It was found, using scanning tunnelling microscopy, that the Ag-on-Au(111) system exhibited morphological instability in the formation of the first monolayer. Monolayer-high Ag protrusions grew out from atomic steps and onto atomic terraces. The structure of the deposits, at the nanometre scale, showed that Ag atoms diffused freely on Au terraces, but were not mobile along, or across, the step edges which separated the terraces. This led to a complex growth front which was characteristic of diffusion-limited aggregation with local relaxation. This produced a marked inhomogeneity of the local coverage. Consequently, even at an average coverage of 1.1 monolayers, there were large (10000nm2) areas of exposed Au surface. A study of step structures which had been produced by tip impact indicated that atoms on step edges were not very mobile at room temperature. Therefore, the dominant mechanism in the local smoothing of these deposits was a relaxation that was intrinsic to the aggregation process.

D.D.Chambliss, R.J.Wilson: Journal of Vacuum Science and Technology B, 1991, 9[2],