Andrew Edmonds
 |
My contact details |
Edmonds
@mq
Introduction and research with the Warwick EPR and Diamond Group
My name is Andrew Edmonds and I was a Research Fellow with the Warwick EPR and Diamond Research Group. I worked on the "EQUIND" project (Engineered Quantum Information in Nanostructured Diamond). This was an European funded project which concerns the use of diamond for quantum information purposes and was a colloboration between seven universities as well as Element Six Ltd. More information regarding this project can be found on the EQUIND website. At Warwick our primary roles include material characterisation (using Electron Paramagnetic Resonance, Fourier Transform Infrared Spectroscopy and Photo Luminescence) and the indentification of new defects that are potential candidates for single photon sources.
My PhD Thesis
In July 2008 I completed my PhD thesis entitled "Magnetic resonance studies of point defects in single crystal diamond". In this work Electron paramagnetic resonance (EPR) was used to study point defects present in synthetic single-crystal diamond grown by chemical vapour deposition (CVD) or high pressure high-temperature (HPHT) methods. The thesis also covers the topic of the quantitative nature of EPR and how the systematic fitting of experimental data can improve the reproducibility of such measurements.
My PhD thesis is available for download in various versions, as listed below:
 |
PhD Thesis download "Magnetic resonance studies of point defects in single crystal diamond"
Version designed for single sided printing (4.6 MB) |
Summary of results chapters:
- An EPR fitting method is introduced which employs generalised lineshape function derived from the Tsallis distribution and pseudomodulation. This method enhances the quality of the fits obtained and permits overlapping EPR spectra to be deconvolved. With this system now incorporated into a tting program, quantitative EPR measurements with a reproducibility of 5% are possible.
- The results from EPR studies of CVD diamond which was intentionally silicon doped with isotopes in natural abundance or isotopically enriched are reported. The observation of hyperfine satellites arising due to the presence of 29Si has provided definitive evidence for the involvement of silicon in two EPR centres in diamond which were previously suspected to involve silicon: KUL1 and KUL3. KUL1 is unambiguously identifed as the neutral silicon split vacancy defect (V-Si-V)0, whilst KUL3 is shown to be (V-Si-V)0 decorated with a hydrogen atom. Data have also revealed that (V-Si-V)0 is preferentially oriented in samples grown on {110} substrates. Some of the results of this chapter have been published in Physical Review B.
- The negative nitrogen-vacancy centre (NV−) has been investigated. Published parameters for the nitrogen hyperfine interaction produce an unsatisfactory fit to the experimental spectra and hence these parameters are redetermined. Optically-excited EPR has been used to estimate the degree of spin polarisation of the NV− ground state and the increase in signal intensity with illumination has permitted the interaction between the unpaired electron and neighbouring 13C atoms to be studied. Two sets of 13C hyperfine satellites have been identied, which account for approx. 100% of the unpaired electron probability density. Additionally, despite the predictions that the neutral charge state of NV should have an S = 1/2 ground state, this charge state has not previously been detected by EPR. Optically excited EPR measurements reveal a trigonal nitrogen containing defect in diamond with an S = 3/2 excited state populated via optical excitation. Analysis of the spin-Hamiltonian parameters and the wavelength dependence of the optical excitation leads to assignment of this S = 3/2 state to the 4A2 excited state of NV0. The NV0 work has been published as a Rapid in Physical Review B.
- Further investigations of the negative nitrogen-vacancy-hydrogen defect are reported. EPR measurements have been obtained at temperatures between 8 and 750K from samples containing 15N and 2H in natural abundance as well as samples where the source gases have been enriched with these isotopes. The previously published experimentally determined spin-Hamiltonian parameters for this centre have been refined and the effect of isotopic substitution is investigated. The first experimental evidence for dynamics of the hydrogen atom in this defect is presented.
Published papers
[1] A. M. Edmonds, M. E. Newton, P. M. Martineau, D. J. Twitchen, and S. D. Williams, Phys. Rev. B 77, 245205 (2008).
"Electron paramagnetic resonance studies of silicon-related defects in diamond"
DOI: 10.1103/PhysRevB.77.245205
[2] S. Felton, A. M. Edmonds, M. E. Newton, P. M. Martineau, D. Fisher, and D. J. Twitchen, Phys. Rev. B 77, 081201 (2008).
"Electron paramagnetic resonance studies of the neutral nitrogen vacancy in diamond"
DOI: 10.1103/PhysRevB.77.081201
[3] A. Tallaire, A. T. Collins, D. Charles, J. Achard, R. Sussmann, A. Gicquel, M. E. Newton, A. M. Edmonds, and R. J. Cruddace, Diam. Relat. Mater. 15, 1700 (2006).
"Characterisation of high-quality thick single-crystal diamond grown by CVD with a low nitrogen addition"
DOI: 10.1016/j.diamond.2006.02.00
