| Due to its promising applications in fields such as quantum information, quantum cryptography, quantum computing, single-spin magnetometry, and biomedical engineering, NV- center has attracted much attention and has been explored extensively in recent years. NV- centers have the property of luminescence and a zero-phonon line at 1.945ev (637nm). Since 1997 when NV- center was first observed by using Scanning Confocal Optical Microscopy and Magnetic Resonance,many studies about stable single-photon sources have been reported. As the spin state can be initialized by optical approaches and be read out by luminescence intensity, NV- center is a good candidate for qubit which attracts a lot of interest in quantum computing. The fluorescent fine-structure of NV- center is influenced by magnetic field, electric field and strain field, so NV- center can be used to detect the local change of the fields. Diamond is also a biocompatible material, thus the fluorescence of NV- centers in nano-diamonds can be used for real-time imaging of cell kinetics to understand the biological and pharmacological process in cells.Most of the applications of NV- center mentioned above rely on the negative charge state, which, however, may be lost temporarily or permanently during real experimental processes. Therefore it’s crucial to study how to maintain the negative charge state for NV. Generally the charge state of defects in material will be affected by the states of neighboring defects. Therefore the interaction between NV- and other defects largely determines the stability of its charge state.In spite of the development in this area, the physics underlying the application of the NV- center is far from being fully understood. In this thesis, using the first-principles calculation methods, we have studied the property of NV, substitutional Nitrogen(Ns), the vacancy (V), N2V etc as well as the interaction between NV and Ns.The detailed contents and main results of this thesis are as follows:First of all, we discuss the finite-size supercell correction schemes for charged defect calculations, and calculate the formation energy and charge transition levels of NV, substitutional (Ns),the vacancy (V). Then the performance of various correction schemes is compared. We propose a new correction scheme for non-cubic supercell. Using this new correction scheme, we calculate the formation energy of the defect complex consist with NV and Ns and the corresponding electronic structures. Based on the results, we analyse the influence of distance between the two defects on the stability of the charge state of NV defect. |
