Incommensurate phase of Sn/Si(100) studied by HR-REM

Abstract

Coverage dependent surface phases of Sn deposited on the Si(100) surface are observed by reflection electron microscopy (REM). As the coverage is decreased from monolayer coverage at 400°C, two kinds of phases are found. One is the admixture of n-fold (5 < n < 11) superstructures found in a wide coverage range: Spacing of the superlattice fringes seen locally in the high-resolution REM (HR-REM) images varies from place to place, while superlattice spots in RHEED patterns are of an average value p of the superstructure period n. The RHEED patterns show always half order spots, which indicates that the Sn layer has a twofold periodicity parallel to the dimer row of the 2 × 1 structure of the Si(100) surface. The other is an incommensurate phase of a superlattice period p = 6.7 ± δ (0 ⩽ δ ⩽ 0.2), formed at a certain coverage. The phase is well-ordered: the corresponding superlattice fringes observed in the REM image have a uniform spacing. In this phase, no half order spots appear in the RHEED pattern, indicating the disappearance of the twofold periodicity in the incommensurate Sn layer.