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

Abstract

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 ${\text{VSi}}_{16}^{+}$, 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 ${\text{TiSi}}_{16}^{+}$, ${\text{VSi}}_{16}^{+}$, and ${\text{CrSi}}_{16}^{+}$. 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.