The spreading of a patch of deposited Ag, with an initial coverage of several monolayers, over Ge(111)-c(2 x 8) was observed by means of the scanning Auger electron spectroscopy of a heated Ge substrate. The final Ag layer was uniform in coverage (one monolayer) and structure (v3 x v3 R30º) with a sharp leading edge. The longitudinal spread parallel to the current, which was dominated by electromigration, was preferentially directed towards the cathode and was linearly proportional to the period of application of a direct current. The transverse spread was proportional to the square root of the elapsed time, and was consistent with the surface diffusivity. The transverse spread exhibited a temperature dependence, with an activation energy of 0.50eV. Theoretical expressions for the spreading were derived, and it was deduced that the effective charge on the Ag adatom could be as large as 13q.

H.Yasunaga, T.Aida: Japanese Journal of Applied Physics 1, 1992, 31[10], 3440-5