Analysis of visible and infrared spectroscopic detection in scattering scanning near-field optical microscopy

Spectroscopic imaging through scattering scanning near-field optical microscopy (s-SNOM) has emerged as a powerful technique for detecting and characterizing nanoscale materials across various fields. At any given wavelength, s-SNOM imaging yields a pair of two complementary images known as amplitude and phase. While amplitude image is usually correlated to the reflectivity, phase-imaging in s-SNOM is especially important because it can unveil material-specific absorption peaks, often found within the mid-infrared spectrum. This explains the relatively limited studies of spectral s-SNOM imaging within the visible range. Here, we examine the spectroscopic detection capabilities of s-SNOM from a theoretical standpoint, considering various spectral domains, sample types, and tip materials, and compare these findings with experimental results.