This investigation studied the growth and characterisation of thin film phosphors to examine the feasibility of enhancing a solid-state neutron scintillation detector system for increased detection resolution and detection rate. Undertaken in collaboration with the neutron facility ISIS at the Rutherford Appleton Laboratory, it was to examine whether an improved radioluminescent detector could be designed, based on the application of thin film phosphors. Optimisation for the detector was in the areas of increased luminescent emission from each neutron captured, increasing the rate of capture for each measurement and improved spatial resolution. The current ZnS:Ag,Cl phosphor used at ISIS was characterised in terms of its luminescent emission properties and comparisons were made to thin films of potential phosphor materials and the source material used to create the thin films. The phosphors were characterised via photo and radio-luminescent excitation to examine the spectral emission and the luminescent decay properties. Thin films were grown onto a silicon substrate from a ZnS:Ag,Cl phosphor source using RF magnetron sputtering and were characterised in terms of morphology, crystallinity and luminescent properties. Thin films grown using this technique were found to not produce visible emission when excited with UV excitation nor alpha excitation. Following further literature research and using the analysis technique of Rutherford Backscattering it was concluded that the chlorine charge compensation dopant was lost during the growth process resulting in incomplete incorporation of the luminescent silver dopant into the lattice. A range of chlorine doping methods were examined in order to promote charge compensation within the thin films, with the most controlled method using ion implantation, carried out at the Ion Beam Facility at Surrey University. Three samples of ZnS were grown to 800nm, followed by implantation of 0.01at% of silver and either 0.01at%, 0.05at% or 0.20at% of chlorine. Following implantation the thin films were thermally annealed to activate the samples and characterised by their luminescent emission via photo- and radioluminescent excitation. The result of the study was that although a luminescent emission was created using laser excitation, the emission using a 241Am source was of such low intensity they were uncharacterisable using the detection setup. The emission spectrum created by ZnS:Ag,Cl using the PL setup was not the standard broadband emission peak centred around 450nm, but was distorted so that it preferentially enhanced the emission around 485nm, hence create a shoulder peak. This is not significant to the optimisation of the detector, but important to know for characterisation purposes. The emission and decay characteristics of the wafer used for neutron detection by ISIS and the ZnS:Ag,Cl powder purchased from Phosphor Technology are the same. Combining this with extensive experience within the research group of growing ZnS and ZnS:Mn thin films made this powder a suitable as a potential target material for thin film growth. Independent of the calibration problem, the PL emission spectrum from thin films grown using RF magnetron sputtering should have been the same as the PL emission spectrum of the target material used in this technique. However, once a thin film had been grown there was no resultant emission observed. Testing the thin films using Rutherford Back Scattering found that although there were relative proportions of zinc, sulphur and silver there was no chlorine detected. Alternative method of forming a thin film of ZnS:Ag,Cl were investigated, with the most significant method using ion implantation. This technique can accurately implant the small concentrations of dopant required into a thin film with good distribution, hence requiring minimal thermal processing for the dopants to be incorporated into the lattice to activate it. The result was a thin film that when annealed in a furnace in air it rapidly oxidised, where as when annealed under vacuum this did not occur. After a period of eight hours annealing at 600°C a PL emission was observed from the implanted thin films. When the emission spectrum was analysed there was a series of emission peaks. There was potential that one of these peaks related to the ZnS:Ag,Cl emission, however there was a prominent peak at 575nm which when further analysed with RBS and PIXE confirmed there had been contamination of manganese in the thin films.

No description available.

No description available.

This thesis investigates the MBE growth, stability and processing of zinc blende (ZB) MgS based structures. Although MgS has already proven effective in several applications, its growth in the ZB phase is still restricted due to a variety of reasons. Therefore, the main emphasis of this thesis is on probing the growth related problems and developing new growth techniques. A new method to control the formation of surface defects which causes the rapid oxidation of MgS layers has been developed first. In contrast to theoretical predictions, the growth of ZB MgS has been successfully demonstrated on GaP, together with GaAs and InP. The Epitaxial Lift-off (ELO) of deposited layers was successfully demonstrated on all three substrates. A new modification to the existing ELO technique, by using polyurethane based flexible carriers, which eliminates the use of wax and thus avoids many associated problems, has been demonstrated and a simple sample passivation method based on amorphous selenium is also explained. An effective method to reduce the number of quantum dots by introducing time delays at various stages of the growth is developed. Finally, the first experimental demonstration of the direct growth of ZB MgS on GaAs substrate is followed by the application of this result in reusable substrates. A single GaAs substrate has been reused five times while still maintaining the epilayer quality, by performing ELO.

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This thesis presents the development of integrated sensors for health monitoring in Microsystems, which is an emerging method for early diagnostics of status or “health” of electronic systems and devices under operation based on embedded tests. Thin film meander temperature sensors have been designed with a minimum footprint of 240 m × 250 m. A microsensor array has been used successfully for accurate temperature monitoring of laser assisted polymer bonding for MEMS packaging. Using a frame-shaped beam, the temperature at centre of bottom substrate was obtained to be ~50 ºC lower than that obtained using a top-hat beam. This is highly beneficial for packaging of temperature sensitive MEMS devices. Polymer based surface acoustic wave humidity sensors were designed and successfully fabricated on 128° cut lithium niobate substrates. Based on reflection signals, a sensitivity of 0.26 dB/RH% was achieved between 8.6 %RH and 90.6 %RH. Fabricated piezoresistive pressure sensors have also been hybrid integrated and electrically contacted using a wire bonding method. Integrated sensors based on both LiNbO3 and ZnO/Si substrates are proposed. Integrated sensors were successfully fabricated on a LiNbO3 substrate with a footprint of 13 mm × 12 mm, having multi monitoring functions for simultaneous temperature, measurement of humidity and pressure in the health monitoring applications.

uperconducting single-photon detectors based on superconducting nanowires offer broadband single-photon sensitivity, from visible to mid-infrared wavelengths. They have attracted particular attention due to their promising performance at telecommunications wavelengths. The additional benefits of superconducting nanowire single-photon detectors (SNSPDs) include low dark count rates (Hz) and low timing jitter (sub 100 ps). SNSPDs have been employed in practical photon-counting applications such as quantum key distribution (QKD), operation of quantum waveguide circuits and quantum emitter characterisation. Major challenges in the development of SNSPDs are the improvement of device uniformity and achieving efficient optical coupling. Nano-optical techniques such as confocal microscopy can be used to image localised areas of SNSPDs providing a direct measurement of the device uniformity. The work in this thesis describes both initial nano-optical testing at visible wavelengths in liquid helium and the construction of a fibre based miniature confocal microscope configuration operating at telecommunications wavelengths for use in a closed cycle refrigerator. In both cases localised areas of SNSPDs can be studied whilst maintaining efficient optical coupling. The miniature confocal microscope configuration has sub-nanometre position resolution over a 30 μm x 30 μm area by way of a piezoelectric X-Y scanner. A full width at half maximum (FWHM) optical resolution of 1305 nm at a wavelength of 1550 nm is achieved. SNSPDs based upon niobium nitride (NbN) nanowires fabricated on magnesium oxide (MgO) have been studied. The microscope system has allowed us to map the temporal response (timing jitter and output pulse timing delay) of constricted (non-uniform) SNSPDs. By fitting to a theoretical model, the variations in output pulse timing delay have been shown to be caused by variations in hotspot resistances across the device. This observation has provided insights into the underlying physics of SNSPDs and especially the origins of timing jitter in SNSPDs. This provides a pathway to exploitation of this effect in next-generation device designs for applications such as imaging.

High skirt selectivity and extended out-of-band rejection is a major challenge for the successful progress of in-line microwave filters. This thesis presents novel filter realizations with improved performance, compatible with the standard single thin all-metal insert in a split-block housing and therefore maintaining the low-cost fabrication characteristics. In addition, significant filter performance improvement is achieved. The synthesis procedure implemented for the filter concept consists of a few steps. Some preliminary steps are a rigorous characterization of a double-ridge coaxial waveguide, and the modelling of an equivalent circuit model for the parallel coupled ridge waveguide devised in the filter concept. From these elements, a full wave electromagnetic analysis shows that parallel-coupled asymmetric ridge waveguides produce strongly dispersive coupling which introduces a transmission zero. Later on this property is extended to parallel-coupled asymmetric ridge waveguide resonators, where it is demonstrated that it is possible to independently control the coupling coefficient and the frequency of the transmission zero. This allows the realization of pseudo-elliptic narrowband in-line bandpass filters in E-plane technology. A general synthesis procedure for high order filters is outlined and numerical and experimental results are presented for validation. The elements employed for the synthesis procedure of the bandpass prototypes are also applied to investigate structures suitable for different applications. In particular, stopband and dual stopband filters are presented with numerical and experimental results. Finally, the study of a microwave chemical/biochemical sensing device for the characterization and detection of cells in chemical substances and cells in solution in micro-litre volumes is also reported.

No description available.