Evidence for an Order-Order Transition on the Ge(111) Surface near 1050 K from High-Resolution Helium Atom Scattering Experiments

Helium atom scattering has been used to investigate the Ge(111) surface phase transition at $T_c=1050\mathrm{}\mathrm{K}$. The elastically scattered helium atoms show sharp, integral-order diffraction peaks that change only in their relative amplitudes at $T_c$ and persist up to 1160 K, the highest temperature studied. Contrary to previous reports based on low-energy electron and x-ray diffraction, ion backscattering, and a recent theoretical study, the present findings show that the surface remains highly ordered above $T_c$, with a reduced height of the top bilayer, and that it may be metallic as was recently observed in electron energy loss spectroscopy.