Step Height Oscillations during Layer-by-Layer Growth of Pb on Ge(001)

Heteroepitaxial growth of Pb on the Ge(001) surface has been studied by He atom scattering. For low substrate temperatures, Pb is found to grow layer by layer with (111) orientation. A detailed analysis of the specular peak profile as a function of the He wave vector reveals that the step height of the growing monatomic terraces oscillates with the film thickness. This variation, initially as large as ±15% around the value of the Pb(111) bulk interlayer spacing, gradually dampens out after the deposition of a dozen monolayers. This is direct evidence of quantum size effects affecting the interlayer distance of a growing metal film.