New Models for the 7×7, 5×5, 2×8 Structures on Si(111) and Ge(111) Surfaces

Abstract

On the basis of a detailed analysis of RHEED intensity distribution along reciprocal lattice rods taken from the Si(111)7×7 structure, a new structure model has been obtained. The structure consists of twelve raised atoms and a vacancy in the unit mesh. The raised atoms are arranged in regular triangular forms with side 2a, a being the size of the bulk unit mesh and they can be classified into four kinds of atoms A, B, C and D. Among their heights of the displacements Z_A, Z_B, Z_C and Z_D, an inequality Z_A>Z_B>Z_C>Z_D has been consequently obtained. The Ge(111)7×7-Sn surface has an identical structure with the Si(111)7×7. Similarly the Ge(111)2×8 structure consists of two of them, A and B, and the Ge(111)5×5-Sn and Si(111)5×5-Ge three of them, C, D and a vacancy.