Energy Materials● Synthesis, Characterisation and Application of Electro- and Thermochromic Metal Oxide Nanoparticles Prepared by Hydrothermal and Solvothermal Synthesis
Smart materials which undergo reversible colour changes in response to external stimuli have a host of potential applications across multiple sectors, including sensors, display technologies, and, on a larger scale, architectural eco-efficient glazes. Metal oxides are the most prominent members of these smart material families, with prototypical examples of WO3 and VO2. A variety of other abundant oxides, such as tin and titanium dioxide, may also exhibit electro- or thermochromic behaviours when doped with suitable redox active dopants including tungsten or antimony. It has been shown previously that particle phase, size, and shape can have a significant impact on behaviour, including transmittance, transition temperature and response time. Tuning these properties and controlling performance is thus of paramount importance from an application perspective. In addition to controlling these factors it is also beneficial to consider the surface modification of these metal oxide nanoparticles to promote dispersibility in solution and thus facilitate device manufacture. Equally production methods must also be environmentally sound and scalable to enable their eventual application on an industrial scale. Here we propose to use green hydrothermal and solvothermal reaction systems, including conventional reactor technologies and custom built reactors, to produce target materials including VO2, WO3, SnO2 and TiO2 with precise phase, size and shape control, and to explore the effect of these parameters on the materials’ behaviour and performance. Doped materials will also be produced to further tune the material properties. Finally routes towards generating easily processable organic-inorganic hybrid analogues will be established towards device manufacture.● Metallocene derivatives of hexa-peri-hexabenzocoronene: where helicenes and foldamers meet
Combining the properties of ferrocene and extended planar aromatics is an exciting prospect. On the one hand, the ferrocenyl moiety (as donor) gives rise to donor−acceptor assemblages that are suitable candidates for NLO materials, electrode surface modifiers, and magnetic surface materials. On the other, the large aromatic substituent (as chromophore) provides low-lying pi*acceptor orbitals and charge separated states which, whether electronically coupled or distinct, are important to optoelectronic applications.
The ferrocenyl−ferrocenium redox couple adds a further dimension to these donor−acceptor compounds and gives rise to potentially tunable magneto properties on the nanoscale. Mixed-valence species, formed when diferrocenyl systems are partially oxidized are known to display classical Class II donor−acceptor behaviour but donor−acceptor chemistry where the ferrocenium cation is the acceptor to an extended aromatic are quite rare. Such materials offer the possibility of modulating the emission characteristics of the fluorophore depending on the nature of the excited states and the different quenching characteristics of the ferrocenyl group and the ferrocenium cation.● Exploiting unexplored bimetallic catalysis in metal oxide reduction to improve solid oxide fuel cell operation
Low temperature efficiencies of solid oxide fuel cells (SOFC) can be improved if catalytic oxygen reduction reaction (ORR) mechanisms of alternative metal-oxide electrode surfaces can be found to work at lower temperatures. One candidate for lower ORR is the Ru/Mn system which will be further investigated. Mechanisms for reduced ORR by Ru or by other 3d/4d/5d metals (e.g. Ir) is of intrinsic interest, with other identified bimetallic electrodes include Ru/Ni, Mn/Ir, Mn/Ni and Mn/Mg. Target temperatures for future low-temperature SOFCs is 500°C where Ru/Mn has already shown evidence for lowered ORR. Ultra-high Vacuum (UHV) surface science approaches to investigating these mechanisms are envisaged, especially as oxygen reduction on Ru/Mn can be achieved controllably over long timescales in UHV. Investigations will involve X-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), physical characterisation techniques (SEM/TEM), all combined with synchrotron-based x-ray emission spectroscopies (XES/RIXS) and x-ray absorption spectroscopies. This combination will seek to clarify surface, bulk and buried interface metallic catalysis contributions to ORR behaviour in these thin/ultra-thin films of Ru/Mn or their bimetallic homogeneous alloys. Atmospheric pressure XPS (APXPS) will help evaluate performance and reversible nature of operation of these bimetallic electrodes surfaces in controllable real-world conditions albeit ORR occurring at significantly faster timescales than in UHV. Synchrotron based APXPS augments these in energy resolution and time resolution. Finally, the thermodynamic stability of these electrode materials in contact with yttrium-stabilised-zirconium (YSZ) electrolytes will be investigated as this is known to be of key importance in SOFC efficiencies.● Metal-Organic Frameworks for Energy Conversion and Catalytic Device Fabrication
Scientific objectives: The project addresses the question of how light-harvesting and catalytically active Metal-Organic Frameworks (MOFs) can be synthesized and deposited or printed on electrodes to produce electro/photo-catalytic devices. The systems will be used to catalyse highly endergonic, energy-related chemical transformations, e.g. H2O oxidation and H2 production reactions. The performance criteria of the devices including catalytic activity, stability, quantum efficiencies and charge mobilities will be investigated. Mechanistical and structural details of the catalytic transformations will be studied in-situ by X-ray absorption spectroscopy and diffraction techniques at synchrotron facilities.
Background: The exceptional interest in MOFs is a result of their advantageous characteristics including high porosity and amenability to chemical modification. MOFs are regarded as key compounds related to energy storage and conversion, as their unprecedented surface areas make them promising materials for gas storage and catalysis. We believe MOFs allow the replication of key features of natural enzymes thus demonstrating how size, shape, charge and functional group availability influences substrate binding and performances in energy-related catalytic reactions. Due to their intrinsic surface areas, many MOFs have high densities of active sites per volume and favourable diffusion coefficients; some MOFs even allow stabilization of highly reactive moieties within their 3D structures - species that are not attainable in parent homogeneous phases. Their processability can be exploited in photo/electro-chemical devices.
A scientific breakthrough in relation to sustainable H2-based energy concepts would arguably be one of the greatest scientific achievements and associated with unprecedented impact to a single country, mankind and future generations.● In situ and operando characterization of heterostructured electrode materials for energy applications
Carbon-based heterostructured electrodes hold potential to combine the desirable properties of functional carbons with those of inorganic nanomaterials as electrocatalysts. Synergetic heterostructured designs can deliver enhancements in catalytic performance in reactions critical for low-carbon energy technologies, e.g. the hydrogen evolution reaction (HER), the oxygen reduction reaction (ORR) or redox processing of bio-derived feeds. Importantly, synergetic enhancements can: (a) overcome limitations and conflicting property requirements in single-component electrocatalysts; and (b) potentially reduce material requirements, such as use of scarce Pt-group electrocatalysts.
Interfacial interactions are thought to be critical for understanding performance/enhancements. The morphology of the phase components (nanoparticles, monolayers etc.), the chemical composition of the carbon phase (N,S doping etc.) and the 3D architecture of the heterostructure all play a role in determining type and importance of such interactions. In this project the student will fabricate heterostructured electrodes with well-defined morphologies and architectures using N-doped carbon materials and compound electrocatalysts, then will use them to probe electrocatalysis using advanced in situ and operando spectroscopies to provide insights on enhancement mechanisms. Our group recently developed thin-film heterostructured electrodes to investigate carbon substrate effects on electrocatalysis and we applied this to carbon-MoS2 studies. We will use this synthetic strategy to fabricate carbon-MS2 or carbon-MCx electrodes with varying composition, amenable to operando characterization via infrared surface spectroscopy in the supervirsor’s lab, followed by advanced characterization using X-ray methods (absorption/microscopy). Changes at the solid/liquid interface will be monitored under potentiostatic/galvanostatic control; studies will be focused on cathodic processes, namely HER and organic reductions.
Biomaterials and Regenerative Medicine● Ultramicroscopy of Biomaterial Structure and its interplay with Intracellular Organelles to Engineer Macrophages and the Foreign Body Response
This project will apply advanced imaging and materials characterisation techniques to gain a deep understanding of fibrosis surrounding biomaterial implants. This fibrosis is an undesirable outcome that causes medical implant failure, hinders therapeutic drug release and worsens patient prognosis, via increased site inflammation and stiffening. An immune cell known as the macrophage; is a major governor of this fibrosis. These cells phagocytose and eliminate perceived- ‘foreign materials’ and when they cannot; they instruct fibrosis. An emerging characteristic of macrophages is the manner in which they generate their energy (metabolism) which is dictated by their response to biomaterials. The interplay of mitochondria with the endoplasmic reticulum and their connections, called mitochondria-associated ER membranes (MAMs), are crucial hubs in such cellular stress and metabolism. this interplay.
The specific research questions are:
i. How do biomaterials, as nanoparticles or nanotextured substrates; affect mitochondrial organisation, size and MAM organisation.
ii. How are the observations in (i) reflective of macrophage metabolism, polarisation, and cytokine signalling
iii. How does this translate in vivo in a mouse intramuscular injury model at 14 days in terms of in vivo metabolism, and fibrosis.
Linking ultramicroscopy to metabolism is major gap in biomaterials and regenerative medicine, immunology and biochemistry. Establishing mechanisms of material directed, macrophage metabolic-dependant polarisation will lend crucial insights into future biomaterial and nanoparticle design for clinical translation. This will instruct an improved biomaterial implant performance and guide the discovery of approaches to reduce fibrosis in other pathological settings.● Characterisation of load structure relationships in passive skeletal muscle: biomaterials advances for applications from rehabilitation to blast injury protection
Skeletal muscle regenerates following minor injuries, but not following severe damage. Biomaterials improve muscle regeneration by presenting chemical and physical cues to muscle cells emulating natural regeneration. For engineered muscle, we need a good understanding of the mechanical structure and response to external loading for passive muscle, to be able to provide a suitable scaffold for seeding muscle cells. However, characterising the response of muscle under mechanical loading has many associated difficulties due to the highly complex, anisotropic, viscoelastic and hierarchical nature of the tissue. The stress response to muscle stretching is two orders of magnitude stiffer for tension than compression, but little is known about the internal pressure in skeletal muscle. We hypothesize that passive muscle mechanics are dominated by incompressible muscle fibres with a high fluid content interacting with the much stiffer surrounding collagen fibres in the extracellular matrix.
Goal: The goal of this project is to provide a platform for testing muscle biomimetic scaffolds for skeletal muscle regeneration. We will do this by characterising skeletal muscle tissue response to applied loading to inform the development of biomaterials for muscle surrogates and injury protection devices. In particular, we will design physical and virtual experiments to investigate the hypothesis that the unexpectedly high internal pressure recently observed in skeletal muscle samples is due to the unusual microstructure.
We will develop a suite of experimental tests to measure the internal pressure in different regions of skeletal muscle tissue during static and dynamic conditions under a range of applied loading (tension/compression/shear). We will make use of a Gaeltec pressure micro-sensor to assess pressure in skeletal muscle tissue under quasi static and droptower testing.
In parallel, will develop constitutive models for implementation in finite element code to test the contribution of the different constituent materials to the overall skeletal muscle response to applied loading.● New magnetic-plasmonic nanomaterials for biosensing applications
Magnetic and plasmonic nanoparticles have been used for a broad range of biomedical applications including cell labelling, drug delivery, hyperthermia treatment and biological imaging. The main goal of this research project is the development of new multimodal “two in one” magnetic-plasmonic nanostructures and their bioconjugates for potential biosensing and detection of viral species. Magnetic alloy core nanoparticles will be produced using appropriate metal salt precursors, coated with a plasmonic gold shell and functionalised with amino-groups. This will be followed by bioconjugation of the core-shell nanoparticles employing specific viral protein binders and our established conjugation protocols. The new bioconjugates will be used for selective binding and isolation of specific influenza viruses from mucus samples by magnetic separation. After that we aim to develop spectroscopic detection of selected viruses using hotspot plasmonic resonance enhancement and a new portable Raman spectrometer available in TCD. Due to the uninterrupted testing and unique point of care (POC) analytical capabilities for fingerprinting, our new technology will also potentially serve as a very useful tool for detection of viral antigens, studies and understanding of virus mutations, interactions between viral receptors and antibodies, and other relevant biochemical processes. The realisation of this project will also result in new rapid virus screening POC technologies including quick diagnostics solutions to the current COVID-19 pandemic and future similar infectious disease outbreaks.● Responsive microstructures for targeted drug delivery
In this project we will develop tumour responsive microstructures by combining state-of-the-art 3D fabrication and characterisation techniques with stimuli-responsive materials.
The synthesis and incorporation of responsive units at the molecular level, combined with precise and sophisticated assembly at the nano/micro-scale via direct laser writing, enables the realisation of microstructures which will be enzymatically triggered to release their cargo specifically at tumour sites to afford targeted therapeutics, providing higher efficacy and lower side effects than systemic treatment.
The proposed project will investigate how bio-responsive units can be integrated into microstructures that can be harnessed for tumour responsive drug delivery. The development of stimuli-responsive micro-structures, in combination with the integration of advanced functionalities such as cargo transport and delivery, will significantly advance the field of smart materials.
To deliver these advances, our research strategy will combine: 1. Responsive polymeric materials that can release cargo in response to enzymes upregulated in the tumour environment. Synthesis of both responsive pendant units and responsive crosslinking units will be investigated. 2. High precision micro-fabrication by direct laser writing via two-photon polymerisation, will enable the fabrication of complex 3D constructs with exquisite control over architecture of the material. 3. State of the art characterisation from molecular to nano/micro and macro scale, including micro-Raman spectroscopy, AFM (in air and liquid), SEM and optical microscopy (including confocal and STED) 4. Characterisation of cargo encapsulation and enzyme stimulated release.● Advanced nanofabrication for single molecule sensing: Toward atomic-scale control in nanopore devices
The detection of single molecules represents an ultimate goal of biological and chemical sensing. Single-molecule sensing allows us to reveal behaviour that is often hidden in ensemble measurements and thus probe dynamic processes at the level of the individual. In recent decades, nanopores have emerged as one of the most promising platforms for DNA sequencing and sensing at the single-molecule level. Nanopore sensors consist of nanometre-wide holes in ultrathin membranes separating two electrolyte solutions. Application of a voltage bias across the membrane causes ions to flow through the nanopores. When an analyte molecule transits through a pore, ion flow is temporarily altered and a change in ionic current is registered. Analysis of this transient change in ionic current can be used to identify analyte molecules and their properties.
While nanopore sensors show enormous promise, a number of open challenges remain. Sensitivity of nanopore detectors is limited by the pore geometry. Control of nanopore dimensions at the sub-nanometre level will support improved device sensitivity. In this work, we consider two routes to control nanopore geometry with atomic-scale precision and improve device performance. Firstly, we will combine helium-ion-beam-induced defect formation in ultrathin SiNx membranes with controlled electrical breakdown to produce uniform arrays of sub-10-nm-diameter nanopores. In parallel, we will fabricate nanopores in atomically-thin layers of h-BN by direct helium-ion-beam milling. In addition to advancing nanopore fabrication methods we will design and fabricate nanopore devices with integrated optical nanoatennas for complementary spectroscopic detection to move toward a new generation of single molecule sensors.
Engineering Materials● Microscopy and microanalylsis of the passive films of reinforcing steel formed in low-carbon concretes
Concrete is the second most used material, after water, on this planet, and manufacturing Portland Cement (PC) produces 7% of annual CO2 emissions globally due to its high carbon footprint (830 kg/t ECO2). One way to produce low-carbon concrete is to replace PC with low-carbon cements, such as alkaline cements, calcium sulphoaluminate cement, blended PC composite cements and magnesium phosphate cement. In the past two decades, intensive research have confirmed that not only the carbon footprint of concrete can be reduced, but the properties of concrete can also be maintained and even improved. However, surprisingly, the industrial application of these low-carbon concretes is still limited. One of the main reasons causing this dilemma is due to the uncertainties related to the potential protection which could be provided by these low-carbon concretes to the reinforcing steel imbedded in concrete. As more than 50% of the durability issues related to reinforced concrete structure is caused by the corrosion of reinforcing steel, a good understanding on the passivity of reinforcing steel in low-carbon concretes is essential for improving the confidence of industry. However, this information is largely missing in the literature. In this project, both the microstructure and chemical composition of the passive films formed in different low-carbon concretes will be investigated using helium-ion microscopy, scanning/transmission electron microscopy and Raman/Photoluminescene spectroscopy. The results will then be used to develop a fundamental understanding on the effect of low-carbon concrete on the passivity of reinforcing steel together with the electrochemical data obtained at University College London. The outcome from this research is expected to not only provide guidance to the industry on how to design durable reinforced low-carbon concretes, but also increase the industrial’s confidence.● Next generation 3D printed photonic structures
Over the past number of years chemists have been engineering materials compatible 3D printing via two photon polymerization. This paves the way for next generation biomimetic inspired photonic structures, which despite being made of low refractive index materials such as chitin and guanine display bright saturated colour by exploiting complex structures. There are many spectacular examples of structural colour in nature such as butterfly wings, beetles, and chameleons, to name but a few. Coupling the structural freedom of 3D printing with emerging dynamic and responsive materials opens up a vast array of exciting possibilities. The challenge is to develop photonic structures which can take full advantage of these newly engineered materials in sensing, display and anticounterfeit applications. We recently demonstrated how the concentration sensitive expansion of a novel hydrogel printed photonic structure manifests as spectral changes in the transmission spectrum. In another example we designed structures for pattern transformation when structures are submerged in solution.
A current challenge is to extend the dielectric permittivity and polarization response of the materials compatible with direct laser writing by two-photon polymerization and to print the photonic structures onto the facet of a fibre for a fully integrated photonic sensor. This dielectric permittivity can be modified by incorporating metallic nanoparticles, higher refractive index dielectric nanoparticles or liquid crystal based components. The metal nanoparticles are formed in the host material using a light actuated chemical process. Such materials offer opportunities for reflective and transmissive applications with a dependence on the polarization of the incident or detected light. A unique offering of this project is the close collaboration between material scientists, Profs. Florea and Delaney, photonics expert, Prof. Louise Bradley and sensing expert, Dr. Yetisen. This project will include the design, fabrication and testing of the materials and photonic structures for lab on fibre sensing (vapor and liquid) applications.
 Delaney, Qian, Zhang, Potyrailo, Bradley and Florea, J. Mater. Chem. C, 2021,9, 11674-11678
Electronic and Magnetic Materials● Structural Characterisation of 3D Block Copolymer Structures for ICT Device Applications
Block copolymer (BCP) microphase separation is an important method for the self-assembly of circuit elements via self-assembly. Thin films (to um thickness) are cast onto a substrate. Under suitable annealing conditions, the BCPS form regular, periodic arrangements of the polymer blocks and the different chemistries can be used to transfer the pattern to a surface or allow incorporation of materials as a template. TCD has been one of the pioneering centres for this work showing applications in both electronic and optical materials. Despite advances, there are critical elements missing from the use of BCPs in devices.
1. The films have relatively simple block arrangements (lamellar, cylindrical, spherical) and lack the complexity and ‘design’ flexibility needed for photonic or advanced electronic architecture design where controlled structural changes through a film are needed.
2. Their structure is not well characterised or understood in 3D. Most imaging is carried out by SEM, TEM or AFM in a top-down fashion with relatively few cross-section studies having been carried out. It is critical to use techniques such as FIB to affect full 3D characterisation. Because of strong interface effects (gas-film, film-substrate), morphologies can be more complex than seen in top-down studies. This can be seen in morphological variation both through and across a film.
The aim of this project is two-fold. Firstly, in TCD we have developed a technique of depositing ultra-thin metal and metal oxide films on a substrate using polymer brushes. Using this method, we can make structurally complex 3D films by depositing successive block copolymer films separated by thin oxide layers and each film can show a different structure or different spacing etc. Secondly, we want to use these structures to develop advanced photonic devices where 3D structural control is required.● Material and algorithm co-design for energy-efficient neuromorphic memristive systems
Recent years have seen a rapid rise of artificial neural networks being employed in a number of autonomous applications. The computing requirements of these structures are increasing at rates much faster than improvements made by current CMOS-based technologies. The demand has contributed to a need for novel technologies and paradigms, including memristor-based hardware accelerators.
Solutions based on memristive crossbars utilise analogue data processing and in-memory computing, promising to improve the overall energy efficiency by orders of magnitude compared to the current state-of-the-art hardware systems.
This project will explore the co-design of oxide-based memristive devices through materials optimisation and specifically tailored deep learning algorithms to yield the optimal balance between performance and energy efficiency. Specifically, the project will include the design of metal-oxide-metal memristive devices, fabrication and materials optimisation and electrical testing. In parallel, the project includes the development of an emulation platform (based in Python) for implementing learning and inference with deep learning algorithms taking into account the non-idealities of fabricated devices. Additionally, the project will explore biology-inspired computational paradigms such as spiking neural networks and reservoir computing. The project's general goal is to answer how the fabrication process, materials optimisation, and co-design of deep learning algorithms inform one another and close an optimisation feedback loop?
Instrumentation & Technique Development● A New Low-cost Electron Detector for 4-dimensional STEM Measurements
The scanning transmission electron microscope (STEM) is a hugely powerful instrument, capable of delivering atomic resolution structural and chemical data. State-of-the-art cameras on such microscopes can now record so-called “four-dimensional data” (2D transmission images at every 2D specimen pixel location) [see also: doi.org/10.1017/S1431927619000497]. These cameras and associated data processing, allow electric and magnetic fields to be imaged within materials at down to atomic resolution. However, these cameras may cost up to €1 million, putting them out of reach for many laboratories and even smaller country’s national labs.
This project proposes to design and build a low-cost alternative 4D camera using repurposed Si photomultiplier arrays found in medical scanners. The work will involve a mixture of skills including:
- fundamental electron-optics and scintillator physics,
- multi-slice image simulation to develop the design,
- CAD and PCB softwares to design the hardware, and
- hands-on fabrication, installation and testing of the outcome.
If successful, the impacts of this work are transformational for electron microscopy hardware. We are targeting a fabrication cost 1/10th of the current amount. This would hugely widen access to this new technology especially in lower R&D spend countries.
The PhD researcher will be expected to:
- learn to independently operate the transmission electron microscopes in the AML,
- work with the group postdocs and engineers to develop and test the new hardware,
- present their work at national and international conferences.● Novel Scanning Acquisition Design and All-digital Detection Strategies in STEM
The transmission electron microscope has been called “A Synchrotron in a Microscope” (L.M. Brown, 1997). Scanning TEM, or STEM, now delivers this analytical power point-by-point for every pixel in a scanned field of view, enabling atomic resolution imaging and chemical analysis.
In recent years, new programmable scan-generators allow the operator to design advanced scanning patterns beyond classical raster scanning. These can be used to improve the image resolution, compensate for flyback hysteresis (doi.org/10.1017/S1431927621013908), or for novel geometries of scan-patterning such as interlacing (doi.org/10.1017/S143192762200856X). However, so far only a small fraction of their functionality has been exploited.
Similarly, recent developments in electron detection has enabled all-digital read out and single electron sensitivity to be reached (doi.org/10.1017/S1431927620024721). These techniques allow for the precise number and timing of every electron scattering event to be recorded.
Each of these new technologies promise to deliver more dose-efficient imaging, and there is now a huge opportunity to combine these state-of-the art approaches. This project will explore the mutually beneficial fusion of these two approaches into a single framework, including:
- Developing an each-electron approach to image simulation design,
- Developing a programmable (Python) framework for novel acquisition design,
- Being able to independently operate atomic-resolution TEM instruments,
- Integrating single-electron sensitive detectors into a time-coded pipeline,
- Synchronisation between illumination and detection events,
- Prediction, measurement and tracking of electron dose exposure, and
- Ultra-high precision and SNR imaging of beam-sensitive materials.