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Title: Single point defect imaging studies in diamond
Author: Diggle, Phil L.
ISNI:       0000 0004 9358 2029
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2019
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This thesis considers the recent advances in synthetic diamond growth. To enable this, it has been necessary to construct a custom confocal photoluminescence scanning microscope to interrogate single point defects in diamond, where detection is constrained by the diffraction limit of light. Complementary techniques have been used to support the understanding of bulk diamond material such as, electron paramagnetic resonance (EPR), absorption spectroscopies in the ultraviolet-visible (UV-vis) and infrared (IR) range, cathodoluminescence (CL) spectroscopy, and X-ray topography (XRT). For boron doped diamond, the inclusion of point defects is not so well understood. Here, a diamond synthesised via chemical vapour deposition (CVD) contained distinct regions of boron doping. Confocal microscopy with 532 nm excitation found single point defects could be identified in these regions. Spectroscopy revealed two dominant classes of zero phonon line (ZPL) emission, centred on 580 ± 10 nm and 612 ± 18 nm. Polarisation measurements on these defects strongly suggest a defect of D2d or C2v symmetry with the optical transition occurring from a ground A state to an excited A state. In addition, the incorporation of these defects follow linear structures, and may therefore imply a decoration of a dislocation in the boron doped region. The remainder of the thesis concentrates on the synthesis of diamond from the high pressure, high temperature (HPHT) method. In high purity, type IIa, HPHT diamond it was found that the growth sector interface between {1 1 1} and {1 1 3} are decorated with single negatively charged nitrogen vacancy (NV−) defects with no preferential orientation. In the bulk {1 1 1} growth sectors it could be found that single and small ensemble negatively charged silicon vacancy (SiV−) defects also do not grow in preferentially orientated, whilst a nickel related defect does. The growth sector dependence of nitrogen and boron incorporation was investigated and found to agree with the Kanda model. Here CL measurements demonstrate a good way to obtain the boron concentration per growth sector, whilst it was necessary to electron irradiate and anneal to understand the growth sector dependence of nitrogen. Furthermore, it was found that both substitutional nitrogen and boron decrease significantly following electron irradiation and annealing to 800 XC. The mechanism for the reduction in boron is not well understood and requires further investigation. Finally, the suitability of HPHT diamond was assessed for quantum applications where the spin decoherence lifetime (T2) was used as a figure of merit. It was found that the NV− centre is sensitive to the local boron concentration. It has been possible to measure the T2 lifetime to be limited by 13C in the as-grown NV− defects for a boron concentration < 50 ppb. An implantation study also revealed the growth sector dependence of the T2 lifetime where the 13C limit is approached in the {0 0 1} growth sector.
Supervisor: Not available Sponsor: Gemological Institute of America
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics ; TP Chemical technology