In order to satisfy societal demand for continual improvements in microelectronic device performance, there is an ongoing drive for transistor miniaturisation so that spatial packing densities can be maximised. However, the associated increases in operational power density leads to increased heat generation and rises in on-chip temperature that can prevent reliable device performance. This represents a tremendous technological challenge and there is a clear need to identify and characterise materials with novel thermal properties that will enable superior thermal energy management at the nanoscale. In particular, the ability to actively control heat flow with an external stimulus (e.g. voltage) could have dramatic implications for the thermal management demands and lifetimes of next generation microelectronics. In this regard, oxide ferroelectric materials present an exciting opportunity. In ferroelectric materials, there exist atomically sharp structural interfaces called 'domain walls' (DWs) that are known to impede heat-flow by disrupting thermal vibrations. What is unique about DWs is their remarkable ability to be created, erased or repositioned inside the material in a fully reversible way by using applied voltages or pressure. This property provides an unprecedented means to actively control heat flow by being able to alter the number of DWs present in the material at a given time and the way in which they are arranged. However, to realise heat flow control using DWs, definitive estimates for the thermal interfacial resistance presented by DWs in different materials must first be determined. Therefore, one of the main goals of this project is to quantify DW thermal resistances through direct thermal conductivity measurements. Ferroelectric material systems having DWs that effectively inhibit heat flow will then be identified. Following this, prototype thermal devices will be fabricated where the relative ease of heat flow through the material will be changed by using applied voltages to reversibly alter the DW pattern. This will also provide the foundation for a longer-term research vision to create a more exotic nanostructured 'thermal mirror' device. In this case, it is envisaged that DWs can be engineered to behave as periodic reflectors of thermal waves in order to maximise the rejection of thermal energy, much like how light is reflected with high efficiency by the multiple layers in a dielectric mirror. Over the last decade, it has become clear that DWs can be considered as a new type of sheet-like functional material with properties that can be remarkably different than bulk. For example, electrical conduction within DWs can be metallic, or even superconducting, when the bulk is comparatively insulating. Prototype active devices have been fabricated where functionality is derived entirely from deployment of electrically conducting DWs. However, the complementary idea that the narrow DW region may have thermal properties entirely of its own is completely new and unexplored. Within conducting DWs, it is likely that heat flow will be enhanced, due to the availability of extra heat carriers (e.g. mobile electrons), and thermal conductivity measurements will be carried out to confirm this. Conducting DWs will also be explored for conversion of waste heat into electricity since recent predictions indicate that the thermoelectric power can be enhanced by up to 100% within DWs, compared to bulk. Overall, ferroelectric DWs are exciting candidates for use as the active elements in thermal devices since the DWs may behave functionally to either enhance or restrict heat-flow. However, neither case is currently well characterised nor understood. The innate reconfigurability of these DWs means there is real potential to design and build new types of active thermal devices based on ferroelectric materials that has yet to be capitalised upon.

This proposal aims to bring to the UK an amazing microscope which will provide new and powerful capability in understanding the properties of light emitting materials and devices. These materials are key to many technologies, not only technologies that utilise the light emission from materials directly (such as energy efficient light bulbs based on light emitting diodes) but also a range of other devices which utilise the same family of materials such as solar cells and electronic devices for power conversion. Some of these technologies are in current use, but their efficiency and performance can be enhanced by achieving a better understanding of the relevant materials. Other target technologies are further from the market, but may represent the building blocks of our future security and prosperity. For example, the new microscope will provide information about light sources which emit one and only one fundamental particle of light (photon) on demand. Such "quantum light sources" are a potential building block for quantum computers and for quantum cryptography schemes which represent the ultimate in secure data transfer. How will the new microscope allow us to advance the development of all these technologies? It is based on a scanning electron microscope, which utilises an electron beam incident on a sample surface to achieve resolutions almost three orders of magnitude better than can be achieved using a standard light microscope. It thus accesses the nanometre scale, which is vital to addressing modern day electronic devices. Standard electron microscopy accesses the topography of a surface, but the incoming electron beam also excites some of the electrons within the material under examination into states with a higher energy. When these electrons relax back down to their usual low energy state, light may be given out, and the colour and intensity of that light is incredibly informative about the properties of the material under examination. This light emission can be mapped on a scale of ~10 nanometres so that nanoscale structures ranging from defects to deliberately engineered quantum objects can be addressed. This technique is known as cathodoluminescence, and has been in use for many years. The new capability of our proposed system is that it will map not only the colour and intensity of the light emission, but also allow us to measure the timescales on which an electron relaxes back down to its low energy state. We use the phrase "in the blink of an eye" to describe something that happens extraordinarily quickly. A real eye blink takes at least 100 milliseconds, whereas the relevant timescales for the electron to return to its low energy state could be almost 10 billion times quicker than this! The new microscope will be able to measure processes occurring on this time scale, by addressing how long after an electron pulse excites the material a photon is emitted. It will even be able to distinguish between photons with different wavelengths (or colours) being emitted on different time scales. Crucially, coupling this time-resolved capability with the ability to vary the temperature, we will be able to infer not only the time scales on which electrons relax to low energy sites emitting a photon, but also the time scales by which electrons reduce their energy by other, non-light-emitting routes. These non-light-emitting processes are what limit the efficiency of light emitting diodes, for example. Overall, across a broad range of materials, we will build up an understanding of how electrons interact with nanoscale structure to define a material's electrical and optical properties and hence what factors limit or improve the performance of devices. The proposed system will be the most advanced in the world, and will give UK researchers working on these hugely important photonic and electronic technologies a global advantage in developing new materials, devices and ultimately products.

In recent years there has been a major surge in the use of wearable electronic devices & sensors (such as fitness monitors, smart watches, electrocardiogram (ECG) sensors etc.). The last decade has led to major advances in the capability of wearable systems; however, performance enhancement inevitably leads to miniaturisation of electronics meaning more sensors and increased power requirements going forward. At present, there is an urgent need to provide a sufficient and autonomous source of clean power to avoid dependence on cumbersome & environmentally unfriendly battery packs. The textile triboelectric nano generator (T-TENG) offers a solution. Triboelectric nano generators (TENGs) use the cyclic contact of two suitably chosen surfaces to convert mechanical energy to electrical energy. T-TENGs are simply TENGs where the tribo-contact materials are incorporated into wearable textiles capable of converting energy in human motions such as daily walking & arm movements into electricity. At present; however, T-TENG performance lags significantly behind that of conventional bulk TENGs and is insufficient to power most e-textile systems. This project will develop a next generation of high performance textile triboelectric nano generator capable of meeting the current and future energy requirements of wearable systems. It will also develop technology to incorporate the T-TENG in fully integrated energy autonomous fabrics. We will achieve this step-change in T-TENG performance via the following approach. First, the problem is intensely multidisciplinary and this has previously hampered development of a full picture. Therefore, this project unties the fields of electronic engineering, tribology, materials chemistry, and textiles technology to create the capability required to understand all key aspects of device performance. Next, recognising the need for a rigorous scientific foundation for device design, we will develop a fundamental understanding of the underlying physics of the tribo-contact of textiles. This will culminate in a predictive model for device performance accounting for both the mechanics and electrostatics of the T-TENG. We know that output is hugely linked to the amount of tribo-change density that can be developed at the interface. Here, we contend that maximising difference in election affinity (i.e. between the tribo-materials) and contact area will be critical. Therefore, we will optimise the materials, fibre architecture and surface topography of the textiles to maximise these two key parameters. On interface materials, we will implement the use of material pairs with maximum difference in electron affinity. This will take the form of metal oxide coated fibres in contact with conventional textile fibres such as polyester and polypropylene. On fibre architecture, we will use our predictive T-TENG model to design a fibre architecture that maximises contact area. On surface topography, we will pioneer the use of branching nano filaments or nano pillars to further enhance contact area. To implement these coatings and surface features on textile fabrics, the project will develop a number of novel processing techniques. All of these aspects will then be united in a single device design which will be further modified and refined. The optimised T-TENG will then be fully integrated with a textile based sensor system to form a fully energy autonomous fabric. Finally, a technology demonstrator will be built to demonstrate output performance to both academia & industry. We will work closely with our industrial partners Kyrima & Pireta who are both highly experienced in developing new technologies for the e-textiles industry. A successful outcome would mean that a host of wearable systems in the medical and entertainment sectors could be powered using a clean and free source of energy: that of simple everyday human motion.

Wide bandgap (WBG) semiconductors offer the potential to deliver electronic devices and systems with advanced power handling performance beyond that achievable in silicon. This stems from their intrinsic ability to operate at higher voltages, as attributed to their larger semiconductor bandgap. Although excellent progress has been made in the development of WBG technologies GaN and SiC, new and emerging materials with even larger bandgap (so called ultra-wide bandgap semiconductors) offer even greater potential performance gains. Maximising the high-power handling capability of such electronic components is essential to address many of the energy and environmental-related challenges that we currently face. For instance, advanced high-power solid-state systems will be required to enable smart power grids for future distribution of electricity and for efficient voltage conversion in electric vehicles. High power systems operating at high frequencies will also be required to meet the performance demands of future communication (e.g. beyond 6G mobile comms) and radar systems. AlGaN is an emerging ultra-wide bandgap (UWBG) material with the potential to deliver superior high-power handling at both low and millimetre wave frequencies than existing WBG semiconductor technologies, while crucially providing integration potential with the largely mature GaN material platform. In contrast to GaN, the introduction of aluminium to produce AlGaN increases the bandgap substantially, allowing for greatly increased breakdown field and even higher-voltage device operation for a higher Al composition. Doping of AlGaN, as required to convert the intrinsic material from an insulator into a semiconductor, is significantly more challenging than GaN however, particularly for higher Al compositions. Exploitation of polarisation-induced doping techniques similar to that used in GaN device technologies may however yield a route to realise the large potential of this material system for next generation high power electronic applications. In this work we will undertake a material investigation and evaluation study to assess and map crucial physical and electronic material properties for AlGaN epitaxial layers with 50% to 100% Al content (whereby the most benefit in terms of high-power device operation potential beyond GaN may be achieved), through a programme of material simulation, design, growth and characterisation. This initial material study will be coupled with and complemented by the development of Field Effect Transistor devices using the most promising of these material layers to demonstrate preliminary device performance potential. The outcomes of this study will be used to i) evaluate the potential of Al-rich AlGaN with a focus on high power RF device applications, ii) identify the technical challenges that need to be addressed to realise this potential for both high power and RF power applications iii) establish an ongoing research and exploitation strategy for UK and Irish academia and industry for Al-rich AlGaN-based technology.

Increasingly fast and reliable communications support the operation of industries, the Internet of things, and consumer electronics, underpinning the exchange of information and knowledge. Most services rely on optical interconnects that provide high-capacity, low-cost, low-power consumption interconnects between data centers, high-performance computing, and the Internet. According to the Cisco report, the network traffic, including the Internet, has increased to 40 Zettabytes of data in 2020. To put the numbers in perspective, the total data generated from the beginning of humanity until 2003 is 0.5% of a Zettabyte. Furthermore, the ever-increasing data traffic accounted for 12% of total global emissions in 2020. As a result, it is crucial to develop efficient networks with higher capacity and reduced power consumption. This project will contribute to more efficient phase shifters, impacting data/telecom and quantum systems. This research will exploit the properties of indium arsenide quantum dots, including 1. the temperature resilience to demonstrate a phase shifter for cryogenic photonic interconnects used in high-performance computing (quantum): indium arsenide quantum dot's temperature resilience will outperform competing developments employing quantum wells. 2. the resilience to threading dislocation, and material stress of quantum dots, will be exploited to integrate the phase shifter over silicon to bring more efficient phase shifters and modulators to the silicon photonic platform. They will outperform current III-V quantum well monolithic integration approaches due to their stress resilience. Due to silicon's weak modulating effects, it is impossible to produce efficient phase shifters. On the other hand, quantum dots exhibit stronger effects than silicon, increasing bandwidth and reducing power consumption. This development will impact the commercial optical interconnects using silicon-based photonic integrated circuits (PICs) and current networks relying on them. Additionally, this work will contribute to the development of cryogenic optical interconnects. This project partners with 1. Carleton University (Canada), 2. Colorado State University (United States), 3. Télécom ParisTech (France), 4. University College Cork and Tyndall National Institute (Ireland), and 5. VTT Technical Research Centre (Finland) to develop the technology.