Clientes y entidades involucradas

This thesis focuses on the investigation of a number of defects found in synthetic material as a result of treatment processes. A number of studies have been ex- ecuted to investigate these defects, considering their symmetry, structure and behaviour by techniques such as annealing, irradiation, uniaxial stress and optical spectroscopy. The application of these techniques and the theory behind them will be introduced to aid the understanding of the later experimental chapters, where new results will be presented and discussed.

Chapter 2 reviews the literature of the field of diamond growth and defect incorporation. Much work exists on the identification of common defects seen by a multitude of observational techniques and yet the catalogue of defects which are understood in terms of their growth conditions, symmetry and composition, is still limited. This review will consider the specific work published on electron and neutron irradiation of diamond and the two most commonly identified impurities in diamond, nitrogen and hydrogen. It aims to provide an introduction to the work presented in later chapters, bringing the reader up-to-date with the field, areas of interests and related challenges.

Chapter 3 will introduce the theory behind the key research techniques ex- ploited in this thesis. Optical absorption spectroscopy plays a fundamental role and its use in identifying defects, considering composition and understanding sym- metry is discussed. The analytical basis of group theory is outlined for use in analysing data from uniaxial stress experiments and identification of crystal sym- metry. Following from this, chapter 4 considers the practical application of these theories and their integration into analytical techniques such as annealing, optical spectroscopy and uniaxial stress experiments.

Chapter 5 is the first of the experimental results chapters presented. This extends the work already published considering the single substitutional nitrogen

defects in the neutral and positive charge states in diamond. Uniaxial stress exper- iments are used to study LVMs observed in infrared absorption spectra originating from substitutional nitrogen defects. Furthermore, evidence for the reorientation of the N0

S defect under uniaxial stress is discussed and evidence for the changing site occupation probability, presented.

Chapter 6 reports conclusive identification of the di-nitrogen interstitial defect. The use of optical spectroscopy in conjunction with uniaxial stress has assigned the structure of this defect, achieving a result that is in excellent accord with theory.

Chapter 7 considers some common hydrogen related defects present in CVD di- amond, specifically those defects responsible for absorption in the 2750–3400 cm−1

C–H stretch region of the infrared spectrum. A conclusive reassignment of the 3123 cm−1 _{defect is made, together with a determination of the conversion fac-}

tor for the quantification of its concentration. The previously proposed structure responsible for the 3107 cm−1 _{LVM is disproved and reassigned to the 3324 cm}−1

LVM. Many questions still surround the structure of the defect responsible for the 3107 cm−1 _{LVM. New data on its production in CVD diamond are presented.}

Chapter 8 presents new data on the effects of neutron irradiation on type Ib and IIa diamond. Annealing and uniaxial stress studies identify the symmetry of some of the more prominent defects and an insight into the repair of irradiation damage is presented. However, this chapter highlights that more work is required considering the effect of neutron damage in diamond.

Chapter 9 aims to summarise the key results of this research and its contri- bution to the field of diamond research. It outlines the areas where substantial further work is still required, giving some suggestions for future experimentation. This thesis aims to be a comprehensive report of the previous three and a half years of experimental work, focussing on gaps in important areas of diamond defect research and contributing to the body of knowledge required for understanding the processing and treatment of diamond.

References

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