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Students who would like to work with us are advised to identify a CCMN area of research that is interesting to them and then contact the relevant academic to discuss their ideas. Submitting research proposals with motivated students is always within our interest, so please do get in touch! PhD and MRes students currently working in the CCMN group are as follows.

Jack Riall

I am a PhD candidate looking into the Switching of Molecular Quantum Dot Cellular Automata for Mixed Valence Molecules, under the supervision of Dr Gerard Edwards and Dr Graham Spink.

Transistors have been continually getting smaller since their invention. This is in part due to the desire to keep up with Moore’s Law, but also because the smaller the transistors, the more can fit on a computer chip. However, we are now approaching an impasse with conventional transistors due to issues like heat dissipation melting the tiny components and leakage current (through quantum mechanical tunnelling) disrupting the binary information. This impasse is where Molecular Quantum Dot Cellular Automata (QCA) can move in and replace the traditional transistor computing paradigm.

Molecular QCA is a nano-computing paradigm first posited by Craig Lent, University of Notre Dame, USA. The idea is that, rather than being held in the current flow through a transistor, the binary information would be held within the charge configuration of a molecule. For example, one of the proposed molecules for this device has three “dots” (charge occupation sites) and a single free charge to occupy them. This means that the molecule has three possible states that it can take, labelled “1”, “0” and “null” (the three states required for computing). The charge in the molecule uses tunnelling to travel between each of the possible dots. The beauty of this idea is that it completely avoids any of the issues with small transistors; the lack of a flowing current in the QCA paradigm means that heat dissipation is significantly decreased, and leakage current is not a problem.

Above: The three states of a QCA cell described in the text: "1" (left), "0" (middle) and "null" (right).

A QCA cell can consist of two molecules, each with three dots and one charge (six dots and two charges total). The idea is to utilise Coulomb repulsion effects between the cells to carry information. When two of these cells are placed next to each other the charges within them will repel each other causing them to align themselves into the same state (“0” or ”1”). This means these cells could replace not just the transistors in a computer but also the wires. QCA can also be used to make the standard logic gates (“AND”, “OR”, “NOT” etc…) as well as a “majority” gate which has three inputs and outputs the majority. The third “null” state of the QCA cell is necessary to allow clocking control. This makes the QCA approach incredibly useful for computing.

The aim of my research is to calculate the switching of QCA to provide further insight into how a device like this would work in a real-life setting. My work builds on previous research by looking into the effect of heat dissipation on the tunnelling effects of the QCA cell in more detail. So far, I have simulated two dot and three dot molecules using different protocols for bit writing and erasure. The next step is to incorporate heat dissipation effects into these simulations showing how this would affect the tunnelling of the charges within the molecules.

Dimitrios Kokkinos

I am a PhD candidate in computational condensed matter physics, looking into charge transport properties in polymer thin films. My work is under the supervision of Dr Theodoros Papadopoulos and Prof Alison Walker, University of Bath, and is funded by a joint URSA studentship between the University of Chester and the University of Bath.

My research is relevant to device modelling of organic optoelectronics applications, such as organic light emitting diodes (OLEDs), and organic photovoltaics (OPVs). The main aim of my work is related to the prediction of charge transport properties in single polymer chains, and the investigation of the effect of dynamic and static disorder on temperature-dependent charge mobility. The methodology I use is based on a Su-Schrieffer-Heeger (SSH) Hamiltonian, according to work by Troisi, Adv. Mater. 19, 2000 (2007), parameterised via Density Functional Theory (DFT). Electron-phonon interactions are taken into account via the so-called Peierls and Holstein couplings. Molecular dynamics and a kinetic Monte Carlo scheme will also be considered in the future. High Performance Computing (HPC) facilities are provided by the University of Bath and the University of Chester.

Before joining the CCMN group, I worked as an experimental physicist developing polymers for OLED and OPV devices for academic and industrial use. I worked respectively for the Lab for Thin Films and Nanotechnology (LTFN), Aristotle University, Greece, and Organic Electronic Technologies (OET), Greece. During my past research, I have become familiar with the advantages and challenges related to the characterisation and fabrication of organic optoelectronic devices, and developed an interest in exploring the potential and limitations of polymer materials. My work on the optical properties of emitting polymers, as investigated by NIR-Vis-far UV spectroscopic ellipsometry, was published in Phys. Status Solidi A 213, 2947 (2016).

Babu Baijnath Prasad

I am a PhD candidate, from the Department of Physics and Center for Theoretical Physics, National Taiwan University (NTU). My PhD studentship is funded by the Taiwan International Graduate Program in Nanoscience and Technology, Academia Sinica, Taipei, Taiwan (R.O.C.). As a visiting PhD student at the University of Chester (UOC), I work under the supervision of Dr Theodoros Papadopoulos and Prof Guang-Yu Guo, National Taiwan University, as part of a Royal Society and Ministry of Science and Technology (MOST), grant awarded to UOC and NTU respectively.

My research primarily focusses on first-principles electronic structure modelling of materials surfaces and interfaces, with applications in optoelectronic devices such as perovskite solar cells (PSCs). Specifically, I look into charge transfer at device interfaces such as between the electron transport layer and perovskite layer. Our task is threefold; we aim to (i) reduce PSCs toxicity by using Pb-free perovskites, (ii) acquire better understanding of the nanoscale variables that influence the energy level alignment at the device interfaces, and (iii) improve device performance by choosing an appropriate combination of materials that reduce device interface energy barriers, hence improving photo conversion efficiency.

My research efforts at NTU under the supervision of Prof Guang-Yu Guo, are towards the study of quaternary arsenide compounds XCuYAs (X=Zr,Hf; Y=Si,Ge) that are part of a family of materials that possesses outstanding physical properties ranging from p-type transparent semiconductors to high-temperature Fe-based superconductors. I study the electronic structure topology, the spin Hall effect (SHE), and the spin Nernst effect (SNE) in these compounds based on density functional theory calculations. My work in this area is published in Phys. Rev. Materials 4, 124205 (2020), in which we first observe that the above four compounds are Dirac semimetals with the nonsymmorphic symmetry-protected Dirac line nodes along the Brillouin zone boundary A−M and X−R and low density of states near the Fermi level. Second, the intrinsic SHE and SNE in some of these compounds are found to be large. In particular, the calculated spin Hall conductivity (SHC) of HfCuGeAs is as large as −514(ħ/e)(S/cm). The spin Nernst conductivity (SNC) of HfCuGeAs at room temperature is also large, being −0.73 (ħ/e) (A/m K). Moreover, both the magnitude and sign of the SHC and SNC in these compounds can be manipulated by varying either the applied electric field direction or the spin current direction. The SHE and SNE in these compounds can also be enhanced by tuning the Fermi level via chemical doping or electric gating. Finally, a detailed analysis of the band-decomposed and k-resolved spin Berry curvatures reveals that these large SHC and SNC as well as their notable tunabilities originate largely from the presence of a large number of spin-orbit coupling-gapped Dirac points near the Fermi level as well as the gapless Dirac line nodes, which give rise to large spin Berry curvatures. Our findings suggest that the four XCuYAs compounds not only provide a valuable platform for exploring the interplay between SHE, SNE, and band topology, but they also have promising applications in spintronics and spin caloritronics.

Mohammed Alharbi

I am a part-time PhD student conducting a system level simulation of Quantum Dot Cellular Automata (QCA) Computer Circuits. I am examining energy dissipation at the device level under the supervision of Dr Gerard Edwards and Dr Richard Stocker.

Quantum Dot Cellular Automata (QCA) is an emerging nanotechnology poised to possibly take over from the current complementary metal-oxide-semiconductor (CMOS) digital integrated circuit (IC) technology. It is a very promising transistor - less paradigm, that can be downscaled to the molecular level, with the potential of tera-scale device integration and ultra-low power dissipation. 

In outline, the PhD project will be to explore the computer architecture aspects of QCA, employing state of the art Simulation Tools QCADesigner and QCADesigner – E. The research will embrace system-level simulation of QCA based central processor unit (CPU) and Digital Signal Processing (DSP) circuits and will focus on Power Dissipation.

Moreover, essential related topics will be covered throughout the PhD research period, that include simulations of QCA based combinational logic circuits, reversible QCA simulations for sequential logic circuits, a reversible computing QCA implementation of an Arithmetic Logic Unit (ALU), designing partially reversible QCA circuits and a QCA based systolic array design.

Thomas Lloyd

I am a student from Birmingham, UK. I studied and completed my bachelor’s degree in physics at the University of Chester from 2018-2021; and in 2021 I am continuing my studies towards an MRes at Chester, exploring surface and interface science under the supervision of Dr Theodoros Papadopoulos. 

My aim is to broaden my computational skills and develop theoretical knowledge in advanced solid state physics of materials surfaces and interfaces as well as electronic structure modelling, with applications in organic and perovskite optoelectronics. The main computational method of choice used for my research would be density functional theory to calculate electronic structure properties such as density of states and band structure. The calculations are conducted computationally involving VASP electronic structure code. Overall, the research explores standard methodology used in nanoscale device physics, relevant to solar cells and LED’s.

Varun Bheemireddy

Alumni: PhD student at the University of Glasgow, U.K.

I completed my Bachelor's degree in Electrical Engineering from Birla Institute of Technology and Science (BITS), Pilani, India. As MRes student in the CCMN lab, I conducted research on modelling of electron transport properties in single-molecule junctions, under the supervision of Dr Theodoros Papadopoulos and Dr Gerard Edwards. Specifically, my research is related to the effect of molecular symmetry on device characteristic curves and its potential impact on organic electronics.

Prior to joining the CCMN group, my research efforts were related to modelling of organometallic chemical sensors and organic ferroelectrics. For further information, please have a look at my google scholar profile.