Local electronic structure and surface geometry of Ag on Si(111)

Scanning tunneling microscopy has been used to evaluate the overall morphology and growth conditions for Ag ordered overlayer and island films on Si(111), and to determine the nature of the √3×√3 Ag/Si(111) structure. Current image tunneling spectroscopy (CITS) is used to examine the energy-dependent tunneling and evaluate possible model structures for the √3×√3 structure. Support is found for a √3×√3 structure composed of Ag trimers embedded below the top layer of threefold coordinated Si atoms. The surface electronic structure for these √3 structures shows a 1.2 eV gap, and exhibits very few intrinsic states near EF. The few defects observed in the √3 areas of this surface introduce deep levels while the most dominant tunneling features near EF appear to be associated with Ag islands that coexist with √3 areas. The implications of the surface perfection and local electronic structure to Schottky barrier formation are discussed.