PLACE-EXCHANGE AS A MECHANISM FOR ADLAYER ISLAND NUCLEATION DURING EPITAXIAL-GROWTH AND RESULTING SCALING BEHAVIOR

The effect of place-exchange with a substrate atom as a possible mechanism for creating nucleation sites for adatom islands during epitaxial growth is examined. Simulations and a rate equation analysis show that this has pronounced effects on the island density as a function of coverage and temperature. At low temperature the usual island density scaling holds, while for higher temperatures place-exchange sets in and the island density actually increases with increasing temperature. This leads to a distinct minimum in the island density as a function of temperature, at constant coverage, and a cross over of the island density curves with increasing coverage for temperatures on either side of the minimum. STM results are presented which verify these ideas; the island density of Ni on Ag(111) in the temperature range of 300-500 K shows the predicted temperature dependence.