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Since the Nobel Prize in Chemistry in 2000 for the discovery and the development of conductive polymers, organic electronics has emerged as a promising technology for the development of a next generation of innovative and smart electro-optical functional devices. Despite the great potential of organic electronic materials and devices, organic light-emitting diodes (OLEDs) for display and lighting applications are currently the only technology that has reached the performance level suitable for a large-scale commercialization. Other organic electronic devices such as solar cells, photodetectors, field-effect transistors (FETs) and thermoelectric generators still need substantial research efforts to improve their properties and realize their full potential for a variety of applications including the Internet of Things, energy harvesting, healthcare and wearable electronics. 

Strong light-matter coupling has been explored in organic semiconductors leading to the observations of polariton condensation and high-efficiency polaritonic emission at room temperature.1 In the recent years, a variety of novel organic optoelectronic device architectures has emerged to exploit the unique features of this strong coupling regime. This research has led to the demonstration of optically-pumped organic polariton lasers,2 highly efficient polaritonic OLEDs with narrow band emission,3 organic polaritonic photodetectors with spectrally extended responsivity4 and polaritonic organic solar cells with reduced photon energy losses.5 Few recent works have also suggested the possibility to use strong coupling for boosting the conductive properties of organic thin films.6 While past research efforts to enhance organic electrical conductivity have been mainly focused on the development of novel materials, recent advances in nanostructured plasmonic metamaterials7 allowing to control the strength of the light-matter interactions could open exciting and still unexplored opportunities to improve the conductive properties of organic electronic devices. 

The successful PhD candidate will investigate the influence of innovative plasmonic metamaterial nanostructures on the electrical and electro-optical properties of novel strongly-coupled organic electronic device architectures. The results will provide new important guidelines to boost electrical conductivity and open a completely new toolbox to improve the performance of organic optoelectronic devices. The student will learn and apply a broad range of organic device fabrication and characterization techniques, work in a state-of-the-art cleanroom and use a cryogenic probe station to study the temperature dependence of the electrical properties of organic electronic materials. This project represents a unique opportunity for a motivated PhD student to work at the forefront of an interdisciplinary and timely research topic, and to gain strong expertise in different areas of research, from the engineering and characterization of advanced organic electronic architectures to the photophysics of organic conjugated materials and the physics of plasmonic metamaterials. 

To be eligible, applicants should hold or expect to receive a minimum 2:1 Honours degree (or the international equivalent) in physics, material science or any related disciplines. The successful candidate should be highly motivated to undertake multidisciplinary research and demonstrate enthusiasm for research, the ability to think and work both independently and in team, excellent analytic and communication skills. Previous experiences in organic electronics will be considered advantageous. The student will work in a new laboratory at the School of Physics and Astronomy of the University of St Andrews, interacting with faculty members, postdoctoral researchers and other postgraduate students involved in the well-equipped Organic Semiconductor Centre. A PhD scholarship of the University of St Andrews is available for Home/EU and international students. Note that non-UK applicants must imperatively meet English language entry requirement (IELTS with a minimum overall score of 6.5 or the equivalent).  The scholarship will cover 3.5 years of stipend and fees, and the School will cover costs associated with any required visa. The position will remain open until a suitable candidate is found. 

Informal enquiries are welcome and should be made by email to Dr Jean-Charles Ribierre (jr43@st-andrews.ac.uk).

[1] J. Keeling, S. Kena-Cohen, Annu. Rev. Phys. Chem. 71, 435 (2020).
[2] S. Kena-Cohen, Nature Photon. 4, 371 (2010); M. Wei et al., Laser & Photon. Rev. 15, 2100028 (2021).
[3] A. Mischok et al., Nature Photon. 17, 393 (2023).
[4] E. Eizner et al., ACS Photon. 5, 2921 (2018).
[5] V.C. Nikolis et al., Nature Comm. 10, 3706 (2019).
[6] E. Orgiu et al., Nature Mater. 14, 1123 (2015) ; K. Nagarajan et al., ACS Nano 14, 10219 (2020), A. Thomas et al., https://arxiv.org/abs/1911.01459; F. J. Garcia-Vidal et al., Science 373, eabd0336 (2021).
[7] P. Wang et al., Chem. Rev. 122, 15031 (2022); P. Huo et al., Adv. Opt. Mater. 7, 1801616 (2019).  

Water is one of the most miraculous gifts to humankind. Our present-day lifestyle, industrialization, farming practices, medical care and warfare activities have given rise to a wide range of contaminants of emerging concerns (CECs). They enter our environment through various pathways, accumulate leading to hazardous effects on ecological and human health.  Optical chemical sensors have a huge potential in sensitive, convenient, cost-effective and real-time environmental monitoring of pollutants. They make use of optical parameters like absorbance; Raman spectrum; and fluorescence intensity, wavelength, lifetime and quantum yield for detection of contaminants. Variation in any of these parameters in presence of specific contaminants gives detectable optical signals for detection.

This project, will develop trace optical sensors for industrial contaminants, and pharmaceuticals in water bodies. Experimental work will include clean-room fabrication of thin-film sensors, optical characterisation of their response to different contaminants, and testing the sensors in real-world environments.

• Organic Semiconductor Centre

Water is one of the most miraculous gifts to humankind. Our present-day lifestyle, industrialization, farming practices, medical care and warfare activities have given rise to a wide range of contaminants of emerging concerns (CECs). They enter our environment through various pathways, accumulate leading to hazardous effects on ecological and human health.  Optical chemical sensors have a huge potential in sensitive, convenient, cost-effective and real-time environmental monitoring of pollutants. They make use of optical parameters like absorbance; Raman spectrum; and fluorescence intensity, wavelength, lifetime and quantum yield for detection of contaminants. Variation in any of these parameters in presence of specific contaminants gives detectable optical signals for detection.

This project, will develop trace optical sensors for industrial contaminants, and pharmaceuticals in water bodies. Experimental work will include clean-room fabrication of thin-film sensors, optical characterisation of their response to different contaminants, and testing the sensors in real-world environments.

EPSRC DTP (Must be within EPSRC remit.)

• Organic Semiconductor Centre

Light-emitting polymers are promising materials for lasers because they combine novel optoelectronic properties with simple fabrication. In addition to being flexible, they have high gain and broad emission spectra. So far, the broad emission spectra have been used to make lasers that can be tuned over a range of wavelengths.
However, broad emission spectra open up another very interesting possibility, namely the possibility of generating short light pulses. This follows from the uncertainty principle DEDt>h/4p. A very short light pulse (small Dt) must contain a range of energies (wavelengths) of light (large DE). Light-emitting polymers can lase over a large range of wavelengths, and so have the potential to generate femtosecond light pulses. This project will explore generating short light pulses from these materials by a range of techniques, and particularly by the process of modelocking in which the phase of different modes is locked together such that their interference gives a train of short light pulses. This new type of laser would be compact, lightweight and generate short light pulses at a range of wavelengths in the visible region of the spectrum.

Metamaterials (MMs) are man made materials with engineered optical properties. They are made assembling their artificial atoms at a scales much smaller than that of light, so as to appear homogenous. They are at the basis of very thought provoking proposals, including super imaging and cloaking applications. In the group of Synthetic Optics we have developed a large portfolio of fabrication techniques for one- and two-dimensional MMs.

The aim of this project is to develop the fabrication protocol and applications of three-dimensional MMs obtained with a bottom up approach. The student will combine the extraordinary physical and optical properties of silica based aerogels with the flexibility of the design of nanoplasmonics to realise effective materials with bespoke optical behaviour. The aerogel is an ultra light material with refractive index close to unity and thermally more insulating than air. Combining these features with the field enhancement offered by infiltrated metallic nano particles is specially suited to address nonlinear effects at ultra-low powers.

This challenging but rewarding project requires a thorough understanding of the physics involved and the experimental rigour to fabricate and test the MMs, but offers the student the chance to learn a broad range of design, fabrication and experimental techniques.

• Synthetic Optics group

Black holes can be understood in a simple picture: Imagine a river flowing towards a waterfall with ever increasing flow speed. Also imagine fishes in the river swimming upstream. At some position in the river the maximum speed of the fish will equal the flow speed and all fish beyond that "point of no return" will be flushed into the waterfall. Here the flow speed corresponds to the gravity of a black hole and the point of no return to the event horizon.
Arguably the most facinating aspects of astronomical black holes is the emission of Hawking radiation from the event horizon, an intriguing quantum effect combining gravity, thermodynamics and quantum mechanics.

Unfortunately, the astrophysical Hawking radiation is far too weak to ever being detected directly. Recently, however, we have invented a method to create moving artificial event horizons with short pulses in optical fibers. Moreover, the expected Hawking radiation is strong enough to be detectable with single photon coincindence counting.

The idea of the PhD programme is the calculation, detection, and characterization of this elusive Hawking radiation for the first time. The work has already gained momentum in our group and a setup is built using optical pulses of just a few cycles pulse length. In addition we will explore further quantum field theory effects in curved spacetime.

• Experimental quantum optics
• Quantum optics and information

Visible light communication is an emerging field that aims to deliver high-bandwidth wireless data through solid-state (LED) lighting. A key challenge in developing this optical version of WiFi is to make optical detectors that have very fast response, are very sensitive, and can receive data signals from any angle. This project aims to develop the next generation of receiver technologies for wireless optical communications.

The project will develop optical data receivers based on luminescent polymer films. Photonic nanostructures embedded within the fluorescent film will modify the radiative lifetime and direction of the light emission to collect and concentrate incoming optical signals onto a fast silicon detector. The student will design novel optical antennas, and fabricate these using thin film deposition and nanoimprint lithography. Working with collaborators at the University of Oxford, these components will be combined with silicon photomultiplier detectors to assess their performance in optical data links.

1. "Optical antennas for wavelength division multiplexing in visible light communications beyond the étendue limit", Manousiadis, P., Chun, H., Rajbhandari, S., Vithanage, D., Malyawan, R., Faulkner, G., Haas, H., O'Brien, D. C., Collins, S., Turnbull, G. A. & Samuel, I. D. W., Advanced Optical Materials 1901139 (2019).
2. "Wide field-of-view fluorescent antenna for visible light communications beyond the étendue limit”, Manousiadis, P., Rajbhandari, S., Mulyawan, R., Vithanage, C. D. A., Chun, H., Faulkner, G., O'Brien, D. C., Turnbull, G. A., Collins, S. & Samuel, I. D. W., Optica 3, 702 (2016).

• Organic Semiconductor Optoelectronics research group

Halide perovskite semiconductors possess many excellent optoelectronic properties making them suitable for a variety of devices such as solar cells, light-emitting diodes and photodetectors. Recently it has been shown that some family of these materials shows ferroelectricity and piezoelectric properties. Ferroelectric materials possess spontaneous polarization even in the absence of an external electric field and find applications in memory devices, energy harvesting, and radiofrequency and microwave devices. The piezoelectric properties would enable the development of ambient mechanical energy harvesters to self-power the small electronic components in the Internet of Things (IoT) and wearable electronics (WE). Even though halide perovskite semiconductors have been thoroughly explored for solar cell applications, their other energy harvesting applications are little explored.
In the proposed project, hybrid perovskite-based thin films will be investigated for their ferroelectric and piezoelectric properties. The ferroelectric properties will be explored using the P-E loop (polarisation-electric field) and piezo-force microscopy (PFM) method. Piezoelectric charge coefficient will be optimized as a function of different halide perovskite compositions to maximise the output power. The project would mainly involve the optimisation of ferroelectric and piezoelectric properties and develop the composition with the optimized properties towards a thin-film based ambient mechanical energy harvester to generate useful electricity to power small electronic components such as temperature sensors applicable to the IoT systems.
References:
1.    Kim et al Energy Environ. Sci., 2020, 13, 2077—2086
2.    Wilson et al APL Mater. 2019, 7, 010901

This project would be eligible for funding including: University Scholarship.

• Energy Harvesting Research Group

Organic semiconductors based on light-emitting conjugated polymers are attracting considerable interest in semiconductor physics and are emerging as exceptional 'plastic-like' materials for optoelectronic applications including displays, lasers and solar cells. We have recently reported the first single-molecule studies regarding the conformation of individual polymer chains in organic solvents commonly used for device fabrication [1-3]. Now, in this project, we aim to combine single-molecule super-resolution spectroscopy with magnetic tweezers to apply force to the polymer chain. By merging these techniques, we will be able to stretch the polymer chain at will and understand in more detail how the conformation of the polymer chain impacts its light-emission properties. Importantly, we will apply for the first-time super-resolution imaging methods to resolve, beyond the diffraction limit, the structure of the polymer chain as a function of applied force. The results will help to develop new solution-processing methods that improve device performance. The project is a collaboration between the groups of Prof Ifor Samuel and Dr Carlos Penedo.

[1] Dalgarno, Paul A., Christopher A. Traina, J. Carlos Penedo, Guillermo C. Bazan, and Ifor D. W. Samuel. (2013) Solution-Based Single Molecule Imaging of Surface-Immobilized Conjugated Polymers. J. Am. Chem. Soc. 135 (19): 7187–93.
[2] Tenopala-Carmona, F.,  Fronk, S., Bazan, G., Samuel, I. D. W., Penedo, J.C. (2018) Real-time observation of conformational switching in single conjugated polymer chains. Sci. Advances, 4: eaao5786.
[3] Brenlla, A., Tenopala-Carmona, F., Kanibolotsky, A. L., Skabara, P., Samuel, I. D. W., Penedo, J.C. (2019) Single-Molecule Spectroscopy of Polyfluorene Chains Reveals β-Phase Content and Phase Reversibility in Organic Solvents. Matter, 1, 1399–1410.

When light is confined on the nanoscale it is possible to observe light-matter interactions that are not normally observed in bulk materials. One example is the strong coupling of photons and excitons in wavelength-scale microcavities, in which the modes of the cavity couple with the exciton to make a hybrid light-matter state called a polariton [1,2]. Polaritons can form a Bose-Einstein condensate [3], and we have demonstrated low threshold polariton lasers [4].
Organic semiconductors are particularly interesting for the study of polaritons because their excitons have binding energies much greater than the thermal energy at room temperature. This means that polaritonic phenomena that are restricted to low temperature in other materials are readily observed at room temperature in organic semiconductors. The purpose of this project is to explore aspects of room temperature polaritons in organic semiconductors. First, the possibility of using strong light-matter coupling to tune the energy levels of organic semiconductors will be explored. Then the effects of polaritons being delocalised will be studied.  Normally excitons in organic semiconductors are localised and can only travel a few nanometers. However polaritons are delocalised and so may access a much larger volume. Finally these two strands of work will be combined to make sensors that are both selective and sensitive. The selectivity will arise from the tuning of energy levels, and the sensitivity from polaritons being delocalised.

[1] C. Weisbuch et al., Phys. Rev. Lett. 69, 3314 (1992)
[2] D.G. Lidzey et al., Nature 395, 53 (1998)
[3] J D Plumhof, T Stöferle, L Mai, U Scherf & R F Mahrt, Nature Materials 13, 247–252 (2014)
[4] Rajendran, S. K., Wei, M., Ohadi, H., Ruseckas, A., Turnbull, G. A. & Samuel, I. D. W.  Advanced Optical Materials. 7, 1801791 (2019)

• Organic Semiconductor Optoelectronics research group