| Popis: |
Nitrogen-vacancy (NV) centres are naturally occurring colour centres in bulk diamond crystals that enable quantum sensing via optically active spin ground states. They have demonstrated high sensitivity in thermometry and magnetometry, reaching a temperature precision of 5mK/√Hz and magnetic field sensitivity of a single nuclear spin. Due to their nanometer size and ability to be chemically functionalised, diamond nanocrystals (nanodiamonds) offer sensing in systems inaccessible with bulk diamonds. Of particular interest is magnetometry and thermometry in biological systems. This thesis explores interfacing nanodiamonds host NV centres with complex systems for decoherence spectroscopy, relaxometry and thermometry. In Chapter 1, it is demonstrated that nanodiamonds can perform NMR experiments with nanoscale sensing volume. In this experiment a dynamical decoupling sequence is used to sense the stochastic and stationary magnetic field at the site of the NV created by the target nuclear spins. The spectral resolution of this technique is sufficient to distinguish between two different nuclear species 1H and 19F. Furthermore, a self-referenced calibration scheme is proposed and verified with experimental data to enhance the accuracy of concentration measurements, previously limited by the geometrical variability between nanodiamonds. In Chapter 3, nanodiamonds are used to study triplet exciton diffusion in an organic semiconductor material. In this experiment, NV relaxometry is used to probe the diffusion process of optically generated triplet excitons. It was observed that the longitudinal relaxation time of NV (T1) is related to the optical excitation of the organic material and that the depolarisation rate saturates at large optical excitation power. A stochastic Liouville equation model is used to model the spin diffusion process. In Chapter 4 and 5, nanodiamonds are used in thermometry to measure time-varying signal in biological cells. In this experiment, the theoretical temperature sensitivity is examined using Fisher information formalism and compared with experimental sensitivity. This forms the basis of optimal ODMR frequency sampling in situations where the ODMR lineshape fluctuates. It was also demonstrated that it is possible to simultaneously perform ODMR measurements and track single nanodiamonds, using an orbital tracking method. This enables a single nanodiamond to be measured over hours despite thermal motion. Simultaneously, the temperature can be determined with a sensitivity of 1.5K/√Hz and the position with an accuracy of 7.7 nm. With these technical improvements the intracellular temperature variation in HeLa cells is measured when the cells are subjected to external temperature modulation or chemical stimuli. Finally, despite the success of NV centres in diamond for room-temperature quantum sensing, in Chapter 6, we explore a novel two dimensional material, hexagonal boron nitride, that offers a more scalable platform for future quantum sensing applications. In this experiment, we identified stable spin-addressable single emitters at room temperature. ODMR experiments reveal the fine structure of the defect which was modelled as a spin triplet. Photokinetic properties are investigated with second order intensity correlation measurements and an optical level structure is proposed to provide a brand new understanding of this novel quantum sensing platform. This provides a basis for tackling the issues facing nanodiamond. |
