Liggins, Stephanie (2010) Identification of point defects in treated single crystal diamond. PhD thesis, University of Warwick.

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Abstract

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.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QC Physics
Library of Congress Subject Headings (LCSH):	Diamond crystals -- Analysis, Point defects
Official Date:	September 2010
Dates:	Date Event September 2010 Submitted
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Newton, M. E. (Mark E.)
Sponsors:	Diamond Trading Company Research Centre
Extent:	xxvii, 203, 6 p. : ill., charts
Language:	eng
URI:	http://wrap.warwick.ac.uk/id/eprint/35522

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