Lighting products are essential in people's daily life. The global lighting market is expected to have over 100 billion euros’ revenue by 2020 (McKinsey & Company 2012), and the introduction of Light Emitting Diode (LED) technology in the lighting sector is leading to a rapid growth of LED-based lighting products. By 2020, it is predicted that the LED-based lighting market share will be almost 70% of the total lighting market (McKinsey & Company 2012). However, lighting products also cause a negative impact on the environment during all the product life cycle stages, especially during the use stage. To date, there are no in-depth studies that have researched how to reduce the environmental impact caused by LED-based lighting products; therefore, research in this area is needed. This research aims to contribute to the body of knowledge in this area by studying the following issues: 1) What the key product-related features are that influence the environmental impact of LED-based lighting products at each product life cycle stage, 2) What design recommendations can contribute to extend the lifespan of LED-based lighting products, 3) What the most effective and efficient method is to assess and compare the environmental impact of LED-based lighting products, and 4) What the most effective and efficient eco-design tools, techniques and methods are to reduce the environmental impact of LED-based lighting products during the design process, and how these can be integrated into an eco-design approach to reduce the environmental impact of LED-based lighting products. The methodological approach followed to gather and analyse the data necessary to understand and answer the issues above mentioned has been based on the utilisation of two research methodologies: 1) Case study research, and 2) Survey. The case study research consisted of the study and critical examination of a real-world eco-design process of an awarded and patented LED-based product designed by the author in collaboration with several manufacturers. The data was collected using direct participatory observation. In addition to this, a survey was also conducted to understand the lifespan and causes of end of life of LED-based lighting products. The data was collected using on-line self-completion close-ended questionnaires. This research contributes to body of knowledge of how to eco-design LED-based lighting products. In particular, it has made the following contributions to knowledge: 1) Identification of key product-related features that influence the environmental impact of LED-based lighting products at each product life cycle stage, 2) Definition of design recommendations to extend the lifespan of LED-based lighting products, 3) Development of a method to assess and compare the environmental impact of LED-based lighting products, and 4) Development of approach to eco-design of LED-based lighting products. These contributions can be utilised to inform product developers' decision-making processes to reduce the environmental impact of this category of products.

Traditional silicon CMOS scaling has approached its limits due to the high leakage current induced by the reduction of the silicon-dioxide gate oxide thickness. Thus, high permittivity dielectric is suggested to replace SiO2 to achieve low gate leakage current while maintaining the same capacitance. Moreover, high mobility materials are being considered to replace Si as channel materials motivated by the requirement for higher drive current and faster switching speed of MOSFETs. Germanium (Ge) has attracted much attention as a channel material, attributed to its high hole and electron mobility. Overall, it could be concluded that a high-κ dielectric for the Ge gate stack could be an effective solution for future CMOS technology which could resolve these two concerns. However, surface passivation between the material high-κ and the Ge channel is a major challenge for this solution. Direct deposition of a high-κ dielectric on Ge suffers from a low-quality interface. The native oxide, GeO2 has been found to form a good interfacial layer on Ge before the deposition of a high-κ dielectric. Two methods are introduced in this work, to passivate the interface. Electrical and XPS characterization is employed to investigate the property of the interface. Several admittance behavior issues related to Ge-based MOS capacitor could lead to errors in the extraction of the interface state density using the conventional C-V or G-V based methods. The availability and scope of these methods are studied in details when applied on the Gebased MOS capacitor. Three issues related to the conductance method as a preferable method are explored. A conduction band notch which represents a potential charge trapping site may exist at the interface between the interfacial native GeO2 and high-κ dielectric layer in a Ge MOSFET gate stack. It could induce threshold voltage instability. The number of electrons and its induced threshold voltage is calculated and the main conclusion is that charge storage in this notch is insignificant at the relevant technology node. The low frequency response of the capacitance voltage characteristic is observed for the Gebased MOS capacitor in the inversion region, even at high frequency. It is considered to be the result of the fast minority carrier generation response. The extraction of activation energies through temperature measurement indicates that the thermal generation process is responsible for the generation of minority carriers at room temperature. The minority carrier generation life time is measured to model the thermal generation in the depletion region for Ge-based MOS. The frequency dispersion apparent in the accumulation regime of C-V plots for Gebased MOS is considered to be caused by oxide traps within the oxide layer. A model is employed to estimate the oxide trap concentration. It is demonstrated that the oxide traps are distributed non-uniformly over both oxide depth and energy level.

The manufacture of nanostructured coatings by thermal spraying is currently a subject of increasing research efforts in order to obtain unique and often enhanced properties compared to conventional coatings. High Velocity Suspension Flame Spraying (HVSFS) has recently appeared as a potential alternative to conventional High Velocity Oxygen-Fuel (HVOF) spraying: for the processing of nanostructured spray material to achieve dense surface layers in supersonic mode with a refined structure, from which superior physical and mechanical properties are expected. The aim of this thesis is to, first, apply CFD methods to analyse the system characteristics of high speed thermal spray coating processes in order to improve the technology and advance the quality and efficiency of the HVSFS process. The second aim is to analyse heat transfer in thin films and thermoelectric thin films. The first part of this thesis aims to deepen the knowledge on such multidisciplinary process and to address current drawbacks mainly due to cooling effects and reduction of the overall performance of the spray torch. In this matter, a detailed parametric study carried out to model and analyse the premixed (propane/oxygen) and non-premixed (ethanol/oxygen) combustion reactions, the gas flow dynamics of HVSFS process, the interaction mechanism between the gas and liquid droplet including disintegration and vaporization, and finally investigation of the droplet injection point (axially, transversely, and externally), at the example of an industrial DJ2700 torch (Sulzer-Metco, Wohlen, Switzerland). The numerical results reveal that the initial mass flow rate of the liquid feedstock mainly controls the HVSFS process and the radial injection schemes are not suitable for this system. The second part of this thesis focuses on investigating the effects of solvent composition and type on the liquid droplet fragmentation and evaporation, combustion, and HVSFS gas dynamics. Here the solvent mixture is considered as a multicomponent droplet in the numerical model. The numerical results can be considered as a reference for avoiding extraneous trial and error experimentations. It can assist in adjusting spraying parameters e.g. the ratio or percentage of solvents for different powder materials, and it can give a way of visualization of the phenomena occurring during liquid spray. In the third part, effects of solid nanoparticle content on liquid feedstock trajectory in the HVSFS are investigated. Theoretical models are used to calculated thermo-physical properties of liquid feedstock. Various solid nanoparticle concentrations in suspension droplets with different diameters are selected and their effects on gas dynamics, vaporization rate and secondary break up are investigated. It is found out that small droplets with high concentrations are more stable for break up, thereby; vaporization is the dominant factor controlling the process which results in leaving some drops without fully evaporation. However, larger droplets undergo sever fragmentation inside the combustion chamber and release the nanoparticles in the middle of barrel after full evaporation. Finally a heat transfer model is developed for nanoparticles traveling inside thermal spray guns. In the absence of experimental data for Nano-scale inflight particles, the model is validated in thermoelectric thin films as candidate applications of the HVSFS process. For this purpose, one dimensional heat conduction problem in a thin film is investigated through solving three different heat conduction equations, namely: parabolic heat conduction equation (Fourier equation), hyperbolic heat conduction equation (non-Fourier heat conduction), and ballistic-diffusive heat conduction equations. A stable and convergent finite difference scheme is employed to solve the hyperbolic heat conduction (HHC) equation and the ballistic-diffusive equations (BDE). The ballistic part of the BDE is solved with the Gauss-Legendre integration scheme. Then these equations are applied across a thermoelectric thin film to investigate the steady-state and the transient cooling mechanism at the cold junction surface. The numerical results indicate that those equations predicted inaccurate results for the transient heat conduction in a thin film lead to less accurate prediction of cooling at cold side boundary, temperature, and heat flux profile in a thermoelectric film.

The evolution of integrated circuit technology over the five decades resulted in scaling down the minimum feature size of a transistor from 10 μm to ~14 nm. The high-k dielectrics were identified as potential candidates to replace SiO2 from 2007 due to the large leakage current observed when scaling down SiO2. These materials captured the attention of many researchers and led them to focus on many emerging applications in addition to metal oxide semiconductor field effect transistors (MOSFET). In this thesis, two emerging applications of high-k dielectrics were investigated: (i) germanium based MOSFETs and (ii) high frequency high speed rectifiers for optical rectennas.

This thesis sets out to identify and characterise the critical properties of two spintronic materials, the half-metallic Fe3O4 and the amorphous rare earth-transition metal alloy GdFe. The critical property of Fe3O4 is its crystal ordering, due to the array of exchange and superexchange interactions which define its conductive and magnetic behaviour. A series of post-oxidized Fe3O4||MgO (001) thin-films have been produced and the oxide growth has been analyzed by high resolution transmission electron microscopy (HRTEM). The quality of the film has been assessed by magnetometry and critical parameters for the growth of quality films are described. Previous procedures on the (001) orientation turn out to have masked much of the disorder in the films. This meant that judgments of quality based on magnetometry conflicted with optic data. By cutting down the (011) plane this research was able to resolve these conflicts and effectively explain the performance of a film as observed from magnetometry data. Previous work has elucidated the theoretical imperfections that can exist in this material. This work confirms the potential for these defects and has identified others. The characteristic visibility criteria for these crystal defects are confirmed and extended. By contrast the critical property of GdFe is the temperature dependent coupling between rare earth and transition metal sublattices. A measurement system was constructed to resolve the temperature dependence of the magneto-optic Kerr effect at femtosecond time scales. By this method, the theoretical timeline of dynamic behaviour has been experimentally validated and enhanced. Observations of resolved sublattice dynamics have been identified and interpreted, including a clear indication of picosecond ferromagnetic ordering. As such this work corroborates and advances existing techniques for the production, analysis and understanding of these spintronic materials.

This thesis is concerned with micro/nano fabrication of polymer materials for organic thin film transistor (OTFT) application and crystallization of solution-processable small molecule and conjugated polymer thin film. A method has been developed to form self-assembled arrays of nano/micro wires by controlling solvent evaporation of a solution film that is trapped in between a substrate and a structured template. Various solution-processable materials were successfully patterned by the developed method, with particular focus on conjugated polymers materials, such as p-type & n-type semiconductor polymers, and conductive polymers. The potential applications of such fine patterned materials were demonstrated on both field effect transistors (FET) and electrochemical transistors (ECT). The polymer FET measurement results demonstrated that the device range of on/off ratio was from 10^3 to 10^5 and the range of charge carrier mobility was from 10^(-4) cm^2/Vs to 10^(-2) cm^2/Vs. For the electrochemical transistor, the device can work under a small applied gate and drain bias (less than 0.5 volts). Pattern formation with complicated geometries, pattern transfer processes, and pattern formation dynamics have been investigated. Further, the recrystallization mechanism of amorphous small molecule thin film spin-coated on different substrate was investigated. It was found that a small molecule film crystallized from different substrates can have different preferential orientations caused by a different scenario of materials-substrate interaction, and this can dramatically influence the conductivity of the crystalline film. The dynamics of recrystallization was studied in detail through examination of both growth and nucleation of crystals from their amorphous matrix. The results showed that both the activation energy the small molecule obtained and the crystal growth preferential orientation on different substrates were different during the crystallization process. The study of both the temperature and annealing time influences on the conjugated polymer crystalline film property were also studied experimentally.

This thesis concerns the manufacture and study of strongly-coupled microcavities containing a series of different organic and biological semiconductors. It contains a simple fitting model developed to describe changes to polariton population distribution observed in microcavities containing a fluorescent molecular dye. Changes are described in terms of direct radiative pumping of polariton states by weakly-coupled states coexisting within the cavity. It also describes the careful selection and characterisation of a series of molecular dyes to evaluate their likelihood of first entering the strong coupling regime and secondly producing coherent emission. The construction of a polariton laser containing one of these dyes is shown. Finally by placing a component of light-harvesting complexes (chlorosomes) harvested from bacteria within a planar microcavity, this work details the first demonstration of strong-coupling in a biological system. Further efforts to modify energy transfer in biological systems (carotenoids) by entering the strong coupling regime are discussed in detail.

In this thesis, the downconversion (DC) and upconversion (UC) luminescence properties of rare earth doped materials were investigated for the spectral conversion of part of the solar spectrum, in order to enhance the performances of silicon photovoltaic devices. Significant progress were achieved regarding the understanding of loss mechanisms which limit the photoluminescence quantum yield (PLQY) of those materials. Achieving high PLQY values is of key importance for the successful realisation of DC- or UC-enhanced photovoltaic devices. It was found that, in high absorbing materials, the PLQY can be reduced drastically by the self-absorption effect. The constraints imparted by this loss mechanism on the optical performances of the luminescent materials were determined using a one dimensional optical model developed by the author. The model was also experimentally validated via spectroscopic characterisation of a downconverting co-doped Ce3+/Yb3+ borate glass. The role of self-absorption within an hypothetical DC-enhanced photovoltaic (DC-PV) device was investigated to find out the physical performance limitations of the device. Moreover, an UC material consisting of Er3+-doped hexagonal sodium yttrium fluoride (β-NaYF4) was theoretically investigated to look at the implications of self-absorption on two experimental situations: the case of a PLQY measurement, and on the effective performance in a UC-enhanced photovoltaic (UC-PV) device. The study demonstrates that an optimization of the thickness is essential in order to reduce the effect of self-absorption and maximize the possible additional photocurrent that could be harvested, and that the optimal thickness takes different values depending on the case considered. As a major progress, an UC material consisting in barium yttrium fluoride (BaY2F8) single crystal doped with Er3+ was optically characterised resulting in a measured external photoluminescence quantum yield (ePLQY) of 12.1± 1.2 % for a BaY2F8:30at%Er3+ sample of thickness 1.75 ±0.01 mm, and a measured internal photoluminescence quantum yield (iPLQY) of 14.6± 1.5 % in a BaY2F8:20at%Er3+ sample with a thickness of 0.49± 0.01 mm. Both values were obtained under excitation at 1493 nm and an irradiance of 7.0± 0.7 Wcm-2. The reported iPLQY and ePLQY values are among the highest achieved for monochromatic excitation in this research field. Finally, the losses due to self-absorption were estimated in order to evaluate the maximum iPLQY achievable by this promising UC material. The estimated iPLQY limit values were ~19%, ~ 25% and ~30%, for 10%, 20% and 30% Er3+ doping level, respectively. The self-absorption model clarifes the origin of the disparity between the theoretical and the experimental PLQY reported for some materials. The results from this work assist with the design and implementation of DC and UC layers for photovoltaic devices, as well as providing a framework for optimization of luminescent materials to other fields of optics and photonics.

This thesis discusses role of thin organic interlayers at the electrode interfaces of polymer light-emitting diodes (LEDs) in increasing their efficiencies. The effect of varying the anode-side IL material, its thickness, and its p-doping level on poly(dioctylfluorene-alt-benzothiadiazole) (F8BT) PLEDs is examined. Then the impact of varying the IL material is explored in Lumation Green 1300 PLEDs to determine whether a relation exists between the role of the IL and the light emitting layer's properties. It is found that excitons are formed in F8BT adjacent to the interface with the IL and are thus exceptionally sensitive to the energetics at that interface, with wide energy gaps helping to reduce luminance quenching significantly. The general effects of ionic cathode-side ILs on PLED efficiencies and response times are investigated. The novel materials used contain imidazolium cationic groups. The impact of varying the ionic IL main conjugated backbone on PLED characteristics is studied, since the conjugated backbone is primarily responsible for the optoelectronic properties of semiconducting polymers. Efficiencies of ~15 lm W-1 at 3 V are achieved. The light emitting layer is varied from F8BT to Super Yellow to probe the influence of the active layer's properties on the role of the IL in determining device characteristics. The exact combination of active layer and IL strongly influence device performance. The influence of the mobile anion and the immobile cationic group of cathode-side ILs on PLED performance is investigated. Our investigation focused on ionic ILs with a F8BT conjugated backbone. Ionic ILs with various mobile counter ions are created to study the role of the mobile ion on charge injection. Increased size of anion leads to poorer device performances. Experiments were carried out to understand what factors determine the response times and efficiencies of PLEDs with ionic cathode-side ILs. Response times of 4.24 μs are recorded and Scanning Kelvin Probe Microscopy (SKPM) experiments on thin films of the ionic polymers are conducted to shed light on the movement of ions within the IL during PLED operation. Good energy level matching with the cathode metal is found for the ionic cathode-side ILs, allowing for good electron injection properties.

Single walled carbon nanotubes (SWNTs) have been successfully employed in a wide range of large-area and low-cost optoelectronic devices, such as field-effect transistors (FETs), light emitting diodes, solar cells, and logic circuits. Most common synthesis methods produce a mixture of nanotube diameters that typically results in one-third of the as-synthesized nanotubes being metallic and the remaining two-thirds being semiconducting. These synthesis procedures have a big impact on many optoelectronic applications, where the presence of metallic SWNTs could dramatically degrade device performances. To overcome this problem and sort semiconducting nanotubes from metallic ones, a post-synthetics process called polymer sorting method has been recently developed. If, on the one hand, significant progress has been made to optimize sorting techniques, on the other hand the ability to accurately characterize the residual metallic content in highly pure semiconducting samples remains a major challenge. The primary aim of this thesis is the study of electronic transport processes occurring in polymer-sorted semiconducting SWNT networks. This is achieved with a detailed surface and material characterization, and with the design, fabrication and electrical characterization of field-effect transistors. In the first part of the thesis, the theoretical background of all materials and devices used is given, followed by the description of all procedures, methods, as well as of the fabrication and characterization techniques. In the second part of the thesis, experimental results on SWNT charge transport percolation, flexible field-effect transistors, flexible logic circuits, and alternative processing techniques are discussed. Best achievements include the quantification of residual metallic nanotubes through the application of the percolation model to FETs, the realization of flexible low-voltage SWNT FETs with a mobility of 8.1cm2V-1s-1, and the fabrication of flexible low-voltage SWNT complementary inverters with a gain higher than 85V/V. These results clearly demonstrate the potential of solution processed polymer-sorted semiconducting SWNTs for plastic electronics.