Clustering effects in a low coverage deposition of gold on the GaAs (001) ?2-(2x4) surface: an STM and theoretical study

A comparative study of gold deposition on the GaAs(0 0 1)-b2(2 4) surface based on scanning tunneling microscopy (STM)-ultra high vacuum (UHV) and Car-Parrinello calculations has been carried out. The theoretical results show that the preferential reactive sites of an isolated Au adatom on the GaAs surface drive a self-organizing process of further Au adatoms onto the surface, thus determining an Au clusterization onto the two-As-dimer cell. On the other hand, STM-UHV images reveal, for Au depositions <1 ML, a decorating effect of gold towards the GaAs(0 0 1)-b2(2 4) unit cell. In detail, gold clusters tend to cover the two-As-dimer cell without modifying the (2 4) reconstruction, in agreement with the theoretical results. Moreover, a fine comparison between the STM images of gold clusters and the theoretical results reveals that each of these clusters can be composed of four Au adatoms directly interacting with the two As dimers of the GaAs unit cell. An STM-UHV analysis of the surface for a deposition >1ML suggests that gold clusterizes into 3D clusters rather than forming a 2D layer.