The remarkable ability of ferroelectric domain walls, boundaries that separate regions of uniform electrical polarisation, to conduct electrical current has opened up dramatic possibilities for their use in nanoelectronics. Reconfigurable ferroelectric domain wall-based nanoelectronics, where unique electronic properties of conductive and simultaneously mobile domain walls can be exploited towards functional devices, represents a truly novel and disruptive approach to existing norms of electronics. In 2017, the Engineering and Physical Sciences Research Council (EPSRC) has funded a four year programme for teams across four institutions (Belfast, Warwick, St Andrews and Cambridge), to investigate novel functional properties in ferroelectric and multiferroic domain walls. A major thrust of this effort is the exploration of the fundamental physics of transport seen in domain walls. As part of this work, carrier types, densities and mobilities are being mapped for domain walls in a number of different materials systems using a new form of scanning probe microscopy, in which the Hall voltage is measured, with nanoscale spatial resolution, using Kelvin Probe Force Microscopy (KPFM). KPFM works by balancing different levels of surface potential on the sample with equal tip potentials, supplied by the atomic force microscope (AFM) itself. In all standard AFMs, the range of internal bias that can be supplied to the tip is +/- 10V, limiting the surface potential that can be mapped to the same range. For our nanoscale domain wall measurements, current is driven along the walls, in the presence of a perpendicular magnetic field, and the resultant Hall Potential is measured along the lines of intersection between the domain walls and the top surfaces of the samples. For systems in which the domain wall conductivity is large, sufficient current to allow a measurable Hall signal, can de driven using modest source-drain potential differences. Frustratingly, for domain walls with lower conductivities, the source-drain potential difference needed to drive sufficient current for measurable Hall signals needs to be significantly larger: up to the order of 50-100V and beyond the range at which internal AFM electronics can supply a balancing bias and hence detect the true potential on the surface . Thus, while we have been able to make categorical measurements of the Hall Effect for domain walls with good conductivity, we have been unable to perform equivalent measurements in systems such as Cu-Cl boracite, LiNbO3, lead germanate and undoped manganites, where equivalent measurements and physical insight into conductivity mechanisms are lacking. This limitation of the Hall voltage microscopy approach can be overcome if a higher voltage (> +/- 10V) can be applied and detected seamlessly by the hardware/electronics configured for the AFM. The manufacturers of the AFM, Asylum Research, have recently started offering a HV module capable of applying voltages between -150V and +150V which could be adapted by our relevant expertise in Hall voltage microscopy to perform fully quantitative Hall potential mapping in the higher voltage regime. This proposal aims to upgrade our AFM with a HV module and subsequently adapt it to perform high-voltage KPFM based Hall voltage mapping at conducting ferroelectric domain walls to allow fundamental insight into the physics of transport at conducting walls across a significantly wider range of ferroelectrics than currently possible. The developed measurement techniques will remove a significant hurdle in directly extracting relevant carrier information and mechanisms of electrical conduction at conducting domain walls in the majority of bulk and thin-film ferroelectrics of interest for domain wall based nanoelectronics. The techniques developed here could also facilitate direct and relatively easy-to-use means for nanoscale spatially resolved mapping of carrier profiles in the existing electronics industry.

Ions are ubiquitous in nature. They play a crucial role in countless processes, from the function of proteins rendering life possible on earth to the formation of minerals and the regulation of the ocean's acidity. In technology, ions are even more important both as structural elements for composite materials and as charge carriers in energy conversion and storage. Whether in living organisms or in cutting edge batteries, ions occupy a central role in transporting, converting and storing energy. This process usually hinges of charge exchanges that occur at the interface between a solid surface and a liquid in which the ions are dissolved. Because of the small size of most ions, exchange and transport processes at solid-liquid interfaces tend to be dominated by structural and chemical features of the solid such as defects; much like a pillar or a puddle disturbing the natural movement of a crowed in a busy underground passage. It is therefore crucial to be able to follow single ions at the interface with immersed solids in order to fully understand ions' dynamics; any averaged measurement smears out the impact of the dominating surface features of the solid. To date this has not been possible due a lack of experimental technique: most existing approach rely of some form of averaging over many ions in order to derive precise information. The goal of this fellowship is to develop a novel type of microscope able to probe locally and in-situ the dynamics of single ions at the surface of immersed solids with a simultaneous spatiotemporal resolution exceeding 1 nanometre and 50 nanoseconds. This new microscope will subsequently be used uncover the molecular mechanisms enabling certain ions to migrate efficiently through composite materials while preventing others. It will also be used to investigate the dynamics of single ions at model biointerfaces and answer otherwise inaccessible questions for biological systems. It will also be Significantly, this experimental platform will open up the possibility to directly compare experimental results with computer simulations conducted on the same spatial and temporal scales.

Condensed matter physics is a major underpinning area of science and technology. For example, the physics of electrons in solids underpins much of modern technology and will continue to do so for the foreseeable future. We propose to create a Centre for Doctoral Training (CDT) which will address the national need to develop researchers equipped with the skill sets and perspective to make worldwide impact in this area. The research themes covered address some very fundamental questions in science such as the physics of superconductors, novel magnetic materials, single atomic layer crystals, plasmonic structures, and metamaterials, and also more applied topics in the power electronics, optoelectronics and sensor development fields. There are strong connections between fundamental and applied condensed matter physics. The goal of the Centre is to provide high calibre graduates with a focussed but comprehensive training programme in the most important physical aspects of these important materials, from intelligent design (first principles electronic structure calculations and modelling), via cutting-edge materials synthesis, characterisation and sophisticated instrumentation, through to identification and realisation of exciting new applications. In addition programme development will emphasise transferable skills including business & enterprise, outreach and communication. As stated in the impact section, physics-dependent businesses are of major importance to the UK economy.

The challenge we have set ourselves is to find fundamentally new ways to store, manipulate and transport information based on our unique approach to materials integration and interface control. Electronic applications and their use are increasing at exponential rates with 6% of the global energy consumed by ICT. As anyone who has used an electronic gadget knows, they rapidly get warm. But the heat is a by-product of the way that they use electric currents which is unsustainably dumped into the environment. Electric currents are used to transfer information, to store it, retrieve it and to perform operations. As devices become smaller, the problem increases because the materials become more resistive to currents and generate more heat. The scale of the problem is huge. As an example, Google reports that significant amounts of energy are used to cool their server farms. In 2021, they used ~12 TWhr of electricity, about the same as a small country, and the trend is increasing. The internet currently has a carbon footprint that is larger than that of the airline industry and is predicted to double from 2020 to 2025. For long-term sustainability we must reduce the consumption of energy in ICT. Spintronics exploits the magnetic property of electrons (spin) for applications. It offers compelling possibilities for new devices that might function at reduced energy. Pure spin currents transfer spin without transferring charge so that information can be exchanged without the heat a charge current generates. Using electric fields in devices can have great advantages over magnetic fields, including using less energy, but usually magnetism cannot be controlled by electric fields. Molecular interfaces can be altered by electric fields and ferroelectrics have a polarisation that can be switched electrically hence tuning the behaviour of a magnet when they are connected. A stumbling block to progress is that these different materials require different techniques of preparation and to be useful in ICT they must be thin - of the order of tens of atoms thick. Such thin layers need to be protected during their fabrication and then the different layers combined. The solution requires bespoke designs and breakthroughs in materials science. The Royce Institute is a key EPSRC investment (£235M) founded to "accelerate the invention and take-up of new material systems that will meet global challenges", driving the UK strategy to increase our ability to compete, not only in science, but in the marketplace. At Leeds we recently installed the Royce Deposition System: a £2.2M suite of chambers each of which is designed to grow a different type of advanced material that requires different deposition methods and environments for processing. The chambers are connected together through ultra-high vacuum tubes so samples can be transferred whilst being protected from the atmosphere and impurities. Crucially, by controlling their interfaces at the atomic level we can grow layers of different materials and bring them together into a single hybrid structure. For example, we can: form 2 dimensional materials with electrical polarisation to control magnets; build molecular thin film interfaces that lead to tuneable emergent magnetic, optoelectronic and superconducting properties; drive magnetic textures using spin currents from topological materials, etc. A complete understanding of these hybrid structures will pave the way to exploitable technology where the initial benefits will enable information processing and storage with less energy, reducing carbon emissions and prolonging battery life. Our approach has the potential to impact many areas of technology such as data storage, sensors, energy storage, and quantum materials.

Materials characterisation is critical to the understanding of key processes in a range of functional and structural materials that have applications across several industrial sectors. These sectors include strategic priorities such as discovery of functional materials, energy storage and conversion and materials manufacturing, and healthcare. Materials characterisation is increasing in complexity, driven by a need to understand how materials properties evolve in operando, over their full lifetimes and over all levels of their hierarchy to predict their ultimate performance. The new generation of materials characterisation techniques will require: 1. Greater spatial and chemical resolution; 2. Correlated information that bridges nano- and centimeter -length scales, to relate the nanoscale chemistry and structure of interest to their intrinsically multi-scale surroundings, and 3. Temporal information about the kinetics of materials behaviour in extreme environments. The CDT will train students in a range of complementary techniques, ensuring that they have the breadth and depth of knowledge to make informed choices when considering key characterisation challenges. Our CDT will use an integrated training approach, to ensure that the technical content is well aligned with the research objectives of each student. This training in specific research needs will be informed by our industry partners and will reflect the suite of research projects that the students will undertake. Our portfolio of research projects will provide an innovative and ambitious research and training experience that will enhance the UK's long-term capabilities across high value industrial sectors. Additionally, our students will receive training in a range of topics that will support their research progress including in science communication, research ethics, career development planning and data science. These additional courses will be distributed throughout the 4-year PhD programme and will ensure that a cohesive training plan is in place for each student, supported by cohort mentors. Each student graduating from the CDT-ACM will leave will a through understanding of the key challenges presented by materials characterisation problems, and have the tools to provide creative solutions to these. They will have first hand experience of collaborating with industry partners and will be well placed to address the strategic needs of the UK Industrial Strategy. Our training will be developed in collaboration with leading partner organisations, and include international collaboration with the AMBER centre, a Science Foundation Ireland centre, as well as national facilities such as Diamond Light Source. Innovative on-line and remote instrument access will be developed that will enable both UK and Irish cohorts to interact seamlessly. Industry partners will be closely involved in designing and delivering training activities including at summer schools, and will include entrepreneurship activities. Overall the 70 students that will be trained over the lifetime of the CDT will receive excellent tuition and research training at two world leading institutions with unique characterisation abilities.