Vollelektronische Terahertz-Nanoskopie

Terahertz scattering-type scanning near-field optical microscopy (THz-s-SNOM) enables THz nano-imaging with a spatial resolution down to 20nm. However, the THz systems used to date still severely limit the scientific applicability of the technique. This work demonstrates a simple approach to fast and sensitive amplitude- and phase-resolved terahertz nanoscale imaging using an all-electronic THz system with heterodyne detection at a frequency of 600GHz. In contrast to complementary ultrafast THz nanospectroscopic methods and alternative cw methods, this method enables the fastest amplitude- and phase-resolved imaging and achieves sensitivities that meet scientific requirements. This makes the system particularly suitable for the investigation of a wide range of resonant electronic excitations, chemical imaging, and imaging of THz (plasmon) polaritons, surface electromagnetic waves at conductive interfaces, as demonstrated in this work. The first part of the work shows the realisation and characterisation of an all-electronic THz-s SNOM based on a commercial atomic force microscope (AFM) for operation in air at room temperature. Crucial requirements on the AFM system, optical components, microwave synthesizer and the THz system itself are identified and the exceptional performance of the THz-s-SNOM is revealed. The second part of the work demonstrates the practical application of the system to investigate contact free the nanoscale electrical charge transport in technologically relevant semiconductors such as doped silicon, lead-halide perovskite thin films for the first time, and exfoliated graphene as a 2D material. The high sensitivity of the THz-s SNOM is impressively demonstrated on exfoliated graphene, in which, for the first time, long-range interference patterns of overdamped ultra-long wavelengths 600GHz plasmon polaritons can be observed.