Asymmetry of lattice vibrations in the vicinity of phase boundaries

Abstract

AbstractIn proceeding papers we could show that in the vicinity of a phase boundary between epitaxially oriented crystal pairs the free energy density is higher than in the bulk crystals (e.g. Ag, Au or Pt/AgCl and LiF/AgCl). This disturbance can be observed up to distances of several lattice constants from the phase boundary. As a consequence of the directed interactions between the interface and the interior of the crystals, asymmetries should arise in this region. Up to now it was not possible to detect asymmetries in lattice parameters in thin films using high energy electron diffraction. We therefore tried to find out whether it is possible to observe asymmetries in the mean vibration amplitudes of the lattice planes in the evaporated films. These amplitudes can be obtained from the temperature dependence of the reflected intensities, according to Debye.We used an UHV‐electron diffraction system with energy filter to eliminate inelastically scattered electrons (Vacuum Generators). The specimen (Ag/AgCl) were obtained by evaporating at first silver (2000 Å) and then silverchloride (50 – 500 Å) onto mica sheets at a residual gas pressure below 10−10 Torr. The temperature dependence of the reflected intensities were measured between 80 K and room temperature. From the results it can be concluded that the mean amplitudes of vibration are slightly anisotropic. The amplitude normal to the film surface is higher than in directions with lower angles to the surface.