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Electron microscopy study of plastically deformed natural brown diamond and surface processing of boron doped diamond electrodes
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Laidlaw, Fraser (2021) Electron microscopy study of plastically deformed natural brown diamond and surface processing of boron doped diamond electrodes. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3684292~S15
Abstract
Plastic deformation of diamond can be seen as a naturally occurring event, often resulting in broad spectral absorption bands that give rise to either a pink or brown colour to the crystal. In this thesis, the effect of plastic deformation on the dislocation and point defect micro-structures in brown type IIa diamond is investigated by electron and optical microscopy techniques. In addition to investigating plastic deformation processes in natural brown diamond, TEM was also utilised to investigate the surface of boron-doped diamond (BDD) after various surface processing stages.
Firstly, the generation and behaviour of intrinsic point defects during plastic deformation is investigated. Vacancy clusters are considered to be the origin of the brown colouration in diamond and it is thought that vacancies generated during the plastic deformation aggregate together into the vacancy clusters. Interestingly, rather than finding direct evidence of vacancy generation, it is found that a large concentration of interstitials are generated, in addition to the vacancies, during plastic deformation. These interstitials condense onto the 90◦ partial dislocations leaving an excess of vacancies behind to cluster. Estimates of the interstitial concentrations generated are similar to vacancy concentrations measured in similar brown type IIa diamond, suggesting equal numbers of interstitials and vacancies are generated by plastic deformation. Atomically resolved Z-type faulted dipoles, also showing interstitial absorption, have been imaged allowing the stacking fault energy of diamond to be calculated, with a value of 472 mJm-2 ± 38 mJm-2 being determined.
The effect of plastic deformation, on the distribution of point defects and dislocation microstructure, is then investigated using correlative electron and optical microscopy techniques. The type IIa diamond observed here shows alternating brown and colourless banding, allowing the differences between pristine and deformed material to be examined. Brown bands show dislocation structures that clearly indicate intrinsic point defect generation has occurred while PL and Raman mapping showing increased concentrations of point defects and stresses associated with plastic deformation within the brown bands.
Lastly, utilising the techniques developed during this PhD work, the results of a collaboration, using electrochemistry and electron microscopy to characterise the surface of boron-doped diamond (BDD) after various surface treatments coverage are presented. For use as an elctrode material, the ability to control the surface sp2 content of the electrodes is necessary, and both electrochemistry and electron microscopy were used to assess the sp2 content at after each processing stage. Laser ablation of the surface was used to generate sp2 on the surface, while the effectiveness of acid and thermal oxidation treatments for removing sp2 carbon was investigated. Laser ablation of the surface forms a layer of highly ordered graphite immediately adjacent to the diamond which is topped by a layer of amorphous carbon, caused by the redeposition of sublimated carbon. Acid treatment removes the majority of the graphite and amorphous carbon layer leaving behind clusters of graphite with basal planes perpendicular to the surface, encapsulated with a thin amorphous layer. These graphite clusters are robust enough to survive any subsequent acid treatments. Finally, thermal oxidation treatment was able to remove all clusters leaving behind a surface with very low sp2 coverage. Characterisation of the surface treatments gives confidence that consistent and reliable BDD electrodes can be manufactured and tailored for specific applications.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QC Physics | ||||
Library of Congress Subject Headings (LCSH): | Diamonds -- Plastic properties, Diamonds, Point defects, Deformations (Mechanics) | ||||
Official Date: | July 2021 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Physics | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Beanland, R. | ||||
Format of File: | |||||
Extent: | xiv, 154 leaves : illustrations (some colour) | ||||
Language: | eng |
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