THz nanoscopy of platinum thin films

Terahertz nanoscopy is emerging as a powerful technique for the study of the optical and electronic properties of materials at the nanoscale, proving particularly important for mapping heterogeneous surfaces and nano-patterned devices. In this work, we apply terahertz scattering-type scanning near-field optical microscopy (THz-SNOM) to study the thickness-dependent conductivity of platinum thin films, with deeply sub-wavelength spatial resolution. Remarkably, our experimental data shows measurable layer contrast in the near-field scattering signal allowing us to detect differences in thin-film thickness down to the nanometer level. Micro four-point probe (M4PP) analysis of the thin-film sheet conductance confirms the trend observed in the THz-SNOM data that the near-field scattering signal, normalized to the response of the substrate, scales proportionately with film thickness. Our data suggests this technique can be widely used to characterize nanoscale variations in conductivity of metallic thin-films, as well as layered two-dimensional materials and nano-patterned devices.