STM studies of initial In growth on Si(100)2x1: The In ad-dimer chain and its I-V characteristics

Initial growth of In on Si(100)2x1 was studied by scanning tunneling microscopy at room and liquid nitrogen temperatures. Indium atoms are found to nucleate preferably around S-B steps and grow into one-dimensional ad-dimer chains. The individual In atoms within an ad-dimer are resolved for the first time through two maxima(Angstrom 3 A apart) for each oblong protrusion in the empty states. Furthermore, the orientation of the ad-dimer is evidently along the chain direction, thereby justifying the parallel ad-dimer model. We also probe the electronic nature of In ad-dimer chains through the I-V characteristics, which shows the existence of a surface-state bandgap (similar to 1.5 eV). The semiconducting property so implied and the ad-dimer chain structure are further rationalized by the Peierls pairing mechanism, that is, the half-filling of the In p-band leads to an electron-phonon coupling that animates the dimerization and opens up a gap just at the Fermi level.