STM STUDY OF AU GROWTH ON S-MODIFIED RU(0001)

We present results of a detailed scanning tunneling microscopy (STM) s tudy of submonolayer nucleation and growth of two-dimensional Au islan ds during deposition on clean versus S-precovered Ru(0001), at room te mperature. In the presence of tiny amounts of S, a dramatic increase i n the mean island densities is observed, corresponding to a decrease i n the effective mobility of Au on Ru(0001). As imaged also by STM, the structure of the S adlayer changes during Au deposition, from a dilut e lattice-gas, at low Au coverages, to an increasingly denser sequence of ordered superstructure p(2 x 2), (root 3 x root 3-R30 degrees) and c(2 x 4) domains, with increasing Au coverage. These findings suggest that the deposited Au atoms displace S adatoms, compressing S domains , a phenomenon consistent with a net repulsive interaction between nei ghboring Au and S mediated by the Ru substrate. (C) 1997 Elsevier Scie nce B.V.