Publication News

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Indeter strain field

12th December 2014

Yield behavior beneath hardness indentations in ductile metals, measured by three-dimensional computed X-ray tomography and digital volume correlation

Prof. James Marrow’s group, in collaboration with the Diamond Light Source, the Research Centre at Harwell and Dr Marina Galano’s group, have studied the three-dimensional deformation beneath hardness indentations using synchrotron X-ray tomography and Digital Volume Correlation.  Analysis of the 3D displacement field was used extract the yield stress and work hardening behaviour of an Aluminium-Silicon Carbide nano composite by reverse modelling. This research has been published in Acta Materialia.

Reconstruction

10th December 2014

Atomically resolved tomography to directly inform simulations for structure–property relationships

Prof. Michael Moody, in collaboration with researchers at the University of Sydney, has developed a methodology to bridge the gap between experimental atom probe data and atomistic simulations. The approach is based on a hybrid data format, blending atom probe and predictive Monte Carlo simulations. This hybrid data was used as direct input into density functional theory simulations to calculate local energetics and elastic properties. This research has been published in Nature Communications.

graphene force balance

10th December 2014

Ultraflat transfer method for graphene surface force balance

A team of Oxford researchers, led by Professor Nicole Grobert and Professor Susan Perkin, have developed a novel method of transferring macroscopic graphene flakes (cm2) (root-mean-square roughness of 0.19 nm) that are free from polymer residues over macroscopic areas (>1 cm2) and which are transparent to visible light, and thus ideal for surface force balance measurements with electrochemical control.  This research paper in Langmuir is currently a topic of a Nanotechnology Spotlight article on Nanowerk

PtPdRh Oxides

10th December 2014

Oxidation and Surface Segregation Behavior of a Pt–Pd–Rh Alloy Catalyst

Platinum gauze catalysts are used extensively in the production of nitric acid from ammonia, where they are subject harsh oxidizing environments. In a study led by Dr Paul Bagot, in collaboration with researchers at University Pierre and Marie Curie and members of the Atom Probe Research Group,  a combination of advanced characterization methods to study how oxidation behaviour influences the surface and near-surface gauze microstructure of a Pt−Rh−Pd gauze. It was shown that Rh and Pd can segregate on different areas of the same surface. Such atomic migration can be linked to mechanisms of detrimental metal loss from these alloys. This research has been published in the Journal of Physical Chemistry C.

Bio Quantum Coupling

28th November 2014

Strong coupling between chlorosomes of photosynthetic bacteria and a confined optical cavity mode

A paper in Nature Communications led by Dr David Coles in the Photonic Nanomaterials Group, as part of the Oxford Martin School project on Bio-inspired Quantum Technologies.

Strong coupling of light harvesting complexes to optical cavity modes is demonstrated, providing a means of modifying energy levels and transfer pathways in the complex. The work is a collaboration between the Oxford Materials group, Prof Robert Taylor (Oxford Physics), and groups at Sheffield, Harvard, and Clark Universities.

Tunable microcavities

24th November 2014

Two-dimensional metal-chalcogenide films in tunable optical microcavities

A collaboration between Aurelien Trichet and Jason Smith of the Photonic Nanomaterials Group and researchers at Sheffield and Manchester universities published in Nano Letters sees quasi-2D semiconductors coupled to tunable optical microcavities for novel photoemissive devices.

Monolayer MoS2 and few-layer GaSe produced by mechanical cleavage of bulk crystals were deposited onto high reflectivity planar mirrors, and microcavities formed with an accompanying concave mirror with radius of curvature of a few micrometres. The photoluminescence properties of the 2D materials are modified by the presence of highly resonant cavity modes, and lead to a reduction of the radiative lifetime by up to a factor of ten. These new cavity coupling experiments pave the way for a host of interesting physics and potential device applications with 2D semiconducting materials.

graphene edges

13th November 2014

Atomic Level Spatial Variations of Energy States Along Graphene Edges

A collaboration between Professor Warner's group in Oxford and Dr Suenaga's group at AIST in Japan, has led to new insights into the properties of individual atoms at the edges of graphene. Using state-of-the-art aberration-corrected scanning transmission electron microscopy combined with electron energy loss spectroscopy, the team probe single carbon atoms and produced the world's first spectroscopic maps showing variations in bonding hybridization in a material composed of only one element and with sensitivity down to an individual atom of carbon. 2D maps enabled for the first time the ability to correlate new energy states in EELS with specific atoms and their local bonding coordination. The results show that energy states in graphene vary both perpendicular and parallel to its edges and that subtle variations in sp2 bonding character can be detected. Density functional theory calculations simulated the EELS and showed excellent agreement with the experimental results, confirming the findings. A crucial step in achieving these results was the use of an in-situ high-temperature heating holder that helped remove surface contamination that normally prohibits the study of graphene.

Reduced Anatase

9th October 2014

Discovery of anatase titanium dioxide phase with a band gap in the visible

A joint experimental-computational study performed as a collaboration between the Max Planck Institute for Solid State Research in Stuttgart and the Department of Materials has been published in Nano Letters.

This study reports the first observation of a new phase of anatase titanium dioxide with a reduced band gap of 2 eV. By combining atomic-resolution STM/STS measurements and DFT calculations the two teams showed that this new phase corresponds to a 'reduced' form of anatase titanium dioxide, whereby the (101) surface misses the outermost layer of oxygen atoms.

Titanium dioxide is the archetypal photocatalyst and a prime candidate for realizing artificial photosynthesis. The only limitation of this material is its large band gap (> 3 eV), which prevents the utilization of a significant fraction of the solar spectrum. The discovery of a new phase of anatase with a band bap in the visible range represents an important breakthrough in solar-driven water splitting.

Research in the Department of Materials was carried out by Miguel Angel Perez, Christopher Patrick, and Feliciano Giustino. For more info visit the Giustino research group page http://giustino.materials.ox.ac.uk.

The Max Planck team includes Christian Dette, Christopher Kley, Paul Punke, Peter Jacobson, Soon Jung Jung, and Klaus Kern. More info at http://www.fkf.mpg.de/kern.

templating quantum dots

1st October 2014

Polystyrene Templated Porous Titania Wells for Quantum Dot Heterojunction Solar Cells

Cheng Cheng, Hazel Assender and Andrew Watt from the Solar Enery Materials Initiative, along with colleagues in Physics designed a nanostructured photoactive layer for quantum dot solar cells.  300 nm polystyrene spheres were used to template a porous titania layer into which PbS quantum dots could be infiltrated.  Thus, a bulk heterojunction  morphology was engineered such that the dimensions of the two phases are at the same scale as the width of the depletion region.  As a result of this structure, the photocurrent generated by the device increased by more than 30% along with a 10% increase in fill factor.

Organic transistors

1st October 2014

Effect of oxygen, moisture and illumination on the stability and reliability of dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) OTFTs during operation and storage

Ziqian Ding, Gamal Abbas and Hazel Assender from the polymers group, along with collaborators from Bangor and Manchester Universities have published an article exploring the stability, in atmospheric conditions, of organic transistors.  Organic semiconductors are typically sensitive to water vapour, oxygen and light, and thus devices made using these materials are often encapsulated in glass.  For flexible technologies it is desirable to use circuits unencapsulated, or encapsulated with modest, flexible barrier materials, so the air-stability of organic devices is of crucial importance.  The transistors we tested showed very good stability in air, unencasulated.  Water vapour did modify the device performance, but, except under extreme conditions, this is a reversible effect with original behaviour being restored as the transistor dried out.  Oxygen was found to affect the devices only under illumination.  In both cases, mechanisms for the effects are proposed.

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