Direct Atomic Simulations of Facet Formation and Equilibrium Shapes of SiC Nanoparticles

Abstract

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.

Diffusion-driven frictional aging in silicon carbide

“…Major nano-ribbons (ribbons traversing boundary to boundary) are present at all temperatures we have examined. These ribbons are formed because the (110) planes have lower energies than the (100) surfaces [23]. At temperatures around 2000 K, we also observe additional small ribbons between the major ribbons.…”

“…rhombic dodecahedron with distance 11.70 nm between the (111) planes and the center of the asperity is carved out making the asperity shape close to the Wulff shape of our model silicon carbide [23]. The asperity is attached to a rigid top plate that is used to impose a normal load and lateral motion on the asperity.…”

“…For example, quartz crystals develop naturally over many years under high pressure and temperature, while diamond formation may take hundreds of millions of years [20]. However, silicon carbide has a relatively low activation energy compared to its melting temperature, and thus it is possible to obtain high self-diffusion in molecular dynamics simulations [21][22][23]. This feature enables atomistic simulations of processes that are impractical for most other materials.…”

The role of particle shape in computational modelling of granular matter

“…The design and testing of specially shaped nanoparticles and colloidal particles have become an emerging technology for creating functional nanostructures 23,24 or smart materials via processes such as reversible assembly 25 and magnetic assembly 26 . On this scale, MD 27,28 is prevalent as a simulation tool. Particle shape has an underpinning role for inactive…”

“…There are two prevailing approaches to aggregating primitives: one simply clumps the primitives together to obtain the best-fit shape profile by allowing arbitrary overlapping between the primitives, exemplified by such methods as sphere-clump particles 37 and cross-shaped particles 38 ; the other is the so-called cluster approach in which the overlap between the primitives is constrained by taking interprimitive interactions into consideration. Typical methods in this category include the sphere-cluster particle and the point-cluster (cloud) particle 27 . The cluster-type particle methods often require many primitives to render sufficient representation of the realistic shape, which may incur increasing computational cost and hinder their application for modelling large-scale systems.…”