SURFACE ELECTROMIGRATION AND DIFFUSION OF AG ON GE(111)

Spread of a deposited Ag patch with coverage of several monolayers over Ge(111)-c(2 x 8) was observed with scanning Auger electron spectroscopy when the Ge substrate was heated by DC current. The spread-out Ag layer was uniform in coverage (1.0 monolayer) and structure (square-root 3 x square-root 3-R30-degrees) with a sharp leading edge. The longitudinal spread parallel to the current, dominated by the electromigration, was preferential towards the cathode with linear proportionality to the time of the DC power supply, while the transverse spread was well balanced and proportional to the square root of the time, consistently with the surface diffusion. The transverse spread exhibited a temperature dependence with the thermal activation energy of 0.50 +/- 0.1 eV. Theoretical expressions for the spreads were derived and compared with the data. The effective charge of the Ag adatom was as large as + (13 +/- 2)q.