A study of point defects in CVD diamond using electron paramagnetic resonance and optical spectroscopy

• Main Author: Hartland, C. B.
• Published: University of Warwick 2014
• Subjects: 530; QC Physics
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.644929

This thesis reports research on the characterisation of the structure of point defects in chemical vapour deposition (CVD) diamond. Electron paramagnetic resonance (EPR) has been used as a tool to determine the constituent nuclei and symmetry of previously unreported EPR active defects. Optical spectroscopy has been employed to track defect concentrations and correlate optical features with EPR active defects. Multi-frequency EPR has been used to identify and characterise a previously unreported EPR signal arising from N2VH0: a vacancy bounded by two substitutional nitrogen atoms and two carbon atoms wherein a hydrogen is bonded along one of the two carbon atoms and the unpaired electron of the system is bonded along the second carbon. This defect exhibits C2v symmetry in both X- and Q-band EPR, suggesting that the hydrogen rapidly reorientates between the two equivalent carbon atoms resulting in a time averaged C2v symmetry. The effects of annealing CVD diamond have been investigated. It has been shown that N2VH0 is produced consistently upon annealing at 1800 °C and continues to increase in intensity up to 2200 °C. The charge transfer behaviour of the N2VH0 defect is reported and the local vibrational mode (LVM) doublet at 1375 and 1378 cm-1 has been correlated with the intensity of the N2VH0 EPR signal. A calibration coefficient for the concentration of N3VH0 as calculated from the integrated intensity of the 3107 cm-1 LVM is proposed and a nitrogen assay of six samples in the as-grown and post-treated states suggest that this is a reasonable estimate. The annealing behaviour of theWAR5 EPR centre has been investigated and found to match density functional theory (DFT) predictions for the binding energy of the OsV defect. It has been reported that the WAR5 signal can be increased in intensity upon the irradiation and annealing at 800 °C of CVD diamond grown from a C:H:O chemistry, further supporting the assignment of this signal to the OV0 defect. A new EPR signal is reported and characterised as arising from a substitutional oxygen adjacent to a vacancy wherein a hydrogen atom rapidly reorientates between the three available carbon dangling bonds (OsVH0). The effect of irradiation and annealing on as-grown and pre-annealed CVD diamond has been investigated. It is shown that the 3324 cm-1 LVM (arising from the Ns:H-C0 defect) can be introduced into CVD diamond upon irradiation and further increased in intensity by annealing at 600 °C. The increase in 3324 cm-1 intensity has been correlated with a loss of NVH allowing a calibration correlation for this centre to be determined. Further, the reintroduction of the VnH- defect has been reported in a diamond sample which has been annealed prior to additional irradiation and annealing treatments.