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How does the fraction of surface atoms change as a cluster grows larger?
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cluster
Figure 1: The four stable geometric structures of the seven-atom cluster of argon, in order of increasing energy: (A) A pentagonal bipyramid. (B) A regular octahedron with one face capped by the seventh atom. (C) A regular tetrahedron with three of its faces capped by other atoms. (D) A trigonal bipyramid with two of its faces capped by other atoms; although this has the highest energy of the four structures, it is very close in energy to the tricapped tetrahedron.
As a cluster grows larger, the fraction of its atoms located on the surface decreases.
In small clusters, a significant proportion of the total atoms are positioned on the surface, which contributes to their unique physical properties, such as enhanced particle mobility and higher vapour pressure compared to bulk matter. For instance, in a 10-nm-diameter nanosphere, approximately 20 percent of the atoms are located at the surface. As the cluster size increases, the ratio of surface atoms to interior atoms diminishes, causing the cluster's properties to gradually shift toward those of the corresponding bulk solid or liquid.12