Trace element analysis of mineral grains by micro-PIXE demands prior knowledge of major element concentrations from which the appropriate matrix corrections are derived. We describe the micro-PIXE determination of maj...
Trace element analysis of mineral grains by micro-PIXE demands prior knowledge of major element concentrations from which the appropriate matrix corrections are derived. We describe the micro-PIXE determination of major elements using 750 keV protons. The major element concentrations measured for a variety of minerals are in good agreement with recommended values.
a-Si:F and a-Si:F:H films have been prepared by ion-beam-assisted deposition using SiF4, SiH4+Ar, or SiF4+SiH4 as the gases for the ion source. Fluorine in a-Si eliminates some dangling bonds, increases the optical ga...
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a-Si:F and a-Si:F:H films have been prepared by ion-beam-assisted deposition using SiF4, SiH4+Ar, or SiF4+SiH4 as the gases for the ion source. Fluorine in a-Si eliminates some dangling bonds, increases the optical gap, and decreases the dark conductivity. The results are influenced mainly by the ion-beam energy used. The a-Si:F films do not exhibit an activated conductivity even up to 150-degrees-C, and no photoconductivity could be detected. However, film properties were significantly improved when a very small amount of H was added to the a-Si:F and much less than 1 at. % H produced films that were photoconducting and had activated conductivities. The properties of these a-Si:F:H are strongly dependent on both the fluorine concentration C(F) and the hydrogen concentration C(H). The deposition rate decreases with increasing SiF4 content in the source gas, and neither C(F) nor C(H) vary linearly with the change in the source gas ratio SiH4/(SiF4+SiH4). Hence, C(H) must be known and controlled in order to evaluate the effect of fluorine on the film's properties. By studying a series of a-Si:F:H samples containing the same C(H), it is noted that incorporating some F does improve the film's electrical properties. Annealing experiments suggest that an observed peak at 2100 cm-1 in the IR spectra of these a-Si:F:H films is not completely due to SiH2, as has been suggested by others.
A first-principles thermodynamic calculation appropriate for metallic glasses is first proposed and is then carried out for the metals Al and Ca0.7Mg0.3. The calculated results are compared with previously obtained re...
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A first-principles thermodynamic calculation appropriate for metallic glasses is first proposed and is then carried out for the metals Al and Ca0.7Mg0.3. The calculated results are compared with previously obtained results for the supercooled-liquid states of pure Al metal. It now appears that, because of the significant change in the derivative of the volume with respect to temperature on going through the liquid-glass transition, the thermodynamic quantities vary drastically in this region, for those metals that can form glasses in the laboratory through the liquid-quenching process.
Acoustic emission during the laser welding of metals with a modulated CO2 laser beam has been investigated. Sharp resonances at many frequencies in the acoustic emission spectra have been observed. This was most notic...
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Acoustic emission during the laser welding of metals with a modulated CO2 laser beam has been investigated. Sharp resonances at many frequencies in the acoustic emission spectra have been observed. This was most noticeable when the average laser power was high enough to produce full penetration welds whose acoustic emission at high harmonics with frequencies that overlap with bands of vibrational frequencies corresponding to eigenmodes of the keyhole are greatly enhanced. Lower harmonics were not clearly observed. However, in partial penetration welding, many harmonic components were observed. These results are not affected by a surface coating of the metal as in the galvanized steel sheet sample. This observation indicates that the keyhole and its surrounding liquid layer act as a frequency selective amplifier for pressure fluctuations induced by changes in the interaction of the laser radiation with the walls of the keyhole. When a continuous wave (CW) beam is used, random fluctuations with frequencies within these allowed bands are amplified to produce a spectrum consisting of a large number of overlapping but discrete frequency components. When the laser beam is modulated, a forced response is elicited resulting in a much simplified emission spectrum.
A quantitative relationship has been identified between the deposition parameters and the electrical and optical properties of a-Si:C thin films. The major effects of the deposition parameters derive from their influe...
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A quantitative relationship has been identified between the deposition parameters and the electrical and optical properties of a-Si:C thin films. The major effects of the deposition parameters derive from their influence on the incorporation of water vapour into the films. Even very small changes in the amount of water vapour, as an ambient during deposition, produce very large changes in the electrical and optical properties of the films. An increase in the ambient water vapour pressure from 1 × 10 −8 to 4 × 10 −8 Torr decreases the room temperature conductivity of the resulting films by as much as three orders of magnitude. The important deposition parameters are expressed in terms of a quantity N H 2 O , which represents the actual amount of water which remains in the film.
An improvement of our previous extended mean-field theory of the liquid-vapour interface of water is described. This revision extends the range of validity of the theory to room temperature. The current theory is impr...
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An improvement of our previous extended mean-field theory of the liquid-vapour interface of water is described. This revision extends the range of validity of the theory to room temperature. The current theory is improved in three aspects: (1) the effective angle-averaged pair potential is obtained by the RAM (reference-averaged Mayer) function approximation, avoiding expansion in inverse powers of temperature;(2) die soft repulsive core of the TIP4P water model pair potential is treated accurately;and (3) the anisotropic interactions are represented by a higher-order (l = 5) multipole expansion. The current theory includes no adjustable parameters;the critical temperature T(c) is found to be 609 K. Detailed calculations are given for room temperature, where molecular-dynamics simulation results are available for comparison. A more detailed representation of the orientational distribution function is reported.
It is shown that the generalised non-local model pseudopotential theory, developed recently, can be applied to the calculation of the thermodynamic properties of liquid metallic Li and Be in a fashion similar to its a...
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It is shown that the generalised non-local model pseudopotential theory, developed recently, can be applied to the calculation of the thermodynamic properties of liquid metallic Li and Be in a fashion similar to its application to the transition metals. The corrections to the effective ionic interaction attributed to one-body plus two-body terms are much less important than those from the three-body plus higher-body terms. In analogy to sd-mixing in the transition metals, the latter are interpreted as arising from sp-mixing effects. These corrections have relatively similar magnitudes in the calculation of the phonon spectra of Li and Be and the latter corrections are required to yield reasonable agreement with observation. Finally, the Be results vindicate the physical interpretation.
The authors' recently suggested approach (1984) for calculating the Helmholtz free energy, including the usual high-order pseudopotential perturbation corrections for the nearly-free-electron-like liquid metals, i...
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The authors' recently suggested approach (1984) for calculating the Helmholtz free energy, including the usual high-order pseudopotential perturbation corrections for the nearly-free-electron-like liquid metals, is critically examined and is now improved so as to be applicable in principle to any sp-type disordered metal in its liquid phase. It appears that the mean atomic volume, the packing density parameter and the related thermal quantities can now be predicted from first principles with reasonable accuracy by the presently described variational thermodynamic calculation for nearly all the sp-type liquid metals.
The generalised model potential theory, developed recently for liquid sp-type metals, is extended to the variational calculation of the Helmholtz free energy for the alloys of these metals. Hence, model potentials, wh...
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The generalised model potential theory, developed recently for liquid sp-type metals, is extended to the variational calculation of the Helmholtz free energy for the alloys of these metals. Hence, model potentials, which include the usual high-order pseudopotential perturbation (HOPP) effects, are obtained for use in alloy calculations. Thesese model potentials are applied to first-principles calculations of thermodynamic quantities and electrical resistivities for some typical liquid metallic binary alloys. The results thus obtained are found to be in reasonable agreement with observation. When compared with the results obtained using the usual low-order pseudopotential perturbation theory, they indicate that HOPP effects become extremely important in the case of the heat of mixing for any metallic binary alloy, whereas for some other properties these effects are essential only for those metallic alloys in which charge transfer is significant.
Hexagonal ZnO films with different observed orientations were deposited on glass substrates at temperatures below 200-degrees-C by r.f. sputtering of a ZnO target using an oxygen and argon gas mixture. Orientations wi...
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Hexagonal ZnO films with different observed orientations were deposited on glass substrates at temperatures below 200-degrees-C by r.f. sputtering of a ZnO target using an oxygen and argon gas mixture. Orientations with the (002) planes of the crystallites parallel to the substrate, or with the (100) planes parallel to the substrate, or films in which the (101) peak is dominant in their X-ray diffraction spectra have been obtained by selecting the deposition parameters. The partial pressure of the oxygen in the sputtering gas, the distance between target and substrate, the substrate temperature during film nucleation and the input power each affect (to varying degrees) the observed crystallite orientation obtained. Polycrystalline ZnO films made in the presence of excess oxygen or at a high sputtering gas pressure tend to have the c axis parallel to the substrate and they exhibit a large photoresponse, while films sputter-deposited with a low partial pressure of oxygen tend to have the c axis perpendicular to the substrate and may have no detectable d.c. photoresponse. The availability of oxygen during sample preparation has a significant affect on the slow photoresponse of the resulting ZnO films.
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