Clustering in Pb thin films on Si(1 1 1) and Pb-induced Si surface ordering

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Pb thin films (10 nm) were deposited from a Knudsen cell on sputter-cleaned Si(1 1 1) substrates under ultrahigh vacuum conditions. Films were deposited at room temperature and subsequently annealed at 300 °C for 30 min. Rutherford backscattering spectrometry and channeling (RBS/C) measurements did not show any channeling in the as-deposited as well as annealed Pb layer. For the annealed sample the spectral broadening in RBS/C spectra occurred due to clustering of Pb, with a simultaneous reduction in the minimum yield from the Si substrate. Prior to Pb deposition the sputter-cleaned Si substrate was annealed at 500 °C, which was insufficient to remove all the damages introduced by Ar + sputtering. Thus the reduction of minimum yield in the substrate for the annealed Pb/Si(1 1 1) system compared to unannealed Pb/Si(1 1 1) may be interpreted as Pb-induced ordering of the Si surface. From the analysis of the step structure observed near the Si edge of the RBS/C spectrum for the annealed sample, it was found that Pb islands (average height ∼35 nm) have been formed on a uniform Pb layer of ∼1 nm thickness. The island formation has been confirmed by atomic force microscopy measurements.