ATOMIC MECHANISMS OF THE FORMATION OF AN ORDERED SURFACE ALLOY - AN STM INVESTIGATION OF MN CU(100)/

Atomic processes important in surface alloy formation for Mn/Cu(100) w ere determined using STM (scanning tunneling microscopy). By exploitin g the pronounced corrugation, incorporated Mn atoms were distinguished from Cu atoms in the STM images. Mn atoms are preferentially incorpor ated in the vicinity of island edges and substrate steps. In the proxi mity of substrate steps, the rate of incorporation into the lower terr ace is correlated with the kink density of the steps. This indicates t hat the interlayer mass transport necessary for Mn incorporation into the lower terrace is particularly efficient close to kinks. Atomic exc hange processes and vacancy mechanisms which proceed in the vicinity o f kinks can explain this observation. Vacancy annihilation by Mn adato ms is the only process which at least qualitatively can account for bo th the observed coverage dependence of Mn incorporation and the import ance of kinks. The alloying of the upper terrace of substrate steps is driven by an attachment of Mn adatoms. This step is essentially indep endent of the step orientation, which explains why the concentration o f incorporated Mn in the vicinity of steps does not depend upon the st ep direction. Subsequent step fluctuations and more importantly, vacan cy-mediated diffusion of incorporated Mn atoms, lead to a more homogen eous Mn distribution with time.