Near-field nano-imaging and nano-spectroscopy of Percolating Thin Gold Films

We investigated the infrared (IR) properties of percolating thin gold films on sapphire substrate at macro- and mesoscopic scale. Using scattering type scanning near-field optical microscopy (s-SNOM), ultra-broadband infrared nano-spectroscopy (ALS SINS), and infrared far-field spectroscopy, we performed a systematic study of the global and local IR spectrum of \textasciitilde 30 nm gold films at 3-25 \textmu m range. The inhomogeneous gold films below or above percolation threshold exhibit distinct DC, IR far-field, and IR near-field responses. We discuss in details the correlation between the degree of percolation and the infrared near-field properties of the films.