Epitaxial growth of gold on Si(001)

We study the formation of nanoscale epitaxial Au islands on Si(001) below the eutectic point. Growth experiments were performed in molecular beam epitaxy, and plausible interface models were derived from electron diffraction and transmission electron microscopy. For these models, formation energies were obtained in density functional theory (DFT). In-situ electron diffraction indicates that during the deposition of the first two monolayers, the Si(001) surface mesh is preserved. Au(110) islands form at a coverage above three monolayers. DFT shows that the formation energy for an atomically flat interface is higher for this (110) orientation than for (001) growth. We propose an interface configuration that promotes Au(110) growth and is kinetically stabilized even though this is not the epitaxial orientation with the lowest mismatch strain. The proposed configuration implies a mixed interface layer containing both Au and Si atoms.