GHz-THz near-field imaging of extreme subwavelength metal structures

Modern scattering-type scanning near-field optical microscopy (s-SNOM) has become an indispensable tool in material research. In this talk we present a home-built GHz-THz s-SNOM using Schottky diodes as both light source and detector, achieving unprecedented spatial resolution at long wavelength (~2 mm). We systematically investigated a series of extreme subwavelength metallic nanostructures at the micrometer scale. The near-field material contrast is found to be greatly impacted by the lateral size and connectivity of the nanostructures, which is drastically different from the cases at shorter wavelengths (e.g. IR s-SNOM). The observed phenomena can be explained by a quasi-static analysis and full-wave electromagnetic simulations. Our results reveal that s-SNOM with long wavelength excitation is an ideal candidate for investigating the electrostatic behavior of metallic devices.