Face-Centered-Cubic Ag Nanoclusters: Origins and Consequences of the High Structural Regularity Elucidated by Density Functional Theory Calculations.

Abstract

Face-centered-cubic (FCC) silver nanoclusters (NCs) adopting either cubic or half-cubic growth modes have been recently reported, but the origin of these atomic assembly patterns and how they are achieved, which would inform our understanding of larger FCC silver nanomaterials, are both unknown. In this study, the cubic and half-cubic growth modes have been unified based on common structural characteristics, and differentiated depending on the starting blocks (cubic vs. half cubic). In both categories, the silver atoms adopt octahedral Ag6 , linear AgS2 (in projection drawing), or tetrahedral AgS3 P binding modes, and the sulfur atoms adopt T-shaped SAg3 and orthogonal SAg4 modes. An additional T-shaped AgS3 mode is oriented on the surface edge in cubic NCs to complete the cubic framework. Density functional theory calculations indicated that the high structural regularity originates from the strong diffusing capacity of the Ag(5d) and S(3p) orbitals, and the angular momentum distribution of the formed superatomic orbitals. The equatorial orientation of μ4 -S or μ4 -Ag determines whether growth stops or continues. In particular, a density-of-states analysis indicated that the octahedral silver atoms are chemically more reactive than the silver atoms in the AgS3 P motif, regardless of whether the parent NC functions as an electron donor or acceptor.