Adsorption and diffusion of single Pb atoms on Si(111)7 × 7 and Si(111)5 × 5 surfaces studied by scanning tunneling microscopy

Abstract

We have shown very recently by means of scanning tunneling microscopy (STM) that single Pb atoms are highly mobile at room temperature (RT) when adsorbed on Si(111)7 × 7 surfaces. In the present work we have undertaken a further STM investigation of RT adsorption and diffusion of Pb on another DAS (dimer-adatom-stacking fault) reconstruction. To do so, substrates with large terraces presenting the Si(111)5 × 5 reconstruction were prepared and ultra-low coverage (≈0.01–0.02 ML) of Pb were deposited at RT. The STM results measured on these surfaces show that single Pb atoms are highly mobile at RT inside (5 × 5) half-cells but diffuse at very low rate to neighboring half-cells, as is the case for (7 × 7) substrates. The implications of these findings on the possible adsorption sites are discussed in comparison with the Pb Si 1117 × 7 system.