Energy Materials● Unravelling the factors that control the activity and stability of catalysts for alkaline water electrolysis
Green hydrogen is an important energy vector in our transition to a net-zero future. Almost all green hydrogen produced today is from alkaline water electrolysis. Earth-abundant catalysts based on NixOyHz are used as catalysts for the cathodic hydrogen evolution reaction. Although alkaline electrolysers are a mature technology, very little is known about the origin of the activity and stability of NixOyHz catalysts used in industrial electrolysers1,2.
It has been reported that for the cathodic hydrogen evolution reaction, the overpotential increases by approximately 0.35 V during the first 40 hours of operation. This drop can be prevented by incorporating Fe into the lattice3. However, it is not clear whether the active catalytic phase is an oxide, a metal or a hydride1. Moreover, the cycling and steady state conditions that trigger and/or amplify the deactivation is unknown. Gaining such insights would allow us to determine the limits to activity and stability of non-precious metal-based catalysts for hydrogen evolution and to design better catalysts that outperform the current state-of-the-art.
In this project, the student will synthesise NixOyHz and Fe-doped NixOyHz catalysts and perform electrochemical activity and stability tests for a range of different operation protocols. The samples will be characterised using X-ray absorption and X-ray photoemission spectroscopy to determine the oxidation state of the metal centre and surface intermediates as a function of potential as well as neutron diffraction and atom probe tomography to determine the morphologies, particularly the presence of (oxy)hydroxide or hydride phases.
1. Hall, D. S., Bock, C. & MacDougall, B. R. J. Electrochem. Soc. 160, F235, (2013).
2. Oshchepkov, A. G., Bonnefont, A., Parmon, V. N. & Savinova, E. R. Electrochimica Acta 269, 111, (2018)
3. Mauer, A. E., Kirk, D. W. & Thorpe, S. J. Electrochimica Acta 52, 3505, (2007).● Water-splitting for renewable hydrogen energy sources: a molecular level approach
Developing renewable routes to hydrogen, a sustainable fuel, is critical to achieving net-zero emissions.1 Photocatalytic devices for water-splitting integrate light harvesting, photogenerated charge separation, and catalysis into a single device and so offer a highly promising route to this end goal. However, key uncertainties remain over the kinetics underlying device function and how these kinetics depend upon materials and device design. There is, for example, significant controversy over exactly how an applied voltage or photoexcitation drives catalysis in kinetically challenging, multi-step reactions such as water splitting.2,3 Addressing these questions forms the main research question behind this project.
In this project you will focus on a range of inorganic catalysts for sustainable fuel synthesis. At ICL you will use time and potential resolved UV-Vis and NIR spectroelectrochemistry to determine the spectral fingerprint of charge carriers in catalysts and photabsorbers, as well as their populations and reaction kinetics, measured under operating conditions. This information will be complemented by operando resonance Raman spectroscopy at UCL, which will give direct chemical insight into the local structure and conformation of these charged species. The combination of these structural and kinetic analyses will enable molecular design principles to be established, allowing greater insight into the factors that determine photocatalytic material and device performance. In turn, this will further the development of a crucial low carbon technology.
1. Adv Energy Mater 11, 2003286 (2021). 2. Nat Rev Mater 1–20 (2021) doi:10.1038/s41578-021-00343-7 3. Nature 587, 408–413 (2020).● Multimodal diffraction-tomography of new cathode materials for Li- and Na ion batteries
To mitigate climate changes, wider adoption of electric transportation and electricity storage of renewable sources are urgently needed. Li ion batteries (LIBs) are the current battery of choice for these applications, but LIB cathodes use relatively expensive transition metals (TMs), e.g. Co, Ni, some of which have unethical issues, and have limited capacities (≤ 200 mAh g-1).
This project aims to design, synthesise and characterise new cathode materials, Li-rich Li1+xTM1-xOy for LIBs. The new cathode materials will contain multiple earth-abundant TMs, e.g. Mn, Fe, to replace the current expensive and scarce TMs while increasing battery capacities with the excess Li (≥ 300 mAh g-1). This project will also explore the equivalent Na-rich Na1+xTM1-xOy cathode materials for Na ion batteries (NIBs) because Na has higher abundancy than Li to widen materials choices.
Current research challenges of the Li1+xTM1-xOy materials are the low endurance (≤ 100 (dis)charge cycles). The supervisory team has a track record of battery materials research and developing novel multimodal characterisation techniques such as XRD-CT to understand degradation mechanisms [1,2]. This project will focus on the following research questions:
• Chemistry – cations: what is the optimal combination of TMs?
• Chemistry – anions: will anion doping such as Li1+xTM1-xOyF2-y prevent O loss and improve material stability through a combination of more covalent TM-O and more ionic TM-F bonds?
• Structure: what are the effects of the TM types and F doping on the crystal structure and material function?
• Design: what are the material design strategies of improving cycle stability, and can we translate the methodology to Na1+xTM1-xOyF2-y to also improve the capacity and stability of NIBs?
The developments will benefit the energy industry through more sustainable and improved energy storage performance.
 C. Huang et al. Advanced Science 2105723, 1-12 (2022)
 D. Matras et al. Journal of Power Sources 539, 231589 (2022)● Probing the factors controlling catalysts for green hydrogen production in water electrolysers
The purpose of this studentship is to use complementary characterisation methods to establish the factors controlling the activity of IrOx-based catalysts for O2 evolution and how they evolve with time.
The increased uptake of renewables is contingent on efficient means to store the energy. Polymer electrolyte membrane (PEM) electrolysers are ideal for this purpose; they split water to form hydrogen, an energy-dense fuel, and their relatively low operating temperature means that they can be started up and shut down quickly and their tolerance to varying electrical power, means they are ideal for coupling with intermittent renewables. The efficiency of these devices is governed by the rate of the oxygen evolution reaction (OER) at the anode. Currently only Ir-based oxides (IrOx) are able to drive this reaction at sufficient rates without excessive dissolution into the acidic electrolyte, but there remains an urgent need to improve their stability as even IrOx dissolves into the electrolyte at a low rate, which is accentuated by potential cycling. Moroever, the scarcity of Ir sets a limit to the long-term scalability of current PEM electrolysis technology without significant thrifting of the Ir loading in PEM systems.
We posit that we will be able to quantitatively describe the catalytic activity a function of experimentally determined binding energies of reactive intermediates, temperature and potential on a number of different catalysts supplied by Johnson Matthey. This would provide us with the ability to relate electrocatalyst kinetics directly to atomistic models of electrocatalysis. We will establish how the performance, structure and composition of the catalyst transforms upon extensive cycling. This will provide us with insight into how to improve the catalyst performance, with a view to decreasing Ir loading and improving the scalability of PEM electrolysis technologies.
1. Rao, R. R., Corby, S., Bucci, A., Garcia-Tecedor, M., Mesa, C. A., Rossmeisl, J., Gimenez, S., Lloret-Fillol, J., Stephens, I. E. L. & Durrant, J. R. Spectroelectrochemical Analysis of the Water Oxidation Mechanism on Doped Nickel Oxides (2022) J. Am. Chem. Soc. 144, 7622-7633.● Understanding the role of interfacial charge transfer states in charge photogeneration and recombination in solar energy conversion materials
Solar energy conversion in molecular electronic materials normally proceeds via photoinduced charge transfer across an interface between electron donating and accepting species. A critical question is how large the energetic driving energy needs to be to enable efficient charge separation and photocurrent generation, and hence what limits energy conversion efficiency. The aim of this project is to understand how the chemical structure and arrangement of the molecules controls the dynamics of charge separation and recombination, using a combined spectroscopic/modelling approach. The work focusses on the role of molecular vibrations in mediating the desired charge separation and the undesired recombination processes. The study will extend to the intriguing recent observation that charge pairs seem to be generated directly by light in some single-component molecular semiconductors without a donor: acceptor interface. Key research questions are:
(1) Under what conditions is efficient charge separation achieved with a small (or zero) driving energy?
(2) How does driving energy affect charge recombination in an operating device?
(3) Can the rates of charge separation and recombination be controlled via chemical design, targeting particular molecular vibrational modes?
This research accesses the exciting new femtosecond stimulated Raman spectroscopy capability enabled by UCL’s new Photon Science Hub. This technique, with other advanced vibrational and absorption spectroscopic techniques spanning femtosecond to millisecond timescales, will be employed to examine charge-carrier generation and recombination in donor: acceptor blends at marginal energy offsets and in single materials. With the aid of computational modelling of the vibrational data, we aim to identify the vibrational features associated with charge relaxation, separation, and recombination in the organic photovoltaic materials, and thereby analyse the effects on device performance.
The project will provide extensive insights into the fundamental processes controlling solar energy conversion in organic molecular materials and ultimately benefit photovoltaic, and other organic photonic, technology.● Near-Infrared Organic Semiconductor Materials for Optoelectronic Technologies
The current success of organic semiconductor technology is mainly driven by the development of organic light-emitting diodes (OLED), which are now routinely employed in display technologies. In the last decade, however, organic photovoltaics (OPV), leveraging the impressive improvement in device efficiency and stability, have gradually moved from a lab curiosity to a niche market. Their recent success has coincided with the rapid development of organic semiconductor materials, both electron donors and electron acceptors, with absorption covering the UV-Vis-NIR part of the light spectrum.1 Through strategic design adopting different chemical building blocks, these new materials afforded high absorption with tuneable energetics into the NIR region of the electromagnetic spectrum. This allowed the development of NIR organic photodetector (OPD), novel photoacoustic probes for bioimaging applications, and more recently enabled the development of quinoidal conjugated polymers with open-shell character with distinctive opto-electronic and magnetic properties.2,3 This synergistic project will build on the expertise of the Schroeder group at UCL in the synthesis of low bandgap organic semiconductors and the know-how of the Gasparini group at ICL in the fabrication and characterisation of high efficiency NIR OPD devices. The project will focus on the design and synthesis of the next generation of NIR absorbing organic semiconductors with an absorption band extending deep into the NIR (~ 1600 nm) and their initial incorporation into OPD devices for NIR photodetection. The aim of this project is (i) to develop and synthesise novel NIR absorbing organic semiconductors and (ii) to obtain OPD with photodetection in the NIR region and low dark current (Jd). The chemical design of organic semiconductors with relatively narrow and specific absorption spectra will allow OPDs to be explored for selective narrowband NIR photodetection, where effective-material choices for biomedical applications and process monitoring remain scarce. 1) Chem. Soc. Rev. 48, 1596–1625 (2019). 2) Adv. Mater. Technol. 3, 1800104 (2018). 3) Polym. Chem. 12, 1347-1361 (2021).● Defect Engineering for Future Energy Technologies
The widespread adoption of renewables hinges on efficiently converting and storing solar, wind and tidal energies at low-cost. Metal oxides are essential to this effort due to their applications as rechargeable battery electrodes, catalysts and in the production of solar fuels. Breakthroughs in our understanding of these functional materials will enable improvements in the efficiency, stability and cost of these technologies. A critical aspect of all such materials is their ability to carry charge. Numerous functional metal oxides pair trapped charge carriers and magnetic order at room temperature, with the latter thought to induce a severe barrier to electronic transport. However, previous experimental studies on the archetypal iron oxide, α-Fe2O3, hint that certain impurities (dopants) may unexpectedly allow modulation of this barrier. We hypothesise that these dilute defects cause local (atomic to nanoscale) disturbances in the long-range magnetic structure, allowing the spin barrier to be bypassed by charge carriers. Using a suite of transport measurements on doped single-crystals of α-Fe2O3 and complimentary single-crystal diffuse neutron scattering – unparalleled in revealing “hidden” defects and correlations – we will interrogate this phenomenon in detail. Universality will be evaluated using the related systems: nickel oxide (NiO, hole transport layer in emerging photovoltaics) and lanthanum ferrite (LaFeO3, fuel cell electrode). As the current understanding is widely accepted, the results of this research program would be disruptive. Thus, success will position the UK as a leader in new understanding central to next-generation energy applications.● High surface-area materials for solid oxide electrochemical cells
We have recently demonstrated that graphene oxide works as a sacrificial template, replicating its nano- and two-dimensionality in different metal oxides such as TiO2 and CeO2 . Resulting nanostructured metal oxides consist of <20 nm nanoparticles in a two-dimensional arrangement. These oxides obtain superior results in a wide range of catalytic applications due to their larger surface area. Moreover, their high-aspect ratio restricts their sintering at high temperatures, preserving higher surface areas. This approach is key to preparing materials for solid oxide cells for chemical-to-electrical and electrical-to-chemical energy conversion, where surface area is compromised by high operating temperatures . In this project the student will exploit graphene sacrificial templating and other novel approaches to develop novel doped ceria-based materials with high surface areas and controlled sintering behaviour. These materials will be extensively characterised covering their novel physico-chemical, structural and electrochemical properties for their application in solid oxide cells. These characterisation techniques will be combined to relate the properties of these materials to their best performance, guiding the design of more efficient solid oxide cells for chemical-to-electrical and electrical-to-chemical energy conversion.  Rood, S.; Ahmet, H.; Gomez-Ramon, A.; Torrente-Murciano, L.; Reina, T. R.; Eslava, S. Enhanced Ceria Nanoflakes using Graphene Oxide as a Sacrificial Template for CO Oxidation and Dry Reforming of Methane, Appl. Cat. B Environ. 2019, 242, 358–368.  S. J. Skinner, Recent advances in the understanding of the evolution of surfaces and interfaces in solid oxide cells, Adv. Mater. Inter. 6 1900580 2019● Solid Oxide Cell electrode performance optimisation via multiscale characterisation of grains and ions transport phenomena in the electrode grain boundaries / Using particle engineering to understand geometric effects on electrode performance of GDC SOCs
The main objective of this project is to increase the lifetime of solid oxide cells (SOCs)s by means of decreasing the rate of degradation and managing overpotential to increase cell efficiency. To achieve that, the effect of packing density and porosity of electrodes would be investigated. Varying particle sizes from micro to nano dimension would provide a variable packing density and porosity of the individual electrodes under investigation. This in turn will change the grain distribution and grain boundary framework. Multiscale characterisation techniques including SEM, ToF-SIMS, TEM and Atom Probe Tomography (ATP) would be utilised to understand the effect of particle size and porosity variation in SOC performance.
The performance of SOFC is governed by the oxygen reduction reaction (ORR) and the mechanism can be split into five elemental steps: i) dissociative adsorption of molecular oxygen at the catalyst surface, ii) surface diffusion of oxygen atoms from the catalyst surface to the triple phase boundary (TPB), iii) charge transfer to produce oxygen ions, iv) oxygen ions incorporation into the ionic conductive electrolyte and finally v) diffusion of ionized oxygen atoms in the bulk of the electrolyte. In this project, three-dimensional flow dynamics of oxygen ions and distribution of electrochemical reaction sites in SOFC cathode will be investigated through active sites imaging by oxygen isotope labelling combined with three-dimensional microstructure observation using the Isotopic Exchange Depth Profiling method followed by ex situ SIMS characterizations and FIB-SEM.
This work would include very close collaboration with Ceres, with at least 3 months of on-site hand-on-experience. Expert industry guidance will also be provided through best-practice-methodologies, design-of-experiment, and measurement diligence.● Combinatorial Analysis of Mixed Metal Coatings deposited via Inkjet Printing
The invention of a modern, efficient and effective characterisation technique for metal coatings would be world changing – the ability to link conductive coatings with their activity would lead the way to the next generation of printed electronics. This project will use advanced characterisation techniques to analyse the product of inkjet printed mixed metal films with compositional gradients. The synthesis will be carried out using combinational chemistry, which have previously been used in drug and materials discovery. Using combinatorial inkjet printing, we will synthesise libraries of unique mixed metal coatings (unique both in terms of composition, structure and layer thickness), and use high throughput advanced characterisation techniques in the search for improved performance in: final conductivity, resistance to oxidation and electromigration. As it stands, there are few reports of hybrid films combinging a range (or ‘hybrid’) of conductive metals, with none characterised for electronic application – coatings of which would find application in electrical circuitry and beyond.
We aim to develop new methods to advance combinatorial characterisation approaches in this area, which could then have potential to be applied in numerous other fields that also employ this high throughput approach to sample preparation. Since samples will have a gradient of composition and therefore properties we aim to develop an integrated system, where standard characterisation techniques such as XRD, XPS, etc can be collected in fast succession to the electronic characterisation (such as resistivity, testing resistance to oxidation and electromigration). This would yield data at unprecedented speeds, that will establish a feedback loop into the design of the next generation of electronics.
To increase our understanding of the links between conductive coating composition and activity, we will use advanced machine learning tools to characterise our experimental data. This provides a rapid route to investigate the effect of a ‘hybrid’ metal composition, which in turn can be applied to printed circuitry.● Advanced Electrodes for Redox Flow Batteries
Redox flow batteries are a promising grid-scale electricity storage solutions, however the microstructure and surface chemistry of their electrodes is currently highly unoptimised and the addition of catalysts in the electrodes is under-studied. In this project, electrospinning will be used to produce tailored and optimised electrodes for RFBs. Electrospinning is a process whereby polymers are drawn out into small fibres via high-voltage bias and factors such as fibre size, voids, alignment, conductivity and surface chemistry can be controlled by changing a variety of parameters. This will be combined with simultaneous electrospraying of metal and metal-oxide nanoparticles to produce catalytically active materials embedded in the structure. The effect of electrolyte additives such as Bi will be studied, particularly in relation to suppression of the hydrogen evolution reaction for vanadium RFBs, using advanced electrochemical mass spectrometry. A modelling aspect of the work can also be studied, investigating the mass flow characteristics of the varied microstructures produced in the project. The main tasks/questions probed will be:
1. Producing optimised electrospun electrodes
2. Investigating the role of microstructure in flow performance of the battery
3. Studying the catalytic properties of doped carbons or metal/metal oxide nanoparticles in the electrodes
4. Can additives supress the hydrogen evolution for vanadium flow batteries?
5. Developing an ultra-thin ‘printed circuit board’ flow battery architecture in conjunction with the industrial placement
If successful, the implementation of optimised electrodes could improve the performance and reduce the cost of RFB systems, making them more competitive with Li-ion in the stationary storage sector.● Simultaneous wide and small angle operando neutron total scattering to probe electrolyte ordering in supercapcitors
Achieving net-zero emissions targets demands new methods for the efficient storage of energy from renewable sources. Here supercapacitors show extraordinary promise, but despite rapid progress, substantial development are still necessary to overcome current limitations in energy and power density. Energy in supercapacitors is stored in the electrical double layer (EDL) of adsorbed ions on high surface area electrodes. However, the structure of EDL has never been measured in atomistic detail due to a lack of suitable methods.
Atomistically-resolved measurements of these systems can be uniquely investigated by the multi-lengthscale diffractometer NIMROD at the ISIS neutron source. The scattering, augmented using multiple isotopically-distinct datasets, is analysed with the aid of computer models, to revealed a full 3D structure in the liquid. NIMROD allows simultaneous analysis of Small-angle scattering, giving details of the pore structure and electrolyte composition in the electrodes, and analysis of the wide angle scattering reveals the solvation structure of the ions and the organisation of the ions and of hydrogen-containing solvents at the electrode surfaces that underpin charge storage.
This 4-year PhD project will develop an operando electrochemical cell for use on NIMROD to make for the first time detailed measurements of the EDL in supercapacitors as a function of charge. A further development will be the enhancement of simulation-based analysis tools specific to high surface area and charged materials. This detailed measurement of the structure of the EDL is only possible at NIMROD and the understanding gained will provide profound insights for those optimising supercapicators and beyond.● Resolving the multifunction demands of sodium battery electrodes
Battery electrodes must simultaneously satisfy a number of property constraints that are inherently in conflict. They must provide both electronic and ionic transport, with low loss; often the conduction paths are in two complementary phases that must both form connected networks. Sodium batteries are particularly promising for grid storage of renewable energy, due to their high capacity and the abundance of sodium. The storage mechanisms are however complex, especially in carbon anodes since direct intercalation is unfavourable, and in general due to the formation of solid-electrolyte-interphase (SEI) over the accessible surfaces. New electrode systems, based on well-defined nanomaterials, offer new prospects for ion intercalation and storage, that may improve the rate and lifetime of the final batteries. Systems passed on graphene, or graphene-related materials such as layered oxides or sulpides are particularly promising. Reassembly of these building block may produce electrode materials with optimized galleries for ion storage. However, nanomaterials create new surfaces that must be passivated with SEI. Detailed atomic resolution studies will visual the internal distribution of both the SEI and the charged ions, as a function of sodiation. Since ions can redistributed over time, cryo-facilities will allow the processes to be frozen at key points. The project will therefore identify the locus of charge storage in existing and potential future electrode materials, as a function of electrochemical performance, and identify the most efficient electrode conditioning strategies. It will contribute both fundamental understanding and methodology, as well as aiding the design of effective sodium battery systems for large scale energy storage.● Developing sustainable anode-free sodium batteries via interfacial chemistry
Conventional Li-ion battery is based on intercalation chemistry and not suitable for large-scale energy storage due to the energy density limit of intercalation chemistry. Also, the price spike and potential supply shortage Li and Co cause great concerns around materials sustainability.
Anode-free Na battery (ANB) is the next-generation energy storage technology that holds two advantages. First, ANB is based on earth-abundant Na and thus cost-effective and sustainable. Second, ANB has zero anode weight and can deliver a step-change improvement of energy density.
The key to high-performance ANBs is to achieve long-term stable Na plating (reduction of Na+ to Na metal) and striping (oxidisation of Na metal to Na+) at the anode side. There are two challenges to achieve stable Na plating/striping: Na dendrite growth on the anode current collector and unfavourable parasitic reactions during Na plating/stripping [Chemical Society Reviews, 10.1039/d0cs00033g]. They are closely connected to the interfacial chemistry and reactions at the Na/current collector/electrolyte interfaces [Energy & Environmental Science, 10.1039/D1EE01346G].
This project will investigate the interfaces to achieve high reversible capacity and long-term cycling stability of ANBs through two innovative approaches. First, architectural surface of the anode current collector will be created using carbon materials (another sustainable materials) to regulate Na+ flux and the interfacial chemistry of Na plating/stripping. Second, thin layers will be coated on the surface of the current collector and/or separator to act as an artificial solid-electrolyte interphase (SEI) that inhibits parasitic reactions. Potential synergy of the two approaches will also be explored. The outcome of the project will have great added value to other sustainable battery technologies such as Na-S and K-S batteries. ANBs are environmentally friendly, cost-effective, and scientifically innovative. This project will demonstrate a promising avenue to sustainable decarbonisation via facilitating scalable energy storage and deployment and therefore contribute to the net-zero emission target.● Characterisation of low activation shielding materials for fusion energy
Fusion energy could provide the UK with safe, baseload, and zero-carbon electricity. A major challenge to its implementation is the development of advanced shielding materials that can protect parts of the fusion reactor from radiation damage. Tungsten carbide ceramics are front-running candidate materials for this due to their excellent thermal, mechanical, and shielding properties, and they are available on industrial scale (e.g. in cutting tools). However, the current industrial formulations contain cobalt additives and other impurities that are unsuitable for fusion applications due to their tendency to form hazardous radioactive isotopes under irradiation.
The student will characterise in detail an alternative, low-activation ceramic material. A key project driver is to determine the impurity content with ultra-high precision using Atom Probe Tomography (some elements, e.g. Nb, must be controlled within the parts per billion range). The related scientific questions are:
• How are the impurities distributed within the microstructure, e.g. are they in solid solution, segregating to grain boundaries, or tied up in nanoscale precipitates?
• How does the microstructure of the material (e.g. grain size, W:C stoichiometry, and presence of second phases) relate to the processing conditions?
• How does the microstructure and impurity content in turn control the thermophysical and mechanical properties?
Answering these questions is critical if a low activation shielding material is to be implemented. To maximise project impact, it is supported by H. C. Starck Tungsten, an industrial supplier of tungsten carbide who will provide the samples; and by the UK’s fusion science laboratory (UKAEA) who will build their “STEP” reactor by 2040. The UKAEA link will be cemented through a parallel PhD project assessing the radiation damage tolerance of the material. Such a tri-partite arrangement between industry, national laboratory, and academia, serves to maximise the overall research impact.● Optimisation, Protection and Advanced Characterisation of Sn-based Photoelectrodes
Photoelectrochemical (PEC) water splitting has attracted considerable attention for converting solar energy into 'green hydrogen’. Metal oxides are potential photoelectrode candidates in PEC systems but the lack of a binary oxide with ideal properties has required investigation of more complex materials. The best known example is BiVO4, for which device efficiencies up to 8% have recently been demonstrated, however it's relatively large bandgap (2.4 eV) limits the theoretical solar-to-hydrogen (STH) efficiency to ∼9%.
Higher efficiencies require materials with smaller bandgaps and α-SnWO4 has attracted attention due to an indirect bandgap between ∼1.64–2.1 eV giving theoretical STH efficiencies beyond 20%.
Blackman has very recently developed (unpublished) a novel yet simple chemical vapour deposition (CVD) route to thin films of α-SnWO4. This will be further developed by the researcher, with properties such as stoichiometry, crystallinity and thickness optimised for PEC performance.
The photocurrent of α-SnWO4 has been found to be intrinsically linked to oxygen defect concentration (https://onlinelibrary.wiley.com/doi/full/10.1002/aesr.202100146). The researcher will have a 3-month placement (Year 2) with Dr Sathasivam (LSBU), an expert in defect properties of n-type oxides, exploring the influence of oxygen defects formed via controlled annealing on the transport properties of α-SnWO4.
Currently all reported α-SnWO4 photoelectrodes have shown photocorrosion after a few cyclic voltammetry scans, attributed to the oxidation of Sn2+ to Sn4+. Recent work has shown that a hole-conducting NiOx layer (produced using pulsed laser deposition; https://pubs.acs.org/doi/10.1021/acs.chemmater.8b03883) can protect the surface of α-SnWO4, drastically improving photocurrent and stability. Atomic layer deposition (ALD) is an ideal technique for protecting photoelectrodes (https://onlinelibrary.wiley.com/doi/10.1002/admi.202002100) and the researcher will work with Blackman to deposit both anti-corrosion layers and co-catalyst (e.g. CoOx) catalyst layers via ALD. Transient absorption spectroscopy (TAS), under the supervision of Kafizas, will be used to understand the influence of such layers at a fundamental level.● Functional Devices from 2D Borophene Oxide
Most 2D materials are notoriously difficult to create, requiring large shear forces to be applied to stacks of the materials to exfoliate to one layer in solution. One very recent exception is the 2019 discovery of so-called 2D borophene oxide (2D BO), dissolves as monolayers spontaneously in solvents , or melts into liquid crystals . The layered parent material is synthesised from simple oxidation and evaporation of potassium borohydride solution, forming long needle-like crystals of 2D covalent B2O3 layers, separated by layers of potassium ions (although recent measurements at UCL have shown surprising, unresolved long-range order). The individual 2D BO is electrically conductive and is thought to contain Lewis acid-base sites, opening the route to applications from transparent conductors for phone screens, to gas sensors, to heterogeneous catalysis.
Given the cutting-edge nature of 2D-BO, it is virtually unexplored, providing great opportunity for discovery. In this project, the student will study and improve the synthesis of 2D BO, and aim to integrate it into the first generation of useful devices. Firstly, we will control its properties through controlled synthesis (e.g. doping) and developing organo-functionalisation reactions, and secondly through controlled assembly into porous architectures for high-efficiency catalysis/gas sensing.
 Kambe, JACS, 2019, 141, 12984-12988. Kambe, Nat Commun., 2022, 13, 1037.
Biomaterials and Regenerative Medicine● Determining the micro-biomechanical signature of lung disease: correlated micromechanical and advanced-optical mapping of lung tissue
The mechanical properties of biological tissues play a key role in diseases from cancer to fibrosis, and can impact the response to treatments from both conventional drugs and immunotherapies. Critically, we are learning that mechanical properties vary rapidly within tissues, hence a micro-mechanical perspective down to scales < 100 m is essential. There is thus a need for new characterization approaches in tissue micromechanics, building on concepts from conventional Materials Science. A vital target for mechanomedicine is lung disease, which excluding the COVID-19 pandemic accounts for c. 20% of all deaths in the UK. Mostly this comprises fibrotic diseases such as COPD, IPF and chronic obstructive pulmonary disease (COPD) and induced pulmonary fibrosis (IPF), with now also unfortunately the potential for new long-term conditions caused by COVID-19. This project will use atomic force microscopy indentation to generate a multiscale mechanical map of lung tissue down to c. 10 m lengthscales. Using both healthy and fibrotic-disease samples, we will determine the micromechanical signature of fibrosis. Importantly, these micromechanical measurements will be correlated to optical images of the same tissues. These will include conventional biomedical histology images, as well as confocal imaging, and advanced non-linear optical methods that reveal fiber-alignment in tissues (second-harmonic generation). The target is for correlated optical and micromechanical imaging to enable micromechanical properties to be inferred directly from optical images. This would empower high-throughput micromechanical tissue analysis, with impact on clinical science.● Alveolar-on-a-chip cellular model to better understand alveolar regeneration during ventilation injury
The lung’s first (air-liquid) barrier is a delicate membranous fatty film, lung surfactant, containing defence proteins, which maintains normal lung function. It is the first barrier against inhaled toxins and microorganisms and the most permeable interface of the human body exposed to the environment. Below the surfactant is the cellular alveolar epithelium which enables gas exchange and secretes lung surfactant. Alveolar epithelium is closely attached to the blood vessel wall capillary endothelial cell by a shared basement membrane. Together, these barriers form the respiratory barrier (RB), an active immune defence barrier, not just a passive scaffold. Compromised integrity and permeability of the RB can lead to generation of factors that trigger inflammation and mediators that, together with some of the particles, can enter the blood and affect the whole body. Furthermore, sustained disruption of the RB can worsen existing disease as alveolar regeneration is normally a slow process that still requires full characterisation. It is not known how the structure and function of the fragile RB and communication (crosstalk) between surfactant and the cells work to provide and maintain RB integrity and selective permeability to protect us, or how injury disrupts this. A major hindrance to investigate communication between the components of the RB is the lack of representative human models that include cell and tissue processes to reveal, in real time, which cellular-molecular mechanisms are involved. Hence, the major aim of our proposal is to develop a unique piece of analytical equipment and establish a dynamic fully integrated 4D alveolus-on-a-chip (AOC) microfluidic model of the RB coupled to an advanced imaging platform, capable of measuring and resolving live-cell events in real-time at the nanoscale. At the same time to monitor factors involved in functional integrity and permeability of the RB.
The AOC system will be integrated into an advanced imaging platform to resolve live-cell events across scales. We will controllably expose RB to increased exposure of different duration of toxicants to resemble damage and monitor how the RB regenerates. We will employ different quantitative imaging approaches to characterise the process focusing on fluorescently labelled lipids and proteins, to reveal changes in cellular stiffness and REDOX state employing genetically modified biosensors to target specific organelles. Quantitative Image correlation spectroscopy imaging methods will draw interaction, oligomerisation, membrane molecular stiffness and diffusion maps. Cytokine and other metabolites analysis will deploy adaptive mechanisms and phenotypes of the new regerated microenvironments.● Deciphering engineering rules underpinning lipid-based nanotherapeutics
The modern pharmaceutical industry is undergoing a revolution driven by the emergence of biological nanomaterials as a therapeutic modality. In part, this is due to the phenomenal success of mRNA covid vaccines, which are underpinned by lipid-based nanoparticles capable of delivering genetic material to cells. Biological and bio-inspired nanoparticles hold immense promise in various biomedical spheres: from gene-editing and CAR T-Cell therapies, to anti-cancer therapies and in treating neurodegenerative conditions.
There exists however, an inconvenient truth: existing lipid nanoparticles used in medicine are surprisingly poorly characterised with respect to their phase behaviours, internal architecture, and morphology. The role of size, curvature, lipid composition, phase, surface functionalisation and mechanical properties is likewise largely unknown. This is proving to be a bottleneck which is impeding the rational design and assembly of new and improved delivery nanomaterials, with extended functionalities and improved efficacy. Form and function are intertwined and our lack of understanding and control of key nanoparticle behaviour means the full potential of such systems is yet to be unlocked.
This oversight, however, presents a tremendous opportunity. In this project the student will use state-of-art characterisation techniques to decipher how the physical, chemical, and morphological features of lipid nanoparticles relate to biomedical performance. The student will use our bespoke microfluidic assembly-line technologies to assemble a diverse library of self-assembled therapeutic nanomaterials. Chemical features of nanoparticles will be characterised using a suite of state-of-the-art techniques, and their relation to performance assessed. An iterative design-build-characterise-learn cycle will be used to constitute ever more sophisticated functional lipid nanoparticles using rational design principles. This will then allow us to assemble an engineering rulebook for the design and construction of nanotherapeutics, which has game-changing implications in industry, biomedicine and beyond.
1. Hou, Xucheng, et al. "Lipid nanoparticles for mRNA delivery." Nature Reviews Materials 6.12 (2021): 1078-1094.
2. Pilkington CP et al. “A microfluidic platform for the controlled synthesis of higher-order liquid crystalline nanoparticles. ChemRxiv 2022. DOI: 10.26434/chemrxiv-2022-xwq9n-v2● Imaging a potential mechanistic link between air pollution exposure and Alzheimer's disease
The World Health Organisation estimates that exposure to ambient air pollution results in 4.2 million deaths/year. Air pollution particulate matter (PM) is a cocktail of soot aggregate, secondary organic aerosols, nitrates, sulphates, dust, bioaerosols and different redox active trace transition metals. PM from vehicle emissions and abrasive wear contain oxidising, neurotoxic metals such as Fe, Cu and other toxic metals that can lead to increased production of damaging reactive oxygen species (ROS), as well as genotoxicity. There is mounting evidence for a causal link between air pollution exposure and neurodegenerative diseases. PM including Magnetite (Fe3O4) nanoparticles have been found in brains retrieved from adult and child human subjects that lived in extremely polluted cities [10.1177/0192623307313011; 10.1073/pnas.1605941113], together with features of early-stage neurodegenerative Alzheimer’s Disease (AD) including Tau cortical tangles, amyloid-β (Aβ) plaques and abnormal neurovascular units. Furthermore, mice that are exposed to polluted air showed an increased level of Aβ plaques and brain inflammation. Although a causal link between metal-rich pollution PM and neurodegeneration in AD has been made, there is no direct experimental evidence for a link between AD and air pollution exposure or the cellular mechanisms involved. The goal of this project is to directly image the effect of air pollution exposure on cultured cells, in the presence and absence of Aβ. Some redox-active transition metals that are present in PM, notably Fe and Cu, are also prevalent endogenously in the brains of patients with AD, can generate ROS and cause aggregation of Aβ that was shown to play a central role in the pathogenesis of AD. We will directly correlate the presence of PM (via EM) with Aβ and degree of its aggregation (confocal microscopy and antibody-based structural characterisation) and subcellular damage (EM+ML) and test whether PM and Aβ together enhance neurotoxicity.
Engineering Materials● Advances in the understanding and use of metal organics in cold forming processes
The cold forming of metals or metal alloys, such as steel, is a widely used process for the forming of the metal into the desired part shape/size. In order to aid this process a combination of a metal organic/metal inorganic conversion layer (often iron oxalate based) and a lubricant are applied to the metal before it undergoes any cold forming operations. Feasibility studies and field trials attempting to apply this system of metal organic and lubricant layers together in one single treatment step have shown a quite unpredictable performance to date, which can lead to an unstable process. There is currently a key knowledge gap regarding make-up of the metal organic layer, both in terms of the surface complex species formed as well as the macroscopic properties of the layer itself. This project will focus upon building an understanding of these factors, leading to improvements in the deposition process towards a more reliable single step deposition of both the metal organic and lubricant layers.● Advanced hybrid materials from tailor-made modified lignins
Lignin is the main component of biomass from plants. It is the second most abundant terrestrial biopolymer following cellulose. Yet, it remains the least utilized biopolymer. The complexity of the lignin structure, which also depends on how lignin is extracted from plant biomass, poses challenges to the utilization of lignin in the chemical and materials industry. In this project, we are looking to develop new strategies to selectively introduce or remove chemical functionalities to Kraft lignin (a side product from pulp and paper production), thus rationally modifying the Kraft lignin properties. Environmentally friendly strategies based on solid-state chemical synthesis are highly desirable in the chemical modification of Kraft lignins (e.g., mechanochemical synthesis). In this endeavor, we want to make Kraft lignin more compatible with synthetic polymers to produce materials suitable for high-end uses. The potential impact of this project will reflect a better understanding of properties-structure relationships that underpin the rational development of high-performance lignin-hybrid materials.● New High Strength Titanium Alloys for Jet Engines
Following on from previous work on dwell fatigue in Ti-6Al-4V and on RR11, we now identify an opportunity to introduce an alloy that is immune to dwell fatigue and has higher usable fatigue strength, whilst not having an overly strong yield strength, limited ductility and processability. This is achieved by nanoscale microstructure control; generating fine scale secondary alpha and limiting the Al content to avoid alpha2-Ti3Al formation, keeping the alloy solvus low. This leads to questions around partitioning at the nanoscale, sympathetic and autocatalytic nanoscale alpha plate nucleation (in 3D), and the avoidance of slip band formation. These are technical areas well suited to 4DSTEM examination and development, to STEM-EDX and EFTEM, and to atom probe analysis (e.g. Worsnop et al, Nature Comms, 2022; Xu et al, Nature Commun 2020; Joseph et al, Acta Mater., 2022).● Imaging 1D and 2D Nanomaterials in Solution Through Advanced Liquid TEM
High aspect ratio nanomaterials such as graphene, phosphorene nanoribbons, and transition metal dichalcogenides underpin a wide array of next generation devices from transistors to solar cells to high strength composites. The scalable synthesis, modification, and assembly of these 1D/2D nanomaterials is commonly undertaken through liquid phase exfoliation (LPE) either through shear-dispersion or spontaneous dissolution. To characterise LPE nanomaterials with atomic precision, we currently remove the liquid to give the solid species for standard materials characterisation approaches (TEM, AFM, STM, etc). Unfortunately, the opportunity to unambiguously study the nature of the species in the liquid dispersion/solution is lost through this approach. For example, 2D C6N9H3 sheets are thought to restack upon drying, but may be simply dispersed as multilayers [A]. Here we will use Liquid-Phase Transmission Electron Microscopy (LP-TEM) to study 1/2D nanomaterials in liquids. Previously, imaging of few-atom thick species was impossible due to wide LP-TEM holder pathlengths and the low contrast from such thin materials. However, recent developments in LP-TEM nanochannel-chip holders have opened the route to potentially imaging these atomically-thin species directly in the liquid-dispersed state. By exploiting these cutting-edge technologies, we will unambiguously monitor their shape, distribution, and atomic structure. A range of nanomaterials will be studied, from easier-to-measure heavy-atom-containing species (e.g. 2D-WS2/MXenes) [B] to challenging light-element species (e.g. graphene/CNTs/gCN).
Beyond, real-time atomistic imaging will allow quantification of dynamic behaviours. 1D/2D nanomaterials are highly flexible will bend/ripple from Brownian effects when dispersed, but state-of-the-art photon-based imaging is limited to ~100 nm resolution and restricted to fluorescing nanomaterials [C], while here we will provide nanometre resolution for all 1D/2D nanomaterials. Understanding these dynamic behaviours will provide direct mechanical information on the nanomaterials and insight into the nanomaterial-solvent interactions. [A] Miller, Nano Lett (2017), 17, 5891; [B] Sokolikova, Nat Commun (2019), 712; [C] Tang, Soft Matter (2022), 18, 5509● In-service catastrophic failure: or controlling the grain boundary network evolution
Hardmetal tools are a key for our production industries relying on cutting, milling, drilling, and turning. Cemented carbides (WC-Co) are one of the most prominent powder metallurgy processed materials use for cutting tool applications. This is due to a combination of excellent hardness/wear resistance and toughness with low cost compared to alternatives such as polycrystalline diamond. During service (e.g. in machining) , however, the composite structure is subjected to a combination of high mechanical and thermal loads, where hard carbide particles are joint by soft cobalt binder, deforms until excessive wear and fracture reduce the performance and lifetime. Crack paths in WC-Co predominantly follow WC/WC and WC/Co grain and phase boundaries at low cobalt concentrations1. While the WC grain boundary character, the grain boundary network, is characterised for differently doped cemented carbides2–5, knowledge of how the grain boundary network evolves during service and ultimately allows for crack formation along grain boundaries is absent.
To understand the grain boundary network evolution, we have recently developed an analysis workflow verified in a case study on Mg2SiO4. During torsional deformation the GB network interacted with dislocations, leading to overall material weakening6. We will follow this study to understand the evolution of the GB network with increasing deformation.
1. Emmanuel, M. et al. Jom 73, 1589–1596 (2021).
2. Kim, C.S., Massa, T.R. & Rohrer, G.S. J. Am. Ceram. Soc. 91, 996–1001 (2008).
3. Yin, C. et al. Materials (Basel). 14, (2021).
4. Yuan, X., Rohrer, G.S., Song, X., Chien, H. & Li, J. Int. J. Refract. Met. Hard Mater. 44, 7–11 (2014).
5. Kim, C.-S. & Rohrer, G.S. Interface Sci. 12, 19–27 (2004).
6. Ferreira, F., Hansen, L.N. & Marquardt, K. J. Geophys. Res. Solid Earth 126, 1–20 (2021).● Extreme ceramics: controlling properties via crystal shapes engineering by pre-melting
The surface of most crystals that build up ceramics are very sensitive to interaction with a melt phase and different frugalities and or impurities related to processing. Often the control of these parameters are used to introduce wetting liquids that allow for better sintering properties. The overall effect of these wetting liquids is well established, their effect on crystal faceting, crystal shape and the localized effects of the grain boundary chemistry are not understood.
In this project we aim to experimentally evolve different microstructures and quantitatively assess their characteristics, including the grain boundary plane distribution. Recent developments in quantitative microscopy where EBSD and TEM are spatially correlated allow the determination of (a) interfacial compositions and the distribution of very small melt phases (b) interfacial areas of different crystallographic surfaces, which are inversely related to the magnitudes of interfacial energies (e.g. The quantified textural changes will be described using adapted existing grain growth laws and equilibrium melt distribution models.● Spinning sustainable carbon fibres for the energy transition
Carbon fibres are widely applied, including to reduce weight, improve fuel efficiency, and extend vehicle range. Whilst contributing to sustainability in use, they are usually made from petrochemicals. This project develops a new approach to spinning sustainably-sourced carbon fibres from lignin (derived from wood). Two patent applications from Imperial (GB applications 2208061.8 and 2208067.5) underpin the incorporation of exceptionally high proportions (>90%) of industrial lignin, and conversion to higher performance fibres with high yield. Demonstrated at single fibre scale, the project will develop the spinning process to create more uniform, more aligned fibres, with improved properties.
The key will be to monitor the complex behaviour of the nanotube/lignin hybrids, in situ, during spinning, through carbonisation, and subsequent graphitisation. Intimate interactions between lignin and nanotubes enable spinning by modifying rheology, increase yield during carbonisation, template improved graphiticity at lower temperatures, and provide direct reinforcement. These effects will be evidenced and understood by detailed characterisation studies and optimised by specially grafting lignins with different chemistries. Shaffer/Launois/Paineau have recently shown that Ge-doped imogolite nanotubes provide an excellent model system for carbon nanotubes, offering similar phenomenology but much better opportunities for in situ characterisation during spinning, exploiting their monodispersity, scattering strength, and optical birefringence (doi.org/10.1021/acsami.1c00971). The project offers the opportunity to develop a new class of carbon fibres that could be developed together with commercial partners. The DoE has set targets for a low-cost, sustainable alternative to petroleum derived carbon fibre at 1.7 GPa strength, 170 GPa stiffness and <£10/kg cost.(doi.org/10.1016/j.carbpol.2020.116918) The proposed technology has the potential to reach these targets by providing a robust system using low-cost renewable lignin feedstocks (£0.3-0.5/kg), as well as low cost and inherently recyclable ionic liquid (£1/kg). There is enormous current interest in bioderived carbon fibres, including from potential commercial partners, once these key performance metrics are met.● How do Carbon Atoms act during Carbon Dioxide Reduction?
In a world facing a global warming crisis due to CO2 emissions, electrochemical reduction of carbon dioxide presents itself as a promising contribution to restoring balance in CO2 levels, and for producing high energy density fuels 1. However, the high cost of CO2 reduction with respect to the energy content in the products it forms makes it economically unfeasible, especially considering its major dependence on Cu-based catalysts, leaving a vast realm of possibilities in other metallic systems. Conventional characterisation techniques cannot resolve some of the important processes happening during the reaction, mainly due to the lack of resolution, and the volatile nature of the reactants and products, leaving our perception of CO2 reduction limited. In this project, we envision the use of cryo-atom probe tomography (APT)2 for the first time since its recent development to “see” the C atoms at the catalytic interfaces during the reaction at the atomic scale. We will be answering unresolved questions regarding the possibility of using other metals such as Ni for CO2 reduction, by tuning its chemical properties through alloy design, electrodeposition and dealloying procedures. Insights from model cryo-APT studies on pure Ni and Cu, in correlation with x-ray absorption studies, will help us design nanoporous Ni-Cu which will be fabricated through selective dissolution (dealloying), and electrodeposition. Structural and chemical characterisation of the developed nanoporous materials will be done using correlative APT and CT techniques.
1. Nitopi, S. et al. Progress and Perspectives of Electrochemical CO2 Reduction on Copper in Aqueous Electrolyte. Chem. Rev. 119, 7610–7672 (2019).
2. El-Zoka, A. A. et al. Enabling near-atomic–scale analysis of frozen water. Sci. Adv. 6, eabd6324 (2020).
Electronic and Magnetic Materials● Harnessing the potential of metal-halide perovskites: photovoltaics and beyond
Metal-halide perovskite materials have had a transformative impact on the research landscape since they were first demonstrated just over a decade ago. Outstanding improvements in the performance of a variety of electro-optical devices have been demonstrated through structural, compositional, and morphological enhancements of active layers and device interfaces. Compositional variation can be readily achieved through substitutional doping, the objective of which is usually modification of electronic properties i.e. bandgap, but in parallel can influence other structural parameters of intertest, including degree of crystallinity, grain size, orientation, roughness and density. In the MM and NG labs a suite of perovskite compositions, additives and interlayers have been developed resulting in high performing devices across a wide technology space, including photovoltaics, light-emitting diodes, photodetectors, and sensors. [1-4] As is the case often in a university setting these advances have been proven only on the small-scale – to exemplify this a typical 1cm2 substrate may contain up-to 8 devices to be prototyped and tested. To deliver their full potential across these technology realms it is necessary to take the small-scale control demonstrated and expand to significantly larger areas using high-throughput processes such as printing. This presents numerous challenges that will lie at the heart of this project, including i) achieving large-area compositional and microstructural homogeneity, ii) implementing solvents with low/no toxicity, iii) development of process compatible with rigid (current) and flexible (future) substrates, and critically iv) multi-lengthscale correlation of structural, electrical, optical and performance characteristics. The suite of tools available across Imperial College will be key to probing and elucidating local characteristics i.e. nm to mm. The time-resolved microwave conductivity probes developed by JL and available in their lab will allow the spatial mapping of electronic properties to be rapidly obtained with an initial target of demonstration using 100cm2 substrates.● Remote control of magnetic nanoparticles assembly
Magnetic nanoparticles have recently emerged as a new revolutionary tool with applications in molecular biology, medicine, cancer, biosensing and many others. What makes them especially powerful is the ability to remotely manipulate their state and position using external magnetic fields. This has recently been used to apply and measure mechanical forces inside individual living cells, which opened new ways to understand mechanisms of genome inheritance and potentially related medical disorders [1,2].
However, there is an inherent challenge related to the nanoparticle size. Particles that are small enough to penetrate cells and diffuse inside them are also too small to generate significant mechanical force. On the other hand, large particles that can exert sufficient forces are too big to be freely delivered to their targets inside cells or tissues.
In this PhD project we will circumvent this limitation by developing tools to direct assembly of magnetic nanoparticles into probes whose size can be remotely controlled. We will generate proteins whose affinities can be adjusted and coat them on magnetic nanoparticles. To gain more insight into the molecular requirements for assembly, we will use computer simulations that will predict how affinities of the protein coats control the average size, distribution, and shape of nanoparticles assemblies. We will create optimized nanoparticles, and characterize their dynamics of assembly/reassembly, the size and shape distributions of the obtained assemblies as well as magnetic properties of their assemblies. Developed technology will allow applying targeted forces inside cells, tissues and organisms as well as steering magnetic particle delivery. In future, these studies will help to reveal fundamental mechanisms that account for broad range of mechanical cellular functions from cell growth, movement to cell division. Technology developed in this project will have strong impact across fields.
1. C. Garzon-Coral, H. A. Fantana, J. Howard, A force-generating machinery maintains the spindle at the cell center during mitosis. Science 352, 1124-1127 (2016). 2. V. I. P. Keizer et al., Live-cell micromanipulation of a genomic locus reveals interphase chromatin mechanics. Science 377, 489-495 (2022).● Electronics based on disordered quantum wells
When electronic materials are formed with dimensions comparable to the atomic length scale, exotic properties emerge, including quantum tunnelling, low-dimensional transport, and sub-band quantization. These phenomena could one day be exploited to enable electronic devices with previously unimaginable capabilities.
A problem faced by such quantum well systems is that they normally require very particular conditions to be fabricated. Typically, growth of quantum wells requires expensive techniques such as molecular beam epitaxy (MBE). Quantum wells are therefore generally considered more useful for studying fundamental physical phenomena than as a commercial technology.
The objective of this project will be to develop quantum wells using structurally disordered semiconductors. These structures will primarily be grown using scalable solution-based techniques such as spin-coating, and therefore will lack the long-range order observed in materials grown using MBE. The student will design, fabricate, and characterise electronic devices based on ultra-thin films of disordered semiconductors. The student will generate knowledge on the challenges faced when introducing structural disorder into quantum wells, the unique electronic properties these structures possess, and how they could be exploited in electronic devices.
The student will need to understand both the structural and electronic properties of these structures. To achieve this, they will use a combination of electronic probes such as device measurements and contactless microwave spectroscopy, in addition to structural techniques such as transmission electron microscopy. In order to carry out unique experiments, the student will also need to develop their own instrumentation and characterisation tools.
If successful, this work will open the door to mass-producible electronic devices based on quantum wells and enable applications in energy generation and storage.
Labram, J.G., et. al.., “Signatures of Quantized Energy States in Solution-Processed Ultrathin Layers of Metal-Oxide Semiconductors and Their Devices”, Advanced Functional Materials, 25, 1727 (2015).● Understanding sustainable polymers: using nanomaterials to characterise self-healing
Polymethacrylates constitute 8% of plastic materials in EU and are popular in industry, due to their wide-ranging application as acrylic glass. Ensuring their sustainability and recyclability is therefore of the utmost importance to avoid contributing to ever-growing plastic waste. Self-healing plays a large role in providing longevity to these materials, particularly in screen and display technologies, where irreversible scratching leads to disposal. Polymethacrylates have recently demonstrated self-healing properties for the first time.[Science, 2018] Though thought to be based on interchain interactions, the mechanisms responsible are poorly understood and methods to probe them are limited. Magnetic nanomaterials could offer a solution. Due to their (magnetically-driven) dipolar interactions with water, even minute changes in surrounding hydrodynamics result in dramatic changes in their magnetic (relaxation) behaviour. These properties have previously been used to understand medical contrast agents and surface-water interactions. Herein, we aim to harness this characterisation technique to probe, for the first time, the dynamic behaviour of self-healing polymers. Through the combination of polymers and magnetic nanoparticles, characterisation of the magnetic (relaxation) of water protons during the healing process will provide insights into this mechanism. Such insights will have high impact in the development of polylmethacrylates for sustainable applications in industry and for commercial use.● Polarisation patterns in nanoscale ferroelectrics for low-power nano-electronics
By analogy with ferromagnets that have a spontaneous magnetisation, ferroelectrics are materials with a spontaneous electrical polarization that can be switched by an applied electric field. While ferroelectrics already have many well-established applications that exploit their superior piezoelectric, pyroelectric and dielectric properties, they are also actively studied as leading materials for the memory, transistors and memristive components in next generation low-power electronics and neuromorphic computing. These applications require ferroelectrics with dimensions at the nanoscale, where their properties change dramatically.
At nanoscale, ferroelectrics exhibit complex exotic polarisation patterns with interesting topologies. Nanoscale ferroelectric domains are extremely responsive to external stimuli, leading to dramatic enhancements in dielectric properties. Perhaps even more excitingly, the domains walls, which locally break the symmetry of the bulk material, can host properties that are distinct from those of the domains that they separate, allowing them to act as functional entities in their own right. Our ability to create and destroy domains at will with electric fields makes them ideal for reconfigurable electronics, overturning the classic idea that our electronic circuits need to consist of fixed hardware components and leading to the emergence of the field of domain wall nanoelectronics.
However, to harness their true potential there is a great deal of fundamental physics yet to uncover. As domain walls are usually only a few atoms thick and highly dynamic, it is essential to characterise them at the relevant spatial and temporal scale.
This project will aim to investigate the physics of complex nanoscale polarisation patterns in ferroelectric thin films and superlattices, including their structure, response to applied stimuli and their effect on the functional properties of these materials.● Superspintronic memory and logic devices
In the last decade, superspintronics – the superconducting analogue of spin-based electronics (spintronics), emerged as an exciting research field. It represents a striking combination of spin-sensitive phenomena in solid state devices with dissipationless quantum coherence of superconductivity allowing the design of ultra-low power spin-based logic and memory devices with unique functionalities not possible with spintronics alone1,2. However, despite a decade-long intense activity such devices remain elusive.
A major reason is the lack of a systematic materials-based exploration of the structure-property relationship in superconductor/ferromagnet (S/F) hybrids such as, film crystallinity, interface transparency between S and F, and magnetism at the nanoscale.
Here, we will take the first steps towards realizing this goal. We will start with a systematic thin-film growth study of the dependence of superconducting properties of S/F hybrids by tuning F layer properties like film crystallinity, layer thicknesses, composition. Beyond traditional 3d elemental and alloy ferromagnets, we will also investigate rare-earth ferromagnets and their alloys (Ho, Gd, Dy). Using X-ray diffraction, reflectivity and spectroscopy, together with scanning probe microscopy (atomic and magnetic), we will build a comprehensive structure-property relationship in these systems.
Based on the optimised systems identified in the first part, we will nanofabricate a superconducting magnetic memory and logic-type device where the magnetic state encodes the information, and the superconducting part is used for reading and logic processing. An example is a Josephson junction with a spin valve barrier incorporated in a SQUID circuit. Here, a key step will be to use PhotoElectron Emission Microscopy at Diamond to understand the role of the micromagnetic structure in controlling the device response in the superconducting state.
Through this highly interdisciplinary project, the student will gain a comprehensive view of a range of advanced characterisation techniques unified by a common aim: engineering functional materials for ultra-low energy information technology devices.
1 Niladri Banerjee Physics World 32 (4) 31 (2019)
2 J Linder and J. W. A. Robinson Nature Physics 11 307-315 (2015)● Bespoke nanostructures for physical machine-learning hardware
The ballooning energy cost of computation is unsustainable, 20% of global energy forecast for IT by 2030. A key problem is that ten times more energy is expended shuttling information between components as in the computation itself (von Neumann bottleneck). A solution is collocating data storage and logic processing functions in the same device. This is brain-like or ‘neuromorphic’ computing. Software machine learning algorithms have multiple ‘hidden layers’ with unknown state, and weights trained to achieve best results. The concept is to replace the hidden layers with a physical reservoir, which does some of the work, and simplifies the computation, enabling more efficient machine learning hardware. Reservoir computing is particularly suitable for machine learning algorithms using dynamical (physical and software) systems that have non-linear response functions with some memory effects.
The Imperial and UCL supervisors have identified an array of nano-magnets (so-called artificial spin ice system) which has excellent physical memory characteristics for reservoir computation, including strong non-linearity and complexity and a controllably fading memory. This project will explore enhancement of the arrays’ physical memory characteristics and development of reservoir computation protocols.
Certain ferromagnetic nanoisland dimensions are bistable as either uniformly magnetized macrospins or as vortices, with a nonlinear coupling that mimics how our brains work. The latest findings can be found here (J. Gartside et al, Nature Nanotechnology 17, 460 (2022)).
Objectives: (1) correlate physical properties with reservoir computer performance by researching task agnostic metrics (2) test which nanostructures yield desired physical characteristics? (3) benchmark performance against chosen metrics (4) compare to different computational architectures.
Instrumentation & Technique Development● Chiral materials for optical, spintronic and quantum technologies
The rapid development of quantum technologies prompts the need for low-cost, sustainable and easy-to-process materials for quantum information purposes. In the pursuit of suitable candidates, it is critical to identify materials in which it is possible to transduce information to and from photons and electrons. Photons are particularly promising carriers of quantum information: they propagate fast, can be easily manipulated and do not interact with their local environment. The relevant degrees of freedom are the spin angular momentum states, which correspond to left- and right-handed circular polarisation. As a result, circular dichroic light-based quantum information processing relies on chiral light-matter interactions. This project will involve the fabrication and characterisation of novel materials systems based on chiral molecules and crystals. Chiral materials offer opportunities for the manipulation and read-out of electron and photon spin at room temperature. To harness the unique properties of chiral functional materials in next-generation technologies, it is crucial we uncover the origins of these spin-selective effects, and advance our ability to amplify chiral light-matter interactions through molecular self-assembly or incorporation with sophisticated photonic platforms. This project will use advanced instrumentation to characterise the magneto- and electro-optical properties of chiral materials systems. Their functional properties will be correlated with molecular/crystalline structure to inform the design of next-generation quantum materials and devices.● Battery Materials investigated by Atomic-scale Cryogenic Microscopy Characterisation
Improving the lifetime and performance of energy storage devices is key to a green-energy society. The interface of the electrolyte and electrode plays the most crucial role in batteries and capacitors. However due to the liquid phase of the electrolyte and the volatile nature of Li, characterising this region is challenging. Cryogenic sample preparation and microscopy analysis exploited for biological research has more recently been used for battery characterisation. The cryogenic vacuum conditions allows one to have an undistorted view of the resulting electrochemical reactions at these very complex interfaces. In this project we will investigate new compositions of nanomaterials and deposition methods for the next generation energy storage. There is a vast field of unexplored fundamental questions to be addressed for these energy materials that is only possible now with the development for cryogenic microscopy instrumentation and direct electron detectors for damage free imaging and spectroscopy. This project will aim to investigate:
• The relationship between the electrode-electrolyte interface and the performance of lithium-ion batteries.
• The complex structure of the solid-liquid interface at the atomic-scale, with an emphasis on probing the light and volatile element such as Li and H.
• Changes in chemical bonding within the interfaces.
The student will be integrated into the new EPSRC UK national centre for cryogenic microscopy facility at Imperial College London (https://www.imperial.ac.uk/centre-for-cryomicroscopy/). The unique facility allows for sample transfer, under controlled atmosphere and at cryogenic temperature, between a high-end aberration-corrected transmission electron microscope and an atom probe, allowing for structural and compositional imaging of materials with an unprecedented precision. The student will also have access and support for data processing and simulations from the Imperial-X, the new centre for artificial intelligence, data science and digital technologies (https://ix.imperial.ac.uk/)● A new spectroelectrochemical method to characterise redox flow reactions in batteries and biocatalysts
Unpaired electrons have an impact on our society on many levels, e.g. in IT/communication (the modern computer) and in fundamentally understanding enzymes underpinning disease or bioinspired technology. We will take advances in the field of quantum technologies and electrochemistry and apply them to electron paramagnetic resonance (EPR) to enable in operando characterisation of redox flow reactions. Key to this is the characterisation of advanced materials as solid supports.
Electrochemical EPR is currently limited by the desire to use highly ionically-conductive solutions for electrochemical purposes with a preference for low relative permittivity materials for EPR, leading to a conflict in requirements. We demonstrated the first direct potential control of redox centres in molecules through film-electrochemical EPR (FE-EPR), achieved by anchoring the redox-active molecules onto tuneable and functionalisable advanced materials based on indium-tin oxides.
In this project we will develop and characterise microresonators composed of and coated with different materials (e.g. Au-coated Yttrium barium copper oxide, YPCO) to generate spins at the point of maximum sensitivity. These materials will simultaneously act as EPR resonator and working electrode (WE), enabling optimal conditions for both electrochemistry and EPR for the first time. Eliminating the ‘conductivity compromise’ and diffusion of the redox-active species to the WE through surface confinement to these advanced materials should enable microresonator FE-EPR to investigate the formation, evolution and nature of very low-concentration radicals during (electro)catalysis and charge storage and hence have a far-reaching impact across many disciplines.
We propose to: (1) Demonstrate proof-of-concept of microresonator FE-EPR (developing and characterising Au-coated microresonators, providing a versatile surface for functionalization); (2) Show its first application to charge generation and storage in battery-relevant nonaqueous and aqueous redox centres such as non-aqueous organic redox species for flow batteries; (3) Apply the technique to characterise biomaterials, to understand how the bacterial protection system MsrP/Q, found in major human pathogens, functions and may be exploited for new antimicrobials.● Ion implantation into semiconductors: studying a new manufacturing technique
This project will use atom probe tomography (APT) to study ion implantation into semiconductors with a new manufacturing and characterisation technique based on ionic liquid beams.
Ionic liquids are mixtures of cations and anions without an intervening solvent. An Ionic Liquid Ion Source (ILIS) is a device in which the liquid covers a sharpened needle. The needle is subjected to electric fields to produce an ion beam. The resulting beam can be used to treat materials.
ILIS provide a large variety of ion chemistries, including organic molecules, simple atomic halogens, and heavily fluorinated species. Fast etching of silicon has been demonstrated after ILIS irradiation, thanks to the reactivity of fluorinated species in the beam . ILIS can be used for manufacturing (e.g. microelectronics fabrication) and in advanced characterisation of materials. The ILIS beam could be focused and used to mill materials at the nanoscale, enabling tomography or the preparation of samples for transmission electron microscopy. ILIS could also be used to perform secondary ion mass spectrometry.
This project will study the implantation of ILIS ions into semiconductors, which should be understood if ILIS is used in manufacturing or characterisation. APT allows analysis of materials in three dimensions with sub-nanometer resolution, and has been used previously to study ion implantation . APT will be used to profile the sub-surface chemical composition of ILIS-irradiated samples. Commercially available silicon pillars will be treated with a variety of ILIS beams. The pillars will then be shaped into atom probes using focused ion beam, and APT will be used to determine the implantation depths of chemical species contained in the ion beam. This work should further develop APT as an implantation characterisation technique.
 C Perez-Martinez et al., J. Vac. Sci. Technol. B 28 (2010) L25
 K Eder et al., Ultramicroscopy 228 (2021) 113334● Structure evolution and deactivation of Gauze catalyst for nitric acid production
50% of the N atoms in our body come from industrial Haber-Bosch process that converts N2 into NH3. One third of those NH3 is then oxidized to nitric acid and to fertilizes that help food production. The overall process requires high N atomic efficiency. This project will help improve N efficiency by understanding the catalyst degradation via advanced imaging techniques.
The scientific question: The oxidation of commercial Pt gauze catalyst into surface PtO2 is the main means of degradation. Those PtO2 will reduce the selectivity towards nitric acid related product. The question is to understand how PtO2 is formed and develop method to prevent PtO2 formation.
Here correlative X-ray and electron imaging of fresh and aged catalysts will be carried out to study: 1. the hot spots of PtO2 formation, 2. The reaction condition that accelerate PtO2 formation, 3, the prevention of the PtO2 formation by alloy Pt with different noble metals. Our multi-scale imaging methods cover from 0.1 nm all the way to centimetre scale, providing both scientific and engineering understanding into this problem.
The potential impacts: This project has the potential to make real impact into the chemical industry. It will help JM develops stable catalyst that can maximum the nitric acid production. One third of the nitric acid production is through JM’s catalysts, which has a global market size of 22,268 million USD in 2019. The demand is also raising along with the increasing world population. In short, the student can change the world via chemistry and chemical engineering.
The project will also have scientific impact by developing advance imaging tools to tackle the materials degradation and aging problem.
Reference: J. Pottbacker, et al. Chem. Eng. J. 2022, 439, 135350.