CRYSTALLOGRAPHY AND FUNCTIONAL EVOLUTION OF ATOMICALLY THIN CONFINED NANOWIRES

This Established Career Fellowship proposal concerns the spatial and time resolved crystallography, structural refinement and functional evolution of one to four atom thick 1D 'Extreme Nanowires' formed inside single walled carbon nanotubes - atomically smooth templates that are thermally robust up to 1130 degrees Centigrade. This is at the practical limit of scalable fabrication, a 'Final Frontier' of materials science and the next and ultimate lowest dimension relative to two-dimensional structures such as graphene or inorganic analogues derived from metal sulphides and similar. It will address the four major aspects of atomically regulated crystal growth deemed to be the most critical in terms of their development: three-dimensional crystallography with atom-by-atom sensitivity; four-dimensional crystallography, addressing the special case of nano-Confined Phase Change Materials, which have potential utility in Non-Volatile Memory; structural refinement based on enhanced information obtained from the forgoing structural studies; and the development of thin film devices, which may be either aligned or misaligned, both for fundamental properties evaluation - including several aspects of Novel Physics - but also for 'Proof of Principle' device creation for potential exploitation in thin film devices including solar cells, chemical sensors, fuel cells, batteries and catalysts, all of which may bring economic benefits.

This project is expected to play a significant role in techniques development both in Warwick and through the Project Partner network based in Oxford, Vienna, Warsaw, Pau and Beijing. The 'Ultimate Scale' physical nature of the materials under examination will both test and help improve the most sensitive characterisation methodologies currently available, especially high performance electron microscopy, associated spectroscopic methods, in situ low-temperature imaging, in situ resistance/conductivity measurements, high performance scanning probe microscopies and thin film device fabrication. This project is expected to have in particular a very significant impact on the current rapidly developing field in high-performance electron microscopy in time-resolved 4D studies in which I will exploit ultrafast imaging and diffraction capabilities available in both Oxford/Diamond and Beijing, taking advantage also of the latest developments in Direct Electron Detection in rapid and more quantitative imaging studies. In this regard, the special category of nC-PCMs will provide an ultimate test being literally the smallest scale (i.e. 1 nm) Phase Change Materials ever observed and these experiments will therefore examine reversible and irreversible phase formation at the smallest scale ever likely to be attempted. The new electron diffraction protocol that I have developed will also allow us to 'scale up' phase transformation in bundles and thin films of the template SWNTs enabling resistance and conductivity changes to be measured in situ at the same time as crystalline/glass transformations and to assess their reversibility. Any exploitable physical properties will then be assessed in simple bolometric-type devices that will be used both in further physical testing but also as exploitable 'Proof of Principle' devices.

These studies will make use of the many state-of-the-art facilities available at the University of Warwick as the project requires but also more dedicated expertise and information available through a Project Partner network based in the Oxford, Vienna, Warsaw, Pau and Beijing all of whom contribute to and benefit from techniques development, reciprocal characterisation and from developing/expanding their own activities in what will be a unique World-leading enterprise lead from Warwick. The PI will lead these activities from the UK which can then potentially add 1D nanostructures to its dominance in 2D Nanomaterials by pursuing this complementary but 'Beyond Graphene' research.

Nanotechnology and Information: A major driving force of nanotechnology is Moore's Law scalability as the minimum feature size of electronic devices gradually approaches the atomic scale. A societal impact of device miniaturisation has been the immense proliferation of hand-held electronic devices, projected to reach 2.9 billion users out of a world population of ~7.5 billion by 2020. This has produced a rapidly developing 'Information Age' that impinges on all aspects of society from health care, economics and politics. The performance of such devices is contingent on processing power, image pixel density, battery capacity, and 'volatile' memory storage, all driven by nanoscale materials and devices. My Fellowship project potentially impacts on several of these aspects - see also below - but on memory storage in particular. Currently, the minimum feature size memory devices is around 20 nanometres but I wish to explore rewritability in Phase Change nanomaterials with feature sizes twenty times smaller than this which could have an immense impact not only on information storage technology itself but also the societal impact that such devices bring.

New Characterisation Methods: The last twenty years have seen incredible advances in Electron Microscopy imaging techniques in terms of spatial resolution, element sensitivity and three dimensional imaging, all of which are also important to my project as my composites are 'Ultimate Specimens' that test these techniques to their limit and assist in furthering their improvement. The 'next big thing' currently being explored by the microscopy community is however time-resolved (i.e. 4D) imaging and here we can expect many further improvements in imaging methodologies regarding the speed and sensitivity with which time-resolved images can be acquired. One of the most exciting aspects of my project will be following atomic scale microstructural changes side-by-side with properties changes made possible by the latest generation of Micro-Electro-Mechanical System (MEMS) holders. In this respect my specimens are also 'Ultimate Specimens' as I will investigate crystalline to glass transformations at the smallest scale ever attempted and also explore how these translate to larger scale samples, especially thin films and nascent devices using novel diffraction approaches which can then be shared with the microscopy community at large.

Nanomaterials, New Materials and New Devices: Besides improving rewritable memory, I will also investigate sensor properties in simple bolometric devices which will make use of physical and chemical changes as conductivity, resistivity, changes in magnetic properties and polarity. These various aspects may find application in devices and composites including but not limited to solar cells, chemical sensors, smart composites for used for example in fabrics, fuel cells, batteries and catalysis, all of which may bring economic benefits.

People and Knowledge: It is anticipated that all of the people involved in this project based in Warwick, Oxford, Europe and China will benefit hugely from various aspects of this project which I have designed with a strong international component in terms of techniques development, new research initiatives and capacity. While initially the project will operate within the comparatively small Network of researchers based in the immediate circle of researchers named in the proposal, the undoubtedly and already demonstrated high profile nature of this project guarantees its future expansion. I am particularly keen to encourage European expansion, in the current political climate, but will seek expansion beyond the boundaries of the EU also. Members of my research team, especially RK and new PhD (TBA), will benefit from extensive international collaboration, will learn new time-resolved microscopy techniques and in presenting results at high profile International conferences in Europe and the US.