Clustering in pb thin films on bromine-passivated si(1 1 1) surfaces

Abstract

Thin Pb films, deposited on clean Si surfaces at room temperature (RT), show spectral broadening in ion backscattering spectra due to clustering of Pb, when annealed [Nucl. Instr. and Meth. B 190 (2002) 641]. In order to study the dynamics of clustering on bromine-passivated Si(1 1 1) substrates, Pb thin films (~1-3 nm) were deposited from a Knudsen cell under ultrahigh vacuum conditions. Each film was deposited at RT and subsequently annealed at 100, 150 and 260 °C for about 4 h. Five Rutherford backscattering spectrometry (RBS) measurements were made at different time intervals for each annealing . Analysis of RBS spectra of as-deposited and annealed Pb films, does not show any significant spectral broadening in annealed Pb films. However, island formation has been confirmed by transmission electron microscopy on a 100 °C-annealed sample. Clustering has apparently occurred in the as-deposited film due to lower surface free energy of the passivated substrate and further detectable growth in cluster height has not occurred in annealing.