Nanoparticles are of great interest in fields such as biomedicine, heterogeneous catalysis, and plasmonics, to name a few. Owing to their large surface-to-volume ratio, many of the novel properties of these particles originate from their surfaces. The properties of these surfaces, in turn, depend strongly on the local atomic configuration, i.e., on the type of faceting. Specifically, small transition metal particles with low twinning energies frequently form multiply twinned particles (MTPs) such as icosahedra and decahedra to minimize their surface energy by solely exposing (111) type facets to the outer world. Hence, controlling the surface (free) energies should provide control over the particle morphologies.
We routinely prepare a variety of metallic nanoparticles (Au, Pt, CuAu, …) with sizes in the range 3-10 nm by means of intert gas condensation. Through the addition of small amounts of O2 to the Ar process gas the (111) facets are energetically de-favoured, and while the particles are mostly MTPs when prepared in pure Ar, the addition of O2 leads to the formation of predominantly single crystalline Au octahedra.
Further reading: D. Pohl et al., Appl. Phys. Lett. 101, 263105 (2012) URL