Anisotropy of lattice vibration amplitudes at the (111)-surface of lead telluride

Abstract

Particles in surfaces of cubic crystals see a reduced symmetry. Therefore the mean square vibration amplitudes become anisotropic. This leads to angle dependent Debye-Waller factors and to angle dependent temperature dependencies of diffracted intensities, when the scattering particles are located in a surface. Using reflecting high energy electron diffraction (RHEED) at glancing incidence at the (111)-surface of lead telluride, this anisotropy could be studied quantitatively. It can be shown that the mean square vibrational displacements form an ellipsoid with u ⊥ 2 u ∥ 2 = 1.4 and u ∥ 2 = u bulk 2 .