Dopant-site dependent properties of nitrogen and boron doped spherical nanodiamond particles from first-principle DFT simulation

We report the effect of nitrogen and boron incorporation in the structure of spherical nanodiamond particles using ab initio density-functional theory. We changed the site of boron and nitrogen impurity from the center to the surface of the particles and calculated structural, electronic, cohesive and surface charge properties of each configuration. By moving the impurity from the center toward the surface, the internal strain of N and B doped nanodiamond drops. Unlike nitrogen, doping of boron causes lower broken bonds around impurity in the central region and also replacement of boron in the surface releases the strain of nanoparticle. We explain this observation by calculating the variation of the surface charge or polarity of the doped particles versus the site of dopant during the movement of impurities toward the surface which reduces the polarity in contrast to behavior of nitrogen doped particle. By moving the boron atom from the center toward the surface of the particle, p-type conduction occurs whereas nitrogen impurity does not create an n-type conduction. Results suggest that boron is a more effective dopant than nitrogen provided that it has not been placed in the central region of nanoparticle.