Melting at Ge(111) Surface Observed by Low Energy Electron Diffraction

Low energy electron diffraction (LEED) observations indicate that the first few atom double-layers at Ge(111) surface lose lateral crystalline order in a continuous phase transition 150K below the bulk Ge melting temperature. The transition has been studied by LEED using improved position-sensitive detection (100 kHz, 256x256 channel resolution). The results indicate a continuous transition with critical temperature Tc = 1058 plus or minus 10K. An observed decrease of surface Debye temperature from 200K for crystal temperature T Tc to 100K for T > Tc supports an assignment of the transition to surface melting. The observed absence of broadening of LEED beams with increasing T rules out an alternative assignment to roughening.