Nanodot Formation on theSi(111)-(7×7)Surface by Adatom Trapping

Abstract
The formation of a superlattice of metallic nanoclusters consisting of nine adatoms each is reported for thallium on the Si(111)(7×7) surface. It is proposed that mobile adatoms are trapped in attractive potential wells on the faulted half of the (7×7) unit cell. Adatom-adatom and adatom-substrate interactions combine within these basins of attraction to create the observed metallic bonding situation. From quasiequilibrium thermodynamic considerations, the energy difference between adsorption on the faulted and unfaulted unit cell halves, that yields the ordered superstructure array, is estimated to 0.075 eV.