New Phase and Surface Melting of Si(111) at High Temperature above the(7×7)−(1×1)Phase Transition

Abstract

The surface structure of Si(111) at high temperatures $(950–1380°\mathrm{C})$ has been studied with reflection high-energy electron diffraction. We have found three different surface structures: (1) A relaxed bulklike structure with adatoms of 0.25 monolayer (ML) is formed $(950–1210°\mathrm{C})$; (2) there is a new phase where the adatom coverage decreases to 0.20 ML $(1250–1270°\mathrm{C})$; (3) the surface melting occurs over $1290°\mathrm{C}$. The crystalline structure below the melting layer can be explained by the vacancy model missing all adatoms and 0.45 ML of atoms in the first-double layer.