV. Sample temperatures investigated cover the range 4 to 300 K, and PL energies both below and above the excitation energies were measured. PL spectra were recorded from approximately 0.7 to 1.8 eV with a dynamic range exceeding 1012 at constant incident power density. The results permit the separation of the one-photon (band-tail to band-tail) and two-photon (two consecutive excitations through silicon dangling bonds) excitation processes. In contrast to the well-known, strong temperature dependence of the PL efficiencies near the PL peak, the PL at the highest energies (> 1.7 eV) depends only weakly on the temperature at constant Ex.
Dangling-Bond Relaxation and Metastability in P-Type Hydrogenated Amorphous Silicon
Authors: Crandall Richard S. , Carlen Martin W. , Lips Klaus , Xu Yueqin 
Published: April 2011

ABSTRACTWe discuss the subtle effects involved in observing slow dangling bond relaxation by studying capacitance transients in p-type hydrogenated amorphous silicon (a-Si:H). The data suggest that neutral dangling bonds are reversibly converted into metastable positive charged dangling bonds by hole trapping. These metastable positive dangling bonds reconvert to neutral dangling bonds upon annealing at elevated temperature. The annealing kinetics for this process are the same as those observed for annealing of quenched in conductivity changes in p-type a-Si:H.
Investigation of the Surface Morphology of a-Si:H by Atomic Force Microscopy and In-Situ Ellipsometry
Authors: Wanka H. N. , Hierzenberger A. , Schubert M. B. 
Published: April 2011

ABSTRACTCombining real-time ellipsometry and atomic force microscopy (AFM) the growth of hydrogenated amorphous silicon (a-Si:H), deposited on crystalline silicon wafers with a native oxide layer on top and on fused silica from a dc glow discharge, has been studied from initial nucleation to the final morphology. By in-situ ellipsometry we detected the evolution of morphology changes. The surface structure has been determined by AFM in the nucleation phase and in the subsequent growth stage. During nucleation on crystalline silicon only few (about 40 per 1μm) flat islands of a-Si:H (up to 4 nm high and up to 50 nm in diameter) grow with a strongly enhanced rate compared to bulk deposition. Once the crystalline surface has completely been covered by a-Si:H, the fast deposition of these islands stops and further surface structures, comparable with the initial ones, start to grow gradually until a homogeneous final roughness up to 5nm high is formed. Nucleation of a-Si:H on fused silica yields densely distributed nuclei (up to 1.5 nm high and up to 25 nm in diameter), indicating a shorter surface diffusion length on this substrate compared to the growth on silicon wafers. The ongoing film deposition, however, finally results in a morphology comparable to the one of a-Si:H grown on crystalline silicon. Using hydrogen dilution we found that the final roughness is affected by the dilution ratio; furthermore infrared spectroscopy reveals the surface structure to be correlated with the hydrogen content of the a-Si:H films.
Solubility of Hydrogen in Amorphous Silicon
Authors: Daey Ouwens J. , Schropp R. E. I. 
Published: April 2011

ABSTRACTWe demonstrate that the exisiting ambiguity between the Nuclear Magnetic Resonance (NMR) and the infra-red (IR) interpretation of the density of clustered hydrogen can be removed by monitoring the effective charge of the silicon hydrogen vibrations in a-Si:H versus the hydrogen content. By monitoring the peak position of the low frequency component (2000 cm−1 mode) of the stretching doublet, we conclude that the 2000 cm−1 and the 2100 cm−1 modes can be uniquely attributed to the monohydride and multihydride bonding configurations, respectively.We show that the parameters describing the IR spectrum depend on the hydrogen content only and do not depend on the deposition technique, deposition conditions or post-deposition annealing treatment.
Fabrication of Boron Compensated Hydrogenated Amorphous Silicon Films with Significantly Improved Stability Using Plasma Enhanced Chemical Vapor Deposition Technique
Authors: Bhan Mohan K. 
Published: April 2011

ABSTRACTWe have systematically investigated the effects of addition of sub-ppm levels of boron on the stability of a-Si:H films and p-i-n devices, deposited by PE-CVD technique. The films thus produced with appropriate amounts of boron, show a significant improvement in stability, when soaked under both AM 1.5 (short-term) as well as 10×sun (long-term) illumination conditions. The opto-electronic properties of the films are quite respectable It is concluded that boron compensates the native impurities by forming donor-acceptor pairs, which reduces the “fast” defects and hence the initial degradation of the films. It is also speculated that boron may also be improving the short-term stability, by reducing the recombination of light generated electrons and holes, by converting D° into D+ states. The long-term stability appears to get affected by hydrogen dilution which seems to reduce the amount of “slow” defects. As a result of B doping of i-layer, the initial conversion efficiency of the devices decreases. It is presumed that our devices may contain an enhanced level of boron impurity, than expected, making them as worse material and to degrade less.
Fabrication of Nanocrystalline Si by SiH4 Plasma Cell
Authors: Otobe Masanori , Kanai Tomonori , Oda Shunri 
Published: April 2011

ABSTRACTNanocrystalline silicon (nc-Si) has been fabricated by a very-high-frequency plasma cell attached to an ultra-high-vacuum chamber using SiH4 gas. Nanocrystalline Si is formed in the gas phase of the plasma cell and is extracted out of plasma cell through the orifice to the ultra-high-vacuum chamber. The shape of nc-Si is spherical or octahedral with the diameter of 3–30nm. Giant Si particles about 100nm in diameter are also formed at the lower cell pressure condition. A 1000keV transmission electron microscopy measurement has revealed that the core region of giant Si particle with the diameter about 30nm was crystalline and the shell region is amorphous. We have demonstrated that the spread of particle size can be decreased using pulsed gas supply of H2 into SiH4 plasma.
Investigations of Tail and Defect States in a-Si0.6Ge0.4:H Alloys by PDS and ESR - Implications for the Interaction of Weak and Dangling Bonds
Authors: Drüsedau Tilo P. , Panckow Andreas N. , Schröder Bernd 
Published: April 2011

ABSTRACTInvestigations on the gap state density were performed on a variety of samples of hydrogenated amorphous silicon germanium alloys (Ge fraction around 40 at%) containing different amounts of hydrogen. From subgap absorption measurements the values of the “integrated excess absorption” and the “defect absorption” were determined. Using a calibration constant, which is well established for the determination of the defect density from the integrated excess absorption of a-Si:H and a-Ge:H, it was found that the defect density is underestimated by nearly one order of magnitude. The underlying mechanisms for this discrepancy are discussed. The calibration constants for the present alloys are determined to 8.3×1016 eV−1 cnr2 and 1.7×1016 cm−2 for the excess and defect absorption, respectively. The defect density of the films was found to depend on the Urbach energy according to the law derived from Stutzmann's dangling bond - weak bond conversion model for a-Si:H. However, the model parameters - the density of states at the onset of the exponential tails N*=27×1020 eV−1 cm−3 and the position of the demarcation energy Edb-E*=0.1 eV are considerably smaller than in a-Si:H.
Trends of Research in Active Addressing of LCDS
Authors: Lueder Ernst 
Published: April 2011

ABSTRACTActive addressing is focused on TFTs and MIMs as pixel-switches. The manufacture of a-Si-TFTs tends to settle down at a three-mask process as long as risky steps can be avoided. Fabrication throughput is being enhanced by increasing the deposition rate for a-Si- and poly-Si-layers processed by PECV.D. For wider process windows and for building row drivers with a-Si-TFTs effective mobility will have to be increased beyond 1 cm2/Vs especially by new TFT-electrodes, a protective sandwich around the a-Si-layer and modified process techniques. Poly-Si-TFTs should be fabricated at temperatures below 450 °C and preferably without laser annealing before they become an economic solution. MIMs still require more materials research to find a dielectric with a larger trap density enhancing speed of operation, lower addressing voltages and electrodes for improved long-term stability. Low-temperature processes are required for LCDs with plastic substrates.
Enhancement of Crystallinity with Fluorinated Amorphous Silicon (a-Si:H;F) Film by XeCl Excimer Laser Annealing
Authors: Choi H. S. , Jang K. H. , Kim K. B. , Han M. K. 
Published: April 2011

ABSTRACTThe Effects of fluorine atoms on laser-induced crystallization have been studied. The defect states of hydrogenated amorphous silicon (a-Si:H) film, which are related to weak hydrogen bonds, were reduced by involving fluorine atoms, before laser annealing. In laser annealing, the crystallinity was also enhanced to 63 %, while that of a-Si:H was 45 % at the energy density of 300 mJ/cm2. It may be considered that the fluorine atoms reduce the hydrogen atoms cause to the degradation of film in laser annealing, and increase the heat capacity which results in promotion of crystallinity in melt-solid phase transition.
DLTS Study on Annealed Low-Temperature GaAs Layers with An n-I(LT)-n Structure Grown by MBE
Authors: Lin Tsai-Cheng , Kaibe Hiromasa T , Okumura Tsugunori 
Published: April 2011

AbstractDeep levels in the annealed low-temperature molecular beam epitaxial (LT-MBE) GaAs layer were successfully characterized by using the capacitance deep-level transient spectroscopy (C-DLTS) as well as photocapacitance quenching technique in combination with a unique sample structure. In this work, we have fabricated the samples by inserting the LT-GaAs layer into two n-type semi-conductive layers, like a sandwich (n-LT-n structure), grown at normal substrate temperatures. DLTS measurements have revealed that one electron trap dominates the annealed LT-MBE GaAs. The dominant electron trap was very similar to the so-called EL3 level. Moreover, we found the midgap level appeared upon 800-900°C RTA, although no midgap level was detected in the as-grown n-LT-n sample (annealed at 620°C) and confirmed with photoquenching measurements that it is the EL2 level.
Nonstoichiometric Defects in Semiconductor SnTe Thin Films
Authors: Nashchekina O. N. , Rogacheva E. I. , Shpakovskaya L. P. , Pinegin V. I. , Fedorenko A. I. 
Published: April 2011

AbstractThe mono- and polycrystalline films of the SnTe1+x semiconducting phase with controlled content of nonstoichiometric defects (NSD) were grown by thermal evaporation and hot wall epitaxy methods from the charges of different composition. The concentration of NSD was determined using X-Ray diffraction method and the measurements of carrier density. The temperature dependences of electrical conductivity and Hall coefficient were obtained in the temperature range of 77 - 300 K. The best results were obtained for hot wall epitaxy method: the perfect monocrystalline films with NSD content corresponding to x =0-0,025 and high mobility of charge carriers were grown.