This thesis presents a system of coupled differential equations as a simple model of quantum electrodynamics (QED). A key feature of the model is the Riemann- Silberstein (RS) representation of the photon. The RS representation leads to a natural configuration-space description for a system of multiple, non-interacting electrons and photons. Relativistic covariance is shown by extending the dynamics to a representation of the Poincar´e group on the space of configuration-space amplitudes. Because the differential system forms a well-posed initial-value problem, this model features a natural concept of time evolution, and concretely parametrises the system even at intermediate times during scattering processes. If QED could be formulated in a framework of this type, both the analysis and rigorous formulation of quantum field theory may benefit from a useful new perspective. Towards this aim, I consider deformation of the free theory, preserving the initial-value nature while incorporating interactions between particles. The deformation takes the form of a coupling between states of different particle content. I present some simple criteria to show whether the deformation is compatible with relativity. For a specific choice of the deformation, I perform a perturbative expansion on this system. I demonstrate agreement between some of the leading terms and QED. Although further extensions are required, these appear to be compatible with the existing framework, and these results are an encouraging first step towards a complete configuration-space/differential representation of QED.

Almost all quantum systems are open; interactions with the surrounding environment generally lead to complex dissipative behaviour with a sensitive dependence on the details of the system-environment coupling. This thesis presents results from theoretical investigations into such behaviour in single and two-site quantum systems with a particular emphasis on strong system-environment coupling regimes, and also the effects of spatial correlations in the environment fluctuations. Within a weak system-environment coupling framework, it is found that an increased level of correlation is able to protect coherence shared between two spatially separated two-level quantum systems. Moreover, it is found that these correlations are in fact able to generate coherence between the two systems, and in certain regimes, cause the systems to become entangled. Using a polaron transform strong coupling master equation technique, the discussion is extended to the strong system-environment coupling or high temperature regime. To assess the validity of this approach in an experimentally relevant system, it is applied to the description of excitonic Rabi oscillations in a resonantly driven quantum dot. For most of the parameters of interest, the strong coupling theory is found to be valid over a far greater range of temperatures and coupling strengths than the standard weak-coupling theory. The coherent or incoherent nature of energy transfer dynamics is then studied by applying the strong coupling theory to a donor-acceptor pair model. Increased spatial correlations are found to extend the range of temperatures which allow coherent energy transfer to take place. Finally, a variational theory is introduced which allows for exploration of certain parameter regimes where both the weak-coupling and strong coupling theories become invalid. The variational theory is then used to investigate the ground state properties of a double two-level impurity model. High levels of spatial correlation are found to suppress the tunnelling amplitude within each impurity.

The two neutrino double beta ( 2 ) decay half-life of the 48Ca to 48Ti ground state transition has been measured by analysing 1555 days of NEMO3 data with 6.99g of 48Ca and was found to be T1=2 = 4:11+0:23 0:20(stat:) 0:26(syst:) 1019 years. This is the world's most accurate result for this isotope from which the matrix element for 2 has been calculated M2 = 0:0247 0:0015. A limit on the neutrinoless double beta ( 0 ) decay half-life for 48Ca has also been obtained at T1=2 > 1:8 1022 years at 90% CL. This corresponds to an upper bound on the e ective Majorana neutrino mass of hm i < 19:8 eV for a 0 matrix element of M0 = 0.72 which is comparable with the best present results for this isotope. The next incarnation of the NEMO3 technology is SuperNEMO which has its demonstrator module currently under construction and is due to begin operation in 2014. SuperNEMO aims to achieve a half-life sensitivity of 1026 years (90% CL) which corresponds to a neutrino mass of 40-100 meV. Calibration of the SuperNEMO detector sub-systems, especially the calorimeter, is important in order to maintain the required sensitivity and determine the detector design. The absolute calibration of SuperNEMO was shown to be achievable with a 6x4 con guration of 207Bi sources inside the detector. The calibration sources strength, position in the detector and the length and periodicity of the calibration runs have been optimised.

Using 9.4 g of Zr-96 and 1221 days of data from the NEMO-3 detector corresponding to 0.031 kgy, the obtained 2vbb decay half-life measurement is [2.35 \pm 0.14(stat) \pm 0.16(syst)] \times 10_{19}yr. Different characteristics of the final state electrons have been studied, such as the energy sum, individual electron energy, and angular distribution. The 2v nuclear matrix element is extracted using the measured 2vbb half-life and is 0.049 \pm 0.002. The 0vbb decay half-life is excluded at the 90% CL to > 9.2 \times 10_^{21}yr corresponding to a limit on the effective Majorana neutrino mass of < 7.2 – 19.4 eV. Limits on other mechanisms of 0vbb have also been set. Due for commissioning in 2012, SuperNEMO is the next generation detector which improves upon the proven technology and success of NEMO-3 to achieve a half-life sensitivity of ~10_{26} yr (90% CL) for Se-82 which corresponds to a neutrino mass of 50-100 meV. An energy resolution of 7% FWHM at 1 MeV has been obtained for the calorimeter baseline design of SuperNEMO which is currently in the R&D phase. This result not only meets the requirement stipulated by the R&D proposal, but is unprecedented for this type of calorimeter design.

Fusion power offers a promising source of clean energy for the future, however, one of the greatest challenges in tokamak reactor design is developing materials suitable to withstand the intense plasma-material interactions. Carbon, mostly in its graphitic form, is currently a favorite plasma facing material in many reactors. Diamond, however, offers many advantages over other materials but is not widely accepted. Although diamond exhibits excellent structural and thermal properties, tritium retention is a major concern for carbon. However, recent experimental evidence suggests that diamond might fare better than other carbon structures as a plasma facing material. This thesis investigates the the cumulative effect of exposing diamond to high thermal shock and tritium bombardment using classical molecular dynamics simulations. Of interest is diamond's resistance to graphitisation and the mechanisms behind tritium retention. Surfaces of different lattice orientation and level of hydrogen termination were incrementally heated to temperatures in excess of 2000 K. Generally, these diamond structures appeared to be stable up to temperatures of about 1000 K. Orientation did play a large part in determining the temperature of phase change, as did the level of hydrogen termination. Greater hydrogen coverages mimicked bulk continuation and increased resistance to graphitisation. These diamond surfaces, as well as a graphite and a diamond grain-boundary surface, were bombarded at a range of temperatures (300-2100 K) with high fluxes (1029 m-2s-1) of 15 eV tritium atoms in studying relative tritium retention at and below the surface as well as sputtered hydrocarbon yields. Below temperatures of graphitisation the diamond structure confined tritium, and thus further structural damage, to the upper surface. The graphitic surface allowed for deeper tritium penetration and retention. The presence of a grain boundary in the diamond slab allowed small amounts of tritium to penetrate deep into the bulk. Diamond surfaces were also bombarded at 300 K whilst independently varying incident ion energy (7.5-30 eV) and incident interval time (0.3-1.2 ps). Greater ion energies caused proportionally greater damage as well as reducing the ability of the structure to disperse incident thermal energy. At these extremely high fluxes sputter yield appeared to not vary with flux but was found to be proportional to fluence.

This thesis studies the dynamics of Feshbach molecule production from a gas of ultracold spin polarised Fermi atoms. A magnetic field is used to vary the strength of the interaction between the atoms exploring the limits of weakly paired atoms and tightly bound diatomic molecules. A mean field approximation is used to study the thermodynamics and dynamics of the system. The two-body interaction is modelled using a separable potential that reproduces the near threshold behaviour of the system close to a Feshbach resonance. For atoms in the same internal state interactions occur in the p-wave, such that they have one quanta of relative orbital angular momentum (ℓ = 1). The presence of a magnetic field fixes a quantisation axis for this angular momentum, leading to a splitting of the resonance feature into three components. It is shown that in certain cases these components may be treated separately on both a two-body and thermodynamic level. Consequently the many-body dynamics are also treated as if these components are distinct. In order to study molecule production the gas is prepared in a state similar to the Bardeen-Cooper-Schrieffer (BCS) state in a superconductor. A linear sweep of the magnetic field through a Feshbach resonance is used to convert the weakly paired atoms into tightly bound molecules. The variation of the molecule production efficiency is studied as the initial temperature, density initial magnetic field and final magnetic field are varied. Also studied is the variation of molecule production as a function of the rate at which the magnetic field is varied. It is shown that high densities are needed to explore a range of initial magnetic fields and sweep rates.

The work in this thesis uses data from the Cassini spacecraft in the Saturnian system to study the ionosphere and magnetic environment of Saturn’s largest moon Titan. The main instrument utilised is the Cassini Plasma Spectrometer – Electron Spectrometer (CAPS-ELS). Following the presentation of relevant background information, the first part of the thesis is concerned with the analysis of electrons in Titan’s ionosphere and exosphere, whereas in the second part we investigate observations of organic negative ions that can reach masses as high as 13,800 amu/q. The first of two electron topics is the study of photoelectrons in Titan’s ionosphere. We report on observations of photoelectrons (Coates et al., 2007a) in Titan’s exosphere and ionospheric tail that were created in Titan’s lower sunlit ionosphere. We compare observations to hybrid model results (Sillanpää et al., 2011) to confirm that photoelectrons can travel to these locations via magnetic field lines and discuss the implications for Titan’s ionospheric environment and magnetic tail. In the second electron topic we explore regions in Titan’s topside ionosphere where electrons undergo a change in energy of up to 100 eV. These events are observed predominantly on the hemisphere of Titan where the electric field of Saturn’s corotating magnetospheric plasma points away from the moon. A number of events also appear to be associated with pick up ions. The negative ion part of this thesis describes the investigation of factors that control the masses and number densities of negative ions (Coates et al., 2007b, 2009). These have been observed in the altitude range 950 – 1400 km which makes up the main part of Titan’s ionosphere. We find that the highest masses and densities are observed at the lower altitudes within this range. In addition, we reveal solar zenith angle trends for different mass groups, including a region of predominantly low densities near the day-night terminator.

This thesis is concentrated on studies on organic interfaces in conjugated polymer devices. Both non-linear properties of devices, photo-physical experiments, surface morphology using scanning probes and conventional device characterisation techniques are used to characterise the structures and physical processes at the specific interfaces. In more detail, the thesis can be divided into two parts. The first part concerns the electrode/semiconductor interface of light-emitting diodes, where the injection layers are investigated both in terms of electrical and photo-physical characteristics, and also their influence on the electro-optical response of the device. The different injection layers studied include a cross-linked hole-injection layer, and a self-assembled monolayer (SAM) for enhanced electron injection. For the former, the additional cross-linking is shown to provide superior hole-injection due to a higher work function and a reduction of impurity states as quantified in electroabsorption experiments. For the latter, the induced dipole of the SAM is shown to reduce the injection barrier for electrons at the cathode. Through electroabsorption it is furthermore shown that the dipole of the SAM adsorbed on thin oxides is bias dependent and its dynamical reorganisation is characterised accordingly. The second part treats the charge/energy transfer properties at the organic/organic interfaces in binary blends both for application in light-emitting diodes (LEDs) and photovoltaic cells (PVs). In LEDs, the emphasis lies in creating non-resonant blends, i.e. to reduce energy transfer between the two materials, in order to achieve two-component electroluminescence that can be tuned to white light. In contrast, binary bulk heterojunction PVs are doped by metal complexes to introduce inter-system crossings to a triplet manifold with the goal to increase the exciton dissociation efficiency. It is demonstrated that the large portion that transfer into triplet states still dissociates and the subsequent free charges can be effectively extracted.

This thesis examines the potential of a class of organic molecules, porphyrin derivatives, for quantum information purposes. The experiments in this thesis follow a simple progression: they begin by exploring the time-independent characteristics of the molecules, then investigate the dynamics and decoherence, and end with a consideration of the potential for controllable coupling. Whilst this methodology is obviously motivated by interest in quantum information processing (QIP), it is hoped that the results will have relevance for a larger group of fields including organic electronics, solar energy and spintronics. QIP is at the forefront of science, requiring an understanding of the coherent properties of materials - an understanding deeper than has ever been required before. Since copper phthalocyanine is a technologically relevant material, with uses in organic electronics and solar cells, and possible applications in the developing field of spintronics, this deep understanding can be fed back to provide interesting new developments. The first experimental chapter, Chapter 4, is such an example, where work focussed on understanding a novel phase of CuPc (the \eta-phase), through magnetometry and electron spin resonance led to the development of a method to measure the magnetic properties of liquids. It is hoped that this could open a path for solution based biological samples to be studied via magnetometry. A discussion of the details of the technique, the interpretation of the data, and a proof of principle are provided in this chapter. Another interesting technological development is discussed in Chapter 5, where the initial characterisation of the thin films of copper phthalocyanine (CuPc) led to a deeper understanding of their nanostructure, an important property for the development of solar cells. This consisted of continuous wave electron spin resonance (ESR) experiments on thin films of CuPc, varying both the percentage of copper and the orientation of the molecules, to allow the interpretation of the ESR spectra of mixed films of CuPc and C60, the mixture that is used in organic solar cells. I demonstrate that the CuPc and C60 form nano-clusters in these films, with a preferred orientation. Since the mixed films are known to be more efficient than a simple two layer device, this result provides new information, which can be used to improve the design of this type of solar cell. Chapter 6 consists of the measurement of the decoherence times of spins in CuPc films, and an understanding of the mechanisms of decoherence. Pulsed ESR is used on both powders and thin films of copper phthalocyanine and the field and temperature dependence is explored. Since it is unlikely that molecules in solution will ever be able to provide a scalable QIP solution, this move to the solid state represents a real advance. It is not trivial however, as the solid state can provide many additional decoherence routes. These times are the first step in proposing a material as a potential vehicle for QIP, and I demonstrate that the decoherence times are long enough that, given its other advantages, CuPc can be taken seriously as a candidate host for qubits. The important distinction of these measurements from those that have been made before on, for instance, molecular magnets is that these decoherence times are achieved in the solid state. The last results chapter is an attempt to make progress on a problem that is particularly relevant for molecular QIP. Since molecules can be made easily, they provide a attractive path to an individual qubit. The identical nature of the molecules comes at a price, though, as it makes it hard to address each qubit independently. Chapter 7 seeks to explore the physics of optically coupling two qubits (in this case TEMPO radicals) through a porphyrin linker. Steady state and time resolved optical absorption and pulsed and transient ESR are used to characterise the spin physics of the samples. I demonstrate that it is very likely a coupling can be controllably switched on (if not, as yet, o). This chapter lays the foundations for a considerable number of future experiments, some of which are discussed at the end, that could demonstrate a truly switchable coherent coupling between qubits.

This thesis is an investigation of the relationships between unsaturated polyester resin composition and permeability to water. The permeabilities of cured unreinforced resins (castings) and glass reinforced polyesters (G.R.P.) made with different resins were studied at 50[sup]oC. In addition, the effect of applied strain on the permeability of castings and laminates made form a single resin were investigated. Six commercial resins were examined in all. Three variables were studied: 1. The effect of chemical constitution of the resin on transmission rate of water. 2. The effect of glass reinforcement on permeability. 3. The effect of applied strain on the permeability of castings and laminates made from a single resin. It was shown that, in the absence of any external strain, the castings made from various resins behaved differently. Castings made from a moderately crosslinked resin shows the highest resistance to water transmission. Castings made from resins with either higher or lower unsaturation showed a higher permeability to water. The dietyhylene propylene fumarate isophthalate resin has an advantage over the propylene fumarate isophthalate resin in having a lower water transmission rate. The permeability of the polyester resin increases with increase in the acid value of the resin. Another feature observed in the study is the decrease in the rate of transmission of water as the volume fraction of glass fibres in the laminates increases. This effect becomes more pronounced for laminates made from resins with high un-saturation. Results show that the observed transmission rates of water through laminates are always less than the product of resin volume fraction and resin permeability. The difference between the calculated and observed values of permeability become larger as the fibre orientation changes from random to bidirectional. This suggests that fibre orientation, as well as fibre volume fraction, is an important factor affecting water transmission through laminates. The effect of external strain on resins and laminates depends on the nature of the resin used. In general, applied strain increases water transmission rates, both in castings and laminates. An exception to this rule was found with laminates made from a moderately crosslinked resin. Glass laminates made from this resin allow the passage of water when under low strain than when unstrained. However permeability increases when the applied strain is higher.