Enhanced infrared spectroscopy using small-gap antennas prepared with two-step evaporation nanosphere lithography.

We use nanosphere lithography in combination with two evaporation steps to create bow-tie like infrared antennas with small gaps. The angle of the sample with respect to the evaporation source is changed between two evaporation steps resulting in a displacement of the respective antenna arrays and, therefore, in decreased antenna-gaps. Furthermore, we demonstrate the gap-dependency of surface-enhanced infrared absorption (SEIRA) spectroscopy using the absorption band of the natural SiO(2)-layer of the silicon substrate and antennas with different gap size. A multi-oscillator-model is used to describe the Fano-like spectral coupling of the antenna resonances with the SiO(2) absorption band.