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Sheffield, United Kingdom

Hata S.,Kyushu University | Miyazaki H.,Mel Build | Miyazaki S.,FEI Company Japan Ltd. | Mitsuhara M.,Kyushu University | And 9 more authors.
Ultramicroscopy | Year: 2011

Electron tomography requires a wide angular range of specimen-tilt for a reliable three-dimensional (3D) reconstruction. Although specimen holders are commercially available for tomography, they have several limitations, including tilting capability in only one or two axes at most, e.g. tilt-rotate. For amorphous specimens, the image contrast depends on mass and thickness only and the single-tilt holder is adequate for most tomographic image acquisitions. On the other hand, for crystalline materials where image contrast is strongly dependent on diffraction conditions, current commercially available tomography holders are inadequate, because they lack tilt capability in all three orthogonal axes needed to maintain a constant diffraction condition over the whole tilt range. We have developed a high-angle triple-axis (HATA) tomography specimen holder capable of high-angle tilting for the primary horizontal axis with tilting capability in the other (orthogonal) horizontal and vertical axes. This allows the user to trim the specimen tilt to obtain the desired diffraction condition over the whole tilt range of the tomography series. To demonstrate its capabilities, we have used this triple-axis tomography holder with a dual-axis tilt series (the specimen was rotated by 90° ex-situ between series) to obtain tomographic reconstructions of dislocation arrangements in plastically deformed austenitic steel foils. © 2011 Elsevier B.V.

Pillai P.B.,University of Sheffield | Desouza M.,University of Sheffield | Narula R.,Free University of Berlin | Reich S.,Free University of Berlin | And 4 more authors.
Journal of Applied Physics | Year: 2015

Signatures of a superlattice structure composed of a quasi periodic arrangement of atomic gold clusters below an epitaxied graphene (EG) layer are examined using dispersive Raman spectroscopy. The gold-graphene system exhibits a laser excitation energy dependant red shift of the 2D mode as compared to pristine epitaxial graphene. The phonon dispersions in both the systems are mapped using the experimentally observed Raman signatures and a third-nearest neighbour tight binding electronic band structure model. Our results reveal that the observed excitation dependent Raman red shift in gold EG primarily arise from the modifications of the phonon dispersion in gold-graphene and shows that the extent of decoupling of graphene from the underlying SiC substrate can be monitored from the dispersive nature of the Raman 2D modes. The intercalated gold atoms restore the phonon band structure of epitaxial graphene towards free standing graphene. © 2015 AIP Publishing LLC.

Rafiq M.A.,University of Aveiro | Costa M.E.,University of Aveiro | Vilarinho P.M.,University of Aveiro | Reaney I.M.,Sir Robert Hadfield Building
Microscopy and Microanalysis | Year: 2012

Piezoelectric materials find important applications in micro- and nano-electromechanical systems (MEMS/NEMS). Pb(Zrx,Ti 1-x)O3 (PZT) is currently the most widely used composition for such applications but due to environmental concerns over the toxicity of lead, lead free alternative materials are required. K0.5Na 0.5NbO3 (KNN) is considered as a potential lead free piezoelectric but the current generation of monolithic ceramics has inferior electromechanical properties as compared to PZT. Consequently, there is great interest in improving the piezoelectric properties of KNN ceramics and various methods such as doping, hot-pressing and texturing are currently being studied. KNN single crystals like lead based single crystals have shown better electromechanical properties as compared to their ceramic counterparts. In addition, the behavior of a ferroelectric is largely dependent on its local domain response to an applied electrical or mechanical loading. Therefore, to understand better the material's macroscopic properties, it is essential to access local ferroelectric domains behavior which collectively determines the electromechanical performance. © Microscopy Society of America 2012.

Lin L.,Sir Robert Hadfield Building | Zhang S.,Sir Robert Hadfield Building | Zhang S.,University of Exeter
Chemical Communications | Year: 2012

We have developed an effective method to exfoliate and disintegrate multi-walled carbon nanotubes and graphite flakes. With this technique, high yield production of luminescent graphene quantum dots with high quantum yield and low oxidization can be achieved. © The Royal Society of Chemistry 2012.

Butler K.T.,Sir Robert Hadfield Building | Lamers M.P.W.E.,Energy Research Center of the Netherlands | Weeber A.W.,Energy Research Center of the Netherlands | Harding J.H.,Sir Robert Hadfield Building
Journal of Applied Physics | Year: 2011

In this paper we present molecular dynamics simulations of silicon nitride, both in bulk and as an interface to crystalline silicon. We investigate, in particular, the bonding structure of the silicon nitride and analyze the simulations to search for defective geometries which have been identified as potential charge carrier traps when silicon nitride forms an interface with silicon semiconductors. The simulations reveal how the bonding patterns in silicon nitride are dependent upon the stoichiometry of the system. Furthermore we demonstrate how having an interphase, where the nitrogen content in silicon gradually reduces toward pure silicon across a boundary region, as opposed to an interface where there is an abrupt drop in nitrogen concentration at the boundary, can result in significantly different numbers of certain important carrier trap. © 2011 American Institute of Physics.

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