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Phononic crystals are composite media, with two different elastic materials modulated in a periodic fashion. The two-dimensional system under study is comprised of an array of cylindrical tubes arranged in a square Bravais lattice. The propagation of a time-harmonic acoustic Bloch waves is investigated experimentally and the findings compared with those obtained from the finite element method. The band structure, that is a well-known characteristic of Bloch wave dispersion, is also determined. This demonstrates the existence of band gaps of forbidden transmission at certain frequency ranges. These arise due to the interference when the wavelength of the incident wave is comparable to the periodic spacing of the modulated media. A second phononic crystal with slotted steel tubes is also studied. The opening in the tube permitting air to flow to the internal cavity, and constituting a Helmholtz resonator. The band structure of such a structure possesses additional band gaps, which arise due to the excitation of the resonators. Furthermore, it has recently been shown that periodically distributed Helmholtz resonator structures, can exhibit negative refraction phenomena. Using the transmission line technique, as outlined by Y.Cheng et al. we demonstrate this behaviour for our experimental system. It is shown that, at certain frequency ranges, the locally resonant phononic crystal exhibits negative effective density and bulk modulus, the two conditions required to obtain a negative index of refraction.

The molecular shape of any nonlinear molecule can be strongly influenced by the coupling between electrons and vibrations (vibronic coupling) via the Jahn-Teller (JT) interaction within the molecule. This influence appears as a distortion of the symmetrical shape of the original molecule. In such molecules, the adiabatic potential energy surface (APES) possesses either a trough of minimum-energy points or several isoenergetic minima ('wells') depending on the nature of the interactions present. In the case when coupling is infinite, the wells are very deep and the system will be locked into one of these distorted states. The vibronic states associated with these wells are good eigenstates of the system in this limiting static case. However, real molecules have finite coupling, so the system can migrate from one well to another in a process that is often referred to as the dynamic JT effect. If the wells are deep, then the motion must involve quantum mechanical tunnelling. Generally, the motion between wells gives the illusion that the molecule has rotated and this type of motion is referred to as pseudorotation. The eigenstates of the general system can then be approximated by symmetry-adapted states (SAS) which are a linear combination of the states associated with the wells. In this thesis, we focus on studying the dynamical nature of the JT effect through investigating the pseudorotation mechanism in different systems using a simple method employing the time-evolution operator. This allows us to obtain analytical expressions for the probabilities that a system that starts off localised in one initial well, may become localised in another well at some later time. These expressions are plotted versus time to show the pseudorotation regime and a comparison between different cases of pseudorotation in different molecules is made. Determination of the rates of pseudorotation leads to a better knowledge of the strength and nature of the vibronic coupling in the system and is a quantity that is, in principle, experimentally measurable. Also, more information about the tunnelling splitting between the SASs can be gained from this study.

This thesis presents theoretical investigations on a range of topics in cold atom physics, primarily by means of wave mechanical simulations, implemented on High-Performance computers. Two particular concerns are the interaction of Bose-Einstein condensates with microfabricated surfaces, and the behaviour of strongly interacting Fermi atoms. In the course of this work. we have developed new theoretical models and computational techniques to handle problems which were beyond the scope of previous calculations.

The technological importance of hard thin films is well established. There is growing recognition that nanometre-scale surface structures can be controlled to the benefit of function. In-process structuring brings these ideas together. This study explores how the morphology, especially the surface topography, and microtribological behaviour of Cr-N films can be controlled during unbalanced magnetron (UBM) sputtering. Experiments varying the sputter power, bias voltage, temperature, total pressure and Ar/N2 ratio during UBM sputtering generated different compositions, crystallite orientations and microstructures, and six associated topography types: pyramidal (type P), grain-like (G), crater-like (CR), ribbon-like (R), conical (C) and hillock-like (H). A new empirical zone model consistently relates these topography types to process parameters. The feature dimensions are also controlled by the deposition parameters. The films have closely reproducible topographical and mechanical properties. The microtribological behaviour for three topography types (P, C and CR) is studied under different conditions relevant to unlubricated contacts, lubricated contacts, and humid environments. Nanostructured surfaces show significantly lower friction than smooth ones, with actual reductions depending on the topography type. Friction strongly correlates with summit density (Ssd). Low friction (Ssd ~ 3 #/µm2) was measured on all type CR surfaces, but only by increasing the lateral dimensions of types P and C. Unlubricated friction is attributed principally to solid-solid adhesion, influenced by the density and curvature of summits. Wear is influenced by the density, shape and size of the surface features and by the mechanical properties of the film. Boundary lubrication reduced friction, with slight dependence on lubricant. Alongside the summits parameters, friction correlates with core fluid retention index. Applying hydrophobic and hydrophilic treatments shows that appropriate nanostructuring reduces the dependence of friction on humidity and sliding velocity, principally by controlling the summit density. In-process structuring is clearly very useful for creating nanostructures in order to enhance the microtribological behaviour of surfaces. Further investigations are recommended into friction optimization by nanostructuring.

The existence and excitation energy of the 9B1⁄2+ state has long been contested. The state exists in 9Be but appears missing in the mirror nucleus 9B, although there are several published (inconclusive) claims. Different theoretical approaches (single-particle potential, R-matrix and microscopic cluster models) have produced a range of excitation energies from 0.9 MeV to 1.8 MeV but agree a width (1-2MeV). States in 9B are unbound, and most are broad and overlapping creating difficult experimental conditions. The most convincing evidence for this state comes from a study of 6Li(6Li,t)9B, performed at Florida State University by the CHARISSA collaboration, published in 1995. The experiment suffered from poor statistics but indicated new structure in 9B. In 2001 new results were reported that highlighted the need for re-analysis of the FSU data. However, this would be severely limited by the poor statistics. Thus the CHARISSA collaboration repeated the 6Li(6Li,t)9B reaction in 2003 at the Australian National University, which offered greater detection efficiency and a data acquisition system better equipped to deal with many channels and high trigger rates. A 60 MeV 6Li3+ beam was impinged on a 240 μg cm-2 6LiF target. The breakup fragments from the decay of the resonant nuclei were detected in six ΔE-E telescopes, consisting of three stages: Si quadrants (70μm), Si strip (500μm), and Csl (1cm). The breakup particles were reconstructed using the technique of Resonant Particle Spectroscopy. This experiment conclusively showed that the 6Li(6Li,t)9B reaction does not populate the 9B 1/2 + state. However, the 6Li(6Li,d)10B reaction was also reconstructed in this analysis and showed 6Li(g.s.)+ɑ, 6Li(2.186 MeV)+ɑ, 8Be+d, and pnɑɑ (9B+n or 9Be+p) decay from 10B. Whilst the a decay channels were found to be most intensely populated, 9B spectra were obtained and showed the presence of the 1⁄2+ state with a broad asymmetric peak around 0.8-1.0MeV (Γ ≈ 1.5 MeV).

For hydrogen-like nuclei (HLN) such as the proton or muon, the quantum zero point energy cannot be ignored. The main objectives of this thesis were to identify practical ways to model this quantatively, and hence i) to gain an understanding of interactions between the HLN and its environment, and ii) to use this understanding to evaluate the wavefunction of such a nucleus within an electronic structure calculation. Several features of the HLN-electron interactions were studied analytically by assuming their interaction to be harmonic in nature. It was shown that the accurate modelling of the HLN-electron correlation was extremely important in the evaluation of the HLN wavefunction. A parametrised correlation model (PCM) was developed, and was shown to accurately reproduce the effective potential energy surface experienced by the HLN when HLN-electron correlation was included. The required parameters showed a simple HLN mass dependence. The PCM was used to study DNA base molecule adducts formed by addition of a single HLN. The relative stability of these adducts was shown to be dependent on the mass of the HLN, and the inclusion of HLN-electron correlation was shown to lead to a stabilisation of the C-X bonds relative to the N-X and O-X bonds. The PCM was used to study the interaction of H and Mu with the diamond dopants sulphur and phosphorus. The PCM correctly predicted differences between the HLN wavefunctions in crystalline and molecular environments. The HLN-electron correlation energy was shown to be large enough to cause the phosphorus-muonium defect complex formation energy to become positive. HLN-impurity-vacancy complexes in diamond were studied using the PCM, and it was found that the lowest energy state was obtained by the HLN saturating a carbon dangling bond, irrespective of the impurity species. It was concluded that the HLN would be effectively localised at a single site.

In this Thesis we apply the Gross-Pitaevskii equation (GPE) to describe properties of a dilute, near zero temperature Bose gas for various confining geometries. We start by reviewing some basic information about the density, the chemical potential and elementary excitations of a dilute atomic condensate confined in a single harmonic trap for a Bose condensate with repulsive and attractive interactions and we also discuss the stability in the case of attractive interactions. We extend our study to a one and three dimensional double-well trap. We investigate the eigenenergy levels and show that the nonlinearity leads to triangular structures which appear either in the ground or excited states for the case of a Bose condensate with attractive or repulsive interactions respectively. We apply the eigenenergy level picture to analyse Josephson effects induced when the barrier IS moved at a constant velocity across the trapping potential or by the application of a time-dependent potential gradient. The GPE simulations are compared to the predictions of a nonlinear two state model. Above a critical velocity there is a transition to a superposition of ground and excited states which leads to sudden changes in the population difference. The direction of Josephson flow depends critically on the initial state of the system and we discuss the feasibility of experimental control of the atomic flow using phase-imprinting. The stability of a low temperature Bose-Einstein condensate with attract interactions in one and three dimensional double-well potentiate is discussed. The condensate is shown to collapse at a critical potential gradient which corresponds to a critical number of atoms in one of the two wells. Finally we investigate the stability and tunnelling effects in a multi-well system.

This thesis discusses the development of an ion beam generation and transport system for the purpose of high current ion implantation and presents a method to achieve high quality beam generation and high transport efficiency. An advanced method of achieving ideal space charge neutralization of an ion beam as well as charge neutralization of implanted targets has also been developed and presented. This study was carried out in five main categories as described below. 1. Beam optics: The optical properties of the ion beam have to be well controlled through various beam transport devices. Beam transfer matrix calculation and Poisson's equation solver were used to determine beam optics. 2. Plasma generation: The ion beam is extracted from a plasma generated in the ion source. Therefore, the quality of ion beams depends largely on the characteristics of the source plasma. Plasma diagnostic tools were used to understand the desired plasma conditions. 3. Space charge neutralisation: Space charge neutralisation is essential to transport high perveance beams because a beam without neutralisation develops a high electric potential in itself that would scatter beam ions away. A plasma based charge neutraliser "Plasma Flood System" was developed to maintain space charge neutrality during implantation. 4. Low energy beam extraction and transport: Beam extraction and transport become difficult at lower energy due to growth of emittance and space charge. Beam divergence had to be minimized by tight optical control. 5. Microwave plasma sources as ultimate ion source: A microwave source was developed to obtain high current, ultra clean ion beams and long source life. The characteristics of microwave plasmas differ significantly from whose generated by other methods such as DC excitation. The source achieved the highest recorded beam currents for various species. All the technology and the methods described above were combined to develop a state-of-the-art high current ion implanter that has achieved world leading beam performance.