Publication News

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H edges in Graphene

10th February 2014

Hydrogen Free Graphene Edges

Graphene edges and their functionalization influence the electronic and magnetic properties of graphene nanoribbons. Theoretical calculations predict saturating graphene edges with hydrogen lower its energy and form a more stable structure. Despite the importance, experimental investigations of whether graphene edges are always hydrogen-terminated are limited.

New results (Nature Communications, 5, 3040 (2014)) published byDr Jamie Warner and DPhil student Kuang He from the Materials Department at Oxford University reveal that C–C bond lengths at the edges of clean graphene in vacuum can have ~86% contraction relative to the bulk and confirm that non-functionalized graphene edges can exist. The research utilized the Oxford-JEOL aberration-corrected transmission electron microscope with sub-Angstrom spatial information to obtain ultra-high resolution images of suspended graphene. The graphene samples were grown by chemical vapour deposition in the labs of Dr Warner and exploited their unique approach to transferring graphene onto special TEM grids to achieve clean surfaces. Collaboration with Prof. Gun-Do Lee and Prof. Euijoon Yoon from Seoul National University enable the experimental results to be corroborated with density functional theory (DFT). The DFT revealed the bond contraction at the edge of graphene is attributed to the formation of a triple bond and the absence of hydrogen functionalization. Time-dependent images revealed temporary attachment of a single atom to the arm-chair C–C bond in a triangular configuration, causing expansion of the bond length, which then returns back to the contracted value once the extra atom moves on and the arm-chair edge is returned. These results provide important insights into the nature of graphene edge states and can be used to build a better understanding of the unique structure of graphene edges.

GPILRUFT reconstruction

8th February 2014

Deterministic electron ptychography at atomic resolution

A collaboration between researchers at the Department of Materials at the University Oxford and the Department of Physics at the University of Melbourne has developed a new method for deterministic ptychographic reconstruction of a specimen exit wave to solve the phase problem.

PHYSICAL REVIEW B 89, 064101 (2014)

This work suggests that a dedicated instrument designed with long-term optical and sample stability as key criteria could be expected to come closer in resolution to the fundamental limit imposed by the wavelength of the electrons used.

Graph

1st February 2014

Aluminium oxide barrier films on polymeric web and their conversion for packaging applications

A recent paper by Hazel Assender and co-workers in Thin Solid Films demonstrates the value in an acrylate overcoat to infiltrate defects in an oxide barrier layer and hence improve the barrier to water vapour. For the first time, this paper decouples the effect of a mechanical protection during winding from the more intrinsic value of the overcoat in modifying the oxide defects.

Thin Solid Films 553 153-156 (2013)

TEM of dislocation loops

4th January 2014

Dislocation instabilities and microstructure in anisotropic alpha-Fe

Steve Fitzgerald of the Defect Dynamics Group, has compared theoretical predictions of the shapes of dislocation shear loops in highly anisotropic crystals with TEM of irradiated alpha-Fe. The microstructures observed provide experimental evidence for a new mechanism for high-temperature plastic deformation which may contribute to the severe loss of strength observed above 500C.

Phil. Mag. Lett. 93(11) 2013 625-630

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