This thesis describes work undertaken to understand the physics of dry-etching AlGaInP/GaAs laser structures in Cl-based plasmas to develop a process that allows the fabrication of high-aspect-ratio, sub-micron features. The effects of the main process parameters on the etch rate, selectivity and post-etch surface roughness were studied to understand how the interactions between the semiconductor materials and the plasma gives rise to different sidewall geometries. The behaviour of the two types of material in the presence of a Cl-based plasma was found to be very different due to the production of InCb when etching the AlGaInP layers which is absent when etching GaAs. This product is involatile and rate limiting in Cl-rich plasmas. Effective removal of the inhibiting InCb was shown to be necessary to selectively etch the AlGaInP layers anisotropically at a reasonably high etching rate. A narrow range of plasma conditions satisfied these requirements. These conditions provided the thermal- and ion-assisted desorption of the InCh such that the removal rate matches the formation rate. In contrast, GaAs was shown to etch anisotropically under a much wider range of conditions as the mechanism for anisotropic etching does not require an inhibitor. With an optimized set of etch parameters, etching of high-aspect-ratio, sub-micron features in AlGaInP/GaAs laser structures was demonstrated. Despite the difference in etch mechanisms of GaAs and AlGaInP and the use of a 2-step process, at the same Ar fraction vertical sidewall features were achieved in both materials when etching sub-micron gratings. Under conditions that provide smooth vertical sidewalls the etch rate was shown to be aspect-ratio dependent due to the depletion of neutral species at the base of the feature. A range of 1-D gratings were etched with lattice constants as short as 200 nm and aspect ratios as high as 20:1. To the best of my knowledge these are the deepest vertically etched structures on this scale in AlGaInP/GaAs. Using this process, a range of devices including laser cavities defined by dry-etched facets and Distributed Bragg Reflectors and an integrated emitter/detector device were fabricated to demonstrate the quality of the etch process.

Previous work has shown that under quasi-isentropic compression above 2.5 GPa water may enter the phase region of ice VII. The liquid remains mostly metastable whilst ice nucleates sporadically over ~100 ns. The phase change occurred reliably when water was compressed between silica surfaces but was not observed when these were made from sapphire. Through further quasi-isentropic compression experiments on a gas gun this work has determined that the nucleation initiates at the window-water interface and that initiation likely depends on the surface energy of the silica. Sapphire, aluminium and reactively sputtered silica did not nucleate the phase change and the water remained metastable. The limit of this metastable liquid water was thought to be at 7 GPa. Through experiments with both silica and sapphire the threshold was found to be closer to 6.5 GPa and appears to cause a homogeneous phase change nucleating throughout the volume of water and independent of surfaces.

As the need to control and manipulate light on the nanoscale increases, intense expectations are being placed on the field of plasmonics to provide novel and consistent ways of controlling light, to achieve the desired optical properties and performance on these scales for both scientific and industrial applications. These properties include, high electromagnetic near-field enhancements, designer optical surfaces with control over scattering and absorption properties and nanoscale light waveguiding. One of the promising properties of plasmonics is their ability to generate electromagnetic (EM) hotspots. These are near-field structures, small in volume, but with extremely high field intensities. To better understand and apply these phenomena, techniques to characterize and image the spatial structure of these fields will become important. This is, in part, due to the extreme sensitivity of these fields to small structural and environmental changes to the plasmonic antenna. Here we present work on a single molecule fluorescence localization based super-resolution technique for the study and imaging of electromagnetic near-field structures generated around plasmonic antennas, with a special interest in the study of EM hotspots. The experimental work encompasses developing a suitable optical setup for fluorescent molecule detection, sample design and fabrication using electron beam lithography, as well as finite difference time domain simulations of plasmonic antenna properties. The technique has been used to probe the near-fields around a variety of plasmonic antennas. Analysis of the results demonstrated that the localization process can be complicated by the coupling of the fluorescence emission with the plasmonic system. When emission-coupled events occur, the results generally do not report the real position of the molecules, nor the EM enhancement distribution at the illuminating wavelength. To circumvent this issue, fluorescent molecules with a large Stokes shift have been used in order to spectrally decouple the emission process of the dye from the plasmonic system, leaving only the absorption strongly in resonance with the enhanced EM field in the antenna's vicinity. The real position of the emitters in this complex but interesting scenario are then found directly. The technique is demonstrated to provide an effective way of exploring either the EM field or the LDOS with nanometre spatial resolution.

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In this thesis, systems of nematic liquid crystals confined between patterned substrates have been studied using molecular computer simulation. The aim of this work, done in parallel with experimentalists in Leeds, has been to investigate the use of chemical patterning as a novel method for controlling liquid crystal alignment. In the first part of this thesis, the study of confined systems of liquid crystalline particles has been addressed. Using the hard needle wall and hard gaussian overlap potentials, homeotropic and planar alignment of model molecules on the substrates has been induced. We have then extended the study of confined liquid crystals systems from the use of unpatterned symmetric susbtrates systems to hybrid anchored systems and, finally, to a system involving one patterned substrate. The results from this initial study show that surface anchoring can be controlled by changing the surface interaction parameter and that, by varying the surface interaction parameter across a model substrate, a pattern can be imposed on the confining surfaces. In the second part of this thesis, the substrate model developed in our initial stripe systems is used to simulate liquid crystal films confined between two identical patterned substrates. This is achieved through a comprehensive investigation of stripe patterned systems. In this, we show that, by varying key parameters like the stripe width, the surface interaction parameters and the film thickness, surface patterning can be used to control the polar anchoring angle and set the azimuthal anchoring. Our results show that a full range of tilt angles can be obtained by changing these key parameters. Following this work on striped systems, we extend our study to 2D patterned substrates (i.e. square and rectangle patterns). Here, the results show that by changing two key parameters, the surface interaction parameter and the shape of the pattern, it is possible to gain more complete control of the bulk tilt angle as the latter variesmonotonically as the key parameters are changed. We close the thesis with brief descriptions of some other substrate patternings that have been considered in this thesis work. These include circle and displaced/rotated stripe systems. We then draw some conclusions and comment on possible directions for future work.

The work presented in this thesis investigates the viability using a laser induced plasmas as a high intensity, UV/VIS/IR benchtop light source for biological spectroscopic applications. It is well known that plasmas make excellent light sources due to their broadband emission throughout the UV/VIS/IR. A detailed account is given of the construction and testing of a prototype benchtop spectrometer that utilised a laser induced plasma as its light source. The parts to build this spectrometer had a total cost of £6480.49, a competitive price for an instrument capable of measuring absorbance/turbidity spectra in the wavelength range of 380 to 700 nm at a rate of up to 5 times a second and to a wavelength resolution of approximately 0.2 nm. The production of shorter wavelength is very possible using this technology but would require a much more expensive, higher repetition rate laser, which was beyond the scope of this project. A review of the physical factors influencing the emission of light from a plasma is first presented. Several noble gases were tested to optimise the intensity and short wavelength output of the plasma. The results showed that argon had the highest emission intensity light for reasonable cost. The prototype instrument can be run in two different modes, static mode and dynamic mode. In static mode, the spectrometer can determine the absorbance spectrum of samples that do not change over time such as coloured dyes. In dynamic mode that monitors the absorbance of samples whose absorbance/turbidity varies with time. The accuracy of the prototype plasma spectrometer was tested by determining the absorption spectrum of holmium oxide in perchloric acid, a standard solution often employed for spectrometer calibration and testing. The prototype spectrometer was then successfully employed to investigate the effect of heparin, in the presence of the cations Fe2+, Zn2+ and Cu2+, on the aggregation rate of the protein human lysozyme, over a range of pHs. The aggregation of lysozyme was an interesting system to monitor, as it has been proposed as a model for the formation of the fibrils found in amyloidal plaques.

This thesis outlines work performed with the intention of producing a novel near- field magneto-optical scanning microscope. This scanning microscope utilises a near field probe, produced through modification of existing atomic force micro- scopy (AFM) probes. In order to achieve the goal of strongly sub-wavelength res- olution imaging of magneto-dynamics, studies of planar plasmonic structures, and their interaction with magnetic materials were made. This was done in order to gain a better understanding of the complex interaction between plasmonic anten- nas, and magnetic materials. Investigations of planar systems, began with finite element modelling of the magneto optical Kerr effect (MOKE) effect, and its in- teraction with plasmonic structures. Initial modelling demonstrated the suitability of the commercial finite element modelling software ”COMSOL Multiphysics" for modelling magneto-optical effects. A series of plasmonic antennas were in- troduced to this model. The simplest of these (a gold disc of 140nm diameter) showed enhancement of the MOKE signal at resonance of up to 40x. A cut- cross antenna (consisting of two crossed cavities of 20nm width, and variable length and depth), which had been selected as a promising candidate for high field confinement, showed a generally smaller enhancement. However the field distribution from these structures was more suitable for the eventual near field microscopy applications. Similar real world structures were fabricated in mul- tilayer stacks consisting of P t(3nm)/ 4x[Co(0.5nm)/ P t(3nm)]/ T a2 O5 (various)/ 5 Au(100nm) layers. This was accomplished by focussed ion beam lithography (FIB) lithography through the gold layer. Magneto-optical characterisation of these structures was not possible, and this was believed to be due to FIB induced gal- lium poisoning of the magnetic layers. A gold floating technique was pursued in order to circumvent the gallium poisoning. New structures fabricated on gold films were shown to be resonant at optical wavelengths, through bright field trans- mission spectroscopic characterisation. However the floating technique in com- bination with the FIB beam produced capillaries that adhere to the underside of the gold film, which again prevent magneto-optical characterisation. Concurrent to the development of planar antenna structures, a platform for performing near field optical measurements of magnetic materials utilising an AFM, and modified probes was developed. This platform was used to obtain time resolved images of permalloy elements with a spatial resolution comparable to that achieved with a diffraction limited laser spot. A number of potential techniques for AFM probe modification that could be used to produce strongly sub-wavelength resolution time-resolved imaging have been explored.

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No description available.

No description available.