The Superstable 25 kDa Monolayer Protected Silver Nanoparticle: Measurements and Interpretation as an Icosahedral Ag152(SCH2CH2Ph)60 Cluster

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• 作者：Indranath Chakraborty ; Anuradha Govindarajan ; Jayanthi Erusappan ; Atanu Ghosh ; T. Pradeep ; Bokwon Yoon ; Robert L. Whetten ; Uzi Landman
• 刊名：Nano Letters
• 出版年：2012
• 出版时间：November 14, 2012
• 年：2012
• 卷：12
• 期：11
• 页码：5861-5866
• 全文大小：396K
• 年卷期：v.12,no.11(November 14, 2012)
• ISSN：1530-6992

文摘

A cluster obtained in high yield from the reduction of a silver-thiolate precursor, Ag-SCH₂CH₂Ph, exhibited a single sharp peak near 25 kDa in the matrix-assisted laser desorption mass spectrum (MALDI MS) and a well-defined metal core of 2 nm measured with transmission electron microscopy (TEM). The cluster yields a single fraction in high-performance liquid chromatography (HPLC). Increased laser fluence fragments the cluster until a new peak near 19 kDa predominates, suggesting that the parent cluster鈥擜g₁₅₂(SCH₂CH₂Ph)₆₀鈥攅volves into a stable inorganic core鈥擜g₁₅₂S₆₀. Exploiting combined insights from investigations of clusters and surface science, a core鈥搒hell structure model was developed, with a 92-atom silver core having icosahedral-dodecahedral symmetry and an encapsulating protective shell containing 60 Ag atoms and 60 thiolates arranged in a network of six-membered rings resembling the geometry found in self-assembled monolayers on Ag(111). The structure is in agreement with small-angle X-ray scattering (SAXS) data. The protective layer encapsulating this silver cluster may be the smallest known three-dimensional self-assembled monolayer. First-principles electronic structure calculations show, for the geometry-optimized structure, the development of a 0.4 eV energy gap between the highest-occupied and lowest-unoccupied states, originating from a superatom 90-electron shell-closure and conferring stability to the cluster. The optical absorption spectrum of the cluster resembles that of plasmonic silver nanoparticles with a broad single feature peaking at 460 nm, but the luminescence spectrum shows two maxima with one attributed to the ligated shell and the other to the core.

Keywords:

Noble metals; clusters; nanoparticles; plasmon resonance; MALDI MS; first-principles electronic structure; projected electronic density of states (PDOS); superatom electronic shells