Robin Nicholas

Abstract:

Large-area synthesis of high-quality graphene by chemical vapour deposition on metallic substrates requires polishing or substrate grain enlargement followed by a lengthy growth period. Here we demonstrate a novel substrate processing method for facile synthesis of mm-sized, single-crystal graphene by coating polycrystalline platinum foils with a silicon-containing film. The film reacts with platinum on heating, resulting in the formation of a liquid platinum silicide layer that screens the platinum lattice and fills topographic defects. This reduces the dependence on the surface properties of the catalytic substrate, improving the crystallinity, uniformity and size of graphene domains. At elevated temperatures growth rates of more than an order of magnitude higher (120 μm min(-1)) than typically reported are achieved, allowing savings in costs for consumable materials, energy and time. This generic technique paves the way for using a whole new range of eutectic substrates for the large-area synthesis of 2D materials.

Abstract:

We investigate nontrivial surface effects on the optical properties of self-assembled crystalline GaN nanotubes grown on Si substrates. The excitonic emission is observed to redshift by ∼100 meV with respect to that of bulk GaN. We find that the conduction band edge is mainly dominated by surface atoms, and that a larger number of surface atoms for the tube is likely to increase the bandwidth, thus reducing the optical bandgap. The experimental findings can have important impacts in the understanding of the role of surfaces in nanostructured semiconductors with an enhanced surface/volume ratio.