TOWARDS AN UNDERSTANDING OF SURFACTANT ACTION IN THE EPITAXIAL-GROWTHOF METALS - THE CASE OF SB ON AG(111)

We address the role of ''surfactant'' adsorbates in determining change s in the homoepitaxial growth mode of metals, discussing the case of S b on Ag (111). From ab initio calculations, we extract evidence that t he mechanism operative in this system is that Sb induces an irregular shape and an increase in density of the growing Ag islands, and an ens uing increase of the number of attempts for an adatom to descend to a lower terrace. This results from a combination of peculiar properties of this system: Sb is adsorbed in substitutional surface sites, leadin g to the formation of a Sb-Ag surface alloy; deposited Ag has reduced mobility on Sb-covered Ag (111), from which follows a higher nucleatio n probability. The island shape is irregular since the surface alloy i s disordered. Surface seggregation of Sb once the growing layer is com pleted furthers the phenomenon for many deposited Ag layers. Our expla nation of the surfactant action of Sb on Ag (111) does not require a r eduction of the downstep diffusion barrier, which may, however, be a c oncurrent factor helpful to interlayer mass transport and layer-by-lay er growth.