Scanning tunneling microscope images of the Ag/Si(111)-√3 × √3 surface have a strong dependence on bias-voltage polarity. Empty-state images show a characteristic honeycomb pattern with two maxima per unit cell. Filled-state images show protrusions in the positions of Ag atoms in the honeycomb-chain-trimer (HCT) model. These images strongly support recent electronic-structure calculations that are based on the HCT model for this surface. The registration of the √3 × √3 features relative to the underlying Si(111) substrate is also measured. As part of this determination, the step height between adjacent √3 × √3 and 7×7 areas is discussed in terms of the electronic structure of the two phases as measured by scanning tunneling spectroscopy.

• Received 25 February 1992

DOI:https://doi.org/10.1103/PhysRevB.45.9509