ALKALI-METAL ADSORPTION ON THE SI(111)7X7 SURFACE

Alkali metal (K, Cs) adsorption on the Si(111)7 X 7 surface has been investigated with the field ion-scanning tunneling microscope. At the initial coverage, K(Cs) atoms adsorb mainly at the on-top site of the center adatoms and are ionized. Some of the adsorbed alkali metal atoms form clusters (often trimers), which have more covalent character with back-donation of the charge distribution, and those clusters become the dominant species on the surface with increasing coverage. When the Si(111)-K surface is heated at 300-degrees-C, a new 1 X 3 phase grows as islands which are made of incommensurate linear chains with misfit defects.