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Postgraduate Research Opportunities

School of Physics Postgraduate Research Expression of Interest

PhD projects currently available in the School of Physics are listed below. If one of these projects interests you, please get in touch with the project leader, providing the necessary information needed for an initial contact. In particular indicate your degree, your final or expected mark, your previous research experience if any, why you are interested in the projects, and why you believe you are a suitable candidate.

Postgraduate research positions available in the School of Physics

Quantum dynamics on adaptive networks

Project Title: Quantum dynamics on adaptive networks
Theme: Quantum Science
Supervisor: Prof Mark Mitchison
Email: MITCHISM@tcd.ie

Funding Information: To be funded via IRC application

Background: One of the defining characteristics of life is its ability to adapt to changes in its surroundings. However, adaptation can also be observed in non-living systems, such as self-assembling polymers, or active colloidal particles that flock together like birds. The aim of this project is to explore quantum-mechanical many-body systems that can adapt to external stimuli. This could describe, for example, electron transport along flexible polymers, quantum simulators using arrays of Rydberg atoms, or networks of coupled quantum sensors under feedback control.

Innovation: A numerical approach has recently been developed by Prof. Mitchison to study quantum dynamics on adaptive networks exactly. The project will exploit this approach together with very recent developments in classical nano-physics and apply them to analyse a new class of quantum many-body systems that are just beginning to be explored in experiments.

Collaboration: The research will be carried out in the theory group led by Prof. Mitchison, with the possibility of working together with Mitchison’s collaborators in Germany and Switzerland.

Objectives and Methodology: The objective of this project is to study the rich quantum many-body physics that arises from the interplay between quantum dynamics and adaptation. The first part of the project will be to carry out numerical simulations of electron transport through a network (e.g. a large molecule) whose structure fluctuates in time (e.g. due to thermal fluctuations of a surrounding solvent). The aim will be to explore what kinds of network structures emerge from the interplay between environmental noise and coherent electron dynamics. This can then be extended in many different directions: analytical solutions, non-equilibrium phase transitions, applications to quantum metrology etc. This marks the beginning of a completely new area of quantum research and the student will have the opportunity to shape its development.

Essential/Desired Abilities: The successful applicant should have an interest in analytical and numerical problem solving and a willingness to learn, and must be on track for a 1st class degree in Physics or a related subject.

Reference: J. England, Dissipative adaptation in driven self-assembly, Nature Nanotech. 10, 919 (2015), https://www.nature.com/articles/nnano.2015.250

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Responsive Photonic Arrays

Project Title: Responsive Photonic Arrays
Theme: Photonics
Supervisor: Prof Louise Bradley
Email: BRADLEL@tcd.ie
Funding Information: IRC application

Background: Over the past decade there has been enormous interest in the development of mechanochromic photonics crystals as visual sensors. There are typically three ways to produce colour; pigmentation, emission or structural colour. Mechanchromic structures explit structural colour resulting from the interference of light. A general term of structues that can be used to manipulate colour in this way is photonic crystals. The reflected or transmitted colour depends on the materials and structure. The structures can be as simple of planar thin films or as complex as the features in the blue morpho butterfly wings or 3D opal crystals. Many structures are inspired by those occurring in nature. Mechanochromic structures use materials which swell in response to a stimulus (liquid, gas, chemical) or which can be stretched or compressed with a resulting changing in the observed colour. The extent of the extent of the colour change, the sensitivity to the stimulus and the response time are all critical parameters that must be considered depending on the specific application. Often the structures fabricated to date are relatively simple, such as multi-planar layers or a grating on a surface, and the range of colour tuning is quite limited.

Innovation: The innovation in this project is that we will investigate structures that can be fabricated via direct laser writing using two photon polymerization. The Florea group is developing a range of responsive materials that are compatible with direct laser writing. The combination of novel materials with 3D printing opens up new horizons for photonic crystals and responsive visual sensors. One can design for a hierarchy of optical properties based on more complex designs which can have greater sensitivity to particular stimuli, and operate in specific wavelength regions. Previously it had been reported that photonic structures made by direct laser writing would operate in the infrared spectral range due to their micrometer length scales. However, we have recently published a paper showing visible colour from grid structures fabricated using a vapour responsive hydrogel. The colour of the structures redshifts as the vapour concentration is increased and the response is sensitive to the different vapours. Visual sensors remove the need for complex equipment and trained personnel for monitoring and testing in many environments from point of care medicine, to chemical testing or environmental testing.

Collaboration: This project is in collaboration with Prof. Larisa Florea in the School of Chemistry. As it is a collaborative project it will offer lots of opportunity for discussion with the material scientists so that we can understand and balance what is possible from a materials perspective with what is required from a photonics perspective to achieve the optimal sensor response. Our contribution to the project is in the structure design, materials characterization, optical characterization of the laser printed structures and simulation of experimental results to understand the material changes and how the sensors can be further optimized. The project is also in collaboration with Dr. Radislav Potyrailo, General Electric Research, USA.

Objectives and Methodology: The objective of the objective of this project will be to develop solution based chemical sensors. A bulk hydrogel has a refractive index close to that of water, and will not be so visible. This project will explore the use of hydrogel with incorporated nanomaterials such that the material has a modified effective index and/or becomes a layer material. These nanomaterials can be dielectric or metallic. The first aspect of the project will be the investigation of photonic crystal designs such as grids, pillars, woodpile, and opal structures using these novel materials. This will determine the volume concentrations of the nanomaterials, the layer spacings within ordered materials and the optimum structures for visual sensors in solution environments. We will also numerically simulate the swelling to investigate the sensitivity of the sensor. The numerical modelling will be carried out using a combination of transfer matrix and finite difference time domain tools available in the Bradley group. The novel materials will be optically characterized using a ranged of techniques such as ellipsometry and dark field microscopy. Selected structures will be fabricated using the direct laser writing and will be characterized using custom built optical testbeds. The angle dependent reflection and transmission spectra will be measured as the structures experience a rage of stimuli of varying concentrations. Simulation of the experimental results provides a feedback loop with the design to understand the level of swelling and refractive index changes that occur in response to the various stimuli in the solution. The PhD student will undertake all elements of the simulation and characterization. They will be fully involved in all aspects of the project.

Essential/Desired Abilities: The ideal candidate will have an Interest in understanding how new materials and fabrication processes can be exploited to create novel visual sensors for chemical, medical, mechanical and thermal applications. The project will have a combination of numerical simulation, design, fabrication and characterization. So the ideal candidate will be someone who is interested in learning a broad range of skills. The candidate must have a 1.1 in their third year exams with a good expectation of a 1.1 final degree classification.

Reference: Direct laser writing of vapour-responsive photonic arrays, C. Delaney et al, J. Mater. Chem. C, 2021, 9, 11674-11678

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Modelling Urban Light Emission for Energy and Environmental Applications

Project Title: Modelling Urban Light Emission for Energy and Environmental Applications
Theme: Energy
Supervisor: Prof Brian Espey
Email: ESPEYB@tcd.ie
Funding Information: IRC application

Background: Monitoring of the Earth at night has become standard and has been driven by the current generation of satellites which provide detailed quantitative light measurements at low radiance. Such night-time imagery can be used to trace energy and economic output as well as the effects of both natural and man-made disasters, e.g. Covid-19. However analysis of such material has primarily been qualitative since the details of the light emission and obstructions (natural and man-made), as well as radiative transfer through a varying atmosphere, have been complex to handle. Until now studies have either attempted to use simplified models of light emission, i.e. a “typical” emitting region and apply this model over entire cities, or involve complex radiative transfer codes which could handle small regions modelled in detail, but which prove computationally intensive to apply over large areas.

Innovation: “Closing the loop” and finding a detailed connection between ground emission and satellite measurements requires an understanding of how light is emitted and in what quantities in terms of both azimuth and elevation angles, i.e. the so-called “city emission function” or CEF. At low angles such light causes light pollution in the surrounding countryside, and at high angles this light is emitted to space. To derive a complete estimate of the energy emitted from either space- or ground-based measurements therefore requires us to estimate the CEF. An approach developed here in Trinity utilises geographical information systems (GIS) software to model large areas by using the large amount of information about light sources as well as 3D urban LiDAR measurements to 1m spatial resolution. Using this approach we have been able to calculate the CEF due to public lighting for a number of urban areas and show that it is similar to that assumed or back-modelled from all-sky measurements from remote sites. This work has been well received internationally.

Collaboration: This project involves international collaboration with partners in Canada (Prof. Martin Aubé) and Austria (Prof. Günther Wuchterl of Kuffner-Sternwarte, Vienna).

Objectives and Methodology: The initial work on this topic demonstrated the practicality of the approach. Since then, more extensive LiDAR mapping data has been made available publically, opening up the opportunity of making the first detailed model of the light emission from an entire city, as well as to derive equivalent results for a range of representative Irish towns. The project would utilise these results to determine if the derived CEF results depend on the type of land use, the importance of sources of light other than public lighting, seasonal dependence (e.g. due to foliage) etc. Results will be compared with observations of light emission in other locations, especially in Canada and Austria and used as input to Prof. Aubé’s Illimina radiative transfer code. The output of this work will be estimates of total light and energy output from Irish towns which can be extended more generally to study the influence of light pollution on the environment.

Essential/Desired Abilities: You need be self-starter who is competent in computational skills and with an interest in applying (astro)physics to practical problems. Software used in this work will centre around the freeware R and QGIS codes, but Python programming will also be required.

Reference: Espey, B. 2021 Empirical Modelling of Public Lighting Emission Functions, Remote Sensing Remote Sens. 2021, 13(19), 3827; https://doi.org/10.3390/rs13193827

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Quantum algorithms for embedded quantum systems in real materials

Project Title: Quantum algorithms for embedded quantum systems in real materials
Theme: Quantum Science
Supervisor: Dr Andrea Droghetti
Email: DROGHEA@tcd.ie
Funding Information: IRC application

Background: Many systems in the material world can be described as “quantum impurities” embedded in an environment. For example, consider a small molecule adsorbed on a metallic surface or a defect in a semiconductor. The molecule/defect is the quantum impurity while the surface/semiconductor is the environment. A characteristic of these quantum impurities is strong electron correlation, which means that the motion of one electron strongly depends on all other electrons owing to the large Coulomb interaction and quantum confinement. In practice electron correlation makes the quantum mechanical description extremely complex (if not even impossible) via analytic calculations, while numerical simulations are extremely expensive and require often out-of-reach computational resources on classical computers. On the other hand, quantum computers can potentially lead to exponential improvement in the computational speed. This is what you are going to address in this project.

Innovation: Quantum computers open a new paradigm for information technologies and high-end computing. Noisy intermediate scale quantum computers are already available, and larger and noiseless quantum computers are expected within the next 10 years. In this context, the proposed project sets timely ambitious tasks expected to advance electronic structure theory towards the new age of quantum computing.

Collaboration: The project will be co-supervised by Prof. Stefano Sanvito (sanvitos@tcd.ie). A close collaboration with Dr. Ivan Rungger at the UK National Physical Laboratory is expected throughout the project.

Objectives and Methodology: The project aims at developing: - Electronic structure methods to effectively describe different material systems (e.g. molecules on surfaces) as impurities embedded in an environment. - Develop quantum algorithms for impurity solvers. - Test these algorithms on quantum computer simulators and eventually on a real quantum computer. You will start by generalizing the embedding method presented in Ref. [1] to describe several technologically relevant material systems as impurities coupled to an environment. You will then implement methods, such as the one-crossing approximation [2], for the solutions of these impurity problems and gain a very solid expertise in quantum many-body theory and high-end (classical) computing. Finally, you will address the solution via methods, such as dynamical mean-field theory, suitable for quantum computing algorithms [3, 4]. You will develop advanced knowledge of Python, and of Python based quantum computing frameworks such as IBM’s Qiskit.

Essential/Desired Abilities: Solid basis of quantum mechanics. Interest and passion for computational problems and coding.

Reference: [1] A. Droghetti and I. Rungger, Phys. Rev. B 95, 085131 (2017). [2] D. Jacob, J. Phys.: Condens. Matter 27, 245606 (2015) [3] B. Bauer, D. Wecker, A.J. Millis, M.B. Hastings, and M. Troyer, Phys. Rev. X 6, 031045 (2016). [4] I. Rungger, N. Fitzpatrick, H. Chen, C. H. Alderete, H. Apel, A. Cowtan, A. Patterson, D. Munoz Ramo, Y. Zhu, N. H. Nguyen, E. Grant, S. Chretien, L. Wossnig, N. M. Linke and R. Duncan, arXiv:1910.04735.

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A study of bimetallic catalysis using surface science and x-ray spectroscopic methods for efficient lower temperature operation of solid oxide fuel cells

Project Title: A study of bimetallic catalysis using surface science and x-ray spectroscopic methods for efficient lower temperature operation of solid oxide fuel cells
Theme: Energy
Supervisor: Prof Cormac Mc Guinness
Email: CMCGUIN@tcd.ie
Funding Information: Funding via IRC application

Background: Cathode materials used within solid oxide fuel cells play a significant role in their operation and efficiency. Bimetallic catalysis and the resultant lower temperature reduction-oxidation behaviour of specific metal oxides on particular elemental surfaces, and/or alloys, has the potential to allow for more efficient lower temperature operation of these solid oxide fuel cells.

Innovation: The innovation in this project is that it will characterise a novel specific bimetallic elemental alloy catalytic system and the mechanism of its low-temperature redox behaviour through in-situ x-ray spectroscopies at the synchrotron, while in parallel develop a robust co-doped metal oxide material to interface with known solid electrolyte. The further development of novel cathode and anode materials in conjunction with electrolytes for solid oxide fuel cells is an imperative.

Collaboration: This project will involve internal collaborations within the School of Physics with Prof. Stamenov and Prof. Jones, and external collaborators in Imperial College London with Prof. David Payne. Experiments will also take place at international synchrotron radiation facilities, such as Diamond Light Source, UK and MAX-IV laboratory, Sweden.

Objectives and Methodology: The objective is to observe, characterise and understand a particular class of bimetallic catalytic reduction-oxidation interactions that can be useful in low-temperature fuel cells. Methodologies encompass a combination of materials thin film deposition, surface science investigations, materials characterisation techniques inclusive of lab based x-ray photoemission spectroscopy (XPS), in-situ ambient pressure x-ray spectroscopy (APXPS), and synchrotron radiation based spectroscopies to examine buried interfaces. These will include x-ray emission and absorption spectroscopies (XES/XAS), resonant inelastic x-ray scattering (RIXS) and hard x-ray photoemission spectroscopy (HAXPES).

Essential/Desired Abilities: An innovative and self-starting student, willing to learn and develop their physical insight.

Reference: Contact Prof. McGuinness for references.

Further information

Enabling two-dimensional memtransistors by plasma modification

Project Title: Enabling two-dimensional memtransistors by plasma modification
Theme: Nanoelectronics and Nanotechnology
Supervisor: Prof Hongzhou Zhang
Email: HOZHANG@tcd.ie
Funding Information: To be funded via IRC application

Background: Memristors are electric switches with programmable and non-volatile resistance. They are potential building blocks for next-generation computational platform. However, to date, poor device reliability and low scalability render conventional memristors uncompetitive for device applications. To address these challenges, Prof Zhang’s group have recently demonstrated a new type of two-dimensional (2D) memtransistor via advanced ion beam technology [1]. The 2D memtransistor shows promising performance and can largely address the reliability issue. However, the ion-beam method is not viable for large-scale fabrication, which limits the prospect of the new devices for large-scale industry exploitation. This project is to meet the scalability issue head-on and develop a plasma-based technology to create new opportunities for the emerging device.

Innovation: The central innovation of the 2D memtransistor is to introduce resistive switching in 2D nanosheet (e.g. 2D MoS2) by the controlled creation of defects via localised and site specific modification [2]. We note defect-free 2D MoS2 does not exhibit resistive switching. In the ion beam approach, we use the helium-ion-microscopy (HIM) technique [2] to introduce the defects, which exploits the preferential milling and highly-localised nature of the helium-ion beam to create site and type specific defects in 2D MoS2. In this project, we will create the defects using plasma treatment, while new approaches will be developed to achieve site-specific introduction of defects via the plasma treatment.

Collaboration: This project will be integrated with our on-going SFI Frontier project, which is focused on the development of HIM-enabled 2D memtransistors. You will be collaborating with Prof Zhang’s group and their academic and industry collaborators (e.g. the leading ion-centre at HZDR and Intel Ireland).

Objectives and Methodology: The project aims to establish the viability of scalable fabrication of two-dimensional (2D) memtransistors via plasma treatment. We plan to tune the electrical resistivity of few-layer/monolayer 2D nanosheets by optimizing plasma conditions [3]. In addition, the plasma treatment can improve the electrical contact between electrodes and 2D materials, enhancing device performance. To develop this technology, you will grasp and develop a range of experimental methodologies for nanodevice fabrication and characterization (e.g. Chemical vapor deposition, electron beam lithography, Raman spectroscopy, etc.). The investigation will also generate new knowledge in relevant fields, e.g. emerging nanoelectronic devices (e.g. the defect-regulated electronic behaviours in 2D system), nanomaterial processing (e.g. the interaction between plasma and 2D lattices) and nanodevice fabrication (e.g. electrical contact with 2D materials).

Essential/Desired Abilities: You would be interested in hands-on experimental approaches in physics and nanoscience. You will have achieved 2.1 class honours for a postgraduate position and 1st class for the IRC application.

Reference: [1] Jadwiszczak, J., et al., MoS2 Memtransistors Fabricated by Localized Helium Ion Beam Irradiation. ACS Nano, 2019. 13(12): p. 14262-14273. [2] Fox, D.S., et al., Nanopatterning and Electrical Tuning of MoS2 Layers with a Subnanometer Helium Ion Beam. Nano Letters, 2015. 15(8): p. 5307-5313. [3] J. Jadwiszczak, et al., “Oxide-mediated recovery of field-effect mobility in plasma-treated MoS2”, 10.1126/sciadv.aao503, Science Advances, 2018. 4(3).

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Inverse Design of Quantum Sensing Protocols

Project Title: Inverse Design of Quantum Sensing Protocols
Theme: Theoretical and Computational Solid State
Supervisor: Prof Paul Eastham
Email: EASTHAMP@tcd.ie
Funding Information: To be funded via IRC application.

Background: Quantum sensing entails using a controllable, engineered quantum system, such as a superconducting circuit, a single atom, or a quantum dot, to make a measurement of its surroundings. Quantum sensors have been designed and implemented to measure electric and magnetic fields, pressure, rotation, temperature, and chemical concentration, among other quantities. At their heart is a sensing protocol, in which the sensor's state is prepared, using external fields, evolves under the action of the quantity to be measured, and is then read out, typically through luminescence or microwave emission. The quantum sensing protocols used so far draw heavily on techniques developed in the area of nuclear magnetic resonance, such as Ramsey interferometry. However, unlike the nuclear spin, which interacts only weakly with its environment, the sensors now being developed have strong interactions with a complex environment. This is both a blessing and a curse: these strong interactions imply high sensitivity to the quantity to be measured, but they also act to destroy the information about that measurement. In this project you will develop an inverse design methodology and use it to discover new protocols that make use of quantum entanglement and strong-coupling to complex environments.

Innovation: In forward design one specifies the proposed device and uses a simulation to assess its performance. In inverse design one starts from the desired result, typically high performance, and uses simulations to explore the vast space of different possible designs and find those which achieve that result. However, this is only possible if a design can be simulated very efficiently. A quantum sensor is a so-called open quantum system: one which interacts with its environment. Simulations of such problems have until recently only been possible under drastic and often unrealistic assumptions. However, we are working with numerical methods which transform our ability to simulate general open quantum systems. This project will use these methods for the inverse design of quantum sensing protocols. You will discover new high-performance protocols, and explore the fundamental limits on quantum sensors in realistic settings. The work could take in other problems in quantum science and technology, such as studying the transmission of quantum information through hot, noisy environments.

Collaboration: You will join the Quantum Theory of Light and Matter Group led by Prof. Eastham, and work in collaboration with him and other group members. You would interact with other P.I.s and their groups, including Profs. Ortwin Hess and John Goold in Trinity, and Drs. Brendon Lovett and Jonathan Keeling of the University of St Andrews.

Objectives and Methodology: 1. Identify models of quantum sensors, and of the state preparation and read-out process. A variety of sensors could be considered, such as the strong-coupling nanoplasmonic assay systems proposed by Prof. Hess's group. 2. Identify quantitative measures of performance (related to the quantum information about the measurement obtained in the read-out) and parameterizations of the state preparation and read-out processes, taking into account the resource costs such as available time or energy for the process. 3. Evaluate these performance measures, using numerical simulations and analytical studies of idealized models, and derive, numerically and analytically, optimized quantum sensing protocols.

Essential/Desired Abilities: You would have completed, or be in the final year, of a degree in which physics is a major component. You would be interested in theoretical and computational approaches and their application to condensed-matter and quantum optics, and looking to make new discoveries that span fundamental quantum physics and its applications.

Reference: https://www.tcd.ie/Physics/research/groups/qlamg easthamp@tcd.ie

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Quantum thermodynamics of continuous measurements

Project Title: Quantum thermodynamics of continuous measurements
Theme: Theoretical and Computational Solid State
Supervisor: Prof Mark Mitchison
Email: MITCHISM@tcd.ie
Funding Information: To be funded via IRC application

Background: Quantum physics underpins the most precise measurement devices that have ever been constructed, such as atomic clocks and gravitational-wave detectors. But what is the energetic cost of such precision? Are there limits to how well we can measure time and space with a limited energy budget? After all, measuring devices are machines and they obey the laws of thermodynamics. There is now a pressing need to update these laws to describe the fundamental limits of quantum measurement. This will ultimately help to design more energy efficient quantum technologies, ensuring their future scalability and environmental sustainability.

Innovation: Recent research by Prof. Mitchison has shown that thermodynamics fundamentally constrains our ability to measure time [1], corroborated subsequently by theory [2] and experiment [3]. This project will investigate the consequences of this finding for the many quantum technologies that rely on precise clocks, as well as extending to other kinds of continuous measurements.

Collaboration: The project will be carried out within the theory group led by Prof. Mitchison, with opportunities to collaborate with other members of the growing team of quantum physicists at Trinity. The research will lead to predictions that may be tested in the laboratories of Prof. Mitchison’s experimentalist collaborators at the University of Oxford or the Johannes Gutenberg University Mainz.

Objectives and Methodology: The student will develop a comprehensive theoretical framework to describe continuously measured quantum systems that are driven out of equilibrium. The goal will be to connect the rate of energy dissipation with the signal-to-noise ratio and the achievable measurement precision. This analysis will involve a combination of advanced techniques from the theory of open quantum systems and quantum information. The theoretical results will be used to derive fundamental precision limits for atomic quantum sensors and molecular electronic devices.

Essential/Desired Abilities: The successful applicant should have an interest in analytical and numerical problem solving and a willingness to learn, and must be on track for a 1st class degree in Physics or a related subject.

Reference: 
[1] Paul Erker, Mark T. Mitchison, Ralph Silva, Mischa P. Woods, Nicolas Brunner, and Marcus Huber, Autonomous Quantum Clocks: Does Thermodynamics Limit Our Ability to Measure Time? Phys. Rev. X 7, 031022 (2017), DOI: 10.1103/PhysRevX.7.031022 
[2] G. J. Milburn, Thermodynamics of clocks, Contemporary Physics 61, 69 (2020), https://arxiv.org/abs/2007.02217 

[3] A. N. Pearson, Y. Guryanova, P. Erker, E. A. Laird, G. A. D. Briggs, M. Huber, and N. Ares, Measuring the Thermodynamic Cost of Timekeeping, Phys. Rev. X 11, 021029 (2021), DOI: 10.1103/PhysRevX.11.021029 

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Using Low-cost Magnetometers to Predict Atomic-scale Imaging Distortions

Project Title: Using Low-cost Magnetometers to Predict Atomic-scale Imaging Distortions
Theme: Microscopy and Characterisation
Supervisor: Prof Lewys Jones
Email: JONESL1@tcd.ie
Funding Information: IRC applicant encouraged, but full funding (EU fees + stipend) available for exceptional candidates.

Background: The scanning transmission electron microscope (STEM) is one of the most sensitive imaging instruments in use in materials research. It can yield magnifications of 40 million times or more and directly image individual atoms within a specimen. In the STEM, images are acquired pixel-by-pixel in a scanned manner with the frame building up over typically a few seconds. This means that, unless the microscope laboratory is perfectly shielded from magnetic interference, the recorded images can contain small distortions from stray fields. The sensitivity of the instrument to image distortion is estimated to be ≈0.5Å/mG [1]. The STEM is not affected by the static magnetic field of the Earth, ≈491mG in Ireland, but rather any time-varying fluctuations (such as from passing cars/trains).

Innovation: In this project we aim to build a low-cost DIY magnetic monitoring device using one or more low-cost PNI-RM3100 three-axis magnetic sensors [2,3]. We will 3D-print the remaining components in the group’s lab. The student will be trained to operate the transmission electron microscopes (TEM) in the Advanced Microscopy Laboratory (AML), and will then record atomic-resolution image series from along with synchronised readings of the magnetic field. Electron beam placement-errors will be evaluated from atomic-resolution image series [4]. Machine learning will be used to identify correlations between the image-distortions and the strength of varying magnetic fluctuations, before mitigation strategies are proposed.

Collaboration: Depending on the success of the project, there is the possibility to collaborate with one of our existing industrial partners. In this case travel to the collaborator within the EU would be likely.

Objectives and Methodology: By the end of the project, the student will have: • evaluated the feasibility of using low-cost sensors for indoor magnetic monitoring, • learnt to independently operate the transmission electron microscopes (TEM), • evaluated the correlation between detected fields and observed distortions in atomic resolution images, and • developed a predictive model and proposals for environmental mitigation.

Essential/Desired Abilities: A first class or upper-second degree at either Masters or Honours Bachelors is required in the areas of Physics, Electronics, Electronic Engineering or related subjects. The ideal student will have an interest in instrumentation design and manufacture. Experience with electronics, Raspberry Pi (or similar), or 3D printing would be a bonus but not essential.

Reference: [1] D. A. Muller, E. J. Kirkland, M. G. Thomas, J. L. Grazul, L. Fitting, and M. Weyland, Ultramicroscopy 106, 1033 (2006). [2] C. Gilbert, AIP Conf. Proc. (2019), p. 070007. [3] M. Hodoň, O. Karpiš, P. Ševčík, and A. Kociánová, Sensors 21, 1 (2021). [4] L. Jones et al., Adv. Struct. Chem. Imaging 1, 8 (2015).

Further information

Simulation of organic molecules for light emitting applications

Project Title: Simulation of organic molecules for light emitting applications
Theme: Theoretical and Computational Solid State
Supervisor: Prof Charles Patterson
Email: CPTTRSON@tcd.ie
Funding Information: IRC Application

Background: Organic light emitting diodes (OLEDs) are the active elements in many smartphones and TV displays. Previous generation OLEDs contain expensive and environmentally damaging heavy elements needed to harvest sufficient light energy to make them commercially competitive. Current OLEDs do not require heavy elements but instead rely on a mechanism known as thermally activated delayed fluorescence (TADF) to achieve high efficiency. Red and green TADF emitters are commercially available, but blue emitters to replace previous generation OLEDs are needed. This project will investigate the mechanism of TADF OLEDs and how the emitter host matrix affects their performance. When electrons and holes combine to form excitonic excited states in organic materials, statistically, triplet spin states dominate singlet states by 3:1 (or 75% to 25%). The latter decay rapidly via fluorescence. The radiative decay rate for the former is slower by several orders of magnitude as it is allowed only via weak spin orbit coupling in C atoms. Heavy element compounds with much stronger spin-orbit coupling than carbon are added to these phosphorescent (Ph)OLEDs to assist radiative decay of triplet states and hence achieve near 100% internal quantum efficiency. These compounds are expensive, toxic and may damage the environment. All-organic OLEDs do not require the heavy element compounds needed to attain high efficiency emission from spin triplet states in PhOLEDs. Instead, when bound triplet exciton states form from injected electrons and holes, clever molecular design ensures that the small difference in the triplet and singlet excited states is of order kT so that triplet states may undergo a reverse inter-system crossing (RISC) to the singlet state and then decay via fluorescence.

Innovation: Triplet excited states of many organic molecules lie around 1 eV below the singlet excited state. Inter system crossing (ISC) is a process in which singlet states relax to the corresponding triplet state. Usually this is a 1-way process because of the large energy difference between states. RISC, in which a triplet excited state converts to a singlet, is possible if the singlet-triplet energy difference is of the order of kT or less (around 25 meV at room temperature). Molecules which have small singlet-triplet energy splittings usually have HOMO and LUMO orbitals located in different regions of the molecule so that the exchange integral which determines level splitting is small. This means that low lying excited states have strong charge transfer (CT) character where the excited electron and hole are in separate parts of the molecule. The large excited state dipole moment couples strongly to any polar environment of the molecule. It has been shown that, especially, singlet CT state (1CT) emission energies can be tuned by varying the host organic compound. This is believed to occur via the interaction of the excited state dipole with its host molecules. Thus an appropriate choice of host matrix for a specific emitter can yield a singlet triplet splitting of the order of kT. This can be done on an empirical basis, but clearly theory can make an important contribution to understanding the emitter-host interaction in obtaining the desired singlet-triplet splitting.

Collaboration: There are opportunities to collaborate with a group in Queens University Belfast in code development

Objectives and Methodology: GW and Bethe-Salpeter equation (BSE) approaches have long been recognised as the state of the art methods for calculating excited states in matter. The Exciton code has been developed by the PI for this project and performs GW and BSE calculations in local basis sets. See references below.

Essential/Desired Abilities: You will have good programming and computational physics skills and an interest in molecular and condensed matter physics. There are opportunities to get involved in software development if you have an interest and aptitude. The project also requires a good knowledge of many-body quantum physics and methods for studying interactions between charged fermions.

Reference: Photoabsorption Spectra of Small Na Clusters: TDHF and BSE versus CI and experiment C. H. Patterson, Phys. Rev. Mater. 3, 043804 (2019) Density fitting in periodic systems: Application to TDHF in diamond and oxides C. H. Patterson, J. Chem. Phys. 153, 064107 (2020) Molecular library of OLED host materials—Evaluating the multiscale simulation workflow A. Mondal, et al. Chem. Phys. Rev. 2, 031304 (2021); doi:10.1063/5.0049513

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Soliton spectroscopy and dynamics in aluminium nitride (AlN) and lithium niobate (LiNbO3) micro-resonators

Project Title: Soliton spectroscopy and dynamics in aluminium nitride (AlN) and lithium niobate (LiNbO3) micro-resonators
Theme:
Supervisor: Prof John Donegan
Email: jdonegan@tcd.ie
Funding Information: to be funded via IRC application

Background: A soliton or solitary wave is a self-reinforcing wave packet that maintains its shape while it propagates at a constant velocity. Solitons are caused by a cancellation of nonlinear and dispersive effects in the medium. Solitons are the key driver in the development of an optical frequency reference, with uncertainty of 1 part in 10^-15. We observe solitons in microresonators that show ultra-broad comb spectra, that is a spectrum with equally spaced lines.

Innovation: We will develop novel comb and soliton sources with particular applications for visible and near-UV sources.

Collaboration: We work with the Guo group for development of novel microresonators.

Objectives and Methodology: Develop new range of solitons in AlN resonators and LiNbO3 (which can be electrically tuned) Fabrication of rings to produce quality factors of 10^7 with e-beam lithography Modelling by nonlinear Schroedinger Equation Use laser devices developed in Donegan group to form a fully integrated system with comb lines from UV through visible to near IR

Essential/Desired Abilities: Students from Physics background or Materials Science. Student must have achieved 1st class honours in 3rd year. The IRC is very competitive.

Reference: Near-octave-spanning breathing soliton crystal in an AlN microresonator Weng, H., Afridi, A.A., Liu, J., ...Guo, W., Donegan, J.F. Optics Letters, 2021, 46(14), pp. 3436–3439 Directly accessing octave-spanning dissipative Kerr soliton frequency combs in an AlN microresonator WENG, H., LIU, J., AFRIDI, A.A., ...DONEGAN, J.F., GUO, W. Photonics Research, 2021, 9(7), pp. 1351–1357

Further information

Confined packings of hard and soft objects

Project Title: Confined packings of hard and soft objects
Theme: Nanobiophysics and Soft Matter
Supervisor: Prof Stefan Hutzler
Email: shutzler@tcd.ie
Funding Information: to be funded via IRC application

Background: Marbles dropped into a cylinder of comparable diameter crystallize spontaneously into an ordered arrangement, as do equal volume soft bubbles. For hard spheres the type of arrangement depends on the ratio of sphere to cylinder diameter; in the case of deformable bubbles the application of an external pressure is a further control parameter. Examples of confined crystalline structures (where the confinement does not have to be cylindrical) are found on many scales, in nature and in the laboratory. They include packings of buckyballs in carbon nanotubes, packings of peas in a pod and also arrangements of cells in the epithelia.

Innovation: The project will build upon the expertise in various types of packing problems developed in the Foams and Complex Systems Group led by Prof. Stefan Hutzler. Examples of this include an experimental realization of the Weaire-Phelan structure in foams, the scutoid structure found in bubbles between curved cylinders, and simulations of buckled chains of hard spheres. In all of the above it was the interplay between theory and simple experiment which led to progress.

Collaboration: The project will benefit from Hutzler’s contacts in the foams and packing communities, in particular with Dr. Adil Mughal’s group in Aberystwyth, Wales, and with Prof Denis Weaire, F.R.S.

Objectives and Methodology: The aim of this project is to develop a generic understanding of confined packings via the development of theoretical and numerical models, together with the design of simple experiments which demonstrate key principles.

Essential/Desired Abilities: computational skills (e.g. Python, Mathematica), image analysis, visualisation, basic experimental lab skills

Reference: Hutzler S, Mughal A, Ryan-Purcell J, Irannezhad A, Weaire D, Buckling of a linear chain of hard spheres in a harmonic confining potential: Numerical and analytical results for low and high compression, Physical Review E 102 022905 (2020). Mughal A, Cox SJ, Weaire D, Burke SR, Hutzler S, Demonstration and interpretation of scutoid cells formed in a quasi-2D soap froth, Philosophical Magazine Letters 98 358 (2019). Gabbrielli R, Meagher AJ, Weaire D, Brakke KA and Hutzler S (2012), An experimental realization of the Weaire-Phelan structure in monodisperse liquid foam, Philosophical Magazine Letters, 92, 1-6 (2012).

Further information

How do inter-nanotube junctions effect the mobility of high-performance printed nanotube transistors?

Project Title: How do inter-nanotube junctions effect the mobility of high-performance printed nanotube transistors?
Supervisor: Prof Jonathan Coleman
Email: colemaj@tcd.ie
Funding Information: To be funded via IRC application

Background: Printed electronics is a rapidly growing field where nanomaterials are solution-processed into electronic devices and extremely low cost is more important than device performance (typical device mobility <10 cm2/Vs). However, printed networks of carbon nanotubes (see image) are extremely promising and have demonstrated mobilities >50 cm2/Vs (c.f. silicon mobility ~ 1000 cm2/Vs). The mobility of nanotube networks is limited by the rate at which electrons can move from nanotube to nanotube, quantified by the so-called junction resistance, Rj. However, very little is known about the size of Rj and there is no simple method to measure it. This is a real problem as increasing mobility is challenging if you can’t even measure the limiting factor.

Innovation: Recently, Prof Coleman derived an equation linking network mobility to factors such as nanotube length, diameter and junction resistance. This allows easily obtainable data such as conductivity versus nanotube length to be fitted outputting Rj. More importantly, it allows AC impedance measurements to be used to output Rj directly. This breakthrough has the potential to revolutionize this device area.

Collaboration: Scope for collaboration with various groups e.g. Newcastle University and Uni Cambridge.

Objectives and Methodology: The objective is to use Colemans equation to develop experimental methods to measure the junction resistance in nanotube networks. This will allow detailed experiments, for example temperature dependent conductivity and impedance studies, to elucidate the nature of the junction resistance.

Essential/Desired Abilities: The successful candidate will be a physics or N-PCAM student.

Reference: DOI: 10.1088/1361-6528/aafbbe

Further information

Understanding what limits mobility in printed nanosheet networks

Project Title: Understanding what limits mobility in printed nanosheet networks
Supervisor: Prof Jonathan Coleman
Email: colemaj@tcd.ie
Funding Information: To be funded via IRC application


Background: Printed electronics is a rapidly growing field where nanomaterials are solution-processed into electronic devices and extremely low cost is more important than device performance (typical device mobility <10 cm2/Vs). While printed networks of 2D nanosheets such as MoS2 or phosphorene (nanosheet mobility 10-1000 cm2/Vs) hold great promise, real experiments have only yielded network mobilities between 0.001 and 10 cm2/Vs. While it is known that network mobility is limited by the nature of the junctions between adjacent nanosheets (see figure), it is not even known what the magnitude of the junction resistance is. Recently, Coleman’s group has developed methods to control the network structure from misoriented to aligned (see image). While one might expect aligned networks to have lower junction resistance and higher mobility, these parameters have not been measured and correlated. If highly aligned networks can be produced, there is scope to achieve extremely low junction resistance and record mobility and thus unprecedented transistor performance.

Innovation: Recently, Colemans group have developed the ability to control the dimensions of 2D nanosheets and the structure of nanosheet networks. In addition, Prof Coleman has derived an equation linking network mobility to factors such as nanosheet mobility, thickness and junction resistance. This allows easily obtainable data such as network conductivity versus nanosheet thickness to be fitted outputting Rj. More importantly, it allows AC impedance measurements to be used to output Rj directly. This breakthrough will allow us to understand the factors limiting network mobility and use this understanding to create networks with minimal junction resistance and so maximal mobility.

Collaboration: Scope for collaboration with various groups e.g. Newcastle University, Strasbourg Uni, Kassel Uni and Uni Cambridge.

Objectives and Methodology: The objective is to control the structure of nanosheet networks with the aim of maximising carrier mobility. We aim to achieve state-of-the-art printed devices with mobility >10 cm2/Vs. We will use different printing methods as well as varying nanosheet dimensions to control the structure of nanosheet networks from misaligned to aligned. In parallel, we will use Colemans equation to measure the junction resistance in these networks as a function of nanosheet alignment. Networks with low junction resistance will be down-selected and fabricated into transistors for mobility measurement.

Essential/Desired Abilities: The successful candidate will be a physics or N-PCAM student.

Reference: An in-press review paper will be provided on request to colemaj@tcd.ie

Further information

Funding Information

Some projects are associated with grants, perhaps from SFI or the EU, which pay a student's fees and a stipend. Others do not and rely on the student applying for funding. These applicants can apply for funding from the following sources:

  • Irish Research Council (deadline 21 October)
  • TCD PG Scholarship and School of Physics Studentship schemes.
  • For Chinese students who are interested in applying to the Chinese Scholarship Council for funding. Further information on the joint TCD-CSC scholarship is available here.
  • Students that are eligible to apply for international PhD scholarships should contact a prospective School of Physics academic supervisor, for more details contact, Dr Colm Stephens (STEPHEC@tcd.ie).