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Lookup NU author(s): Professor Patrick Briddon, Dr Michael Shaw
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We investigate both experimentally and theoretically, low-loss electron energy losses in brown type IIa monocrystalline diamonds both before and after high-temperature, high-pressure anneals which remove the brown colouration. We find additional losses within and near the band edge for brown diamond which are significantly reduced after treatment. The additional losses are not associated with dislocations. Graphitic inclusions are detected by EELS as well as TEM studies for some brown diamonds before treatment. These lead to pronounced subgap absorption. However, all brown diamonds exhibit additional losses which are due to point defects lying in the regions between dislocations. First principles theoretical modelling shows that common dislocations are not responsible for the brown colouration but a pi-bonded vacancy disk lying on {111} planes gives broad bands lying in the diamond band gap, possesses an optical absorption spectrum similar to that of brown diamond, and leads to additional electron energy losses in the band edge region. These and similar defects are suggested to be responsible for the brown colouration. Mechanisms are proposed for their formation and removal.
Author(s): Bangert U, Barnes R, Hounsome LS, Jones R, Blumenau AT, Briddon PR, Shaw MJ, Oberg S
Publication type: Article
Publication status: Published
Journal: Philosophical Magazine
Year: 2006
Volume: 86
Issue: 29-31
Pages: 4757-4779
ISSN (print): 1478-6435
ISSN (electronic): 1478-6443
Publisher: Taylor & Francis
URL: .http;//dx.doi.org/10.1080/14786430600776348
DOI: 10.1080/14786430600776348
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