2-DIMENSIONAL ALLOYING OF AU AND CU OVERLAYERS ON RU(001)

The electronic structure of Au overlayers, and alternate Au and Cu overlayers on Ru(001) has been studied with photoemission spectroscopy using synchrotron radiation. The Au 5d partial densities of states, which are very sensitive to alloying, are used to prove the interaction. At submonolayer and monolayer coverages, the valence-band spectra of Au/Ru(001) exhibit densities of states, in the 1.3-eV region, uncharacteristic of pure Ru and Au. They are attributed to (sub)monolayer adsorbate-induced states with significant Au and Ru contributions. Adsorption of a monolayer of Au and a monolayer of Cu on Ru(001) at room temperature results in the formation of a stable phase of a two-dimensional Cu-Au alloy. This is evident from the Au 5d partial densities of states in the photoemission spectra and a compressed 1 x 1 low-energy electron-diffraction pattern. The implications of these observations are discussed.