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Title: Identification of point defects in treated single crystal diamond
Author: Liggins, Stephanie
ISNI:       0000 0004 2700 4271
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2010
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The research reported in this thesis is focused on the identification of the structure of point defects in diamond using a variety of spectroscopic techniques. The defects studied are introduced by doping during synthesis, irradiation damage and annealing. Diamond produced by high-pressure high-temperature (HPHT) synthesis and chemical vapour deposition (CVD) are studied. The nature of the 1344 cm−1 local vibrational mode attributed to the neutral single substitutional nitrogen defect (N0S), has been studied using fourier transform infrared (FTIR) absorption spectroscopy and uniaxial stress. This work showed that this is a doubly degenerate vibrational mode at a defect with trigonal symmetry. When the stress was applied along the <111> and <110> directions, the N0S defect was observed to preferentially reorientate to <111> directions with lowest energy. It is shown that this is consistent with previously reported electron paramagnetic resonance studies of reorientation. Studies of the IR absorption spectrum from the N0S defect have confirmed, through shifts observed upon 14N:15N isotopic substitution that the peaks at 950/940 cm−1 and 1046/1040 cm−1 are vibrations involving nitrogen in the positive charge state. However, uniaxial stress splitting studies on the 1332 cm−1 mode arising from the N0S defect were inconclusive. The vibrational properties of N2I are fully described and with additional data from isotopic substitution, the uniaxial stress splitting data enables unambiguous assignment of the H1a defect to N2I. The defect responsible for the 3107 cm−1 LVM has not yet been identified. New evidence is presented showing that in CVD diamond, on annealing at 2200ºC (with an applied stabilising pressure), the intensity of the 3107 cm−1 LVM is proportional to the concentration of substitutional nitrogen squared. Possible structures for this defect are discussed. It was found that the defect induced one-phonon absorption observed after neutron irradiation in type IIa CVD diamond could be removed by annealing at temperatures below 1600ºC. The kinetics of the removal of the defect induced absorption cannot be explained in terms of the bulk migration of vacancies or interstitials.
Supervisor: Not available Sponsor: Diamond Trading Company Research Centre
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics