Surface morphologies and electronic structures of Sn thin films prepared on Si͑111͒-Sn͑2 ͱ 3 ϫ 2 ͱ 3͒ R30°s ubstrate are investigated by low temperature scanning tunneling microscopy/scanning tunneling spectroscopy ͑STS͒. A typical Stranski-Krastanov growth is observed at various growth temperatures ͑95-300 K͒, and the Sn islands above wetting layers exhibit the preferential thicknesses of odd-numbered atomic layers. STS measurement shows the formation of well-defined quantum well states with an oscillation period of 2 ML, which modulates the surface energy and accounts for the observed preferential thicknesses. Due to the interplay between large lattice mismatch and symmetry difference, a transition from ␣-Sn to ␤-Sn occurs at 4 ML, which confirms the previous report. From 4 to 11 ML, the mismatch resulted strain manifests the growth via thickness-dependent striplike modulation structures on the surfaces of all Sn islands. Upon room temperature annealing, the as-deposited Sn islands undergo a metal-insulator transition, while the band gaps of wetting layers increase and oppositely shift with respect to the Fermi level for n-and p-type substrates. The change in electronic property is attributed to the electron transfer at the Sn-Si interface, which also affects the growth and morphologies of films.

Surface structure of the Sn islands 5 ML high, prepared on Si(111)-(23×23)-Sn substrate, is investigated by low temperature scanning tunneling microscopy/spectroscopy. Due to the elastic strain relaxation in the islands, the in-plane unit cell structure distorts and the apparent height of the surface atoms varies regularly to form an overall modulated strip structure. The quantum well states are observed to depend on the relative position within this structure, which implies the change of the surface chemical potential induced by the elastic strain relaxation as well.