It was found that scanning tunnelling microscopic images of Ag on (111)Si 3 x 3 surfaces exhibited a marked dependence upon bias-voltage polarity. Empty-state images revealed a characteristic honeycomb pattern, with 2 maxima per unit cell. Filled-state images revealed protrusions of Ag atoms in the honeycomb chain trimer model. It was concluded that these images supported electronic structure calculations, for the surface, that were based upon the latter model. The registration of the 3 x 3 surface with respect to the underlying (111)Si substrate was also determined, and the step height between adjacent 3 x 3 and 7 x 7 areas was explained in terms of the electronic structures of the 2 phases, as measured by means of scanning tunnelling spectroscopy.

K.J.Wan, X.F.Lin, J.Nogami: Physical Review B, 1992, 45[16], 9509-12