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Title: Investigations of the nature, properties and distribution of defects in diamond
Author: Mottishaw, Sinead
ISNI:       0000 0004 7227 5177
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2017
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This thesis presents investigations into the nature, properties and distribution of defects in diamond grown by the methods of chemical vapour deposition (CVD) and high pressure, high temperature (HPHT) synthesis. The experimental techniques used include electron paramagnetic resonance, optical absorption, cathodoluminescence, photoluminescence and secondary ion mass spectroscopy (SIMS). The optical spin polarisation of the neutral silicon vacancy defect (SiV0) was shown to be strongly enhanced by resonant excitation at the zero-phonon energy, although there was significant sample to sample variation in the magnitude. The spin polarisation mechanism is different to that observed for the negatively charged nitrogen vacancy defect in diamond and more than one mechanism may be generating spin polarisation. The spin-lattice relaxation time (T1) of the SiV0 ground state was found to change by six orders of magnitude between room temperature and 11 K, where T1 exceeded 25 seconds. At room temperature the achievable optical ground state spin polarisation is limited by the rapid spin-lattice relaxation. Irradiation and annealing studies of silicon doped CVD diamond samples showed that the silicon vacancy concentration can be increased by irradiation and annealing. However, the same processing conditions can also reduce the concentration of grown-in silicon vacancy defects. This work suggests that the relative incorporation efficiency of silicon in different forms in homoepitaxial CVD diamond may depend on the orientation of the substrate, and that the details of post growth silicon vacancy defect production, especially in boron doped diamond, are not yet well understood. HPHT samples in which the13 C isotopic abundance had been increased up to approximately 10% were studied. The variation of the abundance of13 C with distance from the seed was studied using Raman spectroscopy and SIMS, and the nitrogen incorporation by infrared microscopy. Possible explanations of the variations in both are discussed. The incorporation of point and extended defects into diamond grown by heteroepitaxial CVD was studied in a nitrogen doped sample and another grown with efforts to exclude nitrogen. The samples were highly birefringent when observed through cross-polarisers and exhibited strong dislocation related photoluminescence, suggesting significant concentrations of dislocations and dislocation bundles. The nitrogen doped heteroepitaxial CVD sample contained point defects in relative concentrations typically observed in nitrogen doped homoepitaxial CVD diamond; the total nitrogen impurity concentration exceeded 2,000 ppb, whereas in the intrinsic heteroepitaxial CVD sample it was less than a few ppb. Both samples contained a significant concentration of silicon vacancy defects and the photoluminescence spectra indicated that the point defects were subject to significant strain arising from both extended and point defects.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD Chemistry