Research Projects: Multifunctional Materials and Devices

(i) Ceramics

59 SIMULATING DIFFUSION IN CERAMICS AND MINERALS
Supervisor: Professor J Harding

How fast atoms move and where they end up is a major issue in understanding (and so controlling the properties of ceramics). The first is the problem of diffusion; the second the problem of segregation. This project will investigate the mechanisms of diffusion for a range of ceramics from perovskites to pyrochlores and garnets. It will also consider the segregation of atoms and ions to surfaces and grain boundaries and what difference this makes to the properties of these structures. Of static and dynamic simulation methods will be used including ab initio methods. Depending on the materials chosen, the project could link to a range of experimental work in the Department: from batteries and ferroelectric materials to nuclear waste disposal. The codes to do the calculations already exist, but there will be opportunities for writing scripts and codes if people are interested.

60 SIMULATING NANOSTRUCTURES: A MULTISCALE PROBLEM
Supervisor: Professor J Harding

Nanostructures such as quantum dots, carbon nanotubes, nanowires, nanoparticles and ultra-thin films are sometimes small enough that one can hope to simulate the entire system. Moreover, these systems have unique structures and properties because of the high surface/volume ratio. The problem is that the timescale of the processes you are interested is too long for any simulation to manage. Dynamical simulations last of the order of hundreds of nanoseconds. Processes like diffusion, film growth, self-assembly can take place on timescales of seconds to years. There is no possibility of a direct simulation unless special methods are used. A range of these have been and are being developed. This project would work in collaboration Prof Mark Rodger (Warwick) who are currently developing long timescale codes for the new HECTOR machine in Edinburgh. Depending on your interests, this project could either focus on the development of codes, or their applications to nanostructures, or both.

61 SIMULATING THE CONTROL OF MINERAL GROWTH BY SOFT MATTER
Supervisor: Professor J Harding

Minerals in biological systems (such as shells, teeth and bones) grow into complex shapes, often nothing like the shapes expected from conventional crystal chemistry. Somehow, organic molecules (whether individually or in arrays) are controlling this in the environment where the mineral grows. It is likely that the mineral begins as a soft, hydrated, amorphous materials and only later becomes a hard, crystalline materials. This project will use a range of simulation techniques to investigate how biomolecules and arrays of organic molecules can control the growth of minerals such as carbonates and phosphates. This project is linked to collaborations with experimental groups both in the UK and elsewhere. Most of the codes required to do this have already been written, but there will be possibilities for people to develop programming skills if they so wish.
62 IRRADIATION INDUCED SYNTHESIS OF NANOPARTICLES
Supervisors: Dr G Möbus
Selected compound materials can serve as precursors for the electron beam induced reduction into pure metals. Using carefully chosen irradiation conditions the reduction process can be used for the fabrication of metallic nanoparticles via a diffusion, nucleation and growth process. Of particular interest is the local fabrication of Al, Ag, and Bi nanostructures, as well as of ferromagnetic metals, e.g. Ni and Co. The study will examine: (i) Synthesis of individual particles and nanorods by live observation via in-situ TEM, (ii) Mass fabrication of nanoparticles on a support film, (iii) Metal grain crystallisation in nanocomposites and fabrication of agglomerated architectures of nanoparticles, (iv) Fabrication of metal nanobeads and study of planar defects in fcc-nanostructures. The fabrication will be accompanied by high-resolution imaging and spectroscopy, especially concerning the plasmon resonance of the freshly fabricated particles, with respect to prospective applications in nanooptics. This topic is an example of many more nanomaterials-based possible PhD topics, see
www.moebus.staff.shef.ac.uk/phdtopics.pdf.

63 ATOMIC RESOLUTION DETAILS OF CERIUM OXIDE SURFACES AND SUBSURFACE REGIONS
Supervisors: Dr G Möbus

Latest progress in imaging technology with electron microscopes allows to image ceramic particles in the thinnest areas of the object, such as corners, edges, projected surfaces, etc… The importance of these capabilities is in visualising surface reconstructions, local changes of lattice constants, and possible elemental depletion of layers.
A first emphasis is on the stability of facets against irradiation induced atomic displacements, which would be indicative of surface activity, while the second emphasis is on surface and sub-surface redox-chemistry changes, both aspects being essential for the functional applications of cerium oxide e.g. catalysts. The project is available in various flavours, depending on skills and interest of the student, including synthesis of ceria nanostructures, atomic resolution imaging and spectroscopy, and computer simulation of the image formation process of wedge-shaped model crystals.

64 HIGH RESOLUTION CHARACTERISATION OF HETEROGENEITIES IN FUNCTIONAL CERAMICS
Supervisors: Professor W M Rainforth, Professor A R West, Professor D C Sinclair and Professor I M Reaney

The performance of virtually all ceramics is controlled by interfaces, which are a source of both intentional and unintentional heterogeneity. Not surprisingly, there have been a number of extensive studies of the interface structure using techniques such as HREM, ELNES, XPS etc. Many of the successful studies have been undertaken on model systems (e.g. bicrystals of SrTiO3). Consequently, good interface structural models have been developed, but these only apply to the specific interface structure studied. Of course, real ceramics comprise a wide range of boundary types that rarely conform to the model system. The ability to characterise materials at high spatial resolution, in terms of chemical, physical and electrical structure, is currently going through a revolution. We are in a unique position to take advantage of integrating different techniques to bring a completely new insight to the microstructure/property relationships in real ceramic materials, including existing important materials such as BaTiO3, emerging materials (e.g. CaCu3Ti4O12), thin films, devices and new materials developed within the CCL. Techniques that will be used include: a) Scanned probe microscopy (e.g. Kelvin Probe Microscopy) to characterise local electrical structure: b) Focused ion beam microscopy (FIB) to extract specific boundaries that have been characterised by SPM for characterisation in the TEM. C) High resolution TEM to determine local chemical composition and bonding structure information at the interface of interest. The information from these techniques will be correlated with the processing and electrical characterisation of the ceramic.

65 SUPERSTRUCTURE/PROPERTY RELATIONS IN OXIDES AT THE MESO AND NANOSCALE
Professor I M Reaney and Prof D C Sinclair

The functional properties of oxides often arise from structural transitions which multiply the unit cell. The occurrence of superstructure reflections modes in diffraction and spectroscopic data therefore can be used to interpret the functional behaviour of oxides used in device technology. The project will focus specifically on the combination of advanced transmission electron microscopy and Raman spectroscopy and will emphasise the meso and nano scale superstructure, difficult to resolve with X-ray and neutron diffraction, but intrinsic to material properties.

66 TUNABLE DIELECTRICALLY LOADED ANTENNAS
Professor I M Reaney and Professor D C Sinclair and O Leisten (Sarantel Ltd)

The holy grail of mobile technology is to develop antennas with high efficiency and sufficient bandwidth to cover several frequencies of operation. The current generation of smart phones use antennas with a broad bandwidth but low efficiencies (~5%). Dielectrically loaded antennas offer a very high efficiency (~50%) but a very narrow bandwidth. One approach to solve this problem is to utilise dielectrically loaded antennas which are tunable under electric field. This project pursues this target application using a combination of passive low loss coupled to a tunable dielectric layer. In this manner small changes in permittivity (and thus frequency) may be obtained under the application of an electric field. The project is in collaboration with Sarantel Ltd.

67 LOW SINTERING TEMPERATURE MW DIELECTRIC CERAMICS FOR SUSTAINABLE MANUFACTURING
Professor I M Reaney and Professor D C Sinclair

Recently, several authors have published a number of MW ceramic compositions with ultra low sintering temperatures (<700 oC). The ideal target device for such materials is not clear at the present time but it is evident that such low sintering temperature (low energy cost) materials represent a major step forward towards sustainable manufacturing. This project explores ways in which low sintering temperature ceramics may be utilised in multilayer and bulk geometries to create low energy cost devices. The project will study a range materials varying from in-house composition such as Bi4B2O9 to the recently published Li2WO4.
68 ADVANCED CHARACTERISATION OF FERROELECTRIC THIN FILMS USING TRANSMISSION ELECTRON MICROSCOPY
Professor I M Reaney and Susan Mckinstry (Pennsylvania State University)
The control of the defect- and microstructure of thin films is difficult even using modern advanced deposition equipment. Often defects are present such as vacancies and low angle boundaries which affect the properties by interacting with ferroelectric domain walls and impeding their motion. It is imperative that interaction of defects with domain wall is understood to improve the performance of ferroelectric film. This project is focussed on the characterisation of films fabricated in the group of Susan Mckinstry at Pensylvania State University. The student will use advanced transmission electron microscopy to study defect domain interactions as well as the general microstructure of the films. The student will be expected to spend time in Susan Mckinstry’s group working alongside film depositors.

69 ENERGY MATERIALS: NOVEL THERMOELECTRIC OXIDES
Supervisor: Professor D C Sinclair

We are currently exploring the thermoelectric properties of solid oxides for a variety of energy-related applications. Thermoelectrics are materials that can convert heat into electricity ( in a ‘clean’ fashion) and are proving to be very useful in a raft of ‘portable’ (near room temperature) applications, eg conversion of body heat into electricity and may prove to be extremely useful for converting waste heat from high temperatures (eg > 600 oC). Current materials are based on non-oxides (eg Bi2Te3), are far from optimised and are restricted to operating near room temperature. Recently we have discovered several transition-metal containing oxides that are stable at high temperatures that have promising Thermoelectric properties and we wish to explore these compounds and their properties in more detail. The project would involve synthesis and characterisation of transition metal containing oxides and would involve crystallography (X-ray and Neutron Diffraction) for structure determination, thermal analysis (H2-reduction thermogravimetry, dilatometry, Differential Scanning Calorimetry, Thermal Conductivity), to establish the oxygen-content, the presence of phase transitions and the thermal properties (eg expansion coefficient, conductivity), electron microscopy (ceramic microstructure of ceramics) and electrical characterisation (Impedance Spectroscopy and Seebeck coefficient measurements) to establish the electrical conductivity, carrier-type and Thermo-electric power properties.

70 EXPLORING PEROVSKITE SCIENCE
Prof D C Sinclair, Prof N C Hyatt, Prof J Harding and Prof I M Reaney

Perovskite-based materials (general formula ABO3) exhibit a wide range of useful electrical and/or magnetic properties, such as ferro-/ piezo-electricity, ionic/mixed conduction, metal-insulator transitions, superconductivity and giant magneto-resistance. The key to discovering and understanding these materials and the need to modify/optimise the desired property requires knowledge about the interrelationship between chemical composition, crystal structure, defect chemistry and the desired property. At Sheffield, we study the structure-composition-property relationships of a wide variety of perovskite-based materials with useful functional properties, eg BaTiO3, Ba3LaNb3O12, BaCo1/3Nb2/3O3,CaCu3Ti4O12_ -and wish to expand our knowledge of such materials. All projects will involve some or all of the following; chemical synthesis (compositional control), crystallography (crystal structure determination), atomistic simulations (defect chemistry) and electrical/magnetic property measurements. Perovskites of general interest include; B-site deficient hexagonal perovskites (AnBn-1O3n), oxygen-deficient perovskites (ABO3-) and A or B-site ordered perovskites (A1/4A’3/4BO3, AB1/3B’2/3O3). Technologically important perovskites of interest include; (Na,K)NbO3 and (Na1/2Bi1/2)TiO3 as Pb-free piezoelectrics and doped-BaTiO3 for capacitor applications. Contact Prof Sinclair for further details.

71 DIELECTRIC MATERIALS FOR THE 21ST CENTURY
Supervisors: Professor D C Sinclair and Professor I M Reaney

Dielectric materials (ferro-, pyro-, piezo-electrics and high permittivity, low dielectric loss solids) continue to play an important role in our every day lives, eg computer technology, smart sensors and actuators and in telecommunication devices such as mobile phones and global position systems. Despite the vast array of applications there is a constant need to improve the properties of existing dielectric materials (eg. higher permittivity, piezoelectric coefficients, ferroelectric Curie Temperature and lower dielectric loss) and to find new materials with superior properties or additional functionality (eg multi-ferroics which exhibit both ferro-electricity and ferro-magnetism). For some applications, homogeneous materials are required, whereas for others it is important to engineer chemical heterogeneity (usually by chemical doping and/or close control of oxygen partial pressure), either to create core-shell regions within grains or to produce grain boundaries and/or surface layers with different composition to the grains. In these projects, samples are prepared in the form of ceramics or films and characterised by a wide variety of techniques including; X-ray, Neutron and Electron Diffraction; Scanning, Analytical and Transmission Electron Microscopy; Impedance Spectroscopy (mHz- MHz) and/or Microwave dielectric measurements (GHz) over a wide temperature range (5- 1000K). The overall aim is establish the structure-composition-property relationships in this important class of electroceramics. Please contact Prof Sinclair for more details.

72 ENERGY MATERIALS: SOLID ELECTROLYTES FOR ELECTROLYSIS CELLS
Supervisor: Professor D C Sinclair

There is current interest in using electrolysis cells based on oxide-ion conductors to covert H2O and CO2 into fuel (syn gas H2/CO). One of the limitations is the resistivity of the oxide-ion conducting electrolyte (usually Yttria-stabilised ZrO2(YSZ)). A recent advance to overcome this problem has been to make bilayers consisting of YSZ with a mixed (oxide-ion/electronic)conductor such as Gd-doped CeO2 (GDC). In this project we will use tape-casting to make ceramic bilayers of YSZ with a variety of novel mixed conductors (perovskites and/or Bi-based fluorites) and characterise their microstructure/interfaces by electron microscopy and their electrical microstructure by Impedance Spectroscopy. This should allow us to develop electrolysis cells based on bilayer electrolytes that are capable of working at lower temperatures and/or with higher efficiency. This project involves ceramic processing (eg, powder preparation, tape casting, sintering), and materials characterisation (eg X-ray Diffraction, Electron Microscopy, Impedance Spectroscopy). We will collaborate with a group in Chemical and Biological Engineering (Dr Rachael Elder) to perform testing of the electrolysis cells.

73 NEW AND IMPROVED ELECTRODE MATERIALS FOR RECHARGEABLE LITHIUM BATTERIES
Supervisor: Professor A R West

Rechargeable lithium batteries currently use intercalation cathodes based on LiCoO2 and, more recently, LiMn2O4, which give reversible charge-discharge cycling at ~3.8 V and capacities of ~ 120 mAh/g. Because of the cost and environmental toxicity of Co, and the poor long-term performance of LiMn2O4, there is much interest in finding improved cathode materials. We are currently interested in layered rock salt structured materials, such as Li(Mn,Ni,Fe)O2, which have high capacities and stable long-term cycling performance; new anion materials based on the rutile structure: new oxynitride materials for potential electrode and electrolyte applications. Projects involve a combination of solid state synthesis procedures, crystal structure determination using X-ray and neutron powder diffraction, thermal analysis to assess high temperature stability, electrical property measurements to determine the intrinsic levels of both electronic conductivity and lithium ion conductivity, electrochemical testing by constructing test cells using the new materials. We have a very well-equipped laboratory for such studies, which forms part of the EPSRC-funded Ceramics and Composites Laboratory. This is a fundamental scientific project, with outcomes of direct relevance to the lithium battery industry.

74 IONICALLY-CONDUCTING CERAMIC ELECTROLYTES
Supervisor: Professor A R West

Ceramic materials that exhibit high levels of ionic conductivity have a range of applications, depending on the conducting species, in fuel cells, battery systems and sensors. There is much interest in the discovery of new lithium-ion conducting ceramics, which, if available, could lead to the fabrication of all solid-state, thin-film lithium batteries, without containment problems associated with liquid electrolytes. Several groups of crystalline and glassy materials are of current interest, including materials with the garnet structure and other 3D framework structures. The approach to be used in this project is based on crystal engineering in which synthetic strategies are used to modify a parent crystal structure so as to open up conduction pathways by the introduction of either mobile interstitial ions or the creation of ion vacancies. The project involves a combination of synthesis by solid state reaction methods, diffraction studies to solve the structures of new phases and electrical conductivity measurements. New lithium-ion conducting solids will be tested as potential electrolytes in solid-state lithium test cells.

75 ELECTRONIC CERAMICS
Supervisor: Professor A R West

Many electroceramic materials are heterogeneous electrically and may be regarded as composites on the nanoscale, with grains and grain boundaries that have very different electrical characteristics. This category of materials has increasing applications as ceramic sensors, voltage and current overload protection devices and charge storage materials such as barrier-layer capacitors. We are investigating several groups of such materials with different structure types, including: BaTi2O5 with a complex 3D framework structure, tetragonal tungsten bronze structured phases in materials such as BaO-Nd2O3-TiO2-Ta2O5 and the classic ferroelectric, BaTiO3, doped with an amphoteric ion such as Ho3+. We are also investigating enrirely new materials including the new ferroelectrics, Ag2Nb4O11 and Na2Nb4O11. Projects are available in each of these areas; all involve sample synthesis, ceramic fabrication, microstructural characterisation by electron microscopy, crystallographic studies by X-ray and neutron diffraction and electrical property measurements, using a range of techniques. This project is part of the EPSRC-funded Ceramics and Composites Laboratory and may involve several members of staff in the Department for collaborative studies on, for instance, thin-film fabrication, electron microscopy and electrical property measurements.

76 NANOSCALE PHENOMENA IN OXIDE MATERIALS
Supervisor: Professor A R West

Many phenomena and applications, including catalysis, sensors, redox electrodes and most-recently, memristors, are controlled by nanoscale phenomena at interfaces and contacts, for instance, metal-oxide, oxide-oxide and oxide-air interfaces. In particular, absorption/desorption of oxygen molecules on/from sample surfaces frequently leads to changes in electronic structure at and below the surface of the materials. Memristor action involves charge transfer, both ionic and electronic, across interfaces. Suitable electrodes for use in solid oxide fuel cells must also exhibit interfactial charge transfer phenomena. This project will investigate recently-discovered non-ohmic phenomena in oxide ceramics through a combination of surface characterisation, electrical property measurements and advanced electron microscopy techniques.

(ii) Magnetics

77 CONTROLLED MAGNETIC BEHAVIOUR AT THE EXTREME NANOSCALE
Supervisors: Dr D A Allwood and Dr T J Hayward

The behaviour of ‘soft’ magnetic materials such as Ni80Fe20 can be controlled using the sample shape and scale. Improvements in nanofabrication techniques have led to huge developments in demonstrations of magnetic devices with a characteristic length-scale of hundreds of nanometres. This PhD will use the latest generation of nanofabrication tools to investigate magnetic behaviour in structures with a characteristic length-scale approaching 10 nm. This will make use of a new electron beam lithography system to create well-controlled structures in order to study fundamental magnetism and develop novel devices, such as memory chips. The project will give experience of thin film deposition and patterning, nanomagnetism, computational modelling and a host of structural and analytical techniques relevant to nanoscale magnetism (e.g. magneto-optical magnetometry, scanning probe microscopy, X-ray microscopy).

78 RAPID MANUFACTURE OF MAGNETIC MATERIALS FOR ENERGY APPLICATIONS
Supervisors: Prof M R J Gibbs and Dr D A Allwood

Magnetic materials are at the heart of electrical energy technologies such as transformers, motors and turbines, making them vital to an energy-efficient society. For example, just a 1 % improvement in the performance of ‘soft’ magnetic materials could lead to a 20 M tonne reduction in CO2 emissions worldwide. This PhD project will investigate new alloy compositions and processing routes to achieving improvements in the performance of hard and soft magnetic materials. Sub-micrometre thick films will be deposited by sputter deposition, while novel rapid manufacturing techniques such as inkjet printing and aerosol spray deposition will be used to create thicker samples from solution or nanoparticle precursors. This PhD project will give experience of materials fabrication techniques, energy materials and magnetic materials.

79 HIGHLY RESOLVED OPTICAL MICROSCOPY OF MAGNETIC STRUCTURE
Supervisors: Dr D A Allwood and Prof M R J Gibbs

This PhD project will seek to build and understand better analytical tools for observing nanoscale magnetic structure in bulk, thin film and nanostructured magnetic samples. Optical techniques have the potential to offer high throughput, simple sample preparation requirements, dynamic sensitivity and resolution of a few hundred nanometres but this full potential has not yet been explored. The project will also involve using the improved optical techniques to study nanomagnetic systems in new detail, e.g. domain walls in magnetic nanowires. The project will give experience of optics, thin film and nanoscale magnetism, and computational techniques for performing calculations and experiment control.

80 MAGNETIC NANOSTRUCTURES FOR TRAPPING AND POSITIONING ULTRACOLD ATOMS
Supervisors: Dr D A Allwood and Dr T J Hayward

Certain magnetic nanostructures and magnetic configurations can be used as nanoscale sources of magnetic field. These fields can be strong close to the magnetic surface and have extremely large field gradients, making them good candidates for controlling a secondary system. This project builds on our existing collaboration with atomic physicists at the University of Durham to use the stray field from magnetic nanostructures to trap ultra-cold (sub-milliKelvin) atoms. The magnetic structures will either be made from low magnetocrystalline anisotropy materials, such as Ni80Fe20, with in-plane magnetisation or high anisotropy materials, such as CoPt, with out-of-plane magnetisation. The project will involve developing suitable nanostructures for atom trapping/transporting and understanding better the magnet-atom interaction. This will be achieved using experimental and computational techniques. The long-term goal of this project is to develop magnetic atom chip architectures to perform quantum computation algorithms.

81 MULTIFERROICS
Supervisors: Professor M R J Gibbs, Professor I M Reaney, Dr D A Allwood

As functional materials have to become “smart” in new ways to meet the demands of a growing range of sensor and actuator applications, so multiferroic materials have come under the spotlight. A multiferroic material usually demonstrates both ferroelectric and ferroelastic properties. Whilst the search goes on for monolithic materials showing high multiferroic coefficients above room temperature, this project will study the alternative route of composites of two or more materials with components showing either ferroelasticity of ferroelectric response. In making the composites careful consideration has to be given to interfaces and their effect on overall response. Composites will be made using deposition techniques and/or traditional bonding strategies and performance will be assessed. The project will involve careful materials preparation and a range of characterisation techniques including detaild electron microscopy of the interfaces. A number of applications, including switchable data storage, will be investigated. Micromagnetic and mechanical modelling will support the studies.

82 MAGNETOSTRICTION IN THIN FILMS
Supervisors: Professor M R J Gibbs and Dr J S Dean

A number of ferromagnetic alloys (FeCo. FeGa, a-FeSiB) exhibit large saturation magnetostriction constants; that is an applied field can cause significant dimensional change, or applied strain can change the state of magnetisation. In the form of thin films magnetostriction can be a source of unwanted anisotropies (e.g. NiFe in data storage read heads) or a route to increased device functionality (e.g. in microelectromechani9cal systems (MEMS)). This project will look at routes to the control of magnetostriction in thin films, and its optimisation in such applications as magnetic MEMS. Various thin film deposition (sputtering, thermal evaporation) and characterisation techniques will be used, and modelling of both the micromagnetics and overall systems will be used. There are already a number of known applications in the MEMS area.

83 SIMULATING MAGNETIC NANOPARTICLES
Supervisor: Professor J Harding with Dr C L Freeman

There are increasing numbers of exciting and dynamic uses for magnetic iron-oxide nanoparticles; for example in magnetic resonance imaging and high density media storage. New methods are needed to produce regularly-sized and shaped particles. Current methods are not simple or cheap and required the use of organic solvents or very high temperatures. However, nature has been producing ordered magnetic particles for two billion years. This project will investigate the methods used by magnetotactic bacteria to control the growth of iron oxide particles using computational modelling in collaboration with experimental groups at Leeds. Computational methods will be used to build up models of the magnetite-water interface which will explain the stability of the observed crystal morphologies. The effect of proteins on this interface can then be simulated. How do these molecules bind to the iron oxide surfaces? Do they stabilise particular crystal surfaces? Understanding and control of growth is an ambitious and exiting project which will improve scientific methods and offer benerfits to healthcare and technological systems.

84 UNDERSTANDING AND CONTROLLING STOCHASTIC BEHAVIOUR IN NANOMAGNETIC DEVICES
Supervisor: Dr T J Hayward

Nanomagnetic and spintronic technology is of great importance in many key applications, not least through its now ubiquitous usage in both the read-sensors and storage media of contemporary hard-disk drives. Many other promising nanomagnetic technologies are also under development including magnetic memory devices, devices for medical diagnostics, magnetic logic technologies and microwave resonators. In all of these devices “stochastic” thermal effects introduce randomness into the magnetic behaviour, limiting a device’s effectiveness and inhibiting development of lab-based prototypes into fully fledged technologies. This project will attempt to use a combined experimental and modelling approach to understand, predict and mitigate the effects of stochastic behaviour, thus overcoming an inhibitive problem in the development of new technology.

85 CONTROLLING MAGNETIC DOMAIN WALL BEHAVIOUR IN-PLANE/OUT OF PLANE NANOWIRE SYSTEMS
Supervisor: Dr T J Hayward

The properties of domain walls confined within planar ferromagnetic nanowires are currently of great interest due to their particle-like properties that allow them to be propagated controllably around nanowire circuits in a manner analogous to the movement of electrical charge in standard microelectronics. This has led to designs for memory, sensor and logic devices that use DWs to separate binary data, represented by uniformly magnetised domains. In the past most device designs have been based around “soft ferromagnetic materials” where the materials magnetisation lies in the sample plane and device geometry plays a dominant role in determining magnetic behaviour. More recent studies have favoured the use of “perpendicular anisotropy” materials, where the device’s magnetisation is perpendicular to the sample plane. However, in these systems magnetic behavior is much less sensitive to device geometry making it harder to control. In this
project we will attempt to combine the useful properties of perpendicular anisotropy materials with the shape dependent properties of soft ferromagnetic materials by creating hybrid systems that
contain nanowires fabricated from both kinds of material.

86 CRYSTALLINE AND AMORPHOUS Fe-Ga-Si-B FILMS
Dr N A Morley and Professor M R J Gibbs

The recently discovered Fe-Ga is a novel magnetostrictive alloy, which has great potential for practical applications. This project involves the fabrication of Fe-Ga-Si-B films using dc sputtering and evaporation, in an unique deposition chamber. The additions of Si should produce amorphous films, which in principle could have higher magnetostriction constants compared to the crystalline films. The project will investigate how the magnetic and structural properties of the films vary with composition, with the aim to achieve films with large (>60ppm) magnetostriction constants. The magnetic and structural properties of these films will be characterised using a range of techniques, including magnetometry, XRD, AFM/MFM and electron microscopy.

87 MAGNETIC SHAPE MEMORY ALLOYS
Supervisors: Dr N Morley and Prof I Todd

Magnetic shape memory alloys have giant magnetic-induced strains due to the reorientation of the martensitic variant. This project investigates the magnetic and structural properties of Ni-Fe-Ga as a function of composition in both bulk and thin films. Its aim is to develop a phase diagram which gives the composition at which the largest induced-strain occurs as a function of thickness. The films will be fabricated using a co-sputtering-evaporation technique, while the bulk samples will be fabricated using arc-melting. The structure and magnetic properties will be characterised using a range of techniques including XRD, electron microscopy, magnetometry and strain measurements.

88 DESIGN AND DEVELOPMENT OF A MEMS ENERGY HARVESTER
Dr N A Morley, Dr D A Allwood and Professor M R J Gibbs

Energy harvesters are devices which convert mechanically motions such as vibrations into electrical energy. Energy harvesters can be used for applications where a long-lasting portable power source is required. One application where energy harvesters could be beneficial is in micro-electrical mechanical systems (MEMS), where they could be used rather than batteries to power the devices. This project uses the computer simulation programme COMSOL to design a MEMS energy harvester using magnetostrictive materials. Once the optimum overall design and materials have been determined, the MEMS device will then be fabricated and tested, using the equipment available in the SCAMMD group.

(iii) Polymers

DEVELOPING IMPACT RESISTANT POLYMERS AND COMPOSITES
Supervisor: Dr J Foreman

Fracture toughness measures the ability of a cracked material to resist fracture but it is notoriously difficult to measure accurately and consistently. Recently, we have developed a model based on Griffith fracture mechanics which can predict the fracture toughness for amorphous polymers. The technique takes advantage of the power and speed of Group Interaction Modelling to accurately predict the properties of polymers. The project will involve developing the model to predict fracture toughness across a range of amorphous polymeric resins (e.g. epoxy, phenolic), temperatures and strain rates. Alongside this, an experimental programme will be implemented to provide validation data for the model. Ultimately the model will be used to help develop more impact resistant polymers and composites.

RAPID MULTI-SCALE MODELLING OF POLYMER COMPOSITE STRENGTH
Supervisor: Dr J Foreman

The strength of a polymer composite system is difficult to predict with accuracy due to the huge number of variables associated with a multiphase system. These include complexity associated with linear elastic reinforcements embedded in a thermosetting polymer matrix which displays strain rate dependent viscoelastic properties. Recently, we have developed a multi-scale model which predicts the strength of a polymer composite as a function of temperature and strain rate based on Group Interaction Modelling of polymer properties. The material properties are used to populate a FE/statistical model which predicts composite strength via the transfer of strain between adjacent fibres. This project will involve developing the multi-scale model and comparing it to a range of experimental validation measurements. The overall aim of the project will be to use the model to develop stronger composites by fine-tuning the properties of the constituent materials.

HOW IS THE SERVICE LIFE OF POLYMER COMPOSITES AFFECTED BY ENVIRONMENTAL DEGRADATION?
Supervisor: Dr J Foreman

Over an extended period of time, water and other diluents play a significant role in degrading the properties of polymers and polymer composites. The effects can be rapidly and accurately predicted using a newly-developed modelling technique called Group Interaction Modelling. The main innovation in this project will be to design an extension to the existing model that will predict the amount of diluent each polymer can absorb over time based on the underlying chemistry. This will also involve empirical measurement of water uptake to provide validation and parameterisation. The model will be used to predict how subtle changes to the polymer chemistry or any additives present can be used to enhance the service life of polymer and composite parts.

POLYMER DISCOVERY: SCREENING THOUSANDS OF POLYMERS USING HIGH-THROUGHPUT MODELLING
Supervisor: Dr J Foreman

Drug Discovery is an established technique used in the pharmaceutical industry to screen many thousands of potential candidates for efficacy before expensive and time-consuming experimental synthesis begins. The same principles can be applied to the development of polymers due to recent developments in Group Interaction Modelling. Importantly, the technique allows the rapid prediction of polymers properties and will therefore be developed into a new tool called ‘Polymer Discovery’. This project will develop such a high-throughput model and apply it to arrays containing several hundred polymers or more, many of which will be ‘new’. Samples of the best candidates will then be manufactured and tested to assess how well the model works. The eventual aim of the project is to use the tool to provide new materials and directions for polymer science.

89 SURFACE ADSORPTION AND CHARACTERISATION OF FUNCTIONALISED GRAPHENE NANOSHEETS
Supervisors: Dr B Chen, Professor G Ungar and Dr X Zeng

Graphene, an atom-thick layer of carbon atoms, demonstrated great potential to be used in next-generation molecular devices, nanomedicine, composites,etc. Since 2004 it has attracted substantial interest from Materials Scientists, Physicists and Chemists, and it won its discoverers the Nobel Prize for Physics in 2010. However, many of the fundamental issues in relation to this highly promising material remain unresolved. This project aims to investigate surface chemistry and properties of functionalized graphene nanosheets for manipulating their engineering or functional properties. It involves preparation and functionalization of graphene nanosheets, surface adsorption of nanosheets and characterization of surface properties at the molecular level by using a range of advanced techniques such as grazing incidence small-angle X-ray diffraction, transmission electron microscopy, atomic force microscopy and nanoindentation, in combination with molecular simulation.

90 POLYMER/GRAPHENE NANOCOMPOSITES
Supervisor: Dr B Chen

Polymers and Polymer Composites represent two important classes of materials and can be found in a wide variety of applications including transportation, construction, energy and healthcare. Based on the extraordinary intrinsic properties of graphene (i.e., an atom-thick layer of carbon atoms) such as high strength, stiffness and specific surface area, this project aims to develop graphene-reinforced polymer nanocomposites including biodegradable materials for enhancing the performance and application of existing polymers and composites. It will address two main challenges: (a) scale-up production of high-performance nanocomposites by using cost-effective approaches; and (b) tailing engineering properties according to end-product requirements. The potential candidate will receive training in a broad spectrum of techniques in relation to polymer processing, nanomaterials engineering, micro- and nano- structural characterization, evaluation of processing and engineering properties and beyond.

91 NANOMECHANICAL PROPERTIES OF POLYMERS
Supervisor: Dr S A Hayes

Nanomechanical testing or polymers is not as straightforward as for hard elastic materials, due to their inherent viscoelasticity. They are also frequently used as thin coatings on much harder substrates, and thus it can be difficult to determine the properties of the polymer independently from those of the substrate. Projects under this heading will therefore seek to facilitate a better understanding of the mechanical performance of polymeric materials under nanoindentation, either in the bulk or as thin coatings. The eventual aim is to allow the obtention of a full master curve of the polymers properties using conventional nanoindentation techniques.

92 IMPROVING THE TOUGHNESS OF COMPOSITES
Supervisor: Dr S A Hayes

Laminates produced from unidirectional composite pre-preg are well-known to be susceptible to impact damage, which produces extensive delaminations between layers with different orientation. While there are methods of reducing damage, it is still a major concern when designing composite components, and prevents full optimisation of the mechanical properties. This project will employ patterned interleaves between plies, with controlled mechanical properties, in order to dissipate the impact energy though mechanisms other than fracture. Optimum interleaf patterns will be established using modelling techniques, and the predictions of the model assessed experimentally. The toughness of new systems will be compared with traditional composites to assess the degree of toughness control that the new approach provides.

93 MECHANICAL PROPERTIES OF ALIGNED NANOCOMPOSITE MATERIALS
Supervisor: Dr S A Hayes

This project seeks to manufacture nanocomposite materials with controlled orientation of the reinforcement phase, in order to maximise the influence of the reinforcement on the mechanical properties. In conventional fibre reinforced composites, the maximum mechanical advantage is obtained when the fibres lie in the loading axis. However, with nanocomposites this is difficult to achieve. Currently nanocomposites have been shown to give significant improvement in the mechanical properties of rubbery polymers, but in glassy systems, success has been more elusive. This could be due to the misorientation of the reinforcement, meaning that it effectively acts as a flaw in the polymer, initiating the fracture process. By controlling the orientation it is hoped that such problems can be eliminated and the mechanical properties of nano-scale reinforcements fully exploited.

94 SELF-HEALING POLYMERS AND COMPOSITES
Supervisors: Dr S A Hayes

This project will continue development of recently patented self-healing technologies, which can currently enable an epoxy resin to recover 70% of pre-fracture load upon healing without the addition of new material. It is the aim to apply this technology in the field of advanced composites and also in adhesive resins. Projects are available in both of these areas depending on the applicants’ interests and experience. Typically, projects would involve the development and characterisation of new healing resins using guidelines that exist, followed by investigations into the technology to further our understanding of these novel functional resin systems and facilitate their adoption in commercial applications.

95 RENEWABLE RESOURCES
Supervisors: Prof. G. Ungar, Dr. X. Zeng

Aliphatic polyesters and copolyesters have green credentials both because they are biodegradable and because they can be synthesized from renewable resources such as vegetable oils. However, the mechanical properties do not match those of aromatic polyesters such as PET. Furthermore, aliphatic polyesters are highly susceptible to degradation during processing. For this reason hybrid aliphatic-aromatic copolyesters are being investigated, that would combine the best of aliphatic and aromatic polyesters. It is however important to retain a high level of crystallinity, a property not normally associated with random copolymers. This project will try to help solve this problem by investigating the distribution of aliphatic and aromatic units between the different crystal forms and between crystalline and amorphous domains. In addition to optical and electron microscopy, X-ray diffraction, thermal techniques, and computer modeling, a new technique of neutron fibre diffraction on selectively labeled copolymers will be developed.

96 CONTROLLING SELF-ASSEMBLY OF METAL NANOPARTICLES, QUANTUM DOTS AND GRAPHENE BY DIRECTED MORPHOLOGY OF SEMICRYSTALLINE POLYMERS
Supervisors: Prof. G. Ungar, Dr. X. Zeng

Controlling spatial arrangement of nano-objects is one of the primary concerns of nanotechnology. For example, by ordering gold or silver nanoparticles into strings, layers or 3d superlattices one can tune plasmonic resonance and potentially create negative dielectric permittivity, negative magnetic permeability, or even negative refractive index for applications including “invisible” metamaterials. Similarly embedding semiconductor quantum dots and coupling them with a periodic structure of the surrounding matrix can create new types of lasers and other optoelectronic devices. Attempts to achieve these goals often involve blends of nano-objects with block copolymers or, more recently, liquid crystals. In contrast, this project will focus on utilizing the natural tendency of semicrystalline polymers to create periodic structures on different length scales and harness this property to create controlled ordered arrays of nanoparticles, quantum dots and grapheme layers in novel types of nanocomposite.

97 PERIODIC AND QUASIPERIODIC MOLECULAR HONEYCOMBS AND NANOFRAMEWORKS
Supervisors: Dr. X.B. Zeng and Prof. G. Ungar

It has been shown recently that by combining incompatible rigid and flexible segments in one molecule, and adding weakly interacting groups, one can create novel self-assembled organic structures resembling honeycombs and scaffold-like frameworks. These can have different symmetries and can be modified to serve as catalysts, control-release materials or templates for nanoporous ceramics. Furthermore, there are indications (X.B. Zeng et al., Science 2011, 331, 1302) that some of the honeycombs may be quasicrystals, i.e. having symmetries beyond those achievable by periodic lattices, similar to those recently discovered in supramolecular dendrimers (X.B. Zeng et al. Nature 2004, 428, 157). The discovery of first quasicrystals has earned D. Shechtman the Nobel Prize in 2011. If successful, the new quasicrystalline honeycombs could act as a model for materials with very wide photonic bandgap, acting as media for creating photonic integrated circuits. These new structures will complement those comprised of molecular networks, also being studied in Sheffield (see Zeng et al., Nature Materials 2005, 4, 562). In the projects these emerging materials will be investigated using X-ray (synchrotron) and neutron scattering and atomic force microscopy – see also Chen et al. Science 2005, 307, 96.

(iv) Nanomaterials

CHARACTERISING THE NANOSCALE MORPHOLOGY OF POLYMER: FULLERENE PHOTOVOLTAIC BLENDS
Supervisors: Dr C Rodenburg (Materials Science & Engineering) and Prof. D. G Lidzey (Physics & Astronomy)

A fully funded studentship is available (for UK, EU nationals only) to join the Shine Centre for Doctoral Training starting in October 2013 with a project focused on advancing the development of Organic photovoltaic devices (OPV) through pioneering microscopy techniques in order to understand the complex structures which are critical to OPV operation. OPV could contribute substantially to clean electricity generation, provided devices can be made to operate with high efficiency, have extended lifetime and to be manufacturable at low-cost with high volume. Your task will be in advancing existing microscopy techniques to extract structural and chemical information on multiple length scales, and combine this with electrical measurements on device structures to address issues such a lifetime and high volume manufacturing of OPV. This cross faculty project is jointly funded and supervised the Faculty of Engineering and the Faculty of Science.

Please contact Dr Cornelia Rodenburg ( c.rodenburg@shef.ac.uk ) for more details or submit applications www.sheffield.ac.uk/postgraduate/research/apply by the end of February 2013.

98 SIMULATING MAGNETIC NANOPARTICLES
Supervisor: Professor J Harding with Dr C L Freeman

There are increasing numbers of exciting and dynamic uses for magnetic iron-oxide nanoparticles; for example in magnetic resonance imaging and high density media storage. New methods are needed to produce regularly-sized and shaped particles. Current methods are not simple or cheap and require the use of organic solvents or very high temperatures. However, nature has been producing ordered magnetic particles for two billion years. This project will investigate the methods used by magnetotactic bacteria to control the growth of iron oxide particles using computational modelling in collaboration with experimental groups at Leeds. Computational methods will be used to build up models of the magnetite-water interface which will explain the stability of the observed crystal morphologies. The effect of proteins on this interface can then be simulated. How do these molecules bind to the iron oxide surfaces? Do they stabilise particular crystal surfaces? Understanding and control of growth is an ambitious and exciting project which will improve scientific methods and offer benefits to healthcare and technological systems.

99 STABILITY OF NANOSTRUCTURED BATTERIES
Professor B J Inkson

Many machines vital for modern-day living, including computers, phones and cars, rely on batteries for their function. The development of improved portable energy storage, in the form of batteries, has several key issues including improving capacity and durability whilst simultaneously shrinking battery size. A key problem for battery electrodes is their microstructural stability; high surface area nanomaterials such as nanorod arrays have great potential for electrode and energy applications, however potential problems include nanorod coarsening or dissolution, deformation due to stress (poor mechanical properties), and electrically-induced breakdown.
This project will examine the stability of nanorod arrays for lithium batteries. Nanoelectrodes will be characterised before and after functional testing to determine key stability parameters. In particular, Sheffield NanoLAB technology will enable unique assembly of nanoscale battery circuits, and real-time in-situ imaging of Li loading and electrical nanotesting of the nanoscale functional units within the battery architechtures (such as individual nanorods), enabling dynamical nanoscale break-down mechanisms to be evaluated. This project will be a collaboration with Prof Xiang Yang Kong, Institute of Materials for Mobile Energy, at Shanghai Jiao Tong University (SJTU).

100 NANOSCALE FRICTION EVALUATED BY DYNAMICAL in-situ TEM
Professor B J Inkson

Tribology processes such as friction and wear affect all technology with moving parts. Although many friction (loss of energy) and wear (loss of material) processes occur at the nanoscale, it is extremely difficult to characterise the dynamics of these non-uniform events. Here at Sheffield NanoLAB we have built a new mechanical triboprobe miniaturized to fit inside an electron microscope which will enable two surfaces to be videoed as they rub against each other, and enable real-time evaluation of nanofriction and nanowear.
In three available PhD projects the TEM triboprobe will be used for ground-breaking research into
(a) friction of graphene
(b) friction of carbon nanoparticles including nanodiamond
(c) dynamical friction of ultrathin surface coatings systems
The microstructural changes and conversion of energy occurring during nanoscale impacts of individual particles, and frictional nanocontacts between rubbing surfaces, will be characterised in real-time using high resolution advanced ion and electron microscopy techniques. See www.nanolab.org.uk.

101 NEW MATERIALS FOR WELDING AND SOLDERING AT THE NANOSCALE
Professor B J Inkson

One of the central challenges for the construction, integration and repair of nanoscale systems is to develop reliable methods and materials for joining individual nanoobjects together and to substrates. Although a number of localized joining methods suitable for individual nanoscale objects have recently been proposed, including thermal & laser heating and ion beam deposition of material, they generally lead to some degradation of the nanostructure involved.
In this project nanoscale welding, using nanovolumes of metal solder, will be developed which should radically improves the spatial resolution, flexibility and controllability of nanoscale joins and welds. The use of solder to bond nanoobjects together should offer the opportunity to tailor the mechanical and functional properties of weld by controlling the chemistry, structure and volume of solder material used. A range of nanoscale solder materials will be fabricated, and the influence of solder particle size and chemistry on melting behavior and joining/welding performance will be evaluated using advanced microscopy methods including 3D tomography and in-situ functional testing.

102 3D IMAGING OF TEETH AND TOOTHPASTES
Professor B J Inkson

Our teeth are highly complex structures, engineered at the nanoscale. But they are also under constant attack by oral bacteria and acids from modern foods and fizzy drinks. Using toothpaste is our first line of defence against damage, so it is of great interest to evaluate how toothpaste materials interact with tooth enamel and dentine to reduce bacteria and staining, and manage tooth sensitivity.
This project will use a range of advanced 3D microscopy techniques including X-ray, ion and electron tomography to evaluate the 3D structure of teeth. The interaction of a range of toothpaste particles with the tooth nanostructure will be investigated in 3D to quantify and improve the functionality of toothpastes. In particular it will be systematically investigated whether a reduction in particle size to the nanoscale influences abrasion, surface modification and dentine tubule occlusion processes.

103 LOOKING INSIDE MATERIALS: NANOTOMOGRAPHY AND 3D NANOMETROLOGY
Supervisor: Dr G Möbus

Nanomaterials are intrinsically 3-dimensional materials, as their properties depend on surface-proximity and confinement of electronic or mechanical properties as low dimensional matter. Imaging of surfaces or planar cross-sections is no longer sufficient. In this project we develop new acquisition sequences and new data reconstruction procedures for applying the established technique of computed axial tomography (CAT) to nanomaterials, with special emphasis on 3D chemical and structural mapping. State-of-the-art aberration corrected electron microscopy is available for projection imaging. Applications will e.g. comprise nanoparticles, nanoparticle composites, functional nanotips and nanoporous materials.

104 NANOPATTERNING FOR ENGINEERING OF NOVEL DEVICES AND SURFACES
Supervisor: Dr G Möbus
We use electron beams to drill or cut patterns with sub 5nm dot resolution into inorganic substrates. The research concentrates especially on the physical origins of the ultimate resolution limit of this technique and the chemical processes taking place during ablation of atoms. A second central aim of the project is to study sublattice depletion (such as to remove anions only from a compound) to leave conductive or magnetic purely metallic material behind. Another aspect is the analysis of freshly milled patterns via nanoscale spectroscopy inside the transmission electron microscope. Prospective applications include nano-circuitry, nano-optics, patterns for nanoscale templating.

105 COMPUTATIONAL SIMULATION OF ATOMIC RESOLUTION IMAGING OF NANOPARTICLES WITH ABERRATION CORRECTED TEM
Supervisor: Dr G Möbus

Using latest equipment in the field of transmission electron microscopy, small particles can be mapped for structural and morphology changes down to a single monolayer or atom. The interpretation of images however often requires the understanding of the image formation process from a viewpoint of electron waves. In this project existing computer simulation software shall be used to predict and model the formation of images and diffraction patterns for the new Sheffield aberration corrected TEM facility (Kroto Institute). The project is complemented by post-processing computational evaluation of digital experimental micrographs of nanoparticles, and the student will participate in assisted imaging sessions to generate test data.

106 SELF-ASSEMBLED MOLECULAR WIRES AND LIQUID CRYSTALS IN INORGANIC NANOTEMPLATES
Supervisors: Prof. G. Ungar, Dr. X. Zeng

Straight one-dimensional electronic conductors of nanometre thickness can be produced by self-assembly of conjugated organic molecules or macromolecules. The idea is to incorporate them into molecular-scale electronic circuits. This project will utilize columnar and other types of liquid crystals and incorporate them into nanochannels and nanogrooves produced by electrochemical etching of alumina or ion etching of silicon. The diverse orientation patterns of these high charge mobility “molecular wires” will be investigated. Potentially these composited could result in new materials for molecular electronic and near-field optical devices. Small-angle X-ray diffraction, electron microscopy and high-resolution AFM will be the key characterization techniques, including collaboration on 3D electron tomography.

107 HOLLOW NANOPARTICLES AND NANOFIBRES
Supervisors: Prof. G. Ungar, Dr. X. Zeng

In this project inorganic and organic nanoparticles and their assemblies will be studied, including silica and titania hollow nanoparticles, as well as core-shell particles with conducting polymer shells. Furthermore, novel perforated (hollow) silica nanofibres will be studied, both on their own and enclosed in nanochannels in anodized alumina membranes. Among the potential applications of these materials are controlled drug release, optoelectronic devices, special catalysts, biomedical and environmental sensors and quantum dots. This project spans the areas of inorganic nanoparticles, polymers and liquid crystals. Analytical techniques based on X-ray, neutron and electron diffraction, as well as electron microscopy and AFM will be applied, in combination with molecular simulation. A particularly important technique will be grazing incidence small-angle X-ray scattering (GISAXS) using synchrotron radiation.

108 ARRANGING METAL NANOPARTICLES WITH LIQUID CRYSTALS
Supervisors: Dr. X. Zeng and Prof. G. Ungar

Nanoparticles based on metals, metal oxides or sulphides are currently of great scientific and technological interest. The coverage of nanoparticles with organic groups not only enhances the processability (e.g. solubility) of such systems, but, where suitable functional groups are included, it also allows applications in areas ranging from optics, electronics, and catalysis to biomedical research and medical diagnostics. The novelty of this project is in that the metal nanoparticles will be coated with liquid crystal molecules of different design, so as to achieve previously unavailable modes of 2d and 3d ordering on surfaces and in the bulk. Such use of directed self-assembly would produce arrays and gratings with novel electronic, magnetic and photonic properties. Preliminary studies have already produced several new nanolattices, containing ordered strings of gold nanoparticles with controllable particle spacings (see Zeng et al., Adv. Mater. 2009, 21, 1746). The project is part of the European network NANOGOLD, aiming at generating metamaterials for advanced optical applications.