Equilibrium shapes and surface selection of nanostructures in 6H-SiC

The equilibrium shape of 6H-SiC nanostructures and their surfaces were studied by analyzing nano-void (∼10 nm) shapes, which were introduced in monocrystalline 6H-SiC by high-temperature neutron irradiation, using transmission electron microscopy. The nano-voids were determined to be irregular icosahedrons truncated with six { 1 ¯ 100}, twelve { 1 ¯ 103}, one smaller top-basal, and one larger bottom-basal planes, which suggests that { 1 ¯ 100} and { 1 ¯ 103} are the next stable surface class after the basal planes. The relatively frequent absence of the { 1 ¯ 100} surface in the nano-voids indicated that the ( 1 ¯ 10 3 ¯ ) surface type is energetically rather stable. These non-basal surfaces were found not to be atomically flat due to the creation of nanofacets with half unit-cell height in the c-axis. The { 1 ¯ 100} and { 1 ¯ 103} surfaces were classified as two and four face types according to their possible nanofacets and surface termination, respectively. We also discuss the surface energy difference between the ( 1 ¯ 10 3 ¯) and ( 1 ¯ 103) face types in relation to the energy balance within the equilibrium, but irregular, polyhedron, in which the ( 1 ¯ 103) surface had double the surface energy of the ( 1 ¯ 10 3 ¯ ) surface (∼3900 erg/cm²).