Recent experimental [1,2] and theoretical [3,4] results on the prediction of transition metal (TM) encapsulated caged silicon clusters have effectively resurrected the prospect of controlling the Si clusters and sustaining the Si technology for developing novel nanoforms of Si-based materials and devices. As compared to elemental Si clusters the new species have stronger stability, higher symmetry and size selectivity. Some of these new types of Si clusters have also been predicted to have large energy gaps lying in the visible range. These clusters have thus enormous potential for the development of Si cluster assembled materials as well as functionalization for nanodevice applications.
In this paper further results will be presented on the recently discovered W and Ti caged Sin clusters (n=12, 15, and 16). Based on pseudopotential plane wave and linear combination of atomic orbitals ab initio calculations we will discuss the atomic and electronic structure of the experimentally observed W- and TiSin species. The total energy calculations suggest that all observed Ti@Si14 and Ti@Si15 clusters are of Frank-Kasper type . The stability of the Ti@Si15 clusters is accounted for their atomic shell structure similar to the stable Si(001)2x1 surface reconstruction. Two isonergetic FK Ti@Si16 have different electronic structure depending on the symmetry of the Ti@Si16 clusters. All of the studied clusters have large energy gap that make them very attractive for applications. The existence of other than hexagonal prism high symmetry stable caged Frank-Kasper W@Si12 clusters rules out the 18 valence electron principle to account for the stability of the TM encapsulated Si clusters.
The possible implications of the discovered features on the use of Si-based clusters as experimentally devices or building blocks of Si-cluster-based assembled materials will also be discussed.
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 M.W.Radny, V. Kumar and Y. Kawazoe, to be published
Marian W. Radny
School of Mathematical and Physical Sciences, The University of Newcastle
Callaghan, NSW 2308 Australia
Phone: +61 2 49 21 5447 Fax: +61 2 49 21 9607