Adsorption ofSb4on Ge(001) and Si(001) surfaces: Scanning tunneling microscopy and first-principles calculations

Abstract

We have performed first-principles total energy calculations and scanning tunneling microscopy experiments to study the energetics and the atomic structures resulting from the adsorption of ${\mathrm{Sb}}_{4}$ molecules on the Ge and $\mathrm{Si}(001)\text{\ensuremath{-}}c(2\ifmmode\times\else\texttimes\fi{}4)$ surfaces. Several metastable arrangements are found: ${\mathrm{Sb}}_{4}$ molecules can adsorb as three-dimensional clusters or as flat tetramers. The latter are more stable and can reside either centered on top of the Ge dimer row or half on-top and half over the trench between dimer rows, and in the trenches between two dimer rows. It is found that it is energetically more favorable for ${\mathrm{Sb}}_{4}$ to split into two ${\mathrm{Sb}}_{2}$ dimers adsorbed parallel and on top of the Ge (Si) dimer rows. Simulated scanning tunneling microscopy images are in excellent agreement with the experimental data. The energetics of the diffusion of the dimers into the first Ge (Si) layer is also discussed.