The negatively charged nitrogen-vacancy defect in diamond is an important atomic-scale structure that can be used as a qubit in quantum computing and as a marker in biomedical applications. Its usefulness relies on the ability to optically excite electrons between well-defined gap states, which requires a clear and detailed understanding of the relevant states and excitation processes. Here we show that by using hybrid density-functional-theory calculations in a large supercell we can reproduce the zero-phonon line and the Stokes and anti-Stokes shifts, yielding a complete picture of the spin-conserving excitation of this defect.

Fine structure of exciton complexes in high-symmetry quantum dots: Effects of symmetry breaking and symmetry

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Formation and excitation energies as well charge transition levels are determined for the substitutional nitrogen (N s ), the vacancy (V), and related point defects (NV, NVH, N 2 , N 2 V and V 2 ) by screened non-local hybrid density functional supercell plane wave calculations in bulk diamond. In addition, the activation energy for V and NV diffusion is calculated. We find good agreement between theory and experiment for the previously well-established data, and predict missing ones. Based on the calculated properties of these defects, the formation of the negatively charged nitrogen-vacancy center is studied, because it is a prominent candidate for application in quantum information processing and for nanosensors. Our results indicate that NV defects are predominantly created directly by irradiation, while simultaneously produced vacancies will form V 2 pairs during post-irradiation annealing. Divacancies may pin the Fermi-level making the NV defects neutral.

By accurate quantum mechanical simulations, we show that typical diamond surfaces possess image states with sub-bandgap energies, and compromise the photostability of NV centers placed within a few nm of the surface. This occurs due to the mixture of the NV-related gap states and the surface image states, which is a novel and distinct process from the well-established band bending effect. We also find that certain types of coverages on the diamond surface may lead to blinking or bleaching due to the presence of acceptor surface states. We identify a combination of surface terminators that is perfect for NV-center based nanoscale sensing.

Possible defect structures, arising from the interaction of O 2 molecules with an ideal portion of the SiC/ SiO 2 interface, have been investigated systematically using density functional theory. Based on the calculated total energies and assuming thermal quasiequilibrium during oxidation, the most likely routes leading to complete oxidation have been determined. The defect structures produced along these routes will remain at the interface in significant concentration when stopping the oxidation process. The results obtained for their properties are well supported by experimental findings about the SiC/ SiO 2 interface. It is found that carbon-carbon bonds can explain most of the observed interface states but not the high density near the conduction band of 4H-SiC.

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