X-ray spectroscopy reveals high symmetry and electronic shell structure of transition-metal-doped silicon clusters

Size-selected cationic transition-metal-doped silicon clusters have been studied with x-ray absorption spectroscopy at the transition-metal L_2,3 edges to investigate the local electronic structure of the dopant atoms. For VSi₁₆⁺, the x-ray absorption spectrum is dominated by sharp transitions which directly reveal the formation of a highly symmetric silicon cage around the vanadium atom. In spite of their different number of valence electrons, a nearly identical local electronic structure is found for the dopant atoms in TiSi₁₆⁺, VSi₁₆⁺, and CrSi₁₆⁺. This indicates strongly interlinked electronic and geometric properties: while the transition-metal atom imposes a geometric rearrangement on the silicon cluster, the interaction with the highly symmetric silicon cage determines the local electronic structure of the transition-metal dopant.