SYNCHROTRON X-RAY-DIFFRACTION STUDY OF THE DISORDERING OF THE GE(111) SURFACE AT HIGH-TEMPERATURES

The Ge(111) surface has been reported to undergo a disordering phase transition at approximately 1050 K. Our synchrotron x-ray diffraction study demonstrates that there is, instead, a progressive disordering of the topmost layers, which retain long-range order up to at least 1150 K. Neither diffuse scattering associated with roughening or surface melting nor effects due to surface incommensurability are observed. A model involving a proliferation of surface vacancies gives a consistent description of the data.