Abstract
The growth of three-dimensional ultra-fine spherical nano-particles of silver on few layers of graphene derived from highly oriented pyrolytic graphite in ultra-high vacuum were characterized using in situ scanning tunneling microscopy (STM) in conjunction with X-ray photoelectron spectroscopy. The energetics of the Ag clusters was determined by DFT simulations. The Ag clusters appeared spherical with size distribution averaging approximately 2 nm in diameter. STM revealed the preferred site for the position of the Ag atom in the C-benzene ring of graphene. Of the three sites, the C-C bridge, the C-hexagon hollow, and the direct top of the C atom, Ag prefers to stay on top of the C atom, contrary to expectation of the hexagon-close packing. Ab initio calculations confirm the lowest potential energy between Ag and the graphene structure to be at the exact site determined from STM imaging.
Highlights
The control of material assembly on the nano-meter scale [1,2,3,4] as well as their self-assembly [5,6,7] are the two extremes of the most intensely studied subjects in the fields of nano-science and nano-technology
On relatively inert substrates, such as graphite, many nano-structures can be fabricated in a nearly free-standing state by various deposition techniques such as thermal evaporation [12,13,14]. These structures can be characterized by popular analytical techniques such as scanning probe microscopy and X-ray photoelectron spectroscopy (XPS)
This article presents an investigation by scanning tunneling microscopy (STM) and XPS of individual self-assembled Ag nano-clusters grown by thermal evaporation of Ag atoms on Highly oriented pyrolytic graphite (HOPG) surfaces at room temperature
Summary
The control of material assembly on the nano-meter scale [1,2,3,4] as well as their self-assembly [5,6,7] are the two extremes of the most intensely studied subjects in the fields of nano-science and nano-technology. Studies on properties of deposited silver nano-clusters and particles are of fundamental interest and related to various technologically important fields such as catalysis, electronic devices, and gas sensors [21,22]. These metal clusters can be regarded as the precursors to a new generation of nano-structured materials and devices [10,13,23]. This article presents an investigation by STM and XPS of individual self-assembled Ag nano-clusters grown by thermal evaporation of Ag atoms on HOPG surfaces at room temperature. Brillouin zone sampling was done using the 2 × 2 × 1 special k-point mesh employing the MonkhorstPack scheme [29]
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