Adatom formation and atomic layer growth on Al(111) by ion bombardment: experiments and molecular dynamics simulations

Rare gas ion bombardment of the Al(1 1 1) surface is found to produce adato ms with high efficiency, while at the same time stable vacancy clusters in the bulk are produced, As a result, scanning tunneling microscopy experimen ts show an initial bombardment-induced growth of several atomic lavers inst ead of the expected erosion. This phenomenon is observed for Ne+, Ar+, and Xe+ for temperatures between 100 and 400 K and for ion energies between 0.3 and 8 keV. On the basis of molecular dynamics simulations insight into the atomic mechanism of bombardment-induced growth is gained. Ion bombardment causes local melting of the Al crystal near the surface, The energy is rapi dly transported out of the molten volume, and after a few picoseconds a hig hly undercooled melt results, which has swollen above the initial surface l ayer. During recrystallization of the amorphous zone from the crystal inner towards the surface. vacancy clusters are left at the phase boundary, whic h stabilize part of the swollen material as adatoms, thus leading to the ob served bombardment-induced growth. (C) 2001 Elsevier Science B.V. All right s reserved.