Publication News

3rd February 2012

Researchers from the Department of Materials have synthesised a dyad of two radical centres

An international team, led by K. Porfyrakis, have managed to covalently link the spin-active molecule N@C60 to another spin-active molecule: a Cu-Porphyrin. In their paper published in JACS Liu et al., have shown that the coupling between the adjacent spin centres leads to suppression of the electron spin resonance (ESR) signal of N@C60. Demetalation of the metalloporphyrin moiety of the dyad, which effectively turned the two-radical-center dyad into a single-radical-center dyad, recovered 82% of the ESR signal of N@C60. In this way Liu et al., were able to use Chemistry to effectively switch the spin state of N@C60 on and off. The work could find use in molecular spintronics applications where N@C60 and other endohedral molecules can be used as spin valves.

10th January 2012

Testing the reality of quantum mechanics

This research offers an answer to the question, "How can we know that the strange quantum effect called superposition is REALLY happening in a particular system, rather than being merely a mathematical trick in the theory?". The paper in Nature Communications by an international collaboration describes a new approach to confirming the existence of quantum superpositions. It applies a test developed by Nobel prize-winner Anthony Leggett and his collaborator Anupam Garg in the 1980s - achieving for the first time the "ideal negative result" measurement the pair proposed. The test relies on measuring a quantum system in such a way that the results can't be dismissed as influenced by the measurement. To achieve this we used at exceptional material: cooled, ultra pure silicon with a small scattering phosphorous atoms within it -- it was these "impurities" that whose quantum nature was tested and proven.

 

1st January 2012

Nomenclature of sp2 carbon nanoforms

Carbon’s versatile bonding has resulted in the discovery of a bewildering variety of nanoforms which urgently need a systematic and standard nomenclature. A recent guest editorial in Carbon 50 (2012) 741-747 co-written by Nicole Grobert aims to raise awareness of the issue and stimulate debate, providing a platform for future development of an exhaustive, definitive, yet flexible carbon nomenclature.

15th December 2011

Atomistic modelling of semiconductor-sensitized solar cells

Researchers from the Materials Modelling Laboratory have conducted the first atomic-scale investigation of a novel type of solar cell. The solid-state semiconductor-sensitized solar cell is an evolution of the concepts of dye-sensitized solar cells and hybrid nanocrystal/polymer solar cells. During the past two years semiconductor-sensitized cells based on mesoporous TiO2 and quantum dots of stibnite (Sb2S3) have been fabricated, and cell efficiencies above 5% have been demonstrated. In the article by C. E. Patrick and F. Giustino published on December 20 in Advanced Functional Materials, the authors used atomistic computational materials modelling to investigate semiconductor-sensitized TiO2 surfaces. By virtually screening several potential semiconductor sensitizers the researchers have found that TiO2 films sensitized with antimonselite (Sb2Se3) may lead to higher power conversion efficiencies than those reported for the TiO2/stibnite system. The work constitutes the first step in the direction of engineering semiconductor-sensitized solar cells using rational design at the nanoscale.

31st October 2011

Three-dimensional observations of a growing fatigue crack

The lifetime of a fatigue crack, before it causes failure, is mostly when it is smallest, which is also when it is most sensitive to the material's microstructure. So, to design fatigue-resistant materials we must study how cracks may be slowed by microstructure features. Yet this is the most difficult regime to examine. A collaborative effort, led by James Marrow and published recently in Acta Materialia (http://dx.doi.org/10.1016/j.actamat.2011.07.034), studied short fatigue cracks for the first time in 3-dimensions and in-situ at the European Synchrotron Radiation Facility. A 3D map of grain shapes and crystallographic orientations was produced using non-destructive X-ray diffraction contrast tomography (DCT) . A focused ion beam instrument was used to introduce small notches in selected grains and synchrotron X-ray computed microtomography was used to study the evolution of the fatigue crack through the microstructure. The observed crack retarding interactions between the crack and grain boundaries could be explained in terms of the crystallography of cracking and deformation in the magnesium alloy.

15th October 2011

Observation of individual carbon nanotubes and their electronic, structural and chemical behaviour

Researchers at the Department of Materials have been investigating the impact of current passing through specially synthesised carbon nanotubes. Multi-walled carbon nanotubes (MWCNTs) have long been anticipated as candidates for electrical components in an increasingly miniaturized electronics industry due to their inherent electrical properties. It is possible to manipulate and control these properties by introducing dopants such as N, B, and P. To understand how the tubes will behave in electronic circuits, a study has been carried out looking at the changes in electrical and chemical behaviour in the presence of flowing current. The findings by Aslam & Grobert et al., which are due to be published in Advanced Functional Materials http://dx.doi.org/10.1002/adfm.201101036, show that N-MWCNTs not only undergo current-induced structural transformations, but also - and most importantly—the complete removal of the dopant causing a significant change in the electronic behaviour. This has serious implications for the use of doped CNTs as electronic components, potentially limiting their applications.

3rd October 2011

Resolving strain in carbon nanotubes at the atomic level

Details of how atomic structure responds to strain are essential for building a deeper picture of mechanics in nanomaterials. The article by Jamie H. Warner*, Neil P. Young, Angus I. Kirkland, G. Andrew D. Briggs  published on October 2 in Nature Materials http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat3125.html provides the first experimental evidence of atomic displacements associated with shear strain in single-walled carbon nanotubes (SWNTs) by direct imaging using aberration-corrected transmission electron microscopy. The atomic structure of a zig-zag SWNT is resolved with unprecedented accuracy and the strain induced by bending is mapped in two dimensions. We show the existence of a dominant non-uniform shear strain that varies along the SWNT axis. The direction of shear is opposite to what would be expected from a simple force applied perpendicular to the axis to produce the bending. This highlights the complex atomistic strain behaviour of beam-bending mechanics in highly anisotropic SWNTs.

3rd February 2011

Two-Dimensional Nanosheets Produced by Liquid Exfoliation of Layered Materials

If they could be easily exfoliated, layered materials would become a diverse source of two-dimensional crystals whose properties would be useful in applications ranging from electronics to energy storage. Coleman and Nicolosi et al. in Science http://dx.doi.org/10.1126/science.1194975 show that layered compounds such as MoS₂, WS₂, MoSe₂, MoTe₂, TaSe₂, NbSe₂, NiTe₂, BN, and Bi₂Te₃ can be efficiently dispersed in common solvents and can be deposited as individual flakes or formed into films. Electron microscopy strongly suggests that the material is exfoliated into individual layers. By blending this material with suspensions of other nanomaterials or polymer solutions, we can prepare hybrid dispersions or composites, which can be cast into films. We show that WS₂ and MoS₂ effectively reinforce polymers, whereas WS₂/carbon nanotube hybrid films have high conductivity, leading to promising thermoelectric properties.