Preadsorption of gallium on GaAs(1Â 1Â 1)B surface during the self-catalyst growth of GaAs nanowires

We have investigated the preadsorption of gallium on GaAs(1 1 1)B surface during the self-catalyst growth of GaAs nanowires by first-principles calculations. We found that the Ga adatoms can be stabilized on GaAs(1 1 1)B surface only at low coverage. These Ga adatoms have a tendency to form Ga droplets when the Ga coverage is further increased. The micro-mechanism of Ga droplets formed on GaAs(1 1 1)B surface have also been revealed. The calculated result shows that the Ga adatoms dislike to incorporate on GaAs(1 1 1)B surface. The As adsorption on GaAs(1 1 1)B surface can be promoted by Ga preadsorption. The reason for Ga droplets can be used as collector of As atoms is that the As adatoms can stabilize the Ga preadsorbed GaAs(1 1 1)B surface. Our results are useful to understand the self-catalyst growth of GaAs nanowires.