Publication News

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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.

in-situ microscopy

5th March 2018

Operando Monitoring of the Solution-Mediated Discharge and Charge Processes in a Na–O2 Battery Using Liquid-Electrochemical Transmission Electron Microscopy

Although sodium–oxygen (Na–O2) batteries show promise as high-energy storage systems, this technology is still the subject of intense fundamental research, owing to the complex reaction by which it operates. Research by the Peter Bruce Group and collaborators at CNRS in Amiens as reported in Nature Letters presents for the first time the use of a Na–O2 microbattery using a liquid aprotic electrolyte coupled with fast imaging transmission electron microscopy to visualize, in real time, the mechanism of NaO2nucleation/growth. The formation of NaO2 cubes during reduction occurs by a solution-mediated nucleation process and subsequent oxidation of NaO2 also proceeds via a solution mechanism.

Percolation Threshold

23rd February 2018

Bridging the gap at the percolation threshold

Chemiresistors are electrochemical sensors that monitor the changes in the electrical resistance of a sensing layer in between two electrodes. Conducting polymers have come to the forefront of this technology as ideal sensing layers due to their numerous advantageous properties. However the sensing layer in between the electrodes is usually deposited as a thin film which reduces the sensitivity. Recently researchers in the surface nanoscience group, Dr Krishnan Murugappan and Professor Martin Castell have shown how the sensing layer can be grown electrochemically in-between the electrodes at the percolation threshold. The percolation threshold is the region where there are only a few ‘sensing bridges’ between the electrodes. This dramatically enhances the sensitivity of the sensor as a localised change can be measured compared to the bulk change at the thin film region. This work reported in Electrochemical Communications opens up new opportunities for the use of conducting polymers in ultra-sensitive gas sensing devices.

3DXRD of Strong Neighbour Grains

15th January 2018

Strong grain neighbour effects in polycrystals

High value hexagonal alloys Ti and Zr are used in safety critical applications in the aerospace and nuclear industries.  Understanding and improving their performance requires untangling the complex patterning of stress and strain at the microstructural level. The MicroMechanics Group has used 3D-X-ray Diffraction, coupled with crystal plasticity FEM simulations, to study stress evolution across thousands of contiguous grains in polycrystals loaded in situ at the ESRF ID11.  Large anisotropy in elastic stiffness, thermal expansion and plastic flow stress in these materials ensure that the local grain neighbourhood has a profound effect on stress development in any particular grain.  Indeed the neighbourhood effect is so strong that for many grains the stress level can actually drop despite the global stress state increasing during tensile plastic flow.
The work is available in Nature Communications.

Bio-Nano Imaging

19th December 2017

Complementary Imaging of Silver Nanoparticle Interactions with Green Algae: Dark-Field Microscopy, Electron Microscopy, and Nanoscale Secondary Ion Mass Spectrometry

Increasing consumer use of engineered nanomaterials has led to significantly increased efforts to understand their potential impact on the environment and living organisms. Currently no individual technique can provide all the necessary information such as their size, distribution, and chemistry in complex biological systems. Consequently, there is a need to develop complementary instrumental imaging approaches that provide enhanced understanding of these “bio-nano” interactions to overcome the limitations of individual techniques. Researchers in NanoSIMS group have used a multimodal imaging approach incorporating dark-field light microscopy, high-resolution electron microscopy, and nanoscale secondary ion mass spectrometry, as reported in ACS Nano.

Model of N@C60 with addend

5th December 2017

Synthesis and EPR studies of the first water-soluble N@C60 derivative

Researchers from the Carbon Nanomaterials Group under Professor Kyriakos Porfyrakis have recently published a report in Chemical Communications showing synthesis of the first water-soluble derivative of the paramagnetic endohedral fullerene N@C60,  through the covalent attachment of a single addend containing two permethylated β-cyclodextrin units to the surface of the carbon cage. The capability of the derivative to function as a spin probe for Cu(II) ions is demonstrated in competitive organic solvents using X-band EPR. This research opens the door for medical applications for this endohedral fullerene such as a potential spin probe.  This article was featured on the cover of the journal.

28th November 2017

Keeping Perfect Time With Caged Atoms

Prof Kyriakos Porfyrakis and Dr Edward Laird have published in IEEE Spectrum a feature article about their work on building the world's smallest atomic clock, based on a Nitrogen atom trapped in an endohedral fullerene C60 molecule. They have patented the technology which is being commercially developed under spinout company Designer Carbon Materials. The aim is to one day incorporate a complete atomic clock into one chip, avoiding the need for optical elements used in conventional atomic clocks. An endofullerene-based atomic clock could thus be small, light, and energy efficient. Potentially, it could replace many of the quartz oscillators used in nearly every present-day electronic device to keep time.

17th November 2017

Calculating with light using a chip-scale all-optical abacus

Machines that simultaneously process and store multistate data at one and the same location can provide a new class of fast, powerful and efficient general-purpose computers. An article in Nature Communications  by researchers in the Advanced Nanoscale Engineering Group demonstrates the central element of an all-optical calculator, a photonic abacus, which provides multistate compute-and-store operation by integrating functional phase-change materials with nanophotonic chips. 

 

20th October 2017

Modelling of a vacuum metallization patterning method for organic electronics

The high throughput roll-to-roll patterning of metal thin films could be used to create organic functional devices. Researchers in the Polymers Group have reported in Surface and Coatings Technology research into the compatibility of an in-vacuum selective metallization technique, which uses a sacrificial oil to define the metal electrode pattern for functional devices.  The metal thin film properties were found to be very attractive, compared to solvent based equivalents. The sheet resistance and roughness, 1.59 Ω·sq−1 and 3.24 × 10− 8 m2 respectively, particularly set this high-throughput process apart as a promising technique for creating cost effective flexible electronics and organic devices.

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