School of Physics - Theses
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ItemPhysics of low-dimensional nanostructures( 2012)Nanoscale constructs are offering access to the quantum mechanical regime due to their constrained size. The unusual, and often counterintuitive, behaviours of such constructs are of considerable interest to those developing new devices across several fields, including (but not limited to) quantum computing, communications, in vivo applications such as the bionic eye and bio-sensors, standard electronics and computing, and magnetometry. The physics of zero-, one-, and two-dimensional nanostructures comprised of various dopants or arrays of dopants in either diamond or silicon are presented and discussed. In particular, the zero-dimensional Xe-related defects in diamond are considered theoretically, via density functional theory, lattice dynamics, and thermodynamics. Xe defects have also been characterised experimentally via the probe-enhanced Ra- man spectroscopy (PERS) technique. In silicon, a one-dimensional nanowire consisting of P donors is studied with density functional theory. This wire is monatomically thin in one direction, and two donors wide in the other, with the donors spaced at the currently realisable sheet density of 25%. The two-dimensional case of infinite monatomically thin sheets of P donors is considered, both with effective mass theory and density functional theory (which is again undertaken for the most common experimental sheet density, 25%). The effective mass theory model has been applied to several sheet densities, agrees well with literature calculations of sheets with in-plane disorder, is far more rapid in execution, and offers an analytic scaling theory to describe the dependence of several key results on the sheet density. The density functional theory approach is then extended to the quasi-two dimensional case of bilayers of monatomically thin P sheets, in order to address the approach to minimal two-dimensional confinement.
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ItemThe theory of the nitrogen-vacancy colour centre in diamond( 2012)The nitrogen-vacancy (NV) colour centre in diamond is a model system for many quantum technologies including, metrology, information processing and communications. The NV centre is also highly suitable for employment in various nanotechnology applications, such as biological and sub-diffraction limit imaging, and in tests of fundamental physics, such as cavity quantum electrodynamics and the quantum entanglement of mesoscopic systems. The remarkable properties of the centre are however, not currently fully understood, with several unresolved issues limiting the performance of the centre in its many important applications. As the unresolved issues are interrelated and concern different aspects of the centre's properties, they may only be resolved by the development of a single self-consistent theory of the NV centre. The aim of this work has been to develop such a theory. The theory has been developed using a combination of the molecular model of deep level defects in semiconductors, group theoretical methods and ab initio calculations. The highly structured nature of the theory will enable its future use in the systematic identification of other colour centres that possess properties that exceed those of the NV centre.
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ItemNanoscale quantum sensing using nitrogen-vacancy centres in diamond( 2012)Devices that detect and spatially image magnetic fields are important in many areas of study including chemistry, electronics, materials science and biology. By extending the boundaries of what is currently achievable we may begin to explore areas previously inaccessible to science, such as wide-field imaging of neuron signaling or structural determination of single molecules. Here we present experimental progress towards the development of a nanoscale magnetic sensor operating under ambient conditions using the nitrogen-vacancy (NV) centre in diamond. This thesis describes the construction of a lab-built, confocal microscope capable of detecting single NV centres, with additional microwave control for coherent manipulation of the NV spin. The feasibility of using NV-diamond for real-time detection of the action potential generated by a neuron, and with high spatial resolution is experimentally demonstrated. The quantum coherence of single NV spins is monitored in various chemical solutions, and detection of nanoscale magnetic environments external to the diamond are demonstrated. This work sets the experimental foundation for using manufactured single quantum systems as sensitive probes of external chemical environments. In addition, the first measurements of single quantum coherent spins inside living cells are performed with NV centres in nanodiamonds. These studies on NV centres inside living cells demonstrate their promise as magnetic sensors for biology. Furthermore, alternative quantum sensing technologies emerge including rotational tracking of nanodiamonds and enhanced identification of fluorescent nanoparticles.