This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.
 

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Assuming the crystalline parameters in nanoparticles are the same as those in bulk crystals, an Au (gold) nanoparticle in diameter of ~2.3 nm contains 309 atoms. Those atoms can be packed into a completed polyhedron, such as icosahedrons, ino-decahedrons or cuboctahedrons. [1] In this type of clusters, approximately 50% atoms locate at the surface.

[1] Curley BC, Johnston RL, Young NP, Li ZY, DiVece M, Palmer RE, et al. J Phys Chem C 2007;111:17846–51.