Photoemission and photoabsorption study of the high-temperature phases of the Ge(111) surface

The Ge(111) surface has been studied by photoemission and photoabsorption spectroscopies as a function of temperature up to 1200 K. Up to 1020 K the data indicate the presence of an adatom-restatom reconstruction, with a gradual weak metallization of the surface between 600 and 1020 K. Evidence for a high-temperature phase transition is found between 1020 and 1085 K from core-level spectroscopy. Valence-band photoemission spectra and photoabsorption data indicate a metallic surface layer above this phase transition, About 0.7-1 atomic bilayer is estimated to undergo the semiconductor to metal transition All these data can be interpreted consistently with an incomplete surface-melting scenario. (C) 1997 Elsevier Science B.V.