The formation of a superlattice of metallic nanoclusters consisting of nine adatoms each is reported for thallium on the Si͑111͒-͑7 3 7͒ surface. It is proposed that mobile adatoms are trapped in attractive potential wells on the faulted half of the ͑7 3 7͒ 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. PACS numbers: 61.16.Ch, 61.46. + w, 68.35.Bs, 82.65.Dp The controlled formation of ordered metal nanostructures on solid surfaces by self-organized growth is a fabulous challenge of both fundamental scientific and applied technological research [1]. The nucleation of adatoms into an ordered array of regular clusters of dimensions small enough that quantum mechanical effects determine their properties, i.e., quantum dots or nanodots, is of particular interest, since new properties such as quantum interference effects may emerge [1,2]. Here we describe the formation of an ordered array of two-dimensional nanodot structures of deposited metal atoms on the Si͑111͒-͑7 3 7͒ surface. The process is mediated by the intrinsic attractive potential wells that exist on the faulted halves of the Si͑7 3 7͒ unit cells [3], which effectively trap diffusing metal atoms to create a regular arrangement of islands of well-defined size. This island formation process appears to be controlled thermodynamically by a quasiequilibrium situation and has been discovered during adsorption studies of thallium on the Si͑111͒-͑7 3 7͒ surface.The bonding of adatoms on the Si͑111͒-͑7 3 7͒ surface and the identification of stable binding sites as well as the determination of surface diffusion pathways are important problems of interest for the detailed understanding of the initial stages of metal-Si interface formation. Brommer et al. [4] have applied the concept of "local softness" within density functional theory (DFT) to predict a qualitative pattern of reactive sites for the interaction of atoms and molecules on the Si͑111͒-͑7 3 7͒ surface. Within the framework of a local bonding concept adsorbate atoms are placed at various surface dangling bond sites in the ͑7 3 7͒ unit cell. A somewhat different approach has been put forward recently by Cho and Kaxiras [5,6], who studied the adsorption and diffusion of adatoms on the reconstructed Si͑111͒ surface by DFT total-energy calculations. Their bonding picture is of a more delocalized nature and they introduce so-called basins of attraction, which contain stable adsorbate positions as high-coordination sites rather than surface dangling bond sites.The experimental work which is reported in this Letter was undertaken to elucidate the effects of valency and atomic size on the bonding characteristics of metal adatoms on the Si͑111͒-͑7 3 7͒ surface reconstruction: The group III metal thall...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.