This project will involve the investigation of alternative precursors and deposition technologies in order to improve performance and enable next generation transparent conducting oxide (TCO) films to be developed. Indium tin oxide (ITO) is the current TCO of choice for most industrial applications but it has many limitations, such as modest conductivity (2000-4000 S/cm), a relatively low work function and some optical absorption in the blue-green spectral region. In addition, indium is expensive since it is in relatively short supply, which presents a significant challenge for larger-scale production of next generation photovolatic technologies and flat panel displays. It is therefore crucial to develop alternative TCO materials with no indium with improved optical and electrical properties. Alternatives to ITO include doped ZnO (ZnO:Al, ZnO:Ga, ZnO:SnO2) and doped SnO2 (SnO2:Sb, SnO2:F, ZnO-SnO2) and many of these have been investigated in their bulk form. However, studies of some of these materials as thin films is limited and for many of the applications thin films are required. An ideal method for preparing thin fims for large scale applications is chemical vapour deposition (CVD) given that films with good uniformity and compositional control, large area growth and step coverage can be achieved. However, for a successful CVD process, a volatile precursor is necessary which is prefereably a liquid or low metling solid for atmospheric pressure CVD or highly soluble for liquid based (aerosol assisted) CVD. Current precursors to TCO materials, particularly indium and zinc still suffer from chemical instability, poor reproducibility in the growth process and less than favourable vapour pressures and reactivity for film growth. This work aims to develop highly volatile and soluble precursors based on metal ketoiminates. The advantages of using the ketoiminate ligand include: - reactive complexes can be formed in high yield - complexes with a hign vapour pressure can be formed as monomeric species are isolated - thermal stability of the metal complexes can be increased by tuning the groups attached to the nitrogen atoms - the surface reaction between the metal precursor and the surface of the substrate can be enhanced due to the high chemical reactivity of the complexes. TCO materials to be investigated include doped-ZnO and doped-SnO2. We have the ability to lay down thin films using a new combinatorial aerosol-assisted (AA)CVD reactor for solution based and also a combinatorial APCVD reactor to make films of graded composition. This new reactor enables upto 400 different compositions to be made on a single plate in one CVD experiment. This is important as it will enable us to rapidly screen composition space make idealised and optimised compositions for TCO applications. This combined approach will enable us to investigate different combinations and go towards achieving the next generation TCO materials.

Concerns about climate change and the extinction of fossil fuels have brought much recent attention to alternative ways of producing energy, but also to strategies to reduce energy consumption. It is estimated that the built environment consumes 30-40% of the primary energy in the world, most of which goes to cooling, heating and lighting. Recent research has demonstrated that it is possible to significantly reduce the energy utilisation in buildings by employing "smart" windows, which are capable of adapting to external weather conditions in a way that minimises the need for heating or air conditioning. A very promising technology to achieve this goal is based on coating glass windows with a very thin film of modified vanadium oxide (VO2). This oxide, which does not conduct electricity at room temperature, is known to become a metallic conductor at temperatures above 68 degrees Celsius. This transition can be tuned to take place at room temperature by introducing some impurity atoms (e.g. tungsten), and it is accompanied by a significant change in the optical properties of the material. Thus, in hot weather, the coating film is metallic and reflects most of the infrared radiation from the Sun, keeping the interior cool, but still allows most visible light to pass. During cooler weather the window coating transforms back to the low-temperature phase, which allows more of the infrared radiation to pass, decreasing the need for internal heating. In this way, large amounts of energy can be saved. I propose here to employ advanced computer simulation techniques to investigate a group of phenomena associated with the design and functioning of VO2-based window coatings. I will first focus on the fundamental and not-yet-resolved design problem for this technology: how to dope the VO2 films in a way that not only the transition temperature is shifted to the required value, but also the colour of the films and the optical properties of the film are acceptable for commercial use. Other important associated phenomena will also be investigated. For example, recent experiments have shown that the introduction of gold nanoparticles allows the modification of the colour of the films, which is important for aesthetic reasons, as tungsten-doped VO2 exhibits a rather unpleasant brown/yellow shade. It has even been suggested that doping with gold nanoparticles can decrease the switching temperature of the film, possibly due to electron transfer to the oxide. I aim to provide a microscopic description of these phenomena. Finally, I also want to understand how the films adhere to the window glass. The adherence of current films is not perfect, which can limit their durability or range of applications. So I want to gain insight into the microscopic factors controlling adhesion, with the hope that this knowledge will lead to more robust and versatile coating technologies. Although modern advances in computer power and theoretical algorithms have made possible the investigation of realistic models of many materials, VO2 belongs to a class of compounds which are particularly challenging for computational modelling. In these materials, which mainly include transition metal and rare earth compounds, the interactions between electrons are so strong that the typical independent-electron approximations employed in solid state calculations do not work well. However, in the last few years powerful and efficient new methods have been developed and implemented in mainstream computer codes, allowing for the first time a realistic modelling of these strongly correlated solids. Using these tools, I will be able to offer a microscopic description of the exciting range of phenomena at the basis of the smart windows coating technology.

Smart thermochromic windows whose insulation properties are tuned by the ambient temperature have been investigated extensively over recent years to improve energy efficiency of commercial and residential buildings. These windows are typically coated with thermochromic materials that exhibit a fully reversible, temperature dependent transition between semiconductor and metallic phases. During hot weather, a smart window passes all or part of the visible radiation incident and rejects the majority of the Sun's near-infrared radiation; thus the need for air conditioning is reduced. During cooler weather, both visible and infrared (IR) radiation is fully transmitted, limiting the need for internal heating. A popular material for such intelligent coatings is Vanadium dioxide (VO2) due to i) the radiation stop-band manifesting in the IR region, ii) the advantage that it can easily be applied to large substrates and iii) the ability to lower its phase transition temperature by doping it with metal compounds, most commonly tungsten. Calculations have shown that a VO2 coating can deliver a 30% reduction in energy consumption of buildings in countries with hot climates such as Italy and Egypt. Nonetheless, the merits of VO2 coatings quickly diminish in colder climates and in places like Helsinki or Moscow they, in fact, deliver a negative energy balance. One very important factor for this performance reversal is the high refractive index that VO2 exhibits in its cold-transparent phase, which results in a large portion of the incident light being reflected - 30%-35% in the visible for a 50 nm thick VO2 film on glass. This figure compares with <4% reflectivity in conventional glass windows, meaning that a thermochromic window is much darker and colder than its plain glass counterpart in the winter, which in turn translates to an actual increase in the energy required for lighting and heating a building. In addition, dirt and stains further degrade the transmission properties of a smart window. In order to overcome the above limitations, moth-eye type structures engineered to exhibit broadband and wide-angle antireflection properties are proposed, for the first time, to substantially improve the currently poor transmission properties of thermochromic smart windows and to pave the way for the commercialization of this technology. Our nanopatterned windows potentially have 72% higher transmission compared to existing thermochromic windows and in addition, they exhibit simultaneous self-cleaning properties without additional processing. This challenging, proof-of-concept, 24-month research project focuses on the fabrication and characterization of smart windows enhanced with moth-eye nanostructures and is divided into two research streams: A) Fabrication and characterization of antireflection and self-cleaning moth-eye nanostructures directly onto glass, appropriate for new high-end window products. B) Development of potentially low-cost thermochromic polymer thin-film to retrofit existing non-smart windows.

Concerns about climate change and the extinction of fossil fuels have brought much recent attention to alternative ways of producing energy, but also to strategies to reduce energy consumption. It is estimated that the built environment consumes 30-40% of the primary energy in the world, most of which goes to cooling, heating and lighting. Recent research has demonstrated that it is possible to significantly reduce the energy utilisation in buildings by employing "smart" windows, which are capable of adapting to external weather conditions in a way that minimises the need for heating or air conditioning. A very promising technology to achieve this goal is based on coating glass windows with a very thin film of modified vanadium oxide (VO2). This oxide, which does not conduct electricity at room temperature, is known to become a metallic conductor at temperatures above 68 degrees Celsius. This transition can be tuned to take place at room temperature by introducing some impurity atoms (e.g. tungsten), and it is accompanied by a significant change in the optical properties of the material. Thus, in hot weather, the coating film is metallic and reflects most of the infrared radiation from the Sun, keeping the interior cool, but still allows most visible light to pass. During cooler weather the window coating transforms back to the low-temperature phase, which allows more of the infrared radiation to pass, decreasing the need for internal heating. In this way, large amounts of energy can be saved. I propose here to employ advanced computer simulation techniques to investigate a group of phenomena associated with the design and functioning of VO2-based window coatings. I will first focus on the fundamental and not-yet-resolved design problem for this technology: how to dope the VO2 films in a way that not only the transition temperature is shifted to the required value, but also the colour of the films and the optical properties of the film are acceptable for commercial use. Other important associated phenomena will also be investigated. For example, recent experiments have shown that the introduction of gold nanoparticles allows the modification of the colour of the films, which is important for aesthetic reasons, as tungsten-doped VO2 exhibits a rather unpleasant brown/yellow shade. It has even been suggested that doping with gold nanoparticles can decrease the switching temperature of the film, possibly due to electron transfer to the oxide. I aim to provide a microscopic description of these phenomena. Finally, I also want to understand how the films adhere to the window glass. The adherence of current films is not perfect, which can limit their durability or range of applications. So I want to gain insight into the microscopic factors controlling adhesion, with the hope that this knowledge will lead to more robust and versatile coating technologies. Although modern advances in computer power and theoretical algorithms have made possible the investigation of realistic models of many materials, VO2 belongs to a class of compounds which are particularly challenging for computational modelling. In these materials, which mainly include transition metal and rare earth compounds, the interactions between electrons are so strong that the typical independent-electron approximations employed in solid state calculations do not work well. However, in the last few years powerful and efficient new methods have been developed and implemented in mainstream computer codes, allowing for the first time a realistic modelling of these strongly correlated solids. Using these tools, I will be able to offer a microscopic description of the exciting range of phenomena at the basis of the smart windows coating technology.

The goal of this study is to develop new highly volatile CVD precursors to deposit gallium oxide and indium oxide films free from contamination (e.g. C, F) and for a detailed investigation of the gas sensing and TCO (thermally conductive oxide) properties of the resulting films. Gallium oxide (Ga2O3) is considered to be one of the most ideal materials for application as thin-film gas sensors at high temperature. It is thermally stable and an electrical insulator at room temperature but semiconducting above 400 oC. At temperatures above 900 oC the electric conductivity changes depend on the concentration of oxygen, hence the oxygen concentration can be detected. Oxygen gas sensors have practical use in monitoring and controlling oxygen concentrations in exhaust gases of automobiles, as well as waste gases and chemical processes. Above 400 oC Ga2O3 thin-film operates as a surface-control-type sensor to reducing gases, e.g. CO and EtOH. Therefore, it is possible to switch the function of the sensor with temperature. Indium oxide films are both transparent to visible light and conductive (TCO). Dopants (e.g. Sn) can be used to increase the conductivity of the films and to make them more suitable for applications such as in solid-state optoelectronic devices. Group 13 hydrido species possess several notable characteristics that result in them being attractive as precursors to solid-state materials. Firstly, the lack of metal-carbon bonds has the potential to reduce the amount of carbon impurities in the final material and processing temperatures can potentially be reduced due to the thermally frail metal-hydride bonds. Secondly, group 13 hydrides are attractive as precursors as they are considerably more volatile than alkyl derivatives. Thus, a range of novel volatile hydrido-gallium and indium alkoxide complexes as well as heteroleptic alkoxides will be developed. The deposition of Ga2O3 and In2O3 thin-films from the novel precursors synthesised in this programme via low pressure chemical vapour deposition (LP)CVD and aerosol assisted (AA)CVD will be investigated and the gas sensor properties of the films will be assessed. By utilising a wide range of precursors and deposition techniques we will be able to produce different microstructures and develop a correlation landscape between microstructure and gas sensing response. Indium gallium oxide (GaxInyO3) is an exceptional material for TCO applications with absolute transparency that exceed all other oxides / coupled with extremely high charge mobility. Thin-films of GaxInyO3 will be grown using combinatorial atmospheric pressure (AP)CVD and mixed nanoparticulate Ga2O3 inside host In2O3 by AACVD/APCVD from the novel precursors. We have the ability to lay down thin films using a new combinatorial APCVD reactor to make films of graded composition. This new reactor enables upto 400 different compositions to be made on a single plate in one CVD experiment. This is important as it will enable us to rapidly screen composition space in the gallium-indium oxide system and make idealised and optimised compositions for gas sensing and TCO applications. The ability to optimise composition and hence performance in a single CVD experiment would demonstrate the power of the combinatorial technique. Further we have a new reactor design for making indium oxide with embedded nanoparticles- such as gallium oxide. In this system the aerosol flow enters the deposition chamber below the APCVD gas flow, this has the benefit of allowing composite films to be made in which nanoparticles either present or generated in the aerosol droplet are embedded in the APCVD host film. This combined approach will enable us to investigate different nanoparticle densities, sizes and forms and how these effect the gas sensing properties.