Vacancy induced structural changes in diamond nanoparticles

Although optically active defects in nanodiamond are being considered ad candidates for optical labeling in biomedical applications, development in this area is being hindered the fact that suitable defects are rarely seen in diamond nanoparticles in the size regime required. These defects usually form as a complex with an impurity and a neutral of charged vacancy, so a measurable concentration of vacancy point defects is also necessary. Presented here are results of density functional tight binding computer simulations investigating the stability of vacancies in diamond nanoparticles with different surface structures. The results indicate that both neutral and charged vacancies alter the structure of as-grown diamond nanoparticles and are likely to diffuse out of the particle during synthesis or irradiation. We also find that suitable passivation of the particle may alleviate this problem, and hence facilitate the formation of defect complexes.