The work contained in this thesis focuses on the growth, processing and characterization of II-VI semiconductors for use in opto-electronic devices. Included are efforts to develop both II-VI based distributed Bragg reflectors (DBRs) utilising ZnMgSSe and ZnSe and the epitaxial lift-off (ELO) process pioneered at Heriot-Watt University (HWU). The optical properties of a range of different II-VI compounds (inc. ZnSe, MgS, MnS and ZnMgSSe) are measured using a range of techniques including photoluminescence spectroscopy (PL), optical transmission measurement and spectroscopic ellipsometry. From these measurements, a more accurate value for the bowing parameter of ZnCdSe of 0.37±0.05eV is determined. The effect of lifting structures using an MgS sacrificial layer is investigated by optical microscopy, optical transmission measurement and PL, to allow any structural changes to be determined. The ELO process is also extended to allow structures grown on InP substrates to be lifted by using a magnesium selenide (MgSe) sacrificial layer. The μ-PL measurements of a series of CdSe QDs grown on ZnMgSSe barriers are also reported and compared to previous work on other barrier materials (ZnSe and MgS). The causes of the jitter (spectral diffusion) seen in these samples is also investigated and discussed.

This research concentrates on the establishment of a metalisation and micro-patterning technique that eliminates metal evaporation and/or photoresist molding procedures. The process design is chosen from the analysis of the broad field of direct metalisation techniques where novel photocatalysts or photoreducing agents are increasingly employed to create new processes. The new photolithographic process in this study introduces two novel photoreducing agents for additive metal thin film fabrication: methoxy poly(ethylene glycol) and photosystem I. This work proves the concept of using light energy to directly reduce metal ions incorporated within an ion-exchanged polyimide substrate to produce metal thin films. The patterning step can be operated at atmospheric pressure, in a dry environment, using a coating of the photoreducing agent. This process offers a significant improvement to prior related work that relied on a water layer to enable the metalisation. Of particular importance for this process is the influence of light energy dose and heat treatment, which promote silver nanoparticles growth at the cost of degradation of the substrate polymer. The investigation was carried out thoroughly by laser writing experiments for a selected range of laser power and scan speed. To complement the phenomenon observed in the laser experiments, prolonged UV light exposure time and heat treatment experiments were carried out to confirm the hypothesis postulated in this thesis. The morphology of the silver nanoparticles produced, the changes of the substrate surface and the adhesion of electroless plating were characterised. Results indicate that UV irradiation with the energy density required for reasonable production speed causes inevitable molecular damage to the polymer substrate. Photosystem I was found to be able to catalyse the production of visually similar silver thin film by light sources in the blue region. Using a similar light intensity, the exposure time was reduced by an order of magnitude whilst the degradation phenomenon observed during the UV process appears to be eradicated. With the fundamentals of the process established in this thesis, future optimization is suggested for the transition from a proof of concept to industrial implementation.

Many systems require multi function capability in the filter aspects of systems; the method currently used is filter banks which take up a lot of board space. It is thought that reconfigurable filters hold the key to replacing filter banks in order to save board space and thus potentially increasing functionality of the systems. The aim of this research is to develop electronically reconfigurable microwave filters for future communication systems. The project investigates some key design issues of reconfigurable filters. Circuits were modelled and full-wave electromagnetic simulations were performed for the investigation. Experimental work was carried out to demonstrate advanced reconfigurable microwave devices. The components used in each concept investigated were pin diodes due to their superior performance in wideband and high frequency applications. Firstly a single coupled line concept was looked at for bandwidth reconfigurability. This concept was then further developed for industrial applications by simply cascading these sections to obtain a high selective filter. A design method was developed for any number of cascades both with and without an impedance transformer; the use of LCP was used to increase flexibility due to its desirable characteristics. The most desirable outcome would be filter to simultaneously control bandwidth and frequency. In order to tackle this issue the coupled line concept was adapted to incorporate frequency tunability, along with a design method being presented. Furthermore, a cascaded highpass/ lowpass filter was also explored for this concept for added flexibility in the design of a filter capable of control of both bandwidth and center frequency.

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Inertial navigation systems (INS) are employed for the accurate navigation of military and civil vehicles. Modern non-conventional INS technologies incorporate the use of microelectromechanical systems (MEMS) such as microgyrometers and microaccelerometers to act as the sensing component. The development of bioelectronics has been integrated with microaccelerometer technology to develop a novel sensitive sensing system. The bioelectronic element consisting of a metallised DNA nanowire anchored between a sensing gap to allow the measurement of acceleration. The approach of bottom up fabrication (i.e. building up from constituent parts) has been undertaken for the development of bioelectronics allowing the assembly of novel MEMS microaccelerometers. The use of surface gold thiol (-SH) chemistry has been performed to allow highly specific deposition of deoxyribonucleic acid (DNA) molecules on sensing surfaces. The placement of λ-DNA immobilisation and hybridisation has been analysed in real time by utilising techniques such as surface plasmon resonance (SPR) allowing the suitability of the protocols to be scrutinised for DNA nanowire formation. The design and fabrication of MEMS microaccelerometers was undertaken with exact specifications to allow the immobilisation and subsequent DNA nanowire assembly for the bioelectronic sensing component to be realised. The microaccelerometers were characterised by scanning electron microscopy (SEM) and optical profilometry to determine the suitability for the application. The use of self assembled monolayers (SAMs) was exploited to immobilise DNA specifically on gold sensing electrodes. Sequence specific complementary DNA hybridisation was employed giving the ability to further position the nanowires between gold sensing electrodes. The positioning being achieved using dielectrophoretic (DEP) methods to stretch and align immobilised DNA in the required direction and orientation. Further the DNA was subjected to metallisation to give electrical functionality that allows it to be used as the sensing element. The intercalation of metals such as zinc onto DNA templates was performed and monitored using spectrophotometric methods to allow a future assessment of the electrical properties. The research aim being to develop robust hybridisation protocols for the controlled selective placement and subsequent metallisation of DNA to allow the integration of bioelectronics into novel nanoscale microaccelerometer systems.

The thesis presents a theoretical and practical study of the dynamic behaviour of electromagnetic relays. After discussing the problem of solving the dynamicc equations analytically and presenting a historical survey of the earlier works in the relay and its dynamics, the simulation of a relay on the analogue computer is discussed. It is shown that the simulation may be used to obtain specific solutions to the dynamic equations. The computer analysis provides the dynamic characteristics for design purposes and may be used in the study of bouncing, rebound oscillations and stability of the armature motion. An approximate analytical solution to the two dynamic equations is given based on the assumption that the dynamic variation of the pull with the position of the armature is linear. The assumption is supported by the Computer-aided analysis and experimental results. The solution is intended to provide a basis for a rational design. A rigorous method of analysing the dynamic performance by using Ahlberg's theory is also presented. This method may be justified to be the extension of Ahlberg's theory by taking the mass and frictional damping forces into account. While calculating the armature motion mathematically, Ahlberg considers the equilibrium of two kinds of forces, namely pull and load, and disregards the mass and friction forces, whereas the present method deals with the equilibrium of all four kinds of forces. It is shown how this can be utilised to calculate the dynamic characteristics for a specific design. The utility of this method also extends to the study of stability, contact bounce and armature rebound. The magnetic circuit and other related topics which are essential to the study of relay dynamics are discussed and some necessary experimental results are given.

With the features of low-power and flexible networking capabilities IEEE 802.15.4 has been widely regarded as one strong candidate of communication technologies for wireless sensor networks (WSNs). It is expected that with an increasing number of deployments of 802.15.4 based WSNs, multiple WSNs could coexist with full or partial overlap in residential or enterprise areas. As WSNs are usually deployed without coordination, the communication could meet significant degradation with the 802.15.4 channel access scheme, which has a large impact on system performance. In this thesis we are motivated to investigate the effectiveness of 802.15.4 networks supporting WSN applications with various environments, especially when hidden terminals are presented due to the uncoordinated coexistence problem. Both analytical models and system level simulators are developed to analyse the performance of the random access scheme specified by IEEE 802.15.4 medium access control (MAC) standard for several network scenarios. The first part of the thesis investigates the effectiveness of single 802.15.4 network supporting WSN applications. A Markov chain based analytic model is applied to model the MAC behaviour of IEEE 802.15.4 standard and a discrete event simulator is also developed to analyse the performance and verify the proposed analytical model. It is observed that 802.15.4 networks could sufficiently support most WSN applications with its various functionalities. After the investigation of single network, the uncoordinated coexistence problem of multiple 802.15.4 networks deployed with communication range fully or partially overlapped are investigated in the next part of the thesis. Both nonsleep and sleep modes are investigated with different channel conditions by analytic and simulation methods to obtain the comprehensive performance evaluation. It is found that the uncoordinated coexistence problem can significantly degrade the performance of 802.15.4 networks, which is unlikely to satisfy the QoS requirements for many WSN applications. The proposed analytic model is validated by simulations which could be used to obtain the optimal parameter setting before WSNs deployments to eliminate the interference risks.

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