How Sulfur Controls Nucleation of Ag Islands on Ag(111)

Pre-adsorbed sulfur controls nucleation of Ag islands on Ag(111), at coverages above a very small critical value. Sulfur can exert opposite effects: it accelerates mass transfer of Ag to steps and hence inhibits nucleation under some conditions, but it impedes mass transfer and hence enhances nucleation under others. The effect depends upon sulfur coverage and temperature. The inhibition or acceleration of mass transfer correlates with the existence or absence of a semi-static, ordered arrangement of Ag3S3 clusters.