Nanograin VO2 in the Metal Phase: A Plasmonic System with falling DC Resistivity as Temperature Rises

Institute of Physics (UK)
Publication Type:
Journal Article
Nanotechnology, 2007, 18 (2), pp. 025202 - 25209
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Thin films of vanadium dioxide with grain size smaller than 60nm have a metallic phase with excellent plasmonic response,but their dc resistivity falls as temperature rises to values above the metal-insulator transition. At the transition optical switching is complete, but the switch in dc resistance is incomplete. In the metallic phase nanograin and large grain samples have similar values of both plasma frequency and relaxation rate. However, plasmonic response in nanograins is stronger due to the absence of a low energy interband transition foun din large grain fims. Conductivity rises with thermal activation energy of 108 meV, which is well below that in rthe semiconductor phase. Possible mechanisms for non-metal' like dc behaviour in this plasmonic system are briefly discussed. They include fluctuations which are coherent in nanograins but incoherent for larger grains. Nanoscale systems seem preferable for optical switching applications and large grain structures for dc switching work.
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