Description of Ph.D. project in EXSS for Oct 2021 Entry

Project title: Quantum Cascade Laser s-SNOM for intracellular imaging

Principal Prof Chris Phillips Project No: CCP_1 Supervisor:

Email: [email protected] Telephone x47575

Other Dr Holger Auner, Prof Alexandra Porter, Prof Charles Coombes. supervisors:

Aims of the project:

Very recently we gave found out how to use a Solid- State near field imaging technique, so- called s-SNOM, to look inside cells for the first time. It beats the diffraction limits of ordinary microscopy by a factor of ~3000, and the spatial resolution it gives (~3nm) already rivals the very best of electron microscopy at a fraction of the time effort and cost. We believe it has the potential to transform the biomedical sciences.

We have shown how it can image the organelles inside a cell optically for the first time first time ever. Also , because it works at mid-IR wavelengths where chemical bonds have characteristic vibrational absorption bands that give them spectral “fingerprints” , the technique can be used to provide nanoscal chemical maps that, e.g. reveal where drugs bind inside the cell.

The initial aims of the project will be to trail and develop the technology with Imperial cinicians, with a focus on themes, (1) the pathology pf Breast Cancer, (2) Drug resistance in multiple myeloma, and (3) the nanoscale causes of osteporosis.

However, the potential applications are limitless and we will likely establish more collaborations as the programme progresses.

Also Recent developments in the field of quantum imaging have demonstrated new methods of imaging objects by detecting photons that have not actually interacted with it. In collaboration with colleagues in the optics groups we plan to investigate extending the wavelength of this technique into the mid-IR.

There will also be collaboration with the team developing the diffraction-limited “Digistain” imager for Cancer diagnosis.

Techniques, activities, and equipment used: The s-SNOM signal is small (1 in 10^7) so we will have to use a challenging interferometric phase-sensitive heterodyning method to detect it. This requires ultra-stable operation from the QCL's; difficult to achieve whilst maintaining the wide tunability that is required to do the chemical spectroscopy. Mechanical vibrations will have to be excluded throughout the equipment, at the sub-nanometre level. Ethical issues associated with studying Human tissue will have to be navigated, and the whole project relies on being able to work together and effectively with clinically trained personnel. This is a technically challenging project, but with a potentially very high scientific payoff.

Locations of equipment / collaborators Level 9 Blackett; Hammersmith and Charing Cross Hospitals.

Description of Ph.D. project in EXSS for Oct 2021 Entry

Project title: Mid-IR imaging for Biomedical Applications

Principal Prof Chris Phillips Project No: CCP_2 Supervisor:

Email: [email protected] Telephone x47575

Other Prof Charles Coombs, Prof Chris Bakal supervisors:

Aims of the project:

Mid-IR imaging has proven to be capable of detecting the chemical changes in human tissue biopsies that accompany the onset of cancer. This project will build on this discovery in 3 directions

1) Further refinement and clinical evaluation of a diffraction limited “Digistain” prototype tissue imager.

2) Development of near-field imaging techniques for cancer pathology. Very recently we gave found out how to use a Solid- State near field imaging technique, so-called s-SNOM to look inside cells for the first time. It beats the diffraction limits of ordinary microscopy by a factor of ~3000, and the spatial resolution it gives (~3nm) already rivals the very best of electron microscopy at a fraction of the time effort and cost. We believe it has the potential to transform the biomedical sciences. We have shown how it can image the organelles inside a cell optically for the first time first time ever. The initial aims of the project will be to trail and develop the technology with Imperial clinicians, with a focus on the pathology of Breast Cancer, and mapping out the proteosome in Myeloma cancer cells.

Techniques, activities, and equipment used The digistan imager will need trailing and evaluating for high-frequency low drift amage acquisition, with improved optical throughput and thermal drift.The s-SNOM signal is small (1 in 10^7) so we will have to use a challenging interferometric phase-sensitive heterodyning method to detect it. This requires ultra-stable operation from the QCL's; difficult to achieve whilst maintaining the wide tunability that is required to do the chemical spectroscopy.

Locations of equipment / collaborators Level 9 Blackett; Hammersmith and Charing Cross Hospitals.

Description of Ph.D. project in EXSS for Oct 2021 Entry

Project title: Better mobilities through better theories

Principal Jarvist Moore Frost Project No: JMF_1 Supervisor:

Email: [email protected] Telephone x41167

Other Collaborators: J. Skelton (University of Manchester) supervisors:

Aims of the project: Humanity could really do with some new energy materials. If these are to be more efficient than what we have already, they are likely to be more complex; if they are to be cheaper, then they are likely to be more disordered. Solid-state theory, mostly dating from the 1950s and 1960s, is really best at predicting the behaviour of perfect infinite crystals at zero temperature. So let's make some better theories! Semiconductors are required for a number of applications: they often form one of the electrodes of a battery, they are used as the active material in solar cells, LEDs and solid-state lasers, low-thermal conductivity semiconductors can be used as thermoelectrics to generate electricity from temperature difference. A key (and highly technologically relevant) character of a semiconductor is the charge-carrier mobility. Generally you want this mobility to be as high as possible, and there are mobility thresholds for using a semiconductor in certain devices (e.g. a solid-state laser needs a higher mobility than that required by a solar cell). Charge carrier mobility is a phenomenological quantity, it is a product of a competition between processes with the semiconductor. It is not a direct ground state property of the material, and is strongly temperature dependent. Most theories of semiconductor charge carrier mobility have an empirical parameter (often an effective scattering time, in a Drude like model of mobility). This means that while relative mobility can be predicted within one material class, absolute predictions of mobility are lacking.

The situation is not entirely hopeless though. As electronic structure techniques are getting more sophisticated, it is possible to calculate more subtle aspects of a material, such as the electron phonon coupling (This electron-phonon coupling is between the nuclear and electronic degrees of freedom, which is adiabatically separated and ignored once you apply the Born-Oppenheimer approximation.)

Recently we implemented a 1960s theory of polaron mobility[1,2], in a modern (2017) computer code [3], written in the Julia programming language. These codes can be combined with electron-phonon coupling and effective-mass parameters for real materials calculated with standard electronic structure methods and packages (typically using the density functional theory) to predict the polaron character, and polaron response functions, of technologically relevant semiconductors.

There are a number of different avenues to explore, depending on the interests of the student, and the existence of new experimental data to explain. The model polaron Lagrangian could be extended (while retaining analytic solution) to attempt to increase the accuracy of the approximation, perhaps by extending the Gaussian form to a set of correlated Gaussian processes. The effective Lagrangian could be extended to provide greater material specific detail. Diagrammatic Monte-Carlo can provide direct evaluation of the effective Lagrangian, and a code for this could be written to compare to the Feynman variational results. Further response functions of the polaron variation state could be computed, which enable comparison to experimental observables. For instance, the optical absorption of the polaron state could be compared to transient absorption measurements on these materials; the frequency dependent mobility could be calculated and compared to Terahertz and microwave conductivity measurements.There are theoretical models built on a compatible path integral basis to describe disorder that exists in non-crystalline systems, but so far these have not been interfaced to polaron mobility theories.

As well as immediate method development, there is a large scope to apply these codes to material groups and classes. This requires the characterisation of materials, either by recourse to the material databases of synthetic data derived from electronic structure calculations, such as the Materials Project [4], and through the use of standard electronic structure packages such as VASP and Gaussian.The central aim is to develop methods which can offer fully predictive temperature-dependent mobilities for a wide variety of systems of technical interest, and thereby offer design clues for, and methods to computationally screen, new materials. Though this project is envisaged as theoretical and computational, it will require a deep familiarisation and contact with experimental methods, material specific properties, and interaction with experimental collaborators and peers who are measuring mobilities and response functions in these materials.

[1] Slow Electrons in a Polar Crystal, R. P. Feynman, Phys. Rev. 97, 660 (1955)

[2] Mobility of Slow Electrons in a Polar Crystal, R. P. Feynman, R. W. Hellwarth, C. K. Iddings, and P. M. Platzman, Phys. Rev. 127, 1004 (1962)

[3] PolaronMobility.jl, a Julia language package, https://github.com/jarvist/PolaronMobility.jl, (2017).

[4] https://materialsproject.org/

Techniques, activities, and equipment used: The focus of this project is the development of new simulation methods to model the transient response of semiconductors, starting with extending polaron theories of mobility. This requires some writing of new computer codes, and some development and understanding of theory. The Feynman variational approach to the polaron problem is couched in the path integral formulation of quantum mechanics. It's very unlikely to have come across this form of quantum mechanics as an undergraduate, but interest in learning about it would be a definite bonus!

Locations of equipment / collaborators

Computational resources will be accessed over the network. There will be a tiered use of the Imperial resources (CX1 cluster); and EPSRC tier-1 national facility ARCHER2.

The group of J. Skelton (thermoelectric collaborator) is at the University of Manchester.

Description of Ph.D. project in EXSS for Oct 2021 Entry

Project title: Manipulating excited state lifetime on the path to high efficiency photovoltaics

Principal Jarvist Moore Frost Project No: JMF_2 Supervisor:

Email: [email protected] Telephone x41167

Other Collaborators: H. Bronstein (Cambridge, synthetic chemist); A. Bakulin (Imperial supervisors: Chemistry, spectroscopist); R. Crespo-Otero (QMUL, theorist).

Aims of the project: Organic semiconductors are soft. (At least, compared to inorganic semiconductors.) When a photon of light is absorbed, the material distorts around the new electron density, forming an exciton. The binding energy of these states, the nature and extent of the distortion, and their rate of thermalisation and propagation through the material affect the overall behaviour and efficiency of optoelectronic devices made of this material.

Upon photo-excitation, the material dynamically distorts and propagates quantum-mechanically along excited state potential energy surfaces. Subtle variations in chemical structure can lead to the physics and processes of these states being very different. These processes are difficult to model with current technique and technology. The excited states require different (and usually more expensive, and less reliable) electronic structure techniques than those used in a standard ground-state calculation. Worse, we can no longer make the adiabatic separation between nuclear and electron degrees of freedom (the Born-Oppenheimer approximation). Trying to brute force propagate the combined electronic and nuclear wave- function ends in a vale of tears due to the explosion of computational complexity, even for the very short times we are interested in.

By modelling this process, and applying known empirical chemical design rules, and discovering design rules of our own, we can hope to offer guidance in to what to synthesise next. The long term aim is the design of up-converting materials for high efficiency photovoltaics, which are capable of converting two lower energy photons into one high energy photon (i.e. red to blue light). A key challenge here is the the lifetime of the exciton state is so short, that the chance of absorbing a second photon before decay is minuscule, making the efficiency of any such up-conversion process negligible. Therefore an initial aim will be to try and manipulate (lengthen) these excited state lifetimes, developing empirical rules and intuition about what chemical design needs to take place.

Designing mimics for excited state processes and molecular configurations is a challenge by itself, where little work has so far been done as the required calculations have only just become feasible. There are a number of empirical design rules being developed and applied by synthetic chemists, which would benefit from a careful computational analysis, such as the inversion of the Singlet-Triplet gap[1]. Much of the theory justifying the observed activity is limited to static and often Born- Oppenheimer approximation calculations. Adding dynamic effects, even if at first this is initially with only an approximate theory, would be of definite use to understand what is going on. [1] Inverted Singlet–Triplet Gaps and Their Relevance to Thermally Activated Delayed Fluorescence,

Piotr de Silva, Phys. Chem. Lett. 2019, 10, 18, 5674-5679 (2019).

Techniques, activities, and equipment used

The intent is to develop new computational methods to model excited state and transition state properties, and so enable molecular design of materials to exploit the physics of these non-equilibrium configurations. The base of these methods will be in applying standard electronic structure (quantum chemistry) techniques to characterise these states. As well as the more standard density functional theory, and time-dependent variants, the high accuracy needs post-Hartree-Fock methods to explicitly treat electron correlation. Custom computer codes will be written to simulate the excited state dynamics. This requires the construction of effective Hamiltonians from the output from the previous atomistic simulation. There are a number of different potential methods to apply here, including Tulley's surface-hopping algorithm, multi-reference Hartree method, and path integration, as well as computationally less expensive semi-classical methods.

Understanding the nuclear-electron behaviour and dynamics of current materials upon photoexcitation, will then feed back into exploratory design of new materials to capitalise on empirical design rules discovered, and the explicit predictions of the validated models. In collaboration with synthetic chemists, new materials will be designed and synthesised. The optical nature of these materials will be measured, both within the EXSS group, and with more sophisticated transient laser experiments through collaborators. Films and solutions may be prepared in the Physics clean room.

Locations of equipment / collaborators: The experimental equipment used as part of this project is in the laboratory space of the EXSS group in the Physics Department, Imperial College London. This may include the Cleanroom on Level 1, Undercroft labs, and Blackett Level 9. Computational resources will be accessed over the network. There will be a tiered use of the Imperial resources (CX1 cluster); and EPSRC tier-1 national facility ARCHER2.

The intent is to collaborate with the group of H. Bronstein (Cambridge; synthetic chemist) on design of organic materials, which are then synthesised in the Bronstein group. There is then the opportunity for an experimental component of this project, in characterising these newly synthesised materials with transient photo-luminescence and quench experiments, with the EXSS facilities. Additional more complex time-resolved and pump-probe spectroscopy will be done in collaboration with A. Bakulin (Imperial Chemistry). The theoretical collaborator is the group of R. Crespo-Otero (QMUL), experts in excited state calculations.

Description of Ph.D. project in EXSS for Oct 2021 Entry

Project title: Machine learning tight-binding models

Principal Jarvist Moore Frost Project No: JMF-3 Supervisor:

Email: [email protected] Telephone x41167

Aims of the project: Electronic structure theory enables you to go directly from the positions of atoms in a solid-state material, to a prediction of material properties entirely within a computer. These techniques are now well developed, codes stable and universally available, and there is considerable provision of computational resources. With these techniques, the prediction of e.g. the band-gap of a potential new material are routine.However, many phenomena cannot be described by single-point electronic structure calculation on a fixed lattice. The size of the system required to include thermal effects or disorder makes it impossible to use a fully ab-initio electronic structure method. (Ab-initio theories can reasonably simulate a maximum of 10-1000 atoms.)

The standard approach in these situations is to use a semi-empirical method. Tight-binding is one such method, and is now formally understood as an approximation to density functional theory. So far these tight-binding models have been hand-built by expertise and intuition, without benefiting from modern approximation methods. Via this approach, parameter sets with moderate errors have been generated for the entire periodic table[1,2]. A benefit of such minimal parameter quantum-mechanical models is that the parameters are directly open to interpretation, rather than being a black box. An alternative, modern, approach is to use machine learning to directly build a (very complicated, often expressed via a deep neural network with millions or billions of parameters) function which maps from the atomic arrangement to the value of interest. Careful construction of the representation used can enforce the known symmetries of physics. The main problem with this approach is that it is accurate when tested on data which is in-distribution (i.e. similar to training data), but becomes ill-defined and can produce spurious results when taken to a new area. When you are using these models explicitly for the prediction of new behaviour, and to simulate systems of a size which you cannot reach with a direct ab-initio method, this is a problem. The aim of this project is to combine the best parts of these two methods: machine learn the parameters of well-understood physical quantum-mechanical models, incorporating both expert prior belief and calculated data in an even-handed manner. By using as the base a fully quantum-mechanical model, transferability of the machine learning is engineered in by the underlying physics. A Bayesian model is one which has a statistical distribution of parameters, where this distribution is generated from new evidence combined with the prior expectation Automatically fitting the parameters with a Bayesian parameter optimisation, from data generated by higher level (more computation intensive) calculations, allows selection from the broader distribution of plausible parameters, rather than over-fitting to an isolated peak in the parameter phase-space. With this method we can incorporate previous knowledge (including from the 60+ years of expert creation of tight-binding models) in a statistically literate manner. This probabilistic approach to parameters also enables active learning—the fitting algorithm knows where it should collect further data to increase the predictive power. A well-found computationally efficient model, validated against reality, would then be used with solid-state theories to predict phenomenological quantities such as ion and electron mobilities. These light-weight models can reach length and time-scales totally inaccessible with standard ab-initio techniques. As they can have prior knowledge and physical behaviours enforced in the model, they can potentially be more accurate than ab-initio calculations which make uncontrolled approximations.To bootstrap this project, this method will be initially applied to tune existing tight- binding methods [1,2], including with the incorporation of open machine-learning datasets[3]. The longer term scientific projects will be looking at novel semiconductors, for which we will have to calculate synthetic data ourselves, with density functional theory and other more sophisticated electronic structure methods.Surrogate models, based on minimal parameter quantum-mechanical calculations fitted from higher level calculations, are likely to be a major and successful area of research in the next decades. Little work has been done so far (though see [4] for a highly relevant contribution, where they fit a tight-binding model, but without a Bayesian approach), and this PhD is an opportunity to be at the forefront of this new field.

[1] Gaus, M.; Cui, Q.; Elstner, M. DFTB3: Extension of the Self-Consistent-Charge Density-Functional Tight-Binding Method (SCC-DFTB). J. Chem. Theory Comput. 2011, 7 (4), 931–948. https://doi.org/10.1021/ct100684s.

[2] GFN2-xTB—An Accurate and Broadly Parametrized Self-Consistent Tight-Binding Quantum Chemical Method with Multipole Electrostatics and Density-Dependent Dispersion Contributions | Journal of Chemical Theory and Computation https://pubs.acs.org/doi/10.1021/acs.jctc.8b01176 (accessed Jan 3, 2020).

[3] Smith, J. S.; Zubatyuk, R.; Nebgen, B. T.; Lubbers, N.; Barros, K.; Roitberg, A.; Isayev, O.; Tretiak, S. The ANI-1ccx and ANI- 1x Data Sets, Coupled-Cluster and Density Functional Theory Properties for Molecules. 2019. https://doi.org/10.26434/chemrxiv.10050737.v1 .

[4] Li, H.; Collins, C.; Tanha, M.; Gordon, G. J.; Yaron, D. J. A Density Functional Tight Binding Layer for Deep Learning of Chemical Hamiltonians. J. Chem. Theory Comput. 2018, 14 (11), 5764–5776. https://doi.org/10.1021/acs.jctc.8b00873 .

Techniques, activities, and equipment used: This project is envisaged as being entirely theoretical / computational. Strong programming skills would be a definite advantage. The intent would be to do the majority of code development in the Julia open-source scientific programming language. The benefits of using Julia are that it has high-level features and user-definable types that enable a natural expression of more complex models, yet offers high performance and cutting edge code optimisation and parallelisation features. We may also have to do some software development within the often C and FORTRAN code bases of ab-initio electronic structure packages. It is hoped that the code developed will eventually be merged into and extend the Ortner group's TightBinding package (https://github.com/jarvist/TightBinding.jl/ ), which may be a good place to see what sort of coding will take place in this PhD.

Locations of equipment / collaborators: Computational resources will be accessed over the network. There will be a tiered use of the Imperial resources (CX1 cluster); and EPSRC tier-1 national facility ARCHER2.

Description of Ph.D. project in EXSS for Oct 2021 Entry

Project title: Design, characterisation and understanding of new organic semiconductors for use in application targeted photovoltaics

Principal Jenny Nelson Project No: JN_1 Supervisor:

Email: [email protected] Telephone 020 75947581

Other Professor Martin Heeney, Imperial Chemistry supervisors:

Aims of the project:

Organic semiconductor materials offer attractive features for applications in photovoltaic energy conversion due to the tuneability of their colour and other properties, light weight, flexibility and ease of manufacture. Organic solar cells have enjoyed a rapid improvement in performance recently with power conversion efficiencies now exceeding 18%, thanks to the development of novel acceptor materials and an improved understanding of the basic mechanisms of photovoltaic action. The materials are now viable options for photovoltaic devices for specific applications such as in buildings and for mobile power.

Solar energy conversion in organic semiconductors depends upon a photoinduced charge separation process whereby charge pairs are separated across an interface between electron donating and electron accepting species. Many recent performance improvements have resulted from efficient charge separation in materials where the interfacial driving force is surprisingly small [1]. A critical question is how large the energetic driving energy needs to be to allow efficient photocurrent generation. This can be investigated with the help of new models of interfacial charge separation and recombination mechanisms and spectroscopic and optoelectronic tools [2,3,4]. A second reason for recent performance improvements has been improved control of the properties of the electron and hole-selective interfaces of solar cell devices.

The aim of this project is to develop tools to understand how the chemical structure of the organic semiconductor materials and their physical organisation control the mechanisms of charge separation, charge recombination and current collection. The student will use spectroscopic methods (electro- and photoluminescence, transient absorption and transient optoelectronic spectroscopy), electrical measurements, structural characterisation and modelling to characterise and understand the charge dynamics in selected donor: acceptor systems. He or she will also consider the design and performance criteria for interfacial layers for improved selectivity. The student will work with both materials physicists and synthetic chemists, and will have the opportunity to contribute to materials design.

The studentship is part of a larger research programme on Application Targeted Integrated Photovoltaics, and is closely linked to research into the manufacture and application of devices.

[1] Z. P. Fei et al., An Alkylated Indacenodithieno 3,2-b thiophene-Based Nonfullerene Acceptor with High Crystallinity Exhibiting Single Junction Solar Cell Efficiencies Greater than 13% with Low Voltage Losses. Advanced Materials, (2018). https://doi.org/10.1002/adma.201705209.

[2] M. Azzouzi et al., Nonradiative Energy Losses in Bulk-Heterojunction Organic Photovoltaics. Physical Review X (2018). https://doi.org/10.1103/PhysRevX.8.031055; M. Azzouzi et al, Factors Controlling Open-Circuit Voltage Losses in Organic Solar Cells. Trends in Chemistry 2019 https://doi.org/10.1016/j.trechm.2019.01.010.

[3 ] F. D. Eisner et al, Hybridization of Local Exciton and Charge-Transfer States Reduces Nonradiative Voltage Losses in Organic Solar Cells. Journal of the American Chemical Society (2019). https://doi.org/10.1021/jacs.9b01465.

[4] M. Azzouzi, et al., Overcoming the Limitations of Transient Photovoltage Measurements for Studying Recombination in Organic Solar Cells. Solar RRL (2020). https://doi.org/10.1002/solr.201900581. Techniques, activities, and equipment used:The student will be responsible for the experimental characterisation of molecular semiconductors using a range of spectroscopic, electronic and structural techniques, and for the design, fabrication and testing of solar cells and other test devices. The student will work closely with materials chemists to provide feedback and design ideas for new materials. Depending on the strengths and interest of the student, there will also be an opportunity to use molecular and / or device level simulation method to model the properties of the materials and explain the behaviour of devices.

Locations of equipment / collaborators

The experimental facilities for this project are mainly located in EXSS labs (undercroft, clean room and level 9). Some spectroscopic or chemical characterisation measurements will be done at labs in Chemistry. The project is part of a collaborative research programme with Swansea and Oxford universities, as well as with members of the Chemistry department at Imperial, and the work will involve active teamwork and collaboration.

Description of Ph.D. project in EXSS for Oct 2021 Entry

Project title: Organic Solar Cells – what’s the origin of energetic loss?

Principal Prof Ji-Seon Kim Project No: JSK_1 Supervisor:

Email: [email protected] Telephone ext.47597

Other supervisors:

Aims of the project:

Organic solar cells (OSCs) have attracted enormous interest in scientific research and commercial development due to their low-cost, flexible, solution processable properties. Solution-processed OSC devices are typically based on an organic bulk heterojunction blend consisting of a conjugated donor polymer and a small molecule acceptor. With newly developed non-fullerene acceptors, their efficiencies have reached impressive level of >18%. One of the important device parameters in OSC devices which determine device performance is an open-circuit voltage. The open-circuit voltage is mainly determined by the energy band edge offset of the photoactive organic semiconductors (donor and acceptor) and recombination losses (radiative and non-radiative) in their blend. However, the exact molecular origins of these energetic as well as recombination losses are still unclear and requires further investigation.

Schematics of printing flexible OPV devices (left), printed flexible OPV modules (top right), organic electron acceptors including NFAs (bottom right)

This project aims to identify the molecular origins of energetic differences at donor-acceptor interfaces to get a complete picture of voltage losses induced by energetic offset; within the context of various non-fullerene based organic solar cells. You will investigate the energetics of organic semiconductors in pure and mixed phases via combined photoemission and surface photovoltage spectroscopy techniques. Furthermore, the subtle structural differences of donor and acceptors in their pure phases compared to well-mixed interfaces will be identified by Raman spectroscopy, followed by understanding their impact on the energetics. Surface photovoltage spectroscopy to understand the quasi-fermi level splitting upon illumination and its correlation with device open circuit voltage will be a novel experimental approach in the field of organic solar cells. This project will also involve theoretical simulations of molecules in terms of energy levels and molecular structures utilizing density functional theory.

References:

• NATURE COMMUNICATIONS (2020) 11:4617, https://doi.org/10.1038/s41467-020- 18439-z • Energy & Environmental Science. doi:10.1039/d0ee01338b • NATURE COMMUNICATIONS, 10, 10 pages. doi:10.1038/s41467-019-12951-7 • ADVANCED ENERGY MATERIALS, 9(15), 14 pages. doi:10.1002/aenm.201803755 • ADVANCED ENERGY MATERIALS, 9(27), 10 pages. doi:10.1002/aenm.201901254 • Adv Mater 28, 3814-3830, (2016). • Surface and Interface Analysis 31, 954-965, (2001) • Journal of Physics D: Applied Physics 50, 073001, (2017)

Techniques, activities, and equipment used:

OPV device fabrication and characterisation techniques (such as JV and EQE), as well as advanced spectroscopy techniques including confocal Raman spectroscopy, surface photovoltage spectroscopy (SPV), ambient photoemission spectroscopy (APS) will be used.

Skills to be learned:

• Literature Survey (including device physics, molecular chemistry, and materials science) • Scientific Research: Experimental (optoelectronic characterizations, photoemission spectroscopy, surface photovoltage spectroscopy, Raman spectroscopy); Theoretical (Density Functional Theory); Data processing (scripting), analysis, and interpretation. • Professional skills: teamwork, project management, time management, and scientific presentation.

Locations of equipment / collaborators:

Most equipment for device fabrication and characterisation is based at IC. The project will include collaborations with other academic (e.g. Imperial, Swansea, Oxford, QMUL) and industrial (e.g. CSEM Brasil, KP-Tech, NPL) partners in OPV research. The project will be aligned with our recently awarded ATIP project to develop large area integrated organic solar cells for targeted applications (e.g. in-door photovoltaics).

Description of Ph.D. project in EXSS for Oct 2021 Entry

Project title: 2D/3D Perovskites for Efficient Solar Cells

Principal Prof Ji-Seon Kim Project No: JSK_2 Supervisor:

Email: [email protected] Telephone ext.47597

Other supervisors:

Aims of the project:

Solution-processed three-dimensional (3D) perovskite solar cells have shown remarkable growth in recent years reaching a power conversion efficiency over 25% thanks to the excellent intrinsic properties of the perovskite photoactive layer (e.g. high absorption coefficient, excellent carrier mobility) and the growing scientific understanding leading to continuously improved morphology and interfaces to reduce losses in devices. One main factor still limiting the performance of and stability of perovskite solar cells is their high trap state density within the semiconductor bandgap. Therefore, gaining a fundamental understanding of these trap states in terms of their density and distribution, and finding a way to reduce these trap states will be crucial for further development of perovskite solar cells towards real commercialisation.

Figure 1. Schematic illustration of the dimensionally engineered 2D/3D perovskite thin film bandgap diagrams in mixed and heterostructure devices.

Recently, 2-dimensional (2D)/3D perovskite solar cells have attracted great research interest due to their potential to overcome the single-junction Shockley–Queisser theoretical efficiency limit, as well as to reduce the high trap state density and instability of 3D perovskite solar cells. In this project, we will first control the energy levels of perovskite layers via their dimensionality control (3D and 2D/3D) with varying composition and stoichiometry (applying different cations and anions in the 2D perovskite). We will then identify the nature of trap states in these dimensionality-controlled perovskite layers. The energy levels together with the trap state distribution will be investigated by using ambient photoemission spectroscopy (APS), which will be complemented by surface photovoltage (SPV) measurements to investigate the impact of cascaded energy levels and trap states on photogenerated charge carriers. Finally, the impact of dimensionality-controlled perovskites and their trap states on solar cell performance (efficiency and stability) will be investigated. The advanced spectroscopy techniques such as APS and SPV are relatively new and our expertise in this area will be crucial for the success of the project. The project will also include simulation of APS signals and/or one-dimensional drift-diffusion modelling of device performance and surface photovoltage.

References:

• G. Grancini et al., Nat. Rev. Mater. 4, 2019, • S. Heo, G. Seo et al., Adv. Energy Mater. 31 (8), 2019 • C. T. Lin et al., Adv. Funct. Mater. 30, 2020 • Advanced Functional Materials, 30(25), 1-8. doi:10.1002/adfm.202001482 • ACS Applied Materials & Interfaces, 11(50) 46808-46817, doi:10.1021/acsami.9b16394 • ADVANCED SCIENCE, 5(11), 10 pages. doi:10.1002/advs.201801350

Techniques, activities, and equipment used:

Advanced spectroscopy techniques such as Ambient Photoemission Spectroscopy (APS) and Surface Photovoltage (SPV) Spectroscopy will be used to measure interfacial energetics and traps/defects related structural changes. Solar cell device fabrication and characterisation techniques (such as JV and EQE) will also be used.

Skills to be learned:

• Literature Survey (including device physics, physical chemistry, and materials science) • Scientific Research: Experimental (optoelectronic characterizations, photoemission spectroscopy, surface photovoltage spectroscopy,); Theoretical (Density Functional Theory, one-dimensional drift-diffusion modelling); Data processing (scripting), analysis, and interpretation. • Professional skills: teamwork, project management, time management, and scientific presentation.

Locations of equipment / collaborators: Most equipment for device fabrication and characterisation is based at IC. The project will include collaborations with other academic (e.g. Imperial, Swansea, Oxford, QMUL) and industrial (e.g. CSEM Brasil, KP-Tech, NPL) partners. The project will be aligned with our recently awarded ATIP project to develop large area integrated solar cells for targeted applications.

Description of Ph.D. project in EXSS for Oct 2021 Entry

Project title: Superconducting Spin Qubits

Principal Dr Malcolm Connolly Project No: MC_1 Supervisor:

Email: [email protected] Telephone 4

Other Prof. Lesley Cohen supervisors:

Aims of the project:

Platforms based on the macroscopic phase coherence in superconducting circuits and the spin angular momentum of single electrons confined in semiconductors are at the forefront of efforts to realise scalable high-quality qubits for solid-state quantum computing. While superconducting qubits have modest lifetimes but are easy to fabricate in large numbers, spins have long coherence times but are harder to scale. The aim of this project is to build a hybrid platform that combines the best of both these technologies: a superconducting spin qubit. The spin will actually belong to an electron trapped in a semiconductor channel as it bounces back and forth between the superconducting contacts of a Josephson junction. The main novelty is that quantum state of the spin couples directly to the Josephson supercurrent, a macroscopic degree of freedom that can be easily detected and manipulated using scalable microwave circuits.1The first phase of this project will involve using quantum mechanical transport simulations and DC transport measurements to select the optimal material for hosting the spin to be integrated with the superconductor. Possible materials include III-V and

V-VI semiconductor alloys such as InAs and Bi2Te3, carbon-based (graphene and nanotubes), or even more complex materials such as oxides and ferromagnets. The second phase involves monitoring the quantum state of the spin and creating quantum superpositions using circuit quantum electrodynamics.2 Numerical electromagnetic simulations will be used to design the circuit parameters. In the third phase we can aim in different directions depending on progress. One direction is to scale up to two or more qubits and demonstrate entangled states suitable for fault-tolerant quantum processing.3 Another direction, which will require paying special attention to the number of allowed spin states, aims to create a topologically- protected qubit.4

1 M. Hays, V. Fatemi, K. Serniak, D. Bouman, S. Diamond, G. de Lange, P. Krogstrup, J. Nygård, A. Geresdi and M. H. Devoret, Continuous monitoring of a trapped superconducting spin, Nature Physics 16, 1103–1107 (2020)

2 C. Janvier, L. Tosi, L. Bretheau, Ç. Ö. Girit, M. Stern, P. Bertet, P. Joyez, D. Vion, D. Esteve, M. F. Goffman, H. Pothier, and C. Urbina, Coherent manipulation of Andreev states in superconducting atomic contacts, Science 349 (6253), 1199-1202 (2015)

3 J. Lantz, V.S. Shumeikoa, E. Bratus, G. Wendin, Flux qubit with a quantum point contact, Physica C 368, 315 (2002)

4 R. Aguado and L. Kouwenhoven, Majorana qubits for topological quantum computing, Physics Today 73, 6, 44 (2020) Techniques, activities, and equipment used: The project will primarily use nanofabrication techniques (electron beam- and photo-lithography, wet chemical semiconductor processing, metal and dielectric thin-film deposition), DC electrical transport (critical currents, magnetotransport, field-effect and tunnelling spectroscopy) and microwave quantum control techniques to manipulate electrons at the nanoscale. In-operando millikelving scanning probe measurements will be used to assess, for instance, the connection between device performance and local magnetic and electrostatic properties.

Locations of equipment / collaborators: The main piece of measurement equipment will be a dilution refrigerator hosted at the Quantum Science and Device Facility (QSDF). Nanofabrication will use a combination of lithography systems at the London centre for Nanotechnology (LCN) and Imperial. We will work with a number of collaborators to source different junction materials. These include InAs nanowires and two-dimensional electron gases (2DEGs) from Microsoft Quantum in Copenhagen, graphene and carbon nanotubes from Manchester/Lancaster, complex oxides and V-VI topological insulators from Cambridge/Juelich.

Description of Ph.D. project in EXSS for Oct 2021 Entry

Project title: Superconducting Gatemon Qubits

Principal Dr Malcolm Connolly Project No: MC_2 Supervisor:

Email: [email protected] Telephone

Other Oscar Kennedy supervisors:

Aims of the project: Quantum computers (QCs) process information differently to ordinary computers. QCs are optimised for performing tasks like simulating molecules for drug discovery and breaking secure encryption and running optimization routines. We are, however, a long way from being able to solve these interesting problems on a QC because current quantum processors are too small. While a recent breakthrough by Google demonstrated that the quantum way of processing information is faster,5 building larger quantum processors is a huge engineering problem being tackled by academic and industrial communities around the world. At the heart of QCs are qubits - physical systems capable of encoding information as quantum mechanical superpositions. The best physical system is an open question. A highly-promising qubit technology for scaling are gatemons – superconducting qubits which are controlled via a voltage-tuneable two-dimensional electron gas (2DEG).6 Voltage-control is a significant engineering advantage as it eliminates the need

5 Arute et al., Quantum supremacy using a programmable superconducting processor, Nature 574, 505–510 (2019)

6 Casparis et al., Superconducting gatemon qubit based on a proximitized two-dimensional electron gas, Nature Nanotechnology 13, 915–919 (2018) for running currents at millikelvin and reduces qubit cross talk (where tuning one qubit unintentionally tunes another). Despite early promise, 2DEG gatemon have yet to reach their full potential owing to short coherence times and this has been shown to be due to the type of lossy substrates used for growing the semiconductor junction.

The aim of this project is to use ‘flip-chip’ technology to separate the quantum circuit into modular components. This allows microwave elements to be fabricated on substrates with low microwave loss, and then bonded with the semiconductor junctions on their lossy substrate. This will increase coherence times in these junctions and make gatemons a practical contender as a scalable qubit platform. Leveraging this result, we will investigate new materials for the semiconductor junction and ultimately scale up the number of gatemon qubits to realise a gatemon quantum processor.

Techniques, activities, and equipment used: The project will primarily use nanofabrication techniques (electron beam- and photo-lithography, wet chemical semiconductor processing, metal and dielectric thin-film deposition), DC electrical transport (critical currents, magnetotransport, field-effect and tunnelling spectroscopy) and microwave quantum control techniques to manipulate qubits. In-operando millikelving scanning probe measurements maybe used to assess, for instance, the connection between device performance and local magnetic and electrostatic properties.

Locations of equipment / collaborators: The main piece of measurement equipment will be a dilution refrigerator hosted at the Quantum Science and Device Facility (QSDF). Nanofabrication will use a combination of lithography systems at the London centre for Nanotechnology (LCN) and Imperial. We will work with a number of collaborators to source different junction materials. These include 2DEGs from Microsoft Quantum in Copenhagen and the National Epitaxy Facility in the UK.

Description of Ph.D. project in EXSS for Oct 2021 Entry

Project title: Nanofocusing tips for Scanning Near Field Optical Microscopy.

Principal Prof Rupert Oulton Project No: RFO_1: Supervisor:

Email: [email protected] Telephone x47576

Other Dr Chris Phillips. supervisors:

Aims of the project:

The EXSS group (Prof. Phillips) is pioneering a Solid- State near field imaging technique, called scanning nearfield optical microscopy (SNOM), to look inside cells. It beats the diffraction limit of ordinary microscopy by a factor of ~3000, and the spatial resolution it gives (~3 nm), which rivals electron microscopy at a fraction of the time effort and cost. It has the potential to transform the biomedical sciences.SNOM nanoscopes rely on a metallic “needle”, to concentrate laser light at the point where tip and sample meet. Resolution is set by the needle’s sharpness (< 2.5 nm across) rather than the wavelength. The convention in SNOM is to illuminate the needle from the side– shown schematically in Fig. 1a. However, this results in the illumination dominating the smaller signal from the tip-sample region.

(a) Conventional (b) Nanofocussing (c) Low power Low signal to background ratio means s-SNOM s-SNOM nonlinear NSOM/SNOM the technique has relatively low Pump Signal New Color + sensitivity and image acquisition Pump Signal Signal Pump speeds. In this project, you will eliminate the illumination background by using a “super-focussing” technique, where light is only delivered to the (d) Super-Focussing SNOM Tip Surface Plasmon Focusing scanning needle’s tip (Fig. 10b). Nanofocus Eliminating background noise boosts PUMP sensitivity to tip-sample absorption Gold SNOM Tip with considerably faster acquisition Fig 1. Illustration of superfocusing and nonlinear s- times. These features are imprtant for SNOM nanoscope imaging. (a) conventional s- applying commercial SNOM SNOM resulting in low signal to background noise. nanoscopes to biomedical imaging. The (b) superfocusing s-SNOM eliminates background. dramatically improved sensitivity will (c) nonlinear SNOM images new wavelengths of provide better access to cellular light generated at the tip, further eliminating ultrastructure than currently feasible. background. (d) Schematic of a super-focussing tip The project will also explore alternative structure. contrast mechanisms for SNOM. E.g., strong nonlinear tip-responses generate new colours of light, which are modulated by the tip- sample interaction (Fig 1c). This allows pump light to be filtered, reducing noise.

Techniques, activities, and equipment used

You will fabricate superfocusing tips by modifying commercial high-resolution gold coated silicon scanning probe tips (needles) by etching optical gratings into them, as schematically shown in Fig 1d. The will require working with nanofabrication tools such as electron beam lithography, reactive ion etching and focussed ion beam milling. This will be conducted in our EXSS labs and clean-room.

Some nanofabrication may be undertaken at the London Centre for Nanotechnology. You will test the performance of these elements in our ultrafast laser laboratory. Sample design and optimisation will be aided by computer simulations using Lumerical electromagnetic modelling software based on the Finite Difference Time domain method. You will be working as part of a larger team with the goal of integrating the nanofocusing tips into a commercial s-SNOM.

Locations of equipment / collaborators

Level 9 Blackett; Nanofab lab, cleanroom, 706 and 1015 optics labs, LCN

Description of Ph.D. project in EXSS for Oct 2021 Entry

Project title: Nonlinear physics with extreme fields and Peta-Hertz Optoelectronics

Principal Prof Rupert Oulton Project No: RFO_2 Supervisor:

Email: [email protected] Telephone x47576

Other Dr. Mary Matthews (QOLS) supervisors:

Aims of the project:

When intense electromagnetic fields drive matter close to ionisation, Peta-Hz currents emerge generating extreme UV light and enabling resolution of physics on atto-second (10-18 s) timescales. To achieve the sufficiently intense optical fields, laboratory-based lasers are necessary, most of which are complicated bespoke systems: this is a barrier to wide-scale exploitation of this area of physics. This project explores extreme field opto-electronics essentially on a silicon chip. The primary excitement is the potential to break application barriers, eventually to enable portable and low-power implementations of extreme field physics. Moreover, the integrated opto-electronic setting enables the use of extremely high electrical fields in addition to optical fields. Uniquely, you will explore the mixing of both electrical and optical fields, both independently capable of ionising matter. This provides a unique opportunity to explore new physics.

The capabilities of such opto-electronic devices were demonstrated by our team with a publication in Science Magazine [Science 358 1179 (2017)]. The technique has been honed over the past few years and is now ready to be deployed in this new area. The project will be co-supervised by Dr. Mary Matthews (Royal Society Fellow and Lecturer) who is an expert in extreme optical field and atto-second physics.

Techniques, activities, and equipment used

You will design and fabricate nanophotonic waveguide structures for optical experiments. The design process is conducted using Lumerical electromagnetic software. Nanofabrication will mostly involve electron beam lithography. You will test samples using our ultrafast laser laboratory. You will also have access to the ultrafast laboratories in QOLS to study the atto- second scale (Pet-Hz) responses of these devices.

Locations of equipment / collaborators

Nanofab lab, cleanroom, 1015 optics labs, QOLS group labs

Description of Ph.D. project in EXSS for Oct 2021 Entry

Project title: Complex Photonic Networks

Principal Riccardo Sapienza Project No: RS_1 Supervisor:

Email: [email protected] Telephone 49577

Other supervisors:

Aims of the project:

Electron transfer to an individual quantum dot promotes the formation of charged excitons with enhanced recombination pathways and reduced lifetimes. Excitons are central for the development of very efficient quantum dot lasing, and very bright and tunable single photon sources from single quantum dot LED. We have just observed a 210-fold increase of the emission rate from a CdSe/CdS quantum dot under bias in an electrochemical cell.

Now we want to push this result further and reach a deterministic control over the charge state and emission properties for classical and quantum communication technologies.

The work is mostly experimental, with a 30% theoretical work to model the electromagnetic interaction around the quantum dot (using commercial finite-difference time-domain codes) and the charge dynamics (approximate analytical methods).

Techniques, activities, and equipment used

You will use custom-built single-emitter microscope in a state-of-the-art nanophotonic laboratory.

Locations of equipment / collaborators.

B1016A, in collaboration with Prof. Jenny Nelson (Imperial), and Prof. Iwan Moreels in Gent University (quantum dot fabrication).

Description of Ph.D. project in EXSS for Oct 2021 Entry

Project title: Solid-state nanoscale lasing on a graph

Principal Riccardo Sapienza Project No: RS_2 Supervisor:

Email: [email protected] Telephone 49577

Other Dr. Kirsten Moselund (IBM Zurich) supervisors:

Aims of the project:

You will to develop unconventional laser to be integrated with silicon chip to power next generation optical computation technology. The project, at the interface between random lasing and advanced material science, builds on the latest advances in nanophotonics of disordered media, network theory and lasing, and aims at studying lasing in a mesh of nanoscale waveguide forming a physical graph.

We are seeking an enthusiastic PhD student to undertake experimental research. The project involves design, nanofabrication and optical studies. The successful candidate should have a degree in physics, or material science. Independent thinking and multidisciplinary attitude are sought.

The project is in collaboration with Dr. Kirsten Moselund, in IBM Zurich, and funded through a European EID-ITN project. The candidate is expected to spend 50% of her/his time in IBM.

Techniques, activities, and equipment used.

You will use custom-built lasing microscope in a state-of-the-art nanophotonic laboratory and nanophotonic fabrication tools, such as electron-beam lithography.

Locations of equipment / collaborators.

B1016A, together with Dr. Kirsten Moselund, in IBM Zurich (nanolaser fabrication and integration on chip)

Description of Ph.D. project in EXSS for Oct 2021 Entry

Project title: Photon pair generation from nanoscale dielectrics

Principal Riccardo Sapienza Project No: RS_3 Supervisor:

Email: [email protected] Telephone 49577

Other Prof. Stefan Maier supervisors:

Aims of the project:

You will to develop bright nanoscale quantum sources of light through nanoscale photonic systems and nano-antennas. The project, joint between Prof. Stefan Maier and Dr. Riccardo Sapienza, builds on the latest advances in nanophotonics, plasmonics and single-molecule spectroscopy, which gives powerful tools to control light-matter interaction at the nanoscale.

We are seeking an enthusiastic PhD student to undertake experimental research. The project involves design, nanofabrication and optical studies. The successful candidate should have a degree in physics, or material science. Independent thinking and multidisciplinary attitude are sought.

Techniques, activities, and equipment used.

You will use custom-built single-molecule confocal microscope, and an ultrafast spectroscopy setup.

Locations of equipment / collaborators.

B1016A

Description of Ph.D. project in EXSS for Oct 2021 Entry

Project title: Rewritable Magnetic Nanostructures

Principal Dr Will Branford Project No: WRB_1 Supervisor:

Email: [email protected] Telephone 46674

Other supervisors:

Aims of the project: The functional magnetism group has a strong interest in the magnetic properties of nanostructured materials and devices. We have recently developed a method of writing any magnetic pattern we choose into magnetic nanostructured arrays that are usually called Artificial Spin Ice using a magnetic force microscope.1,2 The aim of this project will be to fabricate artificial spin Ice structures and to use the writing technique to explore the possibilities for two new types of computation. One of these, known as a neural network, is a massively parallel computation based on the collective response of the whole network. The other, known as magnonics3, relies on manipulating spin waves (magnons) within the nanostructures.4 Ferromagnetic resonance, or FMR, is a standard tool used for probing spin waves and spin dynamics in ferromagnetic materials. FMR arises from the precessional motion of the magnetization of a ferromagnetic material in an external magnetic field.

[1] Controlling the network properties from different starting configurations.

[2] Measuring magnetic dynamics in different geometries.

1 J. C. Gartside et al. Sci Rep-Uk 6, 32864, (2016). 2 J. C. Gartside et al. Nat Nanotechnol 13, 53, (2018). 3 D. Grundler. Nature Physics 11, 438-441, (2015). 4 T. Dion et al. Phys. Rev. B 100, 054433, (2019). Techniques, activities, and equipment used: PhD projects in the group will typically involve a mix of sample preparation, structural characterization, magnetic and transport measurements and micromagnetic simulations. Cleanroom sample processing includes deposition of metal films and lithography (optical, e-beam and focused ion beam). Structural studies involve imaging by optical, electron and magnetic microscopy and x-ray diffraction. Magnetic measurement techniques include FMR spectroscopy, vibrating sample magnetometry and magneto-optic Kerr effect (MOKE) spectroscopy. Electrical transport studies include magnetoresistance and Hall effect measurements. These measurements can be performed over a wide range of temperatures and magnetic fields.

Locations of equipment / collaborators: All in the Blackett Lab. Fabrication in the EXSS nanofabrication lab and cleanroom. Other measurements in the functional magnetism laboratory (B815).

Description of Ph.D. project in EXSS for Oct 2021 Entry

Project title: Plasmonic control of Magnetic Metamaterials

Principal Dr Will Branford Project No: WRB_2 Supervisor:

Email: [email protected] Telephone 46674

Other Dr Rupert Oulton supervisors:

Aims of the project: The functional magnetism group has a strong interest in the magnetic properties of nanostructured materials and devices. We have recently developed a method of writing any magnetic pattern we choose into magnetic nanostructured arrays that are usually called Artificial Spin Ice using a magnetic force microscope.1,2 The aim of this project will be to fabricate artificial spin Ice structures, use the writing technique define starting states and plasmonic heating induce controlled relaxation of the magnetic structure. Structures of this type are interesting for neuromorphic computing hardware. Neuromorphic computing is a massively parallel computation based on the collective response of the whole network from a defined starting point. The nanostructures will be of a size such that the magnetic structure is static and can be written in ambient conditions, and then can be selectively heated by interaction with laser light to induce directed magnetic relaxation, which will be used as the computation process.

[1] Controlling the network properties from different starting configurations.

[2] Exploring the evolution of the magnetic structure under laser illumination

1 J. C. Gartside et al. Sci Rep-Uk 6, 32864, (2016). 2 J. C. Gartside et al. Nat Nanotechnol 13, 53, (2018). 3 M. Pancaldi et al. Nanoscale 11, 7656-7666, (2019). 4 J. H. Jensen et al. in The 2019 Conference on Artificial Life. 15-22. Techniques, activities, and equipment used: PhD projects in the group will typically involve a mix of sample preparation, structural characterization, magnetic and transport measurements and micromagnetic simulations. Cleanroom sample processing includes deposition of metal films and lithography (optical, e-beam and focused ion beam). Structural studies involve imaging by optical, electron and magnetic microscopy and x-ray diffraction. Magnetic measurement techniques include FMR spectroscopy, vibrating sample magnetometry and magneto-optic Kerr effect (MOKE) spectroscopy. Electrical transport studies include magnetoresistance and Hall effect measurements. These measurements can be performed over a wide range of temperatures and magnetic fields.

Locations of equipment / collaborators: All in the Blackett Lab. Fabrication in the EXSS nanofabrication lab and cleanroom. Other measurements in the functional magnetism laboratory (B815).

Description of Ph.D. project in EXSS for Oct 2021 Entry

Project title: Barocaloric materials for cooling and heating

Principal Dr Xavier Moya Project No: XM_1 Supervisor:

Email: [email protected] Telephone 47579

Other supervisors:

Aims of the project:

Barocaloric effects are thermal changes that arise in mechanically responsive materials due to changes of applied pressure. These effects have been known for two decades, but have only moved recently into the spotlight due to the prospect of environmental-friendly cooling and heating applications1-4. The aim of this project is to study barocaloric effects in organic materials that display pressure-driven structural phase transitions. In practice, barocaloric materials will be prepared via chemical synthesis and barocaloric properties will be measured using a bespoke high-pressure thermometry and calorimetry suite that is unique in the UK.

[1] Moya et al., Nature Materials 13, 439 (2014).

[2] Lloveras et al., Nature Communications 6, 8801 (2015).

[3] Lloveras et al., Nature Communications 10, 1803 (2019).

[4] Moya et al., Science 370, 977 (2020).

Techniques, activities, and equipment used:

The project will involve sample preparation (typically via chemical methods), structural characterisation (x-ray diffraction, Raman scattering and electron microscopy), thermal measurements (contact thermometry, infra-red imaging and calorimetry) and thermal modelling (Landau analysis and finite-element analysis). The project will also involve experiments in large facilities (Diamond Light Source, ALBA synchrotron).

Locations of equipment / collaborators:

All in the Blackett Laboratory.

Description of Ph.D. project in EXSS for Oct 2021 Entry

Project title: Elastocaloric materials for cooling and heating

Principal Dr Xavier Moya Project No: XM_2 Supervisor:

Email: [email protected] Telephone 47579

Other supervisors:

Aims of the project:

Elastocaloric effects are thermal changes that arise in mechanically responsive materials due to changes of applied stress, and promise environmentally friendly cooling and heating applications1,2. The aim of this project is to study elastocaloric effects in elastomers that display stress-driven structural phase transitions. In practice, elastocaloric materials will be prepared via polymer synthesis methods, and elastocaloric effects will be evaluated using thermal expansion and measured using high-resolution infra-red imaging.

[1] Moya et al., Nature Materials 13, 439 (2014).

[2] Moya et al., Science 370, 977 (2020).

Techniques, activities, and equipment used:

The project will involve sample preparation (typically polymer synthesis methods), structural characterisation (x-ray diffraction, Raman scattering, electron microscopy and mechanical testing), thermal measurements (contact thermometry, infra-red imaging and calorimetry) and thermal modelling (Landau analysis and finite-element analysis). The project will also involve experiments in large facilities (Diamond Light Source, ALBA synchrotron).

Locations of equipment / collaborators:

All in the Blackett Laboratory.