关键词： silicon-germanium   amorphous semiconductor   structural relaxation   structural property   vibrational property  

摘要： Thermally-induced structural relaxation of amorphous silicon-germanium (a-Si1-xGex) alloys has been examined using molecular-dynamics (MD) simulations with the Tersoff interatomic potential. The a-Si1-xGex networks were successfully observed in the present MD simulations. Major changes in the topological short-range order upon annealing occurred within the second coordination shell, while the chemical short-range order was not altered. It was found that the decrease in potential energy associated with the change in the standard deviation of bond angles becomes large as the Ge composition increases. This result was consistent with the heat release due to structural relaxation, which was observed experimentally. We also examined differences in the phonon densities of states between the as-quenched and annealed a-Si1-xGex alloys.

关键词： bulk metallic glass   glass forming ability   thermal stability   reduced supercooled liquid region  

摘要： Thermal stability and glass-forming ability of Zr65-xAl10Ni10Cu15Bex (x = 0, 3, 6, 9, 12.5, 16) bulk metallic glasses were investigated by differential scanning calorimetry, differential thermal analysis, X-ray diffraction and high-resolution transmission electron microscopy (HRTEM). The results show that the substitution of beryllium for zirconium strongly affects the supercooled liquid region (DeltaT(x) = T-x - T-g(onset)), the reduced supercooled liquid region (DeltaT(rg) = (T-g(onset))/(T-i - T-g(onset))) and the reduced glass transition temperature (T-rg = T-g/T-i). With increasing of x values, the three parameters that were used to indicate the glass forming ability and thermal stability increase first and then decrease. It is in agreement with the result that these glasses gradually change from an off-eutectic composition into a eutectic one (x = 12.5) that favours higher glass-forming ability, and then there is again a departure from the eutectic composition. Consequently, a moderate Be content will favor to increase the glass forming ability and thermal stability in Zr65-xAl10Ni10Cu15Bex bulk amorphous alloys. The effect of Be was explained in terms of Miedema's theory, electronegativity difference and atomic size parameter of the amorphous alloys. (C) 2004 Elsevier B.V. All rights reserved.

关键词： amorphous brazing foil   rapid solidification  

摘要： This paper is a detailed and updated review of the properties and specifics of METGLAS amorphous brazing foil (MBF) and a review of the positive qualities it has brought to many applications in the last two decades. The major emphasis is to provide practical guidance for intelligent use that will contain, in the first part. a description of these materials in the virgin as cast state. This state has a unique combination of physical properties. The metallurgical background will also be given in this part to the existing range of available chemical compositions and their potential compatibility with various base metals. The amorphous alloy mechanical properties and thermal stability, wettability over various metals and its dependence on the brazing atmosphere and preform preparation will also be described The second part presents the properties of MBF joints manufactured from various classes of base metals and obtained under optimised brazing conditions for each class of base metals. Particular attention is given to the joint microstructural properties relationships yielding brazements with high strength, ductility and corrosion and fatigue resistance. Finally, the versatile technical and manufacturing features of MBF are underlined These features are the driving force behind the rapid expansion of their applications in various industries. Examples of these applications are also given.

关键词： 61.43.Bn  

摘要： The atomic structure of Te-rich amorphous germanium tellurides has been investigated experimentally with high-energy synchrotron radiation and modeled by means of the reverse Monte Carlo technique. Total and partial structure factors and pair correlation functions were simulated. It is shown that the structure of Ge20Te80 and Ge15Te85 glasses can be described by GeTe4 tetrahedra as structural units which are bridged by Te-Te bonds. (C) 2003 Elsevier B.V. All rights reserved.

关键词： hydrogenated amorphous silicon   germanium alloys   light-induced defects  

摘要： A selected survey of the phenomenon of light-induced deep defect creation in the hydrogenated amorphous silicon-germanium is presented. First a general review of the early studies that established the key salient features of light-induced degradation in a-Si,Ge:H is given. This is followed by a discussion of a couple of complicating issues that have more recently come to light;namely, the possibility that charged defects play a more central role in the alloys, and that both Si and Ge metastable dangling bonds may be playing a significant role in the alloys with germanium fractions below 20 at%. Following this, the results of some recent studies are summarized that have been focusing on the details of degradation in the low Ge fraction alloys to gain insight into the fundamentals of degradation of amorphous silicon materials in general. This review concludes with an overall assessment of the level of our understanding of degradation in the a-Si,Ge:H alloys and where some key issues are still remaining to be resolved. (C) 2002 Elsevier Science B.V. All rights reserved.

关键词： Diffraction gratings   Optical diffraction   Amorphous semiconductors   Surface patterning   Crystal structure  

摘要： We use the interference of two pulsed laser beams (wavelength=355 nm) to produce an optical diffraction grating in amorphous germanium-nitrogen alloy (a-GeN). At the constructive maxima of the interference pattern, the absorption of light leads to crystallization. The crystallized region results of pure microcrystalline germanium (muc-Ge). An indication that Ge-N bonds have broken and nitrogen outdiffused of the film is obtained from infrared spectroscopy and confirmed by Raman spectra. A pattern of alternating a-GeN and muc-Ge lines with a period of about 4 mum acts as an optical diffraction grating due to the difference in optical properties between the two materials, and the three dimensional surface profile, caused by N-2 effusion, that is formed on the sample. (C) 2002 American Institute of Physics.

关键词： Semiconducting films  

摘要： Commonly, the germane fraction (f = flow rate of GeH4/flow rate of SiH4 + GeH4) is changed to vary the optical gap (E-opt) of amorphous silicon germanium alloy (a-SiGe:H) films. We report that for a particular f, the change of deposition conditions, the flow rate of diluent gas (H-2) and the radiofrequency (rf) power density can vary the optical gap (1.67-1.40 eV), the germanium content (41.3-22.5 at%) and the microstructural defect density (0.92-0.42), the mobility lifetime product (eta mu tau;6.81 x 10(-6)-1.46 x 10(-8) cm(2) V-1) in a wide range. Initially, with the increase of the H-2 flow rate up to 20 SCCM for the rf power density of 60 mW cm(-2) and up to 30 SCCM for the rf power density of 30 MW cm(-2), the microstructural. defects decreases, although, the Ge content of a-SiGe:H films increases. The microstructural defects of a-SiGe:H films becomes a direct function of the midgap defect density and a indirect function of eta mu tau. Moreover, the nature of diluent gas is also important. We present that in a wide range of optical gap (1.74-1.36 eV) the defect density is lower, and eta mu tau is higher for the optimized He diluted film compared to those of the optimized H-2 diluted films.

关键词： A200   G150   S180  

摘要： The nanostructure of hydrogenated amorphous silicon germanium alloys, a-Si(1-x)Ge(x):H (x similar to 0.15 to 0.57), prepared by different plasma enhanced chemical vapor deposition (PECVD) techniques was analyzed by anomalous small-angle X-ray scattering (ASAXS) experiments. For alloys with x > 0.2 the Ge component was found to be inhomogeneously distributed with correlation lengths from 0.6 to 1.6 nm. From the analysis of extended ASAXS measurements at 16 X-ray energies in combination with densitometric measurements the volume fractions, densities and Ge-concentrations of the inhomogeneities were deduced. (C) 2001 Elsevier Science B.V. All rights reserved.

摘要： Braying of stainless steel easing nickel based alloys has sometimes been avoided, in spite of its various advantages, because it is a somewhat unreliable process in terms of the mechanical characteristics and corrosion resistance of the brazed joints. Addition of copper to amorphous Ni-Cr-B-Si brazing alloys has been shorn to be a promising method of improving the performance of joints. Because copper cart forma a solid solution with nickel at arty concentration, addition of copper has a great effect on the microstructures of the nickel based filler metal and bra-a seam, by improving the volume ratio of nickel based solid solution to the embrittled intermetallic compounds. As a result, a significant increase in the critical brazing clearance (CBC) was obtained in the present work. Furthermore, copper might increase the electrode potential of nickel based solid solution, so that addition of copper could improve the corrosion resistance of the brazed joints. The results show that can appropriate copper addition to the present Ni-Cr-B-Si group amorphous brazing foil provides an effective method of overcoming the weaknesses of joints brazed using conventional nickel based filler metals, such as low value of CBC and low corrosion resistance.

关键词： CARBON   THIN films   GERMANIUM alloys   SPUTTERING (Physics)   X-ray diffraction  

摘要： Thermomechanical properties of amorphous hydrogenated carbon-germanium alloys prepared by the rf sputtering technique were determined for films in the Oat. % to 100 at. % carbon content range. The stress, thermal expansion coefficient, and elastic modulus were obtained using the thermally induced bending technique. The stress was related to the concentration of hydrogen and argon, to the difference in the Ce-Ge and Ge-C bond length, and to the carbon hybridization. The thermal expansion coefficients of pure amorphous germanium and amorphous carbon are higher than that of their corresponding crystalline counterparts, which was attributed to the compressive stress of the films. The biaxial modulus, on the other hand, are always smaller than that of their crystalline counterparts, but increases as the concentration of carbon increases due to the substitution of Ce-Ge bonds by energetically stronger Ge-C and C-C bonds.