Extraordinary in the Infrared

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Science  23 Jul 2004:
Vol. 305, Issue 5683, pp. 452
DOI: 10.1126/science.305.5683.452b

Nanoarrays of metals can exhibit “extraordinary” transmission of light, meaning that they transmit more light than would be expected on the basis of the combined area of the holes. This effect occurs because surface plasmons that are excited tunnel through the holes and then are emitted as photons on the other side.

Williams et al. have used this effect in the infrared regime to study the oxidation of methanol to formaldehyde on a copper oxide surface. They electrodeposited copper on a commercial nickel mesh until the hole size irised in to 3 to 4 μm. This surface was allowed to oxidize in air for 3 months. After activation with a drop of water to produce surface hydroxyl groups, a drop of methanol was placed on the surface, and the spectra of the adsorbed species that formed could be recorded with a conventional Fourier-transform infrared spectrometer. Extraordinary transmission was suppressed by oxide formation, but upon methanol exposure, two primary resonances (the 1,0 and 1,1) were recovered. Although the origin of the extraordinary transmission for a surface oxide is not fully understood, some of the absorbances, such as those for the methoxy radical species, are more than 100 times greater in intensity than those seen with more conventional surfaces. — PDS

J. Phys. Chem. B 10.1021/jp0489368 (2004).

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