The design and construction of a scanning probe nitrogen vacancy centre magnetometer

Tyler, Ashley (2021) The design and construction of a scanning probe nitrogen vacancy centre magnetometer. PhD thesis, University of Nottingham.

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The isolated spin of the nitrogen-vacancy (NV) centre in diamond, which is formed from a vacancy and an adjacent nitrogen atom replacing carbon atoms in the diamond lattice, provides a highly promising system to realise non-invasive high-sensitivity magnetometry, even at room temperatures. The combination of the atomically sized detection volume, which for a single NV centre is defined by the spatial extent of the wavefunction, and high magnetic field sensitivity makes the NV centre a highly promising sensor to investigate magnetism on the nanoscale. In recent years NV centres have been used to produce 2D maps of magnetic fields with nanoscale resolution by affixing single or small numbers of NV centres to the very tip of a scanning probe. To date, scanning probe NV magnetometers have produced images with some of the smallest probe-sample distances seen in magnetic field sensing, with probe-sample distances of the order 50 nm routinely achieved.

Scanning probe NV magnetometry utilises two established scientific techniques; atomic force microscopy, which provides the scanning probe element required for the formation of 2D images, and confocal microscopy for magnetic field readout out via measurement of the NV centre's magnetically sensitive photoluminescence. Therefore, an instrument designed for scanning probe NV magnetometry will feature both optical instrumentation optimised to collect luminescence from atomically sized sources, in particular NV centres fixed to functionalised AFM probes, and an atomic force microscope that can be operated while simultaneously making optical measurements. In addition to the established imaging techniques of confocal microscopy and AFM, an instrument focusing on NV centre magnetometry requires a method of applying a high-frequency magnetic field for spin state manipulation and a variable strength, variable orientation bias magnetic field. While a prerequisite for NV magnetometry, these final components extend an NV magnetometer's functionality, enabling the study of other species that exhibit magnetically sensitive photoluminescence. As such, an instrument based on a scanning probe NV magnetometer will not only be able to perform high-resolution magnetometry, but also operate in a wide range of imaging modalities, providing a versatile tool for sub-micron sample characterisation. This thesis presents the design, assembly and performance of a custom-built sub-micron characterisation tool based on a scanning probe NV magnetometer.

This research project's main output is the instrument itself, with the key results the figures of merit for each imaging modality. A sample of nanodiamonds deposited onto a silicon/silicon dioxide wafer serves as the test target for most of the imaging modes. The optical imaging modes' performance is presented through diffraction-limited spatial maps, both where photoluminescence and backscattered laser light provide the dominant signal. To demonstrate this instrument's capability to measure the temporal and spectral characteristics from diffraction-limited luminescent sources, time-correlated single photon counting measurements and emission spectra from sources on the nanodiamond sample are presented. The performance of custom-built AFM is demonstrated through the measurement of a calibration sample and then the suitability for NV magnetometry demonstrated by presenting simultaneously recorded AFM confocal microscope measurements. This instrument's capability for NV centre magnetometry is presented by showing optically detected magnetic resonances from photoluminescent sources in nanodiamonds. Finally, the progress towards NV centre magnetometry in this instrument is reviewed.

The recent discovery of photoluminescence originating from single-photon sources in 2D materials, in particular from emitters in hexagonal boron nitride (hBN) which have shown such behaviour at room temperatures, has led to an active area of research investigating the structure and potential applications of point defects in 2D materials. To demonstrate this instrument's versatility and its potential to perform cutting-edge research in this emerging field, preliminary results characterising the nature of photoluminescence in a thin hBN film on a silicon carbide substrate are presented.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Mellor, Christopher
Keywords: Nitrogen-vacancy, NV, Diamond, Magnetometery, Magnetometer, Optically Detected Magnetic Resonance, ODMR, EPR, ESR, Microscopy, Confocal microscopy, Single-photon source, Hexagonal boron nitride, h-BN
Subjects: Q Science > QC Physics > QC811 Geomagnetism. Meteorology. Climatology
Faculties/Schools: UK Campuses > Faculty of Science > School of Physics and Astronomy
Item ID: 66040
Depositing User: Tyler, Ashley
Date Deposited: 31 Dec 2021 04:40
Last Modified: 31 Dec 2021 04:40

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