Study of low energy noble gas ion reflection from monocrystalline surfaces; Influence of thermal vibrations of the surface atoms. II. Calculational evaluation of the sensitivity for model parameters and possibilities for estimation
The sensitivity of the characteristics of low energy noble gas ion reflection from monocrystalline surfaces for thermal properties of the target atoms has been investigated by computer simulation. In addition the uncertainties in comparing experimental results with calculations, introduced by a not well-known interaction potential, have been examined. The calculations have been carried out for 6 keV Ar + ions reflected from a vibrating Cu<100> chain. To achieve the above presented object we varied the mean square value overlineu 2 and the correlation coefficients of the atomic thermal displacements. The used ion-atom interaction potential (a Thomas-Fermi potential in the Molière approximation) has been varied by changing the screening length aF. Under certain conditions the shape of the energy spectra of specularly reflected particles depends pronouncedly on both overlineu 2 and aF. The effects are the most pronounced for scattering angles between about 20° and 30°. The angular distribution shows also a distinct and simultaneous sensitivity for the used potential and the target-temperature. A most interesting feature is the occurrence of a QT peak at higher temperatures, resulting from quasi triple collisions from surface "thermal pit" structures. At a given scattering angle the cut-off temperature of this QT peak can be related to the mean square displacements of the involved atoms. This cut-off temperature appears to be (almost) independent from the used potential, allowing an estimation of overlineu 2. The intensity of the QS peak and the QD peak depend exclusively on the mean square differences of thermal displacements of neighbouring atoms. Correlated atomic displacements have some influence on the angular distributions and on the QT peak intensity. Possibilities to estimate model quantities are discussed briefly.