Single point defect imaging studies in diamond

This thesis considers the recent advances in synthetic diamond growth. To enable this, it has been necessary to construct a custom confocal photoluminescence scanning microscope to interrogate single point defects in diamond, where detection is constrained by the diffraction limit of light. Complementary techniques have been used to support the understanding of bulk diamond material such as, electron paramagnetic resonance (EPR), absorption spectroscopies in the ultraviolet-visible (UV-vis) and infrared (IR) range, cathodoluminescence (CL) spectroscopy, and X-ray topography (XRT). For boron doped diamond, the inclusion of point defects is not so well understood. Here, a diamond synthesised via chemical vapour deposition (CVD) contained distinct regions of boron doping. Confocal microscopy with 532 nm excitation found single point defects could be identified in these regions. Spectroscopy revealed two dominant classes of zero phonon line (ZPL) emission, centred on 580 ± 10 nm and 612 ± 18 nm. Polarisation measurements on these defects strongly suggest a defect of D2d or C2v symmetry with the optical transition occurring from a ground A state to an excited A state. In addition, the incorporation of these defects follow linear structures, and may therefore imply a decoration of a dislocation in the boron doped region. The remainder of the thesis concentrates on the synthesis of diamond from the high pressure, high temperature (HPHT) method. In high purity, type IIa, HPHT diamond it was found that the growth sector interface between {1 1 1} and {1 1 3} are decorated with single negatively charged nitrogen vacancy (NV−) defects with no preferential orientation. In the bulk {1 1 1} growth sectors it could be found that single and small ensemble negatively charged silicon vacancy (SiV−) defects also do not grow in preferentially orientated, whilst a nickel related defect does. The growth sector dependence of nitrogen and boron incorporation was investigated and found to agree with the Kanda model. Here CL measurements demonstrate a good way to obtain the boron concentration per growth sector, whilst it was necessary to electron irradiate and anneal to understand the growth sector dependence of nitrogen. Furthermore, it was found that both substitutional nitrogen and boron decrease significantly following electron irradiation and annealing to 800 XC. The mechanism for the reduction in boron is not well understood and requires further investigation. Finally, the suitability of HPHT diamond was assessed for quantum applications where the spin decoherence lifetime (T2) was used as a figure of merit. It was found that the NV− centre is sensitive to the local boron concentration. It has been possible to measure the T2 lifetime to be limited by 13C in the as-grown NV− defects for a boron concentration < 50 ppb. An implantation study also revealed the growth sector dependence of the T2 lifetime where the 13C limit is approached in the {0 0 1} growth sector

Point defects and interstitial climb of 90° partial dislocations in brown type IIa natural diamond

Multiple electron microscopy techniques have been used to study a brown type IIa natural diamond. Electron backscatter diffraction shows evidence of plastic deformation in the form of slip bands, while cathodoluminescence reveals a network of low-angle grain boundaries, also observed in transmission electron microscopy together with long straight dislocations and dislocation dipoles. Aberration-corrected scanning transmission electron microscopy shows interstitial absorption on the 90° partial of both dissociated dislocations and Z-type faulted vacancy dipoles, forming structures similar to that observed in other fcc materials. The observations indicate an interstitial concentration of 1017 to 1019 cm-3 and calculations of point defect concentrations produced by plastic deformation show that this can be produced by strains of the order of 1%. Brown coloration in diamond has been previously attributed to vacancies and vacancy clusters with concentrations around 1018 cm-3, which suggests that roughly equal numbers of interstitials and vacancies are generated in diamond via plastic deformation. Atomic resolution images of Z-type faulted dipoles allow a stacking fault energy of 472 ± 38 mJ m-2 to be determined

Deep three-dimensional solid-state qubit arrays with long-lived spin coherence

Nitrogen-vacancy centers (NVCs) in diamond show promise for quantum computing, communication, and sensing. However, the best current method for entangling two NVCs requires that each one is in a separate cryostat, which is not scalable. We show that single NVCs can be laser written 6–15-µm deep inside of a diamond with spin coherence times that are an order of magnitude longer than previous laser-written NVCs and at least as long as naturally occurring NVCs. This depth is suitable for integration with solid immersion lenses or optical cavities and we present depth-dependent T2 measurements. 200 000 of these NVCs would fit into one diamond

Spatial distribution of defects in a plastically deformed natural brown diamond

Photoluminescence, Raman mapping, cathodoluminescence and transmission electron microscopy (TEM) have been carried out on a “zebra” diamond, containing both brown and colourless bands. The stone was cut into two and one part was given high-pressure high temperature (HPHT) treatment, removing the brown colouration. The parts were then cut into (110) sections. In the untreated stone the morphology of brown stripes is consistent with that of slip bands formed during plastic deformation and Raman mapping shows they are under strong compressive stress. Photoluminescence from N3 and H3 centres, as well as lines at 406.3 nm, 491.3 nm and 535.9 nm, are correlated with brown bands in the untreated sample, while cathodoluminescence shows that band-A luminescence is anticorrelated. HPHT treatment reduces internal stress, and eliminates or reduces correlated luminescence. TEM reveals long straight dislocations and dislocation dipoles in the brown bands, consistent with deformation by slip and concurrent intrinsic point defect production, while clear bands have curved and tangled dislocation networks. We postulate that vacancies produced by plastic deformation aggregate into clusters responsible both for the brown colouration and an increase in volume that results in compressive stress. The 535.9 nm line has characteristics of an interstitial-type defect and may be formed by the trapping of interstitials generated during plastic deformation

Data for Spatial distribution of defects in a plastically deformed natural brown diamond

Photoluminescence, Raman mapping, cathodoluminescence and transmission electron microscopy (TEM) have been carried out on a “zebra” diamond, containing both brown and colourless bands. The stone was cut into two and one part was given high-pressure high temperature (HPHT) treatment, removing the brown colouration. The parts were then cut into (110) sections. In the untreated stone the morphology of brown stripes is consistent with that of slip bands formed during plastic deformation and Raman mapping shows they are under strong compressive stress. Photoluminescence from N3 and H3 centres, as well as lines at 406.3 nm, 491.3 nm and 535.9 nm, are correlated with brown bands in the untreated sample, while cathodoluminescence shows that band-A luminescence is anticorrelated. HPHT treatment reduces internal stress, and eliminates or reduces correlated luminescence. TEM reveals long straight dislocations and dislocation dipoles in the brown bands, consistent with deformation by slip and concurrent intrinsic point defect production, while clear bands have curved and tangled dislocation networks. We postulate that vacancies produced by plastic deformation aggregate into clusters responsible both for the brown colouration and an increase in volume that results in compressive stress. The 535.9 nm line has characteristics of an interstitial-type defect and may be formed by the trapping of interstitials generated during plastic deformation

Data for Deep three-dimensional solid-state qubit arrays with long-lived spin coherence

Nitrogen vacancy (NV) centers in diamond show promise for quantum computing, communication and sensing. However, the best current method for entangling two NV centers requires that each one is in a separate cryostat, which is not scalable. Here we show that single NV centers can be laser-written 6-15 µm deep inside of a diamond with spin coherence times that are an order of magnitude longer than previous laser-written NV centers and at least as long as naturally-occurring NV centers. This depth is suitable for integration with solid immersion lenses or optical cavities and we present depth-dependent T2 measurements. 200,000 of these NV centers would fit into one diamond

Data for Deep three-dimensional solid-state qubit arrays with long-lived spin coherence

Nitrogen vacancy (NV) centers in diamond show promise for quantum computing, communication and sensing. However, the best current method for entangling two NV centers requires that each one is in a separate cryostat, which is not scalable. Here we show that single NV centers can be laser-written 6-15 µm deep inside of a diamond with spin coherence times that are an order of magnitude longer than previous laser-written NV centers and at least as long as naturally-occurring NV centers. This depth is suitable for integration with solid immersion lenses or optical cavities and we present depth-dependent T2 measurements. 200,000 of these NV centers would fit into one diamond