Abstract

We investigate the vibrational density of states (VDOS) on defective diamonds with different nanoscale defects. The VDOS shows two main peaks, the low-frequency peak slightly below 25 THz, and the high-frequency peak at around 45 THz. We consider spherical diamond nanoparticles, with diameters of 5 nm, 10 nm, and 20 nm. Nanodiamond surfaces provide defects that are augmented by mechanical deformation during nanoindentation, resulting in dislocation generation and a disordered region. The height of the low-frequency peak is not significantly changed, but there is a considerable decrease in the height of the high-frequency VDOS peak as deformation proceeds, with a reduction of 35% at maximum deformation. We find a reasonable linear correlation between peak height decrease and increase in dislocation density, especially for the larger nanoparticle diameters, including long dislocations. The VDOS is also examined for bulk samples with varying vacancy content, with randomly placed vacancies at concentrations from 1% to 10%. Something similar happens for the VDOS of these samples, with peak widths and the low-frequency peak nearly unchanged and the high-frequency peak height linearly reduced as vacancy concentration increases. This linear reduction has been observed for vacancies in graphene and metals, suggesting a general behavior of the VDOS for systems with vacancies. Vacancies also slightly shift the high-frequency peak towards higher frequencies. These results suggest that vibrational properties can be used to estimate the defect content in experimental defective diamond samples.