Influence of oxygen on the mass diffusion of Ag on Cu(110): a laterally resolved photoemission study

We have investigated the influence of oxygen on the mass diffusion of Ag on Cu(110). A silver island of about 1 mm diameter and a thickness of a few monolayers was deposited onto a Cu(110) crystal (diameter 10 mm), either before or after exposition of the whole sample to 25 L of O2. Using a laterally resolving UV-photoelectron spectrometer (resolution in the μm-range), we monitored the diffusion of Ag on both surfaces. On the oxygen-precovered Cu(110) sample, which is (2 × 1)O reconstructed, the diffusion coefficient of Ag at a temperature of T = 370 K is smaller by more than two orders of magnitude as compared to Ag deposited on clean Cu(110). Obviously the dominant diffusion mechanism at T = 370 K, which is an exchange process, is blocked by the presence of oxygen. However, at T = 640 K, the diffusion coefficient of Ag on the Cu(110)(2 × 1)O surface is only about 20% smaller than on the clean substrate. At T = 640 K oxygen does not desorb significantly from Cu(110)(2 × 1)O. However, the presence of the Ag island opens a very effective reaction channel for ‘cleaning’ by diffusion of oxygen onto the Ag island and subsequent desorption.