A novel resonant mechanism involving the interference of a broadband plasmon with the narrowband vibration from molecules is presented. With the use of this concept, we demonstrate experimentally the enormous enhancement of the vibrational signals from less than one attomol of molecules on individual gold nanowires, tailored to act as plasmonic nanoantennas in the infrared. By detuning the resonance via a change in the antenna length, a Fano-type behavior of the spectral signal is observed, which is clearly supported by full electrodynamical calculations. This resonant mechanism can be a new paradigm for sensitive infrared identification of molecular groups.

A sound knowledge and understanding of the thermal stability of nanowires is a prerequisite for the reliable implementation of nanowire-based devices. We investigate the morphology of Au nanowires annealed isothermally at different temperatures. During the processes, triggered by heating, the wires undergo various configurational changes to finally break up into chains of nanospheres at much lower than bulk melting temperatures due to capillary or so-called Rayleigh instability. The role of three parameters, namely, wire diameter, temperature, and annealing time, on the final morphology is investigated. Both the average sphere diameter and the mean spacing between adjacent spheres are larger than the values predicted for materials with isotropic surface energy. Possible reasons are discussed in the paper.

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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.