Metal nanoparticles (MNP) are widely researched for the fabrication of novel low cost and more energy efficient optoelectronic devices. MNPs, which exhibit surface plasmon resonance (SPR), can be incorporated into thin film photovoltaic structures and as well as into substrates for enhancing the Raman spectroscopy performance. Recent demonstration of devices with plasmonic structures has limited utility due to the need for techniques of ordered MNPs for large area fabrication that are not currently available. This work examines the suitability of laser annealing for the fabrication of metal nanoparticles in large area optoelectronic devices, as well as the potential for tuning their optical properties precisely within the structure. Gold (Au), silver (Ag) and AuAg alloy particles were fabricated with laser annealing and fully characterized. Morphology characterization of the metal nanopartlcle films (MNFs) with scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed the control over the size by adjusting initial film thickness· and laser fluence. Optical characterization with UV-VIS spectrometry demonstrated that SPR of MNFs can be tuned by adjusting the alloy composition, the dielectric constant of surrounding medium, and the size distribution. This experimental result was confirmed by simulations. Direct incorporation of large well distributed Au nanoparticles into solar cells demonstrated enhanced performance. Dense MNFs with small particles decreased the photovoltaic efficiency. By contrast, in the case of Raman, small alloy particles with SPR wavelength close to the pump wavelength demonstrated the best enhancement. High resolution metal nanoparticle tracks written by the laser demonstrated gas sensing with good sensory capability. However, their high resistivity imposes difficulties in measurements. We conclude that with suitable optimisations the laser annealing technique studied here could be utilised for the fabrication of metal nanoparticles in large area optoelectronics devices. We demonstrate a number of such applications including solar cells and gas sensors and study the effects of metal nanoparticles within these devices in this thesis.

This PhD research project aimed to develop miniaturised opto-fluidic systems for cell manipulation and analysis which are essential for new medical technologies. These miniaturised systems have distinctive advantages over traditional analysis tools such as faster assays, smaller size, lower cost and much lower sample consumption. In this work, three miniaturised systems were achieved. The first system, miniaturised optoelectronic tweezers (OET), was developed by using a CMOS-controlled GaN micro-light emitting diode (micro-LED) array as an integrated micro-light source. It was demonstrated for the first time that with the spatio-temporal and intensity controllabilities of the emission pattern, the green micro-LEDs are capable of creating reconfigurable virtual electrodes to achieve optoelectronic tweezing. The second system, a miniaturised cell analysis platform, used piezoelectric printing to create micro-patterns of proteins onto a new type of non-adhesive surface, which was then integrated with a microfluidic device. The printed protein pattern has a higher resolution in comparison with previous reported results and remained stable even after extensive washing. Cells seeded on these patterns formed well defined micro-arrays which were successfully used for toxicity studies. The cell micro-arrays were also integrated with a microfluidic device. The third system developed was a miniaturised local cell fluorescence analysis platform. In this system, micro-LEDs with a dedicated thin-film filter and a lens were integrated with a microfluidic network to achieve efficient local fluorescence excitation and detection. By using this system, fluorescence from individual cells has been successfully detected. With their distinctive advantages, the new miniaturised systems developed in this work offer a wide range of clinical and bio-applications.

No description available.

In this study I have looked at two types of voltage programmable liquid optical device. The first is a rotatable liquid crystal waveplate and the second is an amplitude programmable liquid phase grating. The rotatable waveplate was created by confining a droplet of E7 nematic liquid crystal between two glass substrates in a photolithographically produced square well of 60x60x15µm dimensions. The droplet forms a circular disc shape with two nematic defects at opposite edges of the disc. The optical texture has been examined and the most likely n-director orientation is shown to be Bipolar. Electrodes etched into the sandwiching substrate allow an in-plane electric field to be applied and because of the E7's positive dielectric anisotropy the n-director of the droplet aligns itself with the field. The speed at which this rotation occurs is shown to follow the relationship Ø = 0.0472гV 2 and rotation speeds of 450° /s have been achieved. The droplet is multistable and can be rotated to any arbitrary angle. The temperature of the droplet affects its switching ability by changing the shape and size of the droplet within the well. The switching time with voltage at different temperatures has been investigated and shows that at higher temperatures switching is faster. Rounded square droplets have also been seen which exhibit six stable states which can be switched from one state to another by applying various electric fields. The switching speed of these states has been investigated for several different switching regimes. A voltage programmable phase grating has also been demonstrated by inducing an undulation in the surface of a thin film of either hexadecane or 1-decanol oil. The thin film of oil is the result of a dielectrophoretic force created by a non-uniform electric field above a set of interdigitated electrodes. The thickness of the film is almost independent of the applied voltage. At higher voltages, an undulation in the oil air interface occurs which is static and stable with the same period as the electrode pitch. Measurements of hexadecane and 1-decanol oil for a variety of layer thickness on several different electrode pitches show that the amplitude of the undulation is proportional to the voltage squared. This scaling relationship and the exponential dependence on the ratio of oil thickness and the electrode pitch can be explained in terms of the balance between the dielectrophoretic forces created by the non-uniform electric field and the increase in surface energy associated with the surface deformation. For a thin layer of oil with low dielectric constant the higher order spatial harmonics in the electric field cause the undulation to become non-sinusoidal. The extent to which these harmonics shape the surface of the oil is explored and their relationship to oil thickness is shown. The relative contributions of these higher order harmonics are also shown to be independent from the applied voltage. As an example of the devices applications it has been shown to operate as an amplitude programmable phase grating and diffracts the energy of an incoming 543nm laser from the zero straight through order into the higher orders. The diffraction efficiency of 32.8% is very close to that predicted by theory. The device is polarization insensitive and switching times in excess of 40µs have been achieved in switching the first diffraction order from its minimum intensity to its maximum.

This work presents the development of an x-ray detector system for the multispectral detection of x-rays used in a Bottle Scanner. This system is designed to identify liquid explosives concealed within bottles taken onto aircraft. The Bottle Scanner works by calculating the transmission spectrum for a given bottle and its contents. This is then used as a fingerprinting technique in order to identify the presence of liquid explosives. The main focus of this work is the design of the detector signal chain and particularly the pulse height detection algorithms for the acquisition of 32 bin x-ray spectra. The pulse height detection algorithms are implemented on a field programmable gate array (FPGA). The performance of such algorithms at high count rate is a key requirement for this application. Four such algorithms are discussed in this work, each with varying complexity and different approaches to pile up handling. The algorithms are simulated using a Monte Carlo approach where the random arrival rate of photons at the detector is modelled. Algorithms are then emulated using an Agilent DSO90254A oscilloscope before finally being programmed onto an FPGA and tested on a real system. The transmission curves produced in real Bottle Scanner systems show a deviation from those predicted by the underlying physics and exhibit a rollover at high energies. This is shown to be due to pulse pile up effects which are explored in detail. Depth of interaction effects are also investigated experimentally and by simulation using the Geant4 software package. The results of this are used to design a biparametric type algorithm which is capable of simultaneous pile up rejection and depth of interaction correction.

No description available.

In this work, a point by point method for the inscription of fibre Bragg gratings using a tightly focused infrared femtosecond laser is implemented for the first time. Fibre Bragg gratings are wavelength-selective, retro-reflectors which have become a key component in optical communications as well as offering great potential as a sensing tool. Standard methods of fabrication are based on UV inscription in fibre with a photosensitive core. Despite the high quality of the gratings, a number of disadvantages are associated with UV inscription, in particular, the requirements of a photosensitive fibre, the low thermal stability and the need to remove the protective coating prior to inscription. By combining the great flexibility offered by the point by point method with the advantages inherent to inscription by an infrared femtosecond laser, the previous disadvantages are overcome. The method here introduced, allows a fast inscription process at a rate of ~1mm/s, gratings of lengths between 1cm and 2cm exhibiting reflections in excess of 99%. Physical dimensions of these gratings differ significantly from those inscribed by other methods, in this case the grating is confined to a fraction of the cross section of the core, leading to strong and controllable birefringence and polarisation dependent loss. Finally, an investigation of the potential for their exploitation towards novel applications is carried out, devices such as directional bend sensors inscribed in single-mode fibre, superimposed but non-overlapping gratings, and single-mode, single-polarisation fibre lasers, were designed, fabricated and characterised based on point by point femtosecond inscription.

Novel fluorene and spirobifluorene-2,5-diaryl-l,3,4-oxadiazole hybrids 165 and 171, respectively, have been synthesised by Suzuki cross-coupling methodology. Pyridine analogues of 165 and 171,184 and 185, respectively, were also synthesised. Further extension of the π-electron framework was achieved via Wittig reaction to afford compound 177. Single layer organic light emitting devices (OLED)s using blends of MEH-PPV as the emissive material with electron transport (ET) materials 165, 171, 177， 184 and 185 have been fabricated. For all the devices studied electroluminescence (EL) originated exclusively from the MEH-PPV with external quantum efficiencies (EQE)s greatly enhanced (>two orders of magnitude) compared to pure MEH-PPV devices. The incorporation of pyridine in compounds 184 and 185 considerably enhanced the electron affinity of the systems compared to compounds 165 and 171. For a device incorporating PEDOT:PSS in the configuration ITO/PEDOT:PSS/MEH-PPV-185 (30 ： 70% by weight)/Ca/Al an EQE of ca. 0.6% and a luminance efficiency of 1.2 cd A—i at 10.5 V was achieved.

Free-space optical interconnection offers a promising solution to the data bottleneck problems encountered in current computing machinery. Hybrid systems which use electronic processing and optical data connections could alleviate future restrictions on bandwidth. Spatial light modulators (SLMs) are a key part of the input interface between electronic and optical data transfer. The ferroelectric liquid crystal over silicon SLM is a reflective amplitude- or phase-modulation device that has been pioneered at Edinburgh University. The fabrication of such devices still involves delicate manual steps, in part due to the poorly-understood nature of the FLC material. The exacting tolerances involved lead to characteristic error patterns in finished devices, which affect performance in quantifiable ways. One of the most effective ways that the liquid crystal SLM can be used as a data switch is by phase holography, whereby a binary phase pattern on the SLM causes a convolution of input light with the Fourier transform of the binary pattern upon passage through a lens. SLM faults can affect this operation in subtle ways by causing phase errors and contrast loss in the modulation. This is shown using a matrix treatment of birefringence and the output of modified hologram design software. Moreover, the design algorithm can compensate somewhat for the faults in a given SLM by adjusting the phase mask to suit. In a process analogous to adaptive optical techniques, some of the losses can be recovered. This may allow systems to function tolerably even with imperfect modulator devices. Results are presented which show that it is possible to design phase masks to minimize losses due to typical SLM defects. Cell thickness profiles are captured and used to create fault-compensated phase masks.

Transparent conducting oxides (TCO) are used to improve lateral current collection in thin film solar cells while allowing light into the absorber layers. Sputtering, an industrially mature coating technology, is potentially useful for low cost production of high quality TCO films. ZnO:Al films were grown by reactive MF (mid frequency) dual cathode magnetron sputtering from Zn:Al targets on glass with dynamic deposition rates up to 115 nm.m.minˉ¹ compared to 6 nm.m.minˉ¹ by RF sputtering from a single ceramic target. Adjusting the distribution of the oxygen influx improved the uniformity of the thickness and resistivity of ZnO:Al films grown on substrates measuring 30 cm × 30 cm. The ZnO:Al films were texture-etched for light trapping in micro-crystalline silicon (μc-Si:H) solar cells. Optimally textured ZnO:Al films were used as front contacts in 1 cm² single junction μc-Si:H solar cells yielding an initial efficiency of 8.4 % which is comparable to cells on textured RF sputtered ZnO:Al films, despite the much higher deposition rate.