C. LIEWALD, S. MASTEL, J. HESLER, A. J. HUBER, R. HILLENBRAND AND F. KEILMANN
Vol. 5, No. 2 / February 2018 / Optica 159 (2018)
Probing conductivity in a contactless way with nanoscale resolution is a pressing demand in such active fields as quantum materials, superconductivity, and molecular electronics. Here, we demonstrate a laser- and cryogen-free microwave-technology-based scattering-type scanning near-field optical microscope powered by an easily aligned free-space beam with a tunable frequency up to 0.75 THz. It uses Schottky diode components to record background-free amplitude and phase nano-images, for the first time in the terahertz range, which is uniquely sensitive for assessing conduction phenomena. Images of Si with doped nanostructures prove a conductance sensitivity corresponding to 1016 cm−3 mobile carriers, at 50 nm spatial resolution.