Adsorption and tunneling of atomic scale lines of indium and lead on Si(100)

The atomic resolution capability of scanning tunneling microscopy is used to reveal interesting similarities and differences on the adsorption and tunneling behavior of In and Pb on Si(100). While both metals form one-dimensional ad-dimer chains on Si(100), In dimers are symmetric but show sharp contrasts between filled and empty states whereas Pb dimers give similar contrasts for both polarities but are buckled. The charge transfer accompanying the buckling of Pb dimers is imaged selectively for charged Pb atoms at different bias polarities within a dimer. The contrast mechanism of dimer chains is rationalized through a simple picture of spatial orbital extension into the tunneling gap. On the other hand, tunneling spectra show a surface-state band gap of similar to1.2 eV for both In and Pb chains and the resultant absence of length dependency. However, the localized surface states of In chains near the gap are different from those of Pb chains due to the difference in their electronic configurations. Systematic analysis of the local maxima in tunneling density of states and their relations to the surface-state bands induced by metal-metal and metal-silicon interactions will also be presented.