HOMOEPITAXIAL GROWTH ON NI(100) AND ITS MODIFICATION BY A PREADSORBED OXYGEN ADLAYER

Homoepitaxial growth of thin Ni films and the influence of a O c(2 x 2) adlayer on the growth behavior were investigated by scanning tunneling microscopy. At 300 K and 0.3 monolayers/min flux rate Ni film growth on the clean surface proceeds via homogeneous nucleation, lateral growth, and coalescence of two-dimensional, monolayered Ni islands, exhibiting an almost perfect layer-by-layer growth behavior. The relatively high density of 2D Ni islands of 1.8 x 10(12) cm-2 indicates a low mobility of the Ni adatoms. The oxygen adlayer, which floats on the surface in its initial c(2 x 2) structure, has little effect on the growth mode and the actual growth process. Its influence manifests in the dynamics of 2D island growth, where the island edges are reoriented from along [011] on the clean surface to along [001] on the oxygen covered surface. This observation and the simultaneous change from square to pronounced rectangular island shapes are explained in a simple picture based on the registry relation between O c(2 x 2) adlayers on two subsequent Ni layers. A tentative model for the oxygen transport to the surface is proposed involving a simple displacement of O adatoms, during Ni condensation at the island edges.