A model of density waves in atomic structure of nanodiamond by molecular dynamics simulations

Spherical and polyhedral diamond nanocrystals grains terminated by low-index atomic planes (100), (110), and (111) were examined using Molecular Dynamics (MD) simulations. Real space methodology (PDF analysis) was applied for examination of the internal structure of diamond nanograins through performance of virtual diffraction experiments for MD simulated models. The effect of the grain size on, (1), the bond length in the nearest neighbor coordination, (2), the overall lattice parameter, and (3), a presence of internal strains in individual grains were examined. It is shown that, (a), graphite-like bonds are present in the first 2-3 atomic layers, depending on the surface type, (b) in 2-3 nm grains the overall value of alp is about 0.5% larger than the reference diamond lattice parameter and it goes down to the reference diamond lattice in grains of about 10 nm in size, (c), in individual spherical grains the so called "density waves", propagating from the grain center towards the surface, are present. In the "general model" of nanodiamond structure the number of density maxima is the same for grains with sizes between 2.5 and 10 nm, but the amplitude of the waves diminishes with an increase in the grain size.