Surface-enhanced infrared absorption (SEIRA) has been gaining substantial attention by using plasmonic nanoantennas to amplify near-field intensities so that it can extend IR spectroscopy to zeptomolar quantities and ultimately to the sigle-molecule level. Here we report a new nanoantenna for SEIRA detection, consisting of a fan-shaped Au structure positioned at a well-specified distance above a reflective plane with an intervening silica spacer layer. This antenna can be easily tuned to overlap vibrational modes within a broad spectral range from the near-IR into terahertz regimes. Our finite difference time domain (FDTD) simulations reveal a maximum SEIRA enhancement factor of 105 in the antenna junction area, which is corresponding to the experimental detection of 20-200 zeptomoles of octadecanethiol, using a standard commercial FTIR spectrometer. Our optimized antenna exhibits an order of magnitude greater SEIRA sensitivity than previous record-setting designs, which opens new opportunities for using infrared spectroscopy to analyze exceptionally small quantities of molecules.
Xiao Yang, Lisa V. Brown, Ke Zhao, Bob Y. Zheng, Peter Nordlander, and Naomi J. Halas, "Fan-shaped gold nanoantennas above reflective substrates for surface-enhanced infrared absorption (SEIRA) (Presentation Recording)," Proc. SPIE 9554, Nanoimaging and Nanospectroscopy III, 955412 (Presented at SPIE Nanoscience + Engineering: August 11, 2015; Published: 5 October 2015); https://doi.org/10.1117/12.2188477.4519371118001.
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