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ABSTRACT: Hyperfine interactions of fluorine nuclei near trapped hydrogen atoms in CaF2, SrF2, and BaF2 are computed using a valence-bond model that includes electronic charge transfer from the nearest-neighbour fluorine ions to the trapped hydrogen atoms at both interstitial and substitutional sites, termed Hi0 and H20 centres respectively. The best agreement between theory and experiment is obtained by fitting the computed and experimental anisotropic hyperfine constants (HFCs) of the nearest-neighbour fluorine ions in order to assess the amount of charge transfer. The isotropic HFCs are then computed with the resulting wavefunction. In all cases, the amount of charge transfer is very small but nevertheless essential for explaining the anisotropic HFCs and the g-shift. In the case of the Hi0 centre the theoretical isotropic HFCs are smaller than the corresponding experimental values by 20% for SrF2 and BaF2, and by 17% for CaF2. For the H20 centre, on the other hand, quantitative agreement between theory and experiment can be achieved by including a small inward displacement of the nearest-neighbour F- ions, which reduces the undistended F--H distance by about 10%.
Journal of Physics C Solid State Physics 11/2000; 14(17):2319.
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ABSTRACT: Pulsed‐laser cleaning of metal optical surfaces at cryogenic temperatures is modeled. Temperature dependencies of the substrate thermal and optical parameters were taken into account since they are quite sensitive to thermal variations at very low temperatures. Calculations of the heating of clean substrates were done to determine damage thresholds as well as computations of the heating of absorbing and transparent films on the substrates to ascertain the film removal process. The theoretical results are compared to available experimental measurements.
Journal of Applied Physics 04/1994; · 2.17 Impact Factor
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ABSTRACT: Modeling of pulsed laser ablation has been applied to investigate the etching of high‐T c superconducting films of YBa 2 Cu 3 O 7-δ and Bi 2 Sr 2 CaCu 2 O 8 . Calculations based on solutions to the one‐dimensional heat equation and using parameters characteristic of the experiments indicate that diffusion does not play a major role and the dominant process is an evaporation mechanism taking place at the surface. Hence the ablation is modeled by solving the dynamical equations for a very thin heated layer in local equilibrium with the ablated material. With reasonable assumptions for the heat of evaporation (sublimation) and the phase equilibrium curve, the etch depth per pulse can be determined along with a number of other parameters. The results are in accord with observation.
Journal of Applied Physics 12/1990; · 2.17 Impact Factor
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ABSTRACT: The laser‐induced forward transfer technique in which material is ablatively transferred from a thin film to a target substrate by a pulsed excimer laser has been extended to 532 nm using a frequency‐doubled YAG laser. Cu and Ag have been deposited on fused silica substrates using microscope objectives for focusing, resulting in reductions in feature size over that obtainable with the multimode excimer laser. The photothermal deposition process has been modeled using the one‐dimensional thermal diffusion equation, including a moving solid‐melt boundary, with good agreement between theoretical and experimental results.
Journal of Applied Physics 03/1988; · 2.17 Impact Factor
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ABSTRACT: The mechanism of the laser‐induced forward transfer (LIFT) technique for transferring metal features from a film to a substrate is examined by using the one‐dimensional thermal diffusion equation with a moving solid‐melt boundary to model the heating, melting, and vaporization of the metal film by the laser. For typical LIFT conditions the calculations show that the back of the film (i.e., the part exposed to the laser) will reach the boiling point before the film melts through, which supports the qualitative picture that the LIFT process involves vapor‐driven propulsion of metal from the film onto the target.
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 10/1987; · 1.34 Impact Factor
