School of Physics - Theses
Permanent URI for this collection
Search Results
1 - 1 of 1
-
ItemDevelopment of widefield nitrogen-vacancy centre microscopy for application to condensed matter systems( 2021)Microscopy based on the nitrogen-vacancy centre in diamond is an emerging technology that may soon find regular application in characterising a broad range of systems. The development of nitrogen-vacancy microscopy has been benchmarked by key proof-of-concept experiments, each demonstrating the great potential of the technique, without necessarily delivering unique insights into the system studied. In this thesis, we aim to further the development of this emerging technology by applying it to study a range of delicate and complex condensed matter test systems. Specifically, we take a widefield approach which utilises a dense ensemble of near-surface nitrogen-vacancy centres to image magnetic and electric fields over a 100 um field of view with diffraction-limited resolution and good sensitivity. In each application presented, we study physics both intrinsic to the test systems and arising from their interaction with our imaging technique. These observations inspire refinements to our approach that enhance the utility of the technique. Chapter 1 reviews the physics underpinning microscopy with nitrogen-vacancy centres in diamond, and surveys key achievements in the literature. Chapter 2 details our approach to widefield nitrogen-vacancy microscopy. Chapter 3 applies widefield magnetic imaging to ultrathin depositions of nanoparticles on the diamond surface. We observe a strong magnetic noise associated with metallic depositions, even when the deposited material is less than 1 nm thick. This study demonstrates the great sensitivity of widefield nitrogen-vacancy microscopy, allowing the detection of minute sample volumes. Chapter 4 studies magnetic and electric fields associated with graphene field-effect transistors fabricated on the diamond surface. We demonstrate current density mapping under different doping conditions, a significant extension of device studies published at the time, and identify strong electric fields associated with the gating that affect both the spin resonances and photoluminescence of the sensing ensemble. These first two studies motivate the use of a deeper and thicker nitrogen-vacancy ensemble that protects against the short-range noise contributed by the metallic nanoparticles, which mimic common contaminants, and protects the sensing layer from device-related electric fields. Chapter 5 extends our widefield imaging technique to low temperatures (4 K) by incorporating a closed-cycle cryostat into the apparatus, which we use to study a low-critical-temperature system, superconducting niobium wires. By imaging Abrikosov vortices and superconducting transport at various laser powers, we quantify local heating in the sample caused by the excitation laser. This observation motivates a refined nitrogen-vacancy imaging substrate that includes a reflective metallic layer at the diamond surface and an insulating oxide layer, onto which the target sample is deposited. This design mitigates the local heating caused by the excitation laser, an essential component of the imaging technique, and leaves the sample electrically isolated, facilitating advanced studies of low-temperature physics. Chapter 6 deploys this refined nitrogen-vacancy substrate to characterise the magnetic properties of two free-standing ultrathin ferromagnetic materials. We directly quantify the layer-dependent magnetisation of a van der Waals ferromagnet, VI3; a capability lacking in established characterisation techniques. Finally, we identify a threshold size (20 nm) below which a non-layered ultrathin material, magnetite, ceases to show ferromagnetism. This thesis furthers the development of widefield imaging using nitrogen-vacancy centres in diamond, enabling a range of future applications.