With infrared spectroscopic microscopy using synchrotron light, the authors studied resonant light scattering from single metal nanowires with diameters in the 100nm range and with lengths of a few microns. The Au and Cu nanowires were electrochemically grown in polycarbonate etched ion-track membranes and transferred on infrared-transparent substrates. Significant antennalike plasmon resonances were observed in good agreement with exact light-scattering calculations. The resonances depend not only on length and diameter but also on the dielectric surrounding of the nanowire. The observed maximum extinction at resonance corresponds to an electromagnetic far-field enhancement by a factor of about 5.

Various experimental results on surface enhanced infrared absorption reveal asymmetric line shapes. Whereas the order of magnitude of the enhancement can be understood from electromagnetic field enhancement the unusual line shape remains without satisfactory explanation. An interaction with electron-hole pairs would lead to an asymmetric line but this should be restricted to the first monolayer. However, asymmetry is also observed for vibrations at larger distances from the metal-film surface. Here we show strongly asymmetric lines and their enhancement as a consequence of the interaction of adsorbate vibrations with surface plasmons of metal islands. Both the effects and also the baseline change can be estimated by a proper application of well established effective-media models.

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We have measured infrared transmission spectra of CO adsorbed on in situ grown iron films on MgO(001) under ultrahigh vacuum conditions. Even at normal incidence we observed strong absorption lines in the C–O stretch region with number, intensities, positions, and shapes dependent on CO coverage and Fe-film thickness and morphology. This absorption must be due to vibrational dipoles oblique to the substrate surface, e.g., due to molecules at island walls. The distinct absorption lines can be assigned to distinct adsorption sites on crystalline facets of epitaxial Fe islands on MgO(001). For each of the films the strongest CO line shows an asymmetric shape. Additionally, the observed absorption is enhanced by at least two orders of magnitude with respect to adiabatic intensities of, e.g., CO on NaCl. Line shapes and intensity let us suggest nonadiabatic coupling of the adsorbate vibration to electronic transitions.