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The Mg(0001) face is subjected to oxygen adsorption from 0 to 103 L. Three characteristic stages of oxygen adsorption are detected from 0 to 10 L. The AES signal of clean Mg decays exponentially against exposure with slopes α ai such that αA2 (0.75 → 3 L) >αA1 (0 → 0.75 L)>αA3 (3 → 10 L). For increasing exposures, they correspond to: (1) a clear (1 × 1)-Mg(0001), (2) a diffuse (1 × 1)-Mg(0001) and (3) a (1 × 1) with a weaker (1 × 1)-R30°-MgO(111) LEED patterns, respectively. At the end of the third stage, a supplementary ( pattern is observed. In ELS, a very fast intensity decrease of energy loss peaks due to surface and bulk plasmon excitations of the clean metal is recorded during the first stage. The energy loss peak due to the oxidized surface plasmon excitation reaches a maximum intensity at the end of the second stage. Energy loss peaks to be attributed to excitations in bulk MgO appear during the third stage. The work function of the sample decreases and shows a minimum around 6 L, and then slowly increases. Beyond 10 L, a logarithmic relation between oxide thickness and exposure seems to exist. These results are interpreted by the following sequential processes: stage 1: random oxygen chemisorption followed by oxygen incorporation (αA1); stage 2: assembling into islands and lateral island growth (αA2); stage 3: oxide formation (αA3) and stage 4: oxide thickening. Lattice models describing these processes are proposed and discussed. The influence of surface roughness on the results is emphasized. 相似文献
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2 monitor designed for field applications using room-temperature diode lasers are presented. Near-infrared DFB lasers operating
at 1.57 μm and around 2.0 μm have been used for CO2 measurements. At ambient concentration levels a resolution of more than two orders of magnitude has been demonstrated at
1.57 μm, at 2 μm the precision is in the order of 0.1 ppm CO2, and for trace analysis a detection limit of 10 ppb has been obtained. The measurements demonstrate the capability of near-infrared
DFB diode lasers for the precise determination of CO2 concentrations as required for climatological, medical, or industrial applications.
Received: 24 February 1998/Revised version: 27 April 1998 相似文献
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J. Darville 《Journal of Electron Spectroscopy and Related Phenomena》1983,30(1):247-260
The adsorption of water on SrTiO3(100) has been studied by HREELS. Exposure of the defect free surface to water at 100K leads initially to non-dissociative adsorption on surface cation sites with development of losses due to OH stretching and bending modes at frequencies similar to those of free H2O. Further exposure results in progressive attenuation of the surface phonon losses of the substrate with development of a loss spectrum characteristic of an ice multilayer. Binding of water in oxygen vacancy sites generated by argon ion etching is much stronger than to the defect free surface. 相似文献
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A semilinear parabolic transmission problem across either a fractal layer S or the corresponding prefractal layer Sh is studied. Local existence, uniqueness and regularity results for the mild solution, in both cases, are established as well as a sufficient condition on the initial datum for global existence is given. The asymptotic behaviour of the solutions of the approximating problems is studied. 相似文献
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Quinn K Romagnani L Ramakrishna B Sarri G Dieckmann ME Wilson PA Fuchs J Lancia L Pipahl A Toncian T Willi O Clarke RJ Notley M Macchi A Borghesi M 《Physical review letters》2012,108(13):135001
The development of current instabilities behind the front of a cylindrically expanding plasma has been investigated experimentally via proton probing techniques. A multitude of tubelike filamentary structures is observed to form behind the front of a plasma created by irradiating solid-density wire targets with a high-intensity (I ~ 10(19) W/cm(2)), picosecond-duration laser pulse. These filaments exhibit a remarkable degree of stability, persisting for several tens of picoseconds, and appear to be magnetized over a filament length corresponding to several filament radii. Particle-in-cell simulations indicate that their formation can be attributed to a Weibel instability driven by a thermal anisotropy of the electron population. We suggest that these results may have implications in astrophysical scenarios, particularly concerning the problem of the generation of strong, spatially extended and sustained magnetic fields in astrophysical jets. 相似文献
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The parsimony haplotyping problem was shown to be NP-hard when each genotype had k?3ambiguous positions, while the case for k?2 was open. In this paper, we show that the case for k?2 is polynomial, and we give approximation and FPT algorithms for the general case of k?0 ambiguous positions. 相似文献
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It is shown that the constitutive character inducing radial cavitation of elastic balls is carried by the liquid-like portion, if any, of their stored-energy density. 相似文献
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Mass spectrometry (MS) analysis, after enzymatic or chemical deglycosylation, requires preparatory steps to remove salts and buffers. In this work, the glycosylated protein fetuin and a lectin protein isolated from the serum of Alligator mississippiensis were used to evaluate methods for desalting samples after an enzymatic or chemical deglycosylation. Precipitation and dialysis were used to prepare the deglycosylated samples for MS analysis. Both the precipitation and dialysis methods were suitable for sample preparation prior to analysis by matrix assisted laser desorption ionization (MALDI) MS. 相似文献