Energy & Electronic Materials
We create new materials that have desirable functional properties or that exhibit interesting emergent phenomena and we study these materials with a wide range of experimental techniques. Outputs range from nano-textured electrodes for batteries and fuel cells to the discovery of exotic electronic groundstates.
FABILIS: FABrication with Ionic Liquid Ion Sources
We develop new nanomanufacturing technologies based on ionic liquids.
Ionic liquids are mixtures of positive and negatively charged ions that are liquid at room temperature with no intervening solvent. The cations are usually large organic molecules, while the anions may be complex organic or simple inorganic ions. Our work is based on Ionic Liquid Ion Sources (ILIS), which are needle devices that produce a spray of ions from the ionic liquid.
ILIS give the possibility of creating ion beams with many different chemistries, thanks to the variety of ionic liquids available. ILIS can be useful in material treatment applications, for example, we have demonstrated fast etching of silicon with an ILIS reactive beam.
The research areas include characterisation of the interaction of different ionic liquids with a variety of target substrates, exploring the use of ILIS arrays for high throughput nanomachining, ionic liquid deposition, and developing a focused ion beam system based on ILIS.
We develop and apply computational methods to study defects and defect related processes in solids and at interfaces. Of particular interest are metal/oxide/semiconductor and other hetero-structures used for novel memory and transistor devices. We investigate the mechanisms of resistance changes in thin layers of oxides, carbon nanotubes and 2D materials (bP, hBN, MoS2, WS2…), as well as their structural and electrical degradation and dielectric breakdown. Oxide materials include crystalline and amorphous MgO, SiO2, HfO2, Al2O3, TiO2, Ga2O3, ZnO sandwiched between Cu, TiN, Pt and Si electrodes as well as SiO2/H2O/WS2 hetero-structures. We are investigating the mechanisms of electron and hole injection from electrodes into these films, electron and hole trapping inside oxides, and defect creation under applied electric bias. We calculate probabilities of electron tunnelling through defect states determining leakage and breakdown current through dielectric films and consider the mechanisms of field and electron-induced defect reactions inside oxides, including hydrogen and other impurities.
We develop and apply methods to allow large scale calculations on the atomic and electronic structure of materials, concentrating on semiconductor surfaces, and more recently on ferroelectric materials such as PbTiO3. Standard approaches to these calculations are limited in the size of problem that can be studied to a few hundred atoms, but our methods allow calculations of up to 10,000 atoms with no approximation, and over 1,000,000 atoms with specific, well-controlled approximations. This allows us to address problems which are complex and interesting, such as the polarisation texture in thin films of PbTiO3 on SrTiO3 substrates.
Our group carries out research to advance the predictive power of atom-scale computer simulations of materials and (bio)molecules. We also develop multi-scale models that bridge the gap between the atomistic and the experimentally relevant time and length scales. We have a keen interest to apply our methodologies to understand, at a fundamental level, the mechanisms of energy conversion processes in (opto-)electronic materials and to uncover structure-function relations that may help guide the design of improved materials. Recent projects include (i) the development of non-adiabatic molecular dynamics techniques for time-propagation of charge carriers and excitons in organic semiconductors (ii) the development of machine learning methodologies to accelerate ab-initio molecular dynamics with applications to solvation, redox- and electro-chemistry (iii) the development of density functional theory methodologies for the calculation of current-voltage characteristics of proteins in electronic junctions relevant for bioelectronic applications.