Dendritic Plasmonics for Mid-Infrared Spectroscopy

Metallic nanostructures that exhibit tailored optical resonances spanning from the near to mid-infrared spectral range are of particular interest for spectroscopic and optical measurements in these spectral domains that can benefit from localized surface-enhancement effects. Plasmon resonances shifted in the near or mid-infrared range could be used to further enhance the excitation and/or the emission of an optical process. Surface-enhanced infrared absorption (SEIRA) is one of such processes and can particularly benefit from plasmon-enhanced local fields yielding an increase in sensitivity toward the detection of an analyte. Herein, we have fabricated a series of gold dendritic nanostructures, prepared by electron-beam lithography, that exhibit plasmon resonances spanning the near and mid-infrared spectral regions. We explore the influence of the number of branches of the dendritic structures as well as the length of each generation together with the overall effect of the shape and symmetry on the resulting optical resonances. The creation of new resonances that appear upon newer fractal generation is explained in light of an hybridization model. Selected structures were then evaluated for SEIRA measurements toward an analyte.