Publication News

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news-watersplitting2

23rd June 2018

Halide double perovskites for water splitting

Since their discovery in 2016, halide double perovskites that are based on combinations of monovalent and trivalent cations, have been thoroughly investigated as potential lead-free alternatives to lead halide perovskites. In a recent study published in Applied Physics Letters,  researchers George Volonakis and Feliciano Giustino, considered applications beyond photovoltaics and found that the lead-free double perovskites Cs2BiAgCl6, Cs2BiAgBr6, Cs2SbAgCl6 and Cs2InAgCl6 may open new opportunities in solar-driven photocatalytic water splitting. Using first-principles calculations they report on the stability of different surface terminations of the newly synthesised double perovskites, and also report their absolute energy levels. The energy levels of Cs2BiAgCl6 and Cs2BiAgBr6 are matching the redox potential of water. While, Cs2SbAgCl6 and Cs2InAgCl6 could also be suitable for either hydrogen evolution or water evolution. Futher details are in the AIP journal feature article press release.

news-stmresolution

22nd June 2018

Maximising the resolving power of the scanning tunneling microscope

Research by the Surface Nanoscience group and collaborators at Trinity College Dublin as reported in open access Advanced Structural and Chemical Imaging demonstrates that a significant improvement in the resolving power of the STM is achieved through automated distortion correction and multi-frame averaging. We demonstrate the approximately square-root relationship improvement in signal-to-noise ratio upon image averaging, a sub-picometre precision height measurement, and the automated identification of chiral unit cells on a surface. These automated tools, which do not require prior knowledge of the surface structure, promise to facilitate more rapid and higher-precision studies of surfaces, making full use of the experimentalists recorded data sets. This advance allows a new study of surface pico-science to be developed where subtle variations in surface structure can now be seen, that hitherto were not detected because they were buried in noise.

Electrical percolation through a discontinuous Au nanoparticle film

21st June 2018

Electrical percolation through a discontinuous Au nanoparticle film

Researchers in the Surface Nanoscience Group report in Applied Physics Letters evidence of stepwise control of resistivity in thin gold layers. When a thin gold film is deposited the electrical resistance of the film decreases from fully resistive at the start of deposition to close to the bulk resistance for thicker films. We’ve found that, instead of a smooth decrease, this resistance change occurs in discrete steps. The steps are attributed to conduction through newly formed electrical pathways in the discontinuous film being created as more gold is deposited. Scanning electron microscopy images confirm the discontinuous nature of the films and show that thicker layers are more connected. Annealing such films causes them to dewet, decreasing the number of conductive pathways and causing a stepwise increase in the resistance of the film. This control over the electrical resistance of the layer as well as the size and separation of the particles opens up new opportunities for various applications of discontinuous metal films.

news-LiMnOF

15th June 2018

Improving the specific energy of the Li-ion battery with new cathode material

Research by the Peter Bruce Group and collaborators at Japan Synchrotron Radiation Research Institute (JASRI) and Uppsala University as reported in Energy & Environmental Science explains that the greatest barrier to improving the specific energy of the Li-ion battery is the cathode. While Si offers a route to increase the capacity at the anode this needs to be balanced by higher energy storage cathodes. The capacity of the cathode is limited by storing electrons on the transition metal ions alone, such as in LiMn2O4, where electrons are stored on the Mn 3+/4+ redox couple. There is a great deal of interest in increasing charge storage in transition metal oxide cathodes beyond the limit of transition metal redox activity. While redox reactions on sulfur in transition metal sulfides are well known only recently has O redox activity in transition metal oxides been recognised. They report a new intercalation cathode material, a lithium manganese oxyfluoride based on Li2MnO2F, with a high capacity to store charge by invoking redox activity on the Mn cations and O anions. It has a disordered rocksalt structure, which avoids the structural changes and consequent severe changes in voltage observed for O-redox layered transition metal oxide cathodes during the 1st cycle.

news-bijel2018

15th June 2018

Strategy for making bicontinuous conducting composite materials in a controllable fashion

Research by the Peter Bruce Group and collaborators at University of Edinburgh as reported in Materials Horizons  suggests a general strategy for making bicontinuous conducting composite materials in a controllable fashion. Their approach begins with a bicontinuous interfacially jammed emulsion gel (bijel) fabricated from a pre-mix containing a salt, here bis(trifluoromethane)sulfonimide lithium salt (LiTFSI). The resulting structure has interpenetrating ionic conducting and non-conducting domains composed of an ethylene carbonate (EC)-rich phase and a p-xylene (xylene)-rich phase of roughly equal volumes. This is the first time that bijel fabrication has been carried out using a pair of partially miscible liquids whose phase behaviour has been modified due to the addition of salt. Diffusing polystyrene (PS) into the xylene-rich phase enables the facile formation of a PS-filled bijel in place of a multi-step polymerization of added monomers. Drying the bijel results in the selective removal of xylene, reducing the total sample volume without compromising the morphology of the EC domain. Electrochemical impedance spectroscopy of the composite electrolytes confirms the existence of ion conducting pathways.

news-King2018small

15th June 2018

Crossover from lattice to plasmonic polarons of a spin-polarised electron gas in ferromagnetic EuO

Doped oxides can host a wealth of fascinating physical properties driven by strong many-body interactions, such as the dressing of electrons into polaronic quasiparticles from the interaction with bosonic excitations of the system. Besides the more conventional lattice polarons produced by the coupling to the crystal phonons, plasmonic polarons may form when conduction electrons couple with the collective plasmon excitations of their own Fermi sea.
Combining angle-resolved photoemission experiments with first-principles calculations, Fabio Caruso, Carla Verdi and Feliciano Giustino, in collaboration with the group of Phil King at the University of St Andrews, report the observation of lattice and plasmonic polarons in the doped ferromagnetic semiconductor EuO. These findings, published in a paper in the journal Nature Communications, suggest interesting opportunities for tailoring charge carrier properties in dilutely doped semiconductors.

news-lapo-grapheneribbons

4th June 2018

Magnetic edge states and coherent manipulation of graphene nanoribbons

Graphene has been called the wonder material, and its mechanical and electric properties never cease to amaze. Theory predicts that it could show magnetic properties too, if we could control the geometry of ist edges at the single-atom level. Such magnetic graphene would allow testing some very fundamental assumptions about graphene, and yield excellent building blocks for quantum computing machines. Now this theoretical prediction has become true: chemists and physicists have joined forces to create atomically-perfect graphene nanoribbons in huge quantities. In addition to validating and disproving a number of fundamental theoretical proposals, they found out that the quantum properties of the new material are actually astonishingly promising, yielding coherence times good for quantum operations at room temperature already without any type of optimization. Such results, when single-electron transport is realized with similar nanoribbons, could usher a new era quantum electronic devices. 

Details of recent findings are reported in Nature by Professor Lapo Bogani and co-workers.

Predicting Perovskites

12th May 2018

The geometric blueprint of perovskites

Perovskites constitute one of the most versatile and chemically diverse families of crystals. In perovskites the same structural template supports a staggering variety of properties, from metallic, insulating, and semiconducting behavior to superconducting, ferroelectric, ferromagnetic, and multiferroic phases. Approximately 2,000 perovskites are currently known, including those used in high performance solar cells as discovered in Oxford in 2012.  Researchers Marina Filip and Feliciano Giustino report in PNAS and the Oxford Science Blog a library of compositions predicting the existence of 90,000 new perovskites by combining elementary geometric ideas with high-throughput data analytics. These predictions hopefully will lead to the realization of entirely new functional materials for electronics, lighting, energy, sensors, and detectors. 

Nucleation of equiaxed dentrites

17th April 2018

Studying crystallization using X-ray radiography and machine learning

An X-ray radiographic study of the crystallization behaviour of liquid alloys is described by Enzo Liotti, Andrew Lui and Patrick Grant in Crystal nucleation in metallic alloys using X-ray radiography and machine learning  in Science Advances. Working with colleagues from Andrew Zisserman’s computer vision group in the Department of Engineering Science, Liotti et al uses machine learning techniques to teach a computer to automatically detect the nucleation of crystals in terra-bytes of X-ray radiographic videos obtained during solidification experiments at the European Synchrotron Radiation Facility (ESRF). The quality of the videos combined with computer vision techniques allows the alloy composition at the point and instant of nucleation to be determined automatically, which in turn allows an estimate of the temperature and nucleation undercooling for every crystallization event. Studying thousands of nucleation events, they show how undercooling varies with solidification conditions, and explain how sudden bursts of crystallization are linked to the thermal-solute conditions in the liquid. Machine learning computer vision allowed enormous volumes of data that were unanalysable by hand to be converted robustly into distributions of nucleation undercoolings.

Experimental Setup

20th March 2018

Revealing Strain-Induced Effects in Ultrathin Heterostructures at the Nanoscale

Researchers from the Advanced Nanoscale Engineering group have reported in Nano Letters a technique to characterize stress effects at high resolution using Atomic Force Microscopes.  So far it has been very difficult to characterize strain effects in materials and here we have a technique that can do this at the nanoscale. In this paper we use strain sensitive two dimensional graphene based heterostructures as demonstrators and reveal modulation in their work function and junctions with strain.

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