ABSTRACT
Interactions between interior substitutional nitrogen defects and surface unsaturated dangling bonds in synthetic nanodiamonds of â¼25 nm size were explored experimentally and theoretically. The experimental results demonstrate the disappearance of the specific paramagnetism of nitrogen centers in the smallest nanoparticles isolated after processing large micron diamonds in a ball mill, accompanied by the formation of unsaturated surface dangling bonds and internal defects. First principles modelling confirms the vanishing of the magnetic moments related with nitrogen centers even for distances from the surface defects greater than 1 nm. To understand this effect, we consider a bond reconstruction scheme with the formation of several carbon-carbon double bonds in the area between the interior and surface point defects. The scheme is in agreement with the changes in electron density through the distance between the two defects. The developed approach can be used to describe the interactions between various defects in carbon-based systems.
ABSTRACT
Size dependence of physical properties of nanodiamond particles is of crucial importance for various applications in which defect density and location as well as relaxation processes play a significant role. In this work, the impact of defects induced by milling of micron-sized synthetic diamonds was studied by magnetic resonance techniques as a function of the particle size. EPR and (13)C NMR studies of highly purified commercial synthetic micro- and nanodiamonds were done for various fractions separated by sizes. Noticeable acceleration of (13)C nuclear spin-lattice relaxation with decreasing particle size was found. We showed that this effect is caused by the contribution to relaxation coming from the surface paramagnetic centers induced by sample milling. The developed theory of the spin-lattice relaxation for such a case shows good compliance with the experiment.
