Research Challenge Brochure: Department of Materials Science & Metallurgy

DEPARTMENT OF MATERIALS SCIENCE & METALLURGY

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Contents Introduction

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Challenge areas Innovative Characterisation of Materials

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Novel Design and Processing of Materials

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Materials Discovery

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Materials for Aerospace

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Materials for Energy and Sustainability

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Materials for Healthcare

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Materials for Information and Communication Technologies

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Materials for Defence and Security

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Contacts

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Department of Materials Science & Metallurgy

Introduction The Department of Materials Science & Metallurgy has evolved over many years from purely studying metallurgy to today’s broad spectrum of research across a wide range of fields.

In this brochure we have showcased much of this research showing how we are assisting in addressing many of the key challenges facing the UK. Since 2013 the Department has been housed in a new purposebuilt Materials Building which not only accommodates our staff and researchers, but also provides state of the art facilities, such as the Wolfson Electron Microscopy Centre and X-ray Diffraction Lab, which serve the whole of the rapidly-developing West Cambridge Site.

As well as housing internationally-leading research, the Department has a suite of facilities to support its very successful Undergraduate teaching programme. Part of the University’s Natural Sciences Tripos, an increasing number of students are recognising the opportunities that studying materials gives them, whether they choose to specialise in Materials in the 3rd or 4th year or go on to graduate in one of the other subjects within the Tripos.

Hopefully, this brochure gives you a good introduction to the Department, but we hope that you will be able to visit and perhaps engage more directly, whether as a researcher, sponsor or student.

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Innovative Characterisation of Materials

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The Innovative Characterisation Challenge Area focuses on the development of techniques to study the properties of materials in novel ways, and extract quantitative information from imaging, spectroscopy and diffraction data. X-ray scattering, scanning probe and electron microscopy play a fundamental role in this area, while theory and modelling are essential in the design of experiments and interpretation of the results.

Our vision is to test and capture the behaviour of materials under realistic working conditions, from the micron to the atomic scale, with the aim of optimising processes and developing new functionality.

New techniques enable imaging of plastic flow in brittle materials, strain measurement in small-scale tests, 3D nanoscale imaging across a range of materials, in situ electron microscopy of composite nanomaterials, neutron and X-ray scattering of structural materials.

Applications include high toughness ceramics, scaffolds for tissue engineering, superalloys, polymers, catalysts, energy harvesting and energy storage devices.

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Innovative Characterisation of Materials X-ray microtomography (Best and Cameron) X-ray microtomography offers a method of evaluating, non-destructively, the structure of three dimensional biomedical scaffolds and drug delivery systems in different dosage forms. The technique provides detailed information about the nature of porosity in structures ranging from ceramic powders, through drugs and excipients to macromolecular scaffolds. In particular, by controlling the dimensions of fenestrations between the pores in tissue engineering scaffolds, it is possible to determine cell migration - producing a “cellular sieving” effect through structural control. (cube side 1 mm)

Aberration-corrected STEM (Eggeman, Ducati and Midgley) The introduction of lenses with aberration correction has led to new insights into the structure of modern materials. The atomic arrangement can now be realised in STEM images with sub-Ångström resolution, with high clarity and with straightforward interpretation.

Analytical electron tomography

Electron crystallography

(Eggeman, Ducati and Midgley)

The exquisite sensitivity of the electron beam to the crystal potential and thus atom positions, lattice vibration and possible phase transitions makes it an ideal probe to study crystallography with nm spatial resolution. A variety of materials are being investigated including polyethylene, MOFs, zeolites, pharmaceutical crystals, superalloys and carbon nitride.

The remarkable versatility of modern electron microscopes enables the 3D structure and composition of nanoscale materials and devices to be determined by modern electron tomography.

Incorporating analytical techniques such as electron energy loss spectroscopy enables 3D optical and electronic information to be determined and by combining with diffraction a full 3D crystallographic analysis is possible.

(Eggeman, Pickard and Midgley)

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Imaging and diffraction of materials under realistic working conditions

Advanced neutron and synchrotron X-ray scattering (Jones and Stone)

(Eggeman, Pickard, Ducati and Midgley) Dynamic processes can be studied in situ in the electron microscope, under operating conditions compatible with a range of processes. Research includes battery electrodes and charge-discharge cycles, electroless plating and corrosion, caloric and piezoelectric composites, metal-oxide catalytic interactions under controlled gaseous environments. The Wolfson Electron Microscopy Suite is equipped with state of the art FIB, SEMs, and TEMs as well as specimen holders for in situ experiments.

The optimal use of structural materials requires a detailed understanding of the mechanistic origins of their behaviour in service. This is acquired using international neutron and synchrotron X-ray radiation sources equipped with a range of scattering techniques. Measurements are also performed in situ, at service representative conditions, including under applied stress and elevated temperature.

Multi-microscopy (Oliver) Atomic force microscopy was originally envisaged as a technique for measuring nanoscale surface topography. Today, we not only use it to address the electrical properties of materials at the nanoscale, but combine it with other techniques, such as electron microscopies, to relate the electrical properties of a specific nanostructure to the optical properties, the defect structure of the material and its composition.

Plastic flow in brittle materials

Measuring strains on the small scale

(Clegg)

(Clegg)

There is an extensive interest in understanding how brittle materials plastically deform. Direct measurement of yield stresses over a wide range of temperatures, combined with extensive computation, is leading to the discovery of completely new strategies for developing toughness in materials. Â

A major difficulty in small-scale tests is accurately knowing the strains and deformations which the sample has undergone. For the first time, high resolution methods have been demonstrated for mapping the full strain in small-scale test samples using digital image correlation over areas as small as 0.08 x 0.08Â Îźm2.

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Novel Design and Processing of Materials

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Materials design and processing is core to the Department of Materials Science & Metallurgy in Cambridge with many truly novel themes which have wide impact. The topic cuts across all materials types and functionalities, from ultra high strength, high temperature metallic alloys and ceramics to lightweight alloys, tough metallic glasses, biological materials, electronics and energy materials.

Materials are being designed in intelligent ways: new hierarchical structures are being fabricated, new compositions and combinations of materials are being explored and surfaces are being treated in new ways. Materials are being fabricated across all length scales from nanoscale to km scale using a variety of innovative processing techniques developed by different groups across the Department.

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Novel Design and Processing of Materials

Inkjet printing for energic and pharmaceutical materials (Glowacki)

Composites and coatings for demanding environments

Inkjet printing methods for the deposition of functional materials are being explored in collaboration with academic and industrial partners. Current activities include developing methods for printing functionally and compositionally graded coatings, and for combining additive manufacturing and inkjet techniques to deposit multi-material, multi-scale structures for device applications. These methods increasingly require integration with in situ thermal and electromagnetic processing and characterisation techniques. There is a particular interest in applying these methods to superconductors, solid oxide fuel cells and in pharmaceutical applications. Image above from J. Mater. Chem. 22 (2012) 3649-3650, reproduced with permission.

Coatings are being developed for a range of demanding applications, including corrosion resistance, thermal insulation and wear protection, as well as membranes for removal of harmful particulates and pathogens. Customised facilities (lab and industrial scale) are used, including vacuum plasma spraying and plasma electrolytic oxidation as well as rigs for assessment of resistance to thermal shock, thermal cycling, Type II corrosion under applied mechanical loads, response of materials to nanoindentation at high temperature and the performance of filtration and photocatalytic systems.

These studies are supplemented by a wide range of numerical modelling activities.

(Clyne)

Metallic glasses with high flow stress and toughness for structural applications (Greer) Metallic glasses have a wide spectrum of attractive properties, e.g. the highest value of the product of flow stress and toughness, two properties that are normally opposing. The possible range of energy accessible in a metallic glass of a given composition is vast – roughly the same as the heat of melting. How the range of the glassy state can be extended by innovative processing techniques is being explored. Key interests are in ultrastable states with exotic glasstransition behaviour and in high-energy states for ultra-rapid switching. There are also possibilities for optimisation of magnetic and mechanical properties.

Overcoming metallurgical challenges in additive manufacturing (Stone and Jones) Additive manufacturing offers the prospect of producing engineering components with fundamentally new architectures, potentially giving dramatic improvements in efficiency. New alloys are being designed and new manufacturing methods being studied to produce higher quality components for nickel–based superalloys in turbines.

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www.msm.cam.ac.uk/Design

Ultrastrong, lightweight carbon nanotubes for structural and electrical applications (Elliott) High performance yarn-like fibres made from pure carbon nanotubes (CNTs) have the potential to revolutionize several important application areas, from lightweight power cables to composite armour.

Using a chemical vapour process originally developed in the department, Elliott and team synthesize CNT fibres with extremely high strength and stiffness, combined with electrical and thermal conductivities that rival or exceed those of metals in specific terms, and have the potential to match them in absolute terms.

The challenge is to control the structure and orientation of CNTs within the fibre over a hierarchy of length scales, from the molecular to bundle to fibre and to develop processes that translate to industry. The Cambridge team are working with companies to increase throughput.

Designing and fabricating nanoscale composites for electronics and energy (Driscoll)

Microstructural engineering for lightweight alloys and toughening of brittle alloys (Clegg) Deformation mapping with submicron resolution is used to study how the mechanical properties of TiAl alloys are influenced by microstructure. It has been demonstrated that nucleation of damage strongly depends on the way shear localization associated with slip bands or twins is accommodated at the interfaces between grain colonies. Crystal plasticity calculations are also being used to explore conditions that minimize stress concentration at the interfaces. How brittle materials plastically deform and how they can be made tougher is also being studied using techniques pioneered in Cambridge, with a combination of computational and experimental techniques to determine yield stresses over a wide range of temperatures.

Freeze drying of biological materials (Best and Cameron) Ideally, three dimensional scaffold environments should mimic the composition of natural tissue, providing space for cell colonisation and for nutrient and oxygen transport. Freeze-drying, a “clean” process which offers the ability to control structure and mechanical properties, can be used to produce porous collagen scaffolds. The process involves freezing a solution or suspension to form an interpenetrating network of pure ice crystals surrounded by the “rejected” solute. Ice crystals are removed by sublimation, leading to the formation of a porous scaffold. Careful control of the processing parameters is being undertaken to produce a range of different pore sizes and orientations.

Great demands are placed on materials for applications in emerging electronic and energy devices. Complex oxide materials with their wide range of functions have great potential to meet the requirements but they need to be made at the nanoscale and with minimal defects. Although this is very challenging, novel nanocomposite films enable these challenges to be overcome. Processing methods e.g. advanced pulsed laser deposition (PLD), and atmosphericpressure spatial atomic layer deposition (AP-SALD) are being developed to fabricate the structures for key applications in superconducting power, more efficient and faster memory and improved energy harvesting materials.

Prof. Driscoll’s structures and processes have been adopted by industries around the world in the superconductor industry enabling new applications to emerge, e.g. in high field magnet windings and in fault current limiters.

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Materials Discovery

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The discovery of new materials, or innovative uses of existing materials, is essential to making progress in many of the technological challenges we face: from collecting energy from the sun to interfacing with the human body. Research in the Department ranges from the chemical synthesis of new compounds and design of superalloys, to theoretical modelling and even the computational prediction of new materials. Recent highlights include the design and synthesis of non-toxic photovoltaic materials, high temperature superalloys, discovering a way to make brittle materials plastic and a new family of glasses, biomedical scaffolds and a theoretical understanding of a record breaking superconductor.

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Materials Discovery

Hybrid perovskite materials for solar cells (Cheetham and Bristowe) The remarkable performance of hybrid perovskite-based solar cells has transformed photovoltaic research. Power conversion efficiencies have increased from around 4% to 20% in just six years. However the prototypical light-harvesting material, [CH3NH3]PbI3, contains the toxic and moisture-sensitive element lead and this will probably limit its widespread commercialization.

The challenge therefore is to discover a lead-free alternative which retains its favourable optoelectronic properties, ease of synthesis and practical utilization. By combining the predictive power of density functional theory with the simplicity of hydrothermal synthesis, a systematic chemical evaluation of a range of lead-free hybrid perovskites has been performed, focusing on phase stability, band structure and mechanical properties. It has been found that the performance of these materials can be optimized by an appropriate choice of organic cation and inorganic framework. The atomic structure of a hybrid double perovskite and single crystals of a lead-free compound grown in the Department are shown.

A new family of glasses (Bennett and Cheetham) Existing melt-quenched glasses are characterised as inorganic (non-metallic), organic and metallic, and widely used in DVD technology, solar cells and telecommunications. An entirely new family of hybrid glasses has been discovered, which combine all of the attributes of the existing divisions, and circumvents the existing problem of limited chemical functionality in noncrystalline materials. The glasses are formed by melting hybrid crystalline materials called metal-organic frameworks (MOFs) which contain both inorganic, and organic components. The atomic configurations of a Zn(C3H3N2)2 crystal and glass, with accompanying optical images.

Development of alloys for high temperature (Jones and Stone) The drive for more efficient civil air transportation requires the next generation of jet engines to operate at higher temperatures. Current materials are already operating at their limit and as a result it is critical to develop new materials with higher temperature capability. Research in the department is taking place to develop a range of new materials, including Ni-base and Co-base superalloys, High Entropy Alloys and Refractory Metal-base alloys. The approach combines empirical relationships, thermodynamic and first principles calculations, as well as neural networks to identify promising candidate materials prior to evaluation through rapid small scale alloy prototyping. An electron image of a novel Ni-based superalloy developed in the Department is shown.

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www.msm.cam.ac.uk/Discovery

Computational materials discovery (Pickard) The combined power of modern computers and robust first principles codes has made computational materials discovery possible. Ab initio random structure searching (AIRSS) can be used to predict crystal, defect or grain boundary/interface structure, with little or no experimental input. Recent applications include the discovery of two dimensional ice structures (top), and understanding the crystal and electronic structure of the record-breaking (Tc=204K) superconductor, hydrogen sulphide at high pressure (bottom).

Plasticity in brittle materials

Biomedical materials

(Clegg)

(Best and Cameron)

A major difficulty in developing materials for use at high temperatures is that in most oxidation resistant materials, the predominant obstacle to dislocation motion is due to the changes in misfit energy as a dislocation moves, causing them to be brittle. At present, there is virtually no understanding of how to design brittle crystals to give easy plastic flow. Using density functional theory calculations, it has been found that small modifications to the electronic structure and elastic deformation of crystals can drastically affect plastic flow. This appears to be a general method by which dislocation properties may be controlled to allow easier flow and this concept is consistent with observations in crystals.

Furthermore, it is a substantial effect suggesting that such an approach might be used as a general way of tailoring plasticity in crystals. Image above shows deformation of a MAX phase crystal.

In order to direct cell adhesion and proliferation, the chemistry of biomedical scaffolds with three dimensional porous architectures is being controlled using biochemical surface modification.

Triple helical peptide (THP) sequences are used to mimic defined functions.

These peptides have been synthesised by collaborators in the Department of Biochemistry. Using the high integrin affinity ligand, GFOGER, cell reactivity has been shown to be promoted. The mechanism for integrin binding to peptide sequences in collagen is shown.

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Aerospace Materials

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The movement of people and goods around the world is a key part of modern life.

Air travel is increasing by ~4% per year and by 2034 the latest estimates expect over 7 billion passengers to take to the skies. However, the majority of current transport options involve the combustion of hydrocarbon fuels, which produce undesirable emissions. The need to reduce these emissions is one of the highest priorities of government policies across the globe but meeting the ambitious targets that have been set will only be possible by overcoming several key technological challenges.

A significant portion of the Department’s research activity tackles these challenges, exploiting the wide range of our staff’s expertise. Activity is focused on the civil aerospace sector, working closely with large multi-national manufacturers and their supply chain. This enables our research to help optimise the systems that are already in service, provide the advanced materials for the next generation technologies and explore the options for the radical, new, step changing technologies of the future.

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Materials for Aerospace

Enabling enhanced performance (Rae, Knowles, Clegg and Jones)

Lighter stronger materials (Bhadeshia, Ooi, Jones and Clyne) One approach, commonly exploited by the aerospace industry to increase efficiency is to reduce the weight of the airframe and engine. Replacing heavier materials requires the development of viable alternatives with lower densities and higher strengths.

Within the Department, work in this area includes the design of new steels for stronger shafts and more wear resistant bearings, the optimisation of high strength titanium alloys for numerous airframe applications and the continued development of composite materials.

Using materials at their limits requires a detailed understanding of their intrinsic behaviour. One of our specialities is characterising this behaviour from the atomic level up. We have expertise in; dislocation activity in turbine blades during creep and thermo-mechanical fatigue regimes, twinning in hexagonal phases for fan blade impact events, plasticity in gamma TiAl components, functional behaviour of shape memory and superelastic materials and the development of durable turbine blade tip sealing systems.

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www.msm.cam.ac.uk/Aerospace

Surviving hostile environments (Rae, Stone, Clegg and Clyne) The high temperatures experienced within gas turbine engines lead to an extremely hostile and corrosive environment. Protecting components from excessive damage is critical to their continued operation. Within the Department, we have activity relating to the native protective oxides that form in these materials, as well as studying the deposition and evolution of advanced external coating systems.

We also investigate the corrosive nature of certain atmospheres, including those that contain volcanic ash.

Higher temperature materials

Future technologies

(Stone, Rae, Jones and Clegg)

Whilst gas turbine engines remain the technology of choice at the present time, the aerospace industry is actively exploring the viability of other propulsion options. One possibility is the use of electric motors to power a large number of fans. Such motors would need to be highly efficient in order to reach the required power densities and our work focuses on the development and testing of composite superconducting permanent magnets, thought to be capable of delivering the required performance.

Gas turbine engines become more efficient when operated at higher temperatures. Modern jet engines are already using today’s materials at the limit of their capability and so significant efforts are being made worldwide to develop new options capable of operating at higher service temperatures. Within the Department, several different candidate systems are being investigated, ranging from Ni-base superalloys, to refractory and intermetallic options, high entropy alloys and even ductile ceramics.

(Glowacki and Rae)

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Materials for Energy and Sustainability

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It is vital to search for alternative energy sources that are renewable, and to find new ways of using energy more efficiently. Any such new technology will most likely rely on new materials with outstanding functional properties.

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Materials for Energy and Sustainability

Oxides in solar cells

Solid electrolytes

Nanogenerators

(Driscoll)

(Driscoll)

(Kar-Narayan)

To develop cheaper and higher performance alternatives to silicon, new compounds such as doped binary oxides are fabricated using scalable processing focusing on bandgap engineering, defect engineering, and carrier concentration and mobility tuning to optimise properties.

To develop near room-temperature solid electrolytes for batteries, fuel cells and sensors, a new nanostructuring thin film approach has been pioneered with remarkable enhancement in ionic conductivity.

Harvesting energy from vibrations and waste heat is a viable power solution for wireless sensors, portable, flexible and wearable electronics and biomedical implants. High-performance and durable polymer-based nanomaterials are being developed with the aim of pioneering commercially viable “nanogenerator� designs.

Superconducting materials (Driscoll and Glowacki) Prof Driscoll has pioneered novel precision nanoengineering methods to develop highperformance, low-cost copper oxide superconductors, taken up by industries worldwide. Separately, Prof Glowacki has led the development of practical superconducting wires and tapes.

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www.msm.cam.ac.uk/Energy

Metal-oxide photocatalysts (Kumar) A new metal–oxide photocatalyst composite, capable of absorbing both UV and visible light with very fast reaction rates, has been developed for disinfecting water and for destroying air pollutants.

A spin-out company (CamSES Ltd) has been set up to exploit the findings, with trials being conducted with local communities in Tanzania.

MOFs for hydrogen storage (Glowacki) High surface area carbonaceous and metal-organic framework sorbents nano-decorated with metal promoters are being investigated for efficient near room-temperature hydrogen storage applications.

Caloric materials for efficient cooling

Ionomer thin films in fuel cells (Elliott)

(Mathur and Moya)

The behaviour of the ionomer-catalystsupport interface is a key limiting factor in performance and lifetime of fuel cells.

Computational modelling offers key insights into understanding the factors affecting performance of membrane electrode assemblies.

Magnetocaloric, electrocaloric and mechanocaloric effects are reversible thermal changes that occur in magnetically, electrically and mechanically responsive materials due to changes in magnetic field, electric field and stress field. These effects could be exploited for energy-efficient cooling applications.

Materials for safer nuclear energy (Clegg)

GaN LEDs

Accident-tolerant fuel cladding materials, based on ternary carbides, are being investigated for use in nuclear reactors, relating the electronic structure of the ternary carbide to the ease of plastic flow, required for making reliable coatings.

Gallium nitride LEDs have the potential to reduce global electricity usage, but this requires development of low-cost, high-performance devices. Research towards this goal includes detailed materials growth and characterization to understand and engineer the nanoscale structure of these devices.

(Humphreys and Oliver)

Metallic glasses (Greer)

Materials for efficient turbines (Clegg)

Innovative processing techniques are being developed that may permit optimisation of soft-magnetic properties of metallic glasses without the embrittlement brought about by conventional annealing treatments. These materials could lead to reduced energy loss in power transmission and in devices.

NiAl-based alloys are being developed for improved efficiency in power generation by gas turbines. The degradation processes in polycrystalline cubic boron nitride are being studied to enable sustainable, dry precision metal cutting.

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Materials for Healthcare

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The Healthcare Challenge Area aims to optimise the efficacy of medicalinterventions and drug delivery devices through a combination of cell biology and innovative development of novel materials and structures. Our vision encompasses projects that address specific clinical needs, through to those that offer a novel technological “push� - with corresponding levels of translation readiness. The research includes strong outward linkages with clinicians, biologists, biochemists, physicists, chemists and engineers.

Applications include devices for neural conduits, dermal grafts, cardiovascular patches, orthopaedic implants, model systems for the development of cancer therapies, bioreactor substrates, sensing and analysis, materials and strategies for wound healing, pharmaceutical materials science, monitoring equipment-related hardware and healthcare photonics.

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Materials for Healthcare

Orthopaedic biomaterials (Best and Cameron) To develop next generation orthopaedic implants, it is essential to understand the chemical, biological and mechanical properties of both the natural tissue and the structures intended to replace them. Research in the area encompasses computational modelling, materials development and advanced in vitro cell culture techniques.

Pharmaceutical processing (Glowacki) In a drive towards personalised medicine ink-jet printing is being used for Pharmaceutical Process Innovation and Advanced Manufacturing, in collaboration with the University of Limerick.

A “touchscreen� for cells (Kar-Narayan) To interface with the exceptionally small forces and length-scales in cellular systems, a sensing element has been created using piezoelectric nanowires of poly lactic acid (PLLA). The aim is to incorporate them into a grid of electrodes, to give appropriate spatial resolution for force measurements - thereby creating a touch sensor for cells.

Biomedical imaging (Glowacki) MgB2 conductors and joining techniques are being developed for MRI applications in collaboration with Siemens Magnet Technology, and industrial MgB2 wire production is being pursued in partnership with the start-up company Epoch Wires.

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www.msm.cam.ac.uk/Health

Computational simulations for pharmaceutical powders (Elliott)

Collagen scaffolds (Best and Cameron)

In pharmaceutical product development, it is important to understand the complex relationships between powder flow and compaction behaviour to determine the ease of manufacture of a particular compound or formulation. Recent advances in numerical modelling have enabled optimisation of process- and materials design. Parameters calculated from molecular crystal structures in larger scale particle-based models can be used to analyse larger amounts of powder through constitutive relations in finite element simulations. Processes such as tablet spray coating can also be studied, where intrinsic variations in coating thickness are linked to tablet mixing through geometric and frictional forces between the tablets.

Scaffolds for tissue regeneration need to offer the appropriate chemistry and three dimensional environment for cell penetration throughout the structure. Using freeze drying, it is possible to produce a range of different pore architectures. Selective cell growth and migration can be encouraged by mimicking the heterogeneous nature of the tissue environment and there is the potential to control scaffold surface chemistry both through choice of macromolecular structure and selective peptide attachment.

A number of target applications have been identified for this technology, including dermal grafting, nerve conduits and cardiac repair using stem cells.

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Materials for Information Communication Technologies

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The development of new materials for Information and Communications Technologies (ICT) is fundamental to innovation, device performance, and energy efficiency for low-power (portable appliances) and high-power (data centre) applications. Research in the Department on materials for ICT is cross disciplinary and encompasses the development of devices for information processing and storage, and communication. Recent highlights are giant and reversible magnetocaloric effects in epitaxial ferromagnetic thin films, the discovery of spin-polarised supercurrents, transmission of electron spin information through carbon materials, scaled-up processing of gallium nitride light emitting diodes for visible light communications, control over the properties of functional oxide thin films, and world-leading developments in predicting material structure and properties from first-principle calculations.

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Materials for Information Communication Technologies

Superconducting spintronics (Robinson, Blamire and Barber) Following our breakthrough in demonstrating spin-polarized supercurrents, we are leading the world in understanding the coupling of magnetism and superconductivity to enable radical new methods of spin/ charge coupling for future low energy computing technologies. Our vision is to combine these two technologies in order to develop the radically new field of “Supeconducting Spintronics”, which has the potential to eliminate size and heating constraints of memory/logic technologies based separately on superconductivity (RSFQ) and spintronics. Image shows one of the Department’s state-of-theart computer-controlled systems used for this research for sputtering metallic and insulating films with sub-nanometer thickness control.

Magnetoelectrics for memory and field sensing (Mathur, Driscoll and Moya) Magnetoelectric effects arise when magnetic and electrical signals are interconverted. We study ferromagnetic films that experience voltage-driven strain from ferroelectric underlayers. The resulting magnetic changes are imaged using techniques such as magnetic force microscopy (MFM) – e.g. the image above shows magnetic domains in a manganite film (image diameter = 10 µm). We are also developing low-power, high-density, high-speed non-volatile magnetoelectric RAM. Currently, there is no single-phase material with a sizeable magnetoelectric effect at room temperature and so there are no practical devices. We are exploring new materials compositions or combinations to solve this problem by creating interface-coupled systems in superlattices and self-assembled nanocomposites.

Software for materials science (Pickard and Elliott) The full exploitation of powerful modern computers requires the development of well designed, efficient and robust computer codes. Pickard is a leading developer of the CASTEP code, which uses density functional theory (DFT) to predict a wide range of materials properties. CASTEP (licensed to Biovia by the University of Cambridge) has been used by industry for over two decades and the UK research community has free access through the UKCP consortium.

A new generation of computational scientists is being trained in the EPSRC Centre for Doctoral Training in Computational Methods for Materials Science, co-directed by Elliott. Image above shows a grain boundary structure in graphene predicted by DFT with armchair and zigzag regions.

Graphene spintronics (Mathur) The ability to send spin-polarized electrons through a non-magnetic channel running between ferromagnetic electrodes could be exploited in future logic and memory devices. Having previously shown that a carbon nanotube can carry spin-polarized electrons without significant depolarization, we have now done likewise with graphene. An important step on the journey was to perfect magnetic switching in highly spin-polarized manganite electrodes. The image left shows a magnetic image of this good switching, obtained in collaboration with Sarnjeet Dhesi at Diamond Light Source.

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www.msm.cam.ac.uk/ICT

New forms of non-volatile RAM and cognitive computing

Internet of things and visible light communication

(Driscoll)

(Oliver, Wallis and Humphreys)

There are emerging non-volatile RAM technologies that offer the promise of faster, higher density, lower energy memory than is currently possible. Oxide resistive RAM is one technology, but there are challenges of reproducibility and endurance. This is because electronic and ionic processes are coupled and the resistive channels in the devices form randomly at defect sites. We are exploring nanoengineered structures where ionic and electronic channels are separated, and which offer tuneable onoff ratios, endurance and reproducibility.

This research includes investigating ‘neuromorphic’ cognitive computing and ‘in-memory’ logic, for new non-von Neumann computing. The photograph shows a recently setup state-of-the-art pulse laser deposition system in the Department for layer-by-layer growth of oxides thin films.

Wireless data transfer is a normal part of everyday life, and the future promise of ever more connectivity places ever increasing demands on the available bandwidth for data transfer.

These demands are giving rise to new communication technologies, such as visible light communication, also known as LiFi, which exploits micro light emitting diodes (micro-LEDs) based on gallium nitride to transfer data at ultrahigh speeds via high speed modulation of light intensity - which could mean an imperceptible flicker of your normal room lights, combining energy efficient lighting with data transfer. In collaboration with industry, the GaN Group are developing the materials and technologies to render this new technology manufacturable at the large scale, and are installing Veeco MOCVD systems for high throughput production on large area wafers.

Quantum light sources (Oliver) Light sources which emit a controlled number of photons on demand, either a single photon or a pair of entangled photons, have the potential to revolutionise future computing and communications. Their possible applications range from providing a source of genuinely random numbers for conventional computers to enabling perfectly secure data transfer via quantum key distribution for cryptography. They could allow the development of ultraparallel computing: linear optical quantum computation. Whilst the first single photon emitters developed in Cambridge operated at a few degrees above absolute zero, engineering the materials from which they are made has allowed us to develop GaN devices operating at temperatures accessible by on-chip cooling, bringing practical application of this quantum technology a step closer to reality.

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Materials for Defence and Security​

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The Defence and Security Challenge Area is concerned with the development of novel materials in which structural control can be achieved at the nanoscale to yield dramatic improvements in strength, stiffness and toughness, and yet are still able to be produced in large quantities at a reasonable cost. Our vision is to provide greater resilience for defensive structures, combined with enhanced flexibility of deployment through lightweighting, improved thermal stability and excellent performance at high strain rates. We are working actively with defence research establishments and commercial manufacturers in both UK and worldwide to translate these developments into materials for practical use.

Applications include steels for gun barrels and armour plating, fibrous materials for personnel and light armoured vehicle protection, and composite panel structures for vehicular and aeronautical use.

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Materials for Defence and Security​ Fig 1. (left) Microstructure of Super Bainite armour, showing ultra-thin plates of bainitic ferrite (dark blue/white) embedded in austenite matrix (red).

Fig 2. (right) Perforated Super Bainite armour produced at Port Talbot in UK. The product, PAVISE™ Ultra HighHardness Perforated Armour Steel, is attracting approvals and initial orders from France, Germany, USA and India.

Super bainite: the first bulk nanocrystalline metal (Bhadeshia) Imagine a material that is cheap, can be made large in all its three dimensions, in huge quantities, has a nanocrystalline structure, and does not require severe processing or dramatic heat treatments during manufacture. This has been achieved by developing the theory for solid-state phase changes to create a steel

which can be transformed at incredibly low temperatures into slender plates of bainitic ferrite, only 20-40 nm thick embedded in austenite, as shown in Fig 1.

Bhadeshia and his research team have worked with the Ministry of Defence (MOD) on designing a steel for gun-barrels, and discovered a bainitic steel that had very desirable ballistic and mechanical properties (strength 2.5 GPa; toughness 40 MPa m1/2). Furthermore, the Defence

Science and Technology Laboratory (DSTL) found that when perforated the steel has a ballistic resistance exceeding that of well-established armour materials. Drilling and hole-punching prior to heat-treatment results in an ultra-hard perforated plate (as shown in Fig 2.). The steel as a perforated strike face is one of the best metallic armours ever produced.

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www.msm.cam.ac.uk/Defence

2D hierarchical carbon nanostructures for armour (Elliott)​ One of the main challenges to realising the ultra-high strength (over 2 GPa) and stiffness (over 400 GPa) of carbon nanotube (CNT) fibres is the production of macroscopic assemblies that retain the properties of the original materials. Elliott and his research team are exploiting the hierarchical properties of CNT fibres (shown in Fig 3.) to obtain materials with specific properties exceeding the best available commercial polymer fibres (such as Dyneema or Kevlar) but with improved thermal stability and performance at high strain-rates. The fibres can be assembled into 2D sheets in both woven (see Fig 4.) and non-woven forms, and impregnated with polymer resin, making them suitable for lightweight armour application. The group is currently working with several defence companies and US Army and US Navy to develop commercial prototypes.

Fig 4. Carbon nanotube fibre (with standard sewing needle shown for scale) woven into a 2D sheet which retains high strength and stiffness of original fibres, and also has high thermal conductivity. (Image courtesy of T. Gspann)

Fig 3. Hierarchical structure of carbon nanotube (CNT) fibres produced by catalytic chemical vapour deposition, showing: (a) model of fibre composed of bundles of CNTs (grey) with residual catalyst particles (gold) and polymeric impurities (green); (b) optical micrograph of condensed fibre; (c) scanning electron micrograph showing CNT bundles within fibre; and (d) transmission electron micrograph showing individual CNTs within the bundles.

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