Comparison of Theoretical Binding of Pb and Au Adatoms on Ge(111) and Ge(110) with Experimental LEEM Measurements

Using first principles density functional theory, we have calculated the energies of the most favorable binding sites for a Pb ad-atom on the Ge(111) and Ge(110) surfaces. We compared three different sites on the Ge(111) surface and two different sites on the Ge(110) surface. The surfaces were modeled by five layers of Ge atoms, with the top two layers being allowed to relax. The calculated charge distributions that illustrate properties of the binding of Pb to Ge are compared with those for Au ad-atoms on the same surfaces. The dangling bonds of near-neighbor Ge atoms form covalent bonds with Pb atoms, whereas Au ad-atoms, which have no p-valence electrons, are simply polarized towards neighboring Ge atoms. The theoretical results will be compared with structural data from low energy electron microscopy (LEEM) images of Pb and Au islands on Ge surfaces. These include movies that show the collective diffusion of Pb atoms to form islands on Ge(111) [1] and the motion of Au-Ge alloy droplets on Ge(110) due to temperature gradients.[2]

[1] A.R. Kim, Ph.D. dissertation, UC Davis (2022).

[2] B. H. Stenger et al, Ultramicroscopy, 183, 72, (2017).