Electronic structure and optical properties of transition metal doped silicon clusters on surfaces - Building blocks for cluster assembled materials

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Because of their fascinating properties, doped semiconductor clusters are promising candidates as building blocks for cluster assembled materials. By doping with transition metal atoms, small silicon clusters can be stabilized in endohedral cage structures with exceptional stability. These clusters are characterized by large highest occupied{lowest unoccupied molecular orbital (HOMO-LUMO) gaps, electronic shell closures, and a silicon cage surrounding the dopant atom. According to theoretical predictions, the HOMO-LUMO gap can be controlled by varying both the dopant atom and the host cluster size. There is even experimental evidence of hydrogen-free doped silicon clusters with no dangling bonds at the cluster surface. In this project, we aim at an understanding of the electronic and optical properties of transition metal doped silicon clusters MSin (M=Cr, Ti, W; n < 20) after deposition onto metal and semiconductor substrates. We will focus on special `magic' clusters with chemical stability, which are suited as building blocks for cluster assembled materials. These clusters will be studied by photoluminescence and photoelectron spectroscopy in the laboratory, accompanied by X-ray absorption spectroscopy at synchrotron storage rings. With these methods, we will clarify fundamental issues of cluster photoluminescence and technologically relevant questions of cluster stability on surfaces, as well as possible electroluminescence in deposited clusters.