TOF-ICISS observation of Pb growth on the Si(111)−3×3 − Ag surface

We have investigated the Pb thin film growth on Si(111)-7 X 7 and Si(111)- √3 X √3-Ag surfaces at room temperature using time-of-flight impact collision ion scattering spectroscopy (TOF-ICISS). From the angle-resolved TOF spectra of the Pb film grown onto each of these two different substrates, we found that Ag atoms on the Si(111) surface promote epitaxial growth of Pb film at room temperature. The crystalline quality of Pb(111) overlayers grown on the Si(111)-√3 X √3-Ag surface is much better than that grown on the clean Si(111)-7 X 7 surface, although the growth of the Pb film on the former surface occurs by the Stranski-Krastonov (SK) growth mode as well as the growth on the latter. In the presence of the √3 X √3-Ag layer, the Pb overlayer epitaxially grows with the orientation of Pb(111)[011]||Si(111)[011], which is the same as for the one grown on the clean Si(111)-7 X 7 surface. Also, we have found that the coverage of the 2D Pb layer in the SK growth is 1.35 ML on the Si(111)-7 X 7 surface, while it is 1.0 ML on the Si(111)-√3 X √3-Ag surface.