Time-resolved THz time-domain near-field microscopy of exfoliated single flakes of WS2

Terahertz spectroscopy is a powerful and contactless technique that enables to measure charge carrier properties in metals and semiconductors. However, the relatively long wavelengths of THz radiation and the diffraction limit imposed by optical imaging systems, reduces the applicability of THz spectroscopy considerably. We have developed a time-resolved terahertz near-field microscope that allows measurements of the carrier dynamics with sub-diffraction resolution. This microscope is used to measure an exfoliated flake of a 2D transition metal dichalcogenide crystal with a few tens of microns' resolution. Mapping carrier dynamics of semiconductors, non-invasively, and on micron length scales, opens new possibilities for material characterization.