RHEED study of alkali metals on Si(111) surface

Abstract

Adsorbed structures of Li or K on a Si(111) surface are investigated by RHEED and AES. For Li adsorption on a Si(111) surface, the RHEED pattern is changed from 7x7 to 1x1 with deposition time. Subsequent heating of the Si(111)1x1Li surface results in a 4x4 structure. Then 3 × 3 , 1×1 and 3×1 structures appear successively in the RHEED pattern with decreasing Li coverage. The 4x4 and 3 × 3 patterns are observed for the first time. On exposing hydrogen atoms to a Li/Si(111) surface, the Li atoms are substituted for hydrogen atoms at room temperature. After the substitution, the 7x7 and 3x1 patterns due to reconstruction of the silicon matrix are preserved as Si(111)7x7H and Si(111)3x1H, and the other patterns are changed to a Si(111)1x1H. The Si(111)3x1H structure is first obtained by the substitution. By comparison of rocking curves of RHEED intensities from Si(111)7x7Li and from Si(111)7x7H, we conclude that the 7x7 structures are the same. For adsorption of Li on the Si surface, twelve SiLi 3 clusters are formed on the first layer by cutting backbonds of the adatoms of the dimer-adatom-stacking-fault (DAS) structure. For K adsorption on a Si(111) surface, saturation coverage is observed at room temperature. At the saturation coverage the RHEED pattern is quite different from that of Si(111)7x7Li. After heating of the surface, the Si(111)7x7K pattern is gradually reduced to the Si(111)7x7 pattern. By kinematical analysis of the RHEED pattern, we propose a model such as K atoms adsorbed on all dangling bonds of the DAS structure.