Au onW(001):Change in structure and orientation

Abstract

Ultraviolet photoemission spectroscopy (UPS) measurements during the deposition of Au on form$\mathrm{W}(001)$ at 150 K show that over 30 ML of Au have to be deposited before the electronic structure of the deposit stabilizes. This large film thickness before a stationary growth situation is reached is a result of the large misfit between various orientations of Au with the $\mathrm{W}(001)$ surface. The orientation at characteristic thicknesses is analyzed with a combination of reflection high-energy electron diffraction, x-ray photoelectron diffraction (XPD), and UPS. The first 3.5 ML form a pseudomorphic body-centered-tetragonal layer that is thermally stable at least up to 900 K. The surface layer of the pseudomorphic triple layer shows a hexagonal reconstruction and consists of 1.5 ML of atoms. After this initial range, the film continues to grow in the bcc (001) orientation up to 10 ML at both 150 and 300 K. Beyond this coverage the orientation changes and a fcc (001)-oriented film is observed for coverages above 23 ML. At 150 K, a (111) orientation appears between 10 and 23 ML, which can be obtained in a pure and perfect form by annealing at 600 K. The transition to fcc (001) shifts to higher coverages with increasing deposition rate.