SCANNING TUNNELING MICROSCOPY AND SPECTROSCOPY OF RT PB/SI(111)-7 X 7

We have obtained atomically resolved STM images and tunnelling spectra from the metastable room temperature Pb/Si(111)-7 x 7 surface. Two different surface structures are observed: one corresponding to small triangular clusters, each located centrally on one half of a 7 x 7 unit cell and the other corresponding to the initial stages of an 8 x 8 Pb overlayer on the Si(111)-7 x 7 unit cell. Tunnelling spectra from these two different structures show marked differences both to each other and to tunnelling spectra from clean Si(111)-7 x 7. The spectra are discussed with reference to other published data from the Pb/Si(111) surface.