Distortion of SiC lattice induced by carbon-coating on (100) and (111) surfaces- ab-initio and molecular dynamics study

Lattice distortion in cubic SiC lattice induced by surface relaxation at C-terminated low-index atomic planes (100) and (111) was studied by means of molecular dynamics (MD) and ab-initio DFT simulations. DFT results served as a reference for choosing the best MD potential which was next used for examination of lattice distortion for models of SiC particles considerable larger than those accessible by quantum-mechanical calculations. The distortions underneath the surface were examined for stoichiometric lattice naturally terminated by a single monoatomic C layer and also for surfaces covered by one or two excessive carbon layers. It is found that interatomic distances underneath the surface change in lateral and normal directions down to the depth of about 2-3 nm. Surface relaxations at extended surfaces simulated under 2D periodic boundary conditions as well as at surfaces of free standing nanograins were analyzed and compared. It is shown that structural changes induced in SiC lattice by the strains appearing at the grain surfaces are functions of crystallographic orientation of the surface and in case of isolated nanocrystals also depend on their size and shape.