Single walled carbon nanotubes (SWCNTs) have been doped with nitrogen (N) by two ion-mediated approaches: directly through irradiation with N+ ions and by a novel indirect technique, creating defects through Ar+ ion irradiation which then react with nitrogen upon annealing in a N2 atmosphere. X-ray photoelectron spectroscopy (XPS) was then employed to determine the chemical environment of the nitrogen within the resulting SWCNT material. Depending upon the exact preparation conditions, nitrogen in graphitic (substitutional) pyridinic and pyrrolic configurations could be identified. Nitrogen doping through the novel method was found to introduce the largest concentration of chemisorbed nitrogen within the SWCNT films, dominated by thermodynamically unstable pyrrolic species at low process temperatures (500ºC). The maximum concentration of nitrogen in graphitic sites was achieved by direct ion bombardment, although both XPS and Raman spectroscopy indicated that this approach to doping led to the greatest damage. The ability to vary both bsolute and relative composition of chemisorbed nitrogen species is expected to be valuable for a range of fundamental studies, particularly of the catalytic behaviour of these materials. The growth of graphene on copper under atmospheric pressure using a soft solid source (nonadecane) is reported. It is found that the growth rate is best described by a model which involves the continuous supply of reactive species during the entire growth period. This observation is explained in terms of the formation of decomposition produces which reside on an otherwise clean surface after nonadecane desorption and provide a series of ‘mini carbon sources’ for graphene growth. XPS analysis indicates that, as expected, increased growth temperature leads to greater graphitisation at the surface (and hence graphene ‘quality’) which is not accompanied by any substantial change in island size and coverage. It is found that although graphene islands can be produced it is not possible to form continuous films, demonstrating the limitations of this technique. Although limited in some ways, the use of soft solid precursors for graphene growth allows the ready introduction of potential dopant materials. XPS, Raman and SEM data provide strong evidence that a PDMS precursor can be employed in atmospheric pressure solid-phase CVD to produce graphene heavily doped with silicon, which has not been previously achieved. Since silicon-doped graphene is predicted to possess a band gap related to the Si concentration, this may provide a route to produce a graphene-based material of use in digital electronics.

The evolution of galaxies across cosmic time, from the first galaxies to the local Universe, are studied using cosmological hydrodynamical simulations. It is demonstrated that, for the first time, a hydrodynamical simulation can reproduce the observed evolution of galaxy stellar masses and the trends in star formation rates. The success of the simulation in producing galaxies with similar histories to those observed increases the potential for using hydrodynamical simulations to explore galaxy formation physics. With this intention, we consider the effects of the environment and active galactic nuclei (AGN) quenching on the galaxy population and the shape of the galaxy stellar mass function (GSMF). We find environmental processes are effective at quenching galaxies in the simulation and operated on short timescales. AGN feedback, which produces a large passive fraction at high stellar masses, drives the exponential break in the GSMF. Specific star formation rates (SFRs) in simulations, both hydrodynamical and semi-analytical, have been shown to be discrepant with observations. We investigate proposed solutions to this problem using a suite of cosmological hydrodynamical simulations. The offset in the simulations, at the level of 0.2 to 0.4 dex, can only be resolved by employing an extreme model that does not recover any of the observed trends in stellar mass or the cosmic star formation rate density. This study implies that the observed star formation rates across comic time are inconsistent with the growth of stellar mass. Two galaxy populations are then explored in more detail. We examine the first galaxies and their potential to reionize the Universe. We find that low-mass galaxies, undergoing extreme star formation for their stellar mass, produce the majority of ionizing photons at redshifts 6 and above. The second study considers the most highly star forming galaxies in the simulation, which represent an extreme population. These galaxies have similar stellar and gas masses to the observed sub-mm population, however, their SFRs are lower. On further investigation, the selection of galaxies based on SFRs is not adequate to compare the simulation to the sub-mm population, in particular at high redshift. These results highlight the importance of dust temperature in the selection.

This thesis investigates photonic spectroscopy and its use in astronomy. In chapter two the theory associated with both astronomical spectroscopy and photonic spectroscopy is shown. The convergence of the two in the field of astrophotonics is discussed along with existing work in the field. In chapter three models of the Integrated Photonic Spectrograph are created and compared like-for-like with existing instruments. The results suggest that the Integrated Photonic Spectrograph will be similar to existing instruments in terms of size and will require more detector pixels for a full instrument. In chapter four the modelling is extended, examining the areas where pho- tonic spectroscopy could show advatanges over conventional instrumentation. This is done by varying spectral resolution, telescope diameter, seeing and num- ber of objects sampled. The results show that the Integrated Photonic Spec- trograph will perform best when the telescope is close to the diffraction-limit, both in terms of size and number of detector pixels required. Science cases are presented for these areas. In chapter five different concepts for a redesigned Integrated Photonic Spec- trograph are presented and the advantages and disadvatanges of the variations are commented upon. The two that are chosen for development require the telescope Point Spread Function to be reformatted to a long slit. This device, which we have named the photonic-dicer is presented in chapter six. Its design, manufacture and testing is discussed both in the laboratory and on sky in conjunction with the CANARY adaptive optics system. Finally chapter seven presents our concluding remarks and discussions for future work.

My research has centred around establishing the nature of dark matter haloes by investigating their abundance as a function of halo mass, the formation his- tory of each halo, commonly called the merger tree, and the internal structure of the halo, in terms of their radial density profiles and angular momentum. In the first part of this thesis, I present a new algorithm which groups the subhaloes found in cosmological N-body simulations by structure finders such as subfind into dark matter haloes whose formation histories are strictly hier- archical. One advantage of these ‘Dhaloes’ over the commonly used friends-of- friends (FoF) haloes is that they retain their individual identity in cases when FoF haloes are artificially merged by tenuous bridges of particles or by an over- lap of their outer diffuse haloes. Dhaloes are thus well suited for modelling galaxy formation and their merger trees form the basis of the Durham semi- analytic galaxy formation model, galform. Applying the Dhalo construction to the ΛCDM Millennium-2 simulation we find that approximately 90% of Dhaloes have a one-to-one, bijective match with a corresponding FoF halo. The remaining 10% are typically secondary components of large FoF haloes. Although the mass functions of both types of haloes are similar, the mass of Dhaloes correlates much more tightly with the virial mass, M200, than FoF masses. Approximately 80% of FoF and bijective and non-bijective Dhaloes are relaxed according to standard criteria. For these relaxed haloes all three types have similar concentration– M200 relations and, at fixed mass, the concentration distributions are described accurately by log-normal distributions. In the second part of this thesis, I present distributions of orbital parameters of infalling satellite haloes at the time of crossing the virial radius of their host halo. Detailed investigation of the orbits is crucial as it represents the initial conditions which determine the later evolution of the substructure within the host. I use merger trees in a high resolution cosmological N-body simulation to trace the satellite haloes and measure their orbits when they first infall into the host halo. I find that there is a trend of the orbital parameters with the ratio between the satellite halo mass and the host halo mass at infall. I find that the more massive satellites move along more eccentric orbits with lower specific angular momentum than less massive satellites. I also search for possible correlations between different orbital parameters and provide accurate fitting formulae for the two independent orbital parameters (the total velocity and the radial-to-total velocity ratio). Using combinations of these formulae, we successfully fit all the other orbital parameters.

With the Large Hadron Collider about to start its second run, we are in an era of high-energy collider physics. The discovery of a Standard Model-like Higgs boson with a mass of 125 GeV is a fantastic achievement, but the non-observation of supersymmetry (or any other mechanism of choice that stabilises the electroweak scale) is a tantalising puzzle. In this work, we investigate the possibility that a particular non-minimal realisation of supersymmetry - one with Dirac gauginos - can be a reasonably natural way of explaining this non—observation, but can still can stabilise electroweak physics. We construct a simple UV completion of a model with Dirac gluinos dubbed 'Constrained Dirac gluino mediation' and determine the characteristic low energy spectra, the production cross sections of key processes at the Large Hadron Collider and the degree of fine tuning for a representative range of parameters. Noting that theories with Dirac gluinos have a tendency to lose asymptotic freedom due to the presence of extra matter content, we then cast our eyes towards Seiberg Duality and its generalisation to include adjoint chiral superfields - Kutasov duality and investigate how a Dirac mass maps across this duality. We provide evidence that a Dirac gaugino mass maps between electric and magnetic Kutasov descriptions in a particular form using renormalisation group arguments and harmonic superspace techniques.

We use the semi-analytic galaxy formation model, GALFORM, to explore the implications of results from multi-wavelength galaxy surveys within the context of the hierarchical structure formation paradigm. Specific topics which we investigate include (i): the biases that can be introduced by using spectral energy distribution fitting to infer stellar masses from broad-band photometry, (ii) the reasons why galaxy formation models struggle to reproduce the exponential drop with time in star formation rates of star-forming galaxies inferred from a wide range of observations, (iii) the physical processes that control the evolution in the median relationship between stellar mass and halo mass predicted by galaxy formation models. We show that stellar masses of compact dusty star-forming galaxies could be underestimated by SED fitting as a result of assuming a uniform foreground dust screen geometry. We explain how the standard implementation of supernova feedback and gas reincorporation within galaxy formation models results in flat predicted star formation histories for star forming galaxies. We show that this is inconsistent with observational data which imply that these star formation histories should instead be peaked at intermediate redshift. We also show how the supernova feedback and gas reincorporation implementations within standard galaxy formation models result in a baryon conversion efficiency within haloes that is roughly independent of cosmic time at fixed halo mass. Consequently, the median stellar mass versus halo mass relationship is predicted by these models to not evolve significantly.

In this thesis we carry out a detailed investigation of a class of four-dimensional N=1 gauge theories, known as Bipartite Field Theories (BFTs), and their utility in integrable systems and scattering amplitudes in 4-dimensional N=4 Super-Yang-Mills (SYM). We present powerful combinatorial tools for analyzing the moduli spaces of BFTs, and find an interesting connection with the matching and matroid polytopes, which play a central role in the understanding of the Grassmannian. We use the tools from BFTs to construct (0+1)-dimensional cluster integrable systems, and propose a way of obtaining (1+1)- and (2+1)-dimensional integrable field theories. Using the matching and matroid polytopes of BFTs, we analyze the singularity structure of planar and non-planar on-shell diagrams, which are central to modern developments of scattering amplitudes in N=4 SYM. In so doing, we uncover a new way of obtaining the positroid stratication of the Grassmannian. We use tools from BFTs to understand the boundary structure of the amplituhedron, a recently found geometric object whose volume calculates the integrand of scattering amplitudes in planar N=4 SYM theory. We provide the most comprehensive study of the geometry of the amplituhedron to date. We also present a detailed study of non-planar on-shell diagrams, constructing the on-shell form using two new, independent methods: a non-planar boundary measurement valid for arbitrary non-planar graphs, and a proposal for a combinatorial method to determine the on-shell form directly from the graph.

The fabrication and processing by solid-state heat-treatment, mechanical ball milling and hot isostatic pressing of microcrystalline and nanocrystalline niobium carbonitride is reported. This material is subjected to a number of characterisation measurements including x-ray diffraction, resistivity, ac-susceptibility, dc-extraction and heat capacity. The resultant measurement data are used to assess the adequacy of the material’s processing and quality with respect to the fundamental superconducting characteristics, transition temperature, T_c, upper critical magnetic field, B_c2, and critical current density, J_c. It is shown that a substantial increase in B_c2 from ~ 11 T (in the microcrystalline material) to ~ 21 T (in the nanocrystalline material) has been produced. A fortyfold increase in J_c from 1.8 x 107 Am^(-2) (in microcrystalline material measured at 3 T and 6 K) to 7.4 x 108 Am^(-2) (in nanocrystalline material measured at 3 T and 5.9 K) has also been produced. These substantial increases have been made with only a 32 % reduction in T_c from ~17.6 K to ~ 11.9 K, well above the temperature of liquid helium. The accurate large quantity metrology of 10,000 Nb3Sn samples for the International Thermonuclear Experimental Reactor toroidal field coils is also reported and an overview analysis of the data provided. In particular, all seven measurement types; critical current, hysteresis loss, residual resistivity ratio, diameter, chromium plating thickness, twist pitch and copper to non-copper volume ratio are discussed in relation to the accuracy with which they were performed. The methodology in performing the heat-treatments and measurements is discussed and the detail of the necessary equipment set up is given. The results from some additional experiments that deal with the effect of heat-treatment cleanliness and sample geometry on various measurement types is provided.

This thesis has focused on using experimental and simulation based techniques in an attempt to understand the interactions between polymer hosts and phosphorescent dopants in Organic Light Emitting Devices (OLEDs). The viability of the SEmiconducting Thin Film Optics Simulation (SETFOS) software as a modelling tool has been established using the well documented material poly(3,4-ethylenedioxythiophene) (PEDOT). Parameters including resistivity and work function were extracted using SETFOS and the trends observed compared favourably to the commercially provided values, despite some limitations. SETFOS was then used, along with steady state and transient electroluminescence characterisation, to investigate the effects of both phosphorescent dopant colour and concentration on device performance and extract important device parameters, such as the density of states and carrier mobilities. Different device behaviours were observed depending upon the dopant colour and concentration, highlighting the importance of both to device performance. SETFOS was again found to be able to produce quantitative values for a number of device parameters, but several more limitations within the models were identified, which makes further analysis and investigation necessary. Having gained an understanding of host and dopant interactions in OLED devices, the information gathered was used in the characterization of novel high triplet host polymers for OLED applications. Seven polyfluorene based copolymers were investigated in devices with a range of different coloured phosphorescent dopants and charge transport molecules. Unfortunately, they were found to be unsuitable for use as host materials in OLEDs, acting instead as charge traps. These polymers, along with four others, were alternatively assessed on their ability to perform as deep blue, or violet, fluorescent materials in undoped Polymer LED (PLED) devices. These devices were found to have some of the highest device characteristics currently detailed in the literature, and represent a variety of new ways of achieving efficient deep blue emission using PLED devices.

This thesis investigates an area of beyond the Standard Model (BSM) phenomenology associated with the presence of additional light, “weakly interacting slim particles” (WISPs). Particular attention is given to the hidden photon, the gauge boson associated with an additional U(1) gauge group that mixes kinetically with hypercharge. The theoretical foundation of the interactions studied lies in effective field theory, and the first part of the thesis investigates a so-far untested aspect of effective theories, namely effective non-locality in particle propagation. There are no observable effects of hidden photons if they are massless. We investigate the impact on experimental signatures in the case that the hidden photon gets its mass during compactification from a higher dimensional theory. WISPs make good dark matter candidates, and are especially compelling in light of the lack of observation of heavy WIMP (“weakly interacting massive particle”) dark matter. Nonetheless, it is shown that if WIMP dark matter is composed of a Dirac fermion that couples to the SM only through a pseudoscalar, indirect detection may be our only experimental window, and that it may already be appearing as a gamma ray excess at the Galactic Centre. There is considerable interest in dark matter searches at beam dump facilities, in particular for light dark matter coupled through a similarly light mediator particle. We investigate this set up in the context of the E613 beam dump experiment. Owing to the light mediator, the low-Q^2 kinematic region of deep inelastic scattering is especially important. We present a new treatment of dark particle scattering in this region via a light vector mediator (such as a hidden photon), and find that it enhances constraints.