AU ON W(001) - CHANGE IN STRUCTURE AND ORIENTATION

Ultraviolet photoemission spectroscopy (UPS) measurements during the d eposition of Au on 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 re ached is a result of the large misfit between various orientations of Au with the W(001) surface. The orientation at characteristic thicknes ses 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 th ermally stable at lease up to 900 K. The surface layer of the pseudomo rphic 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 t his coverage the orientation changes and a fee (001)-oriented film is observed for coverages above 23 ML. At 150 K, a (111) orientation appe ars between 10 and 23 ML, which can be obtained in a pure and perfect form by annealing at 600 K. The transition to fee (001) shifts to high er coverages with increasing deposition rate.