Abstract
The high-temperature phase transition occurring on the Ge(111) surface at Tc = 1050 K has been investigated by elastic and inelastic helium atom scattering (HAS) techniques for surface temperatures between 1000 and 1150 K. In addition to sharp diffraction peaks in the angular distributions, single phonon peaks could be detected in the time-of-flight spectra. No changes in the widths and line shapes of the phonon peaks were observed directly below and above Tc. Moreover, the dispersion curves of the surface Rayleigh modes in both the first and second Brillouin zones were found to be unaltered at the phase transition indicating the preservation of the surface crystalline structure up to 1100 K. These results are fully consistent with earlier HAS observations of an order-order surface phase transition on the Ge surface.