Direct atomic simulations of facet formation and equilibrium shapes of SiC nanoparticles

Understanding the shapes of nanoparticles is an important interdisciplinary problem because particle shapes can affect their properties, functionality, and applications. Advances in nanoscale imaging probes have revealed exquisite details of nanofaceting phenomena. However, quantitative theoretical predictions have not kept up the pace with experimental advances, and the atomic pathways of facet formation are largely unknown due to a lack of direct observations and simulations. Here we examine facet formation in spherical and cubic SiC nanoparticles and in SiC nanowires using molecular dynamics simulations reaching microseconds. We characterize layer-by-layer formation, diffusional motion along edges and corners, and determine energy barriers. We find that the equilibrium shapes are identical regardless of the initial shape of SiC nanoparticles or nanowires. For spherical and cubic nanoparticles, (110) facets form within 10 ns by lateral liquid-like diffusion of atoms. In contrast, faceting in SiC nanowires also involves normal diffusional motion with a higher energy barrier and hence much longer faceting times. These results have important implications for molecular-level understanding of the synthesis and stability of ceramic nanocrystals and nanowires.