Terahertz (THz) radiation is a valuable tool to investigate the electronic properties of lead halide perovskites (LHPs). However, attaining high-resolution information remains elusive, as the diffraction-limited spatial resolution (∼300 μm) of conventional THz methods prevents a direct analysis of microscopic effects. Here, we employ THz scattering scanning near-field optical microscopy (THz-sSNOM) for nanoscale imaging of cesium lead bromide (CsPbBr3) thin films down to the single grain level at 600 GHz. Adopting a scattering model, we are able to derive the local THz nanoscale conductivity in a contact-free fashion. Increased THz near-field signals at CsPbBr3 grain boundaries complemented by correlative transmission electron microscopy–energy-dispersive X-ray spectroscopy elemental analysis point to the formation of halide vacancies (VBr) and Pb–Pb bonds, which induce charge carrier trapping and can lead to nonradiative recombination. Our study establishes THz-sSNOM as a powerful THz nanoscale analysis platform for thin-film semiconductors such as LHPs.

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Terahertz (THz) biosensing has emerged as an important research field, mainly driven by the resonant behavior of many biomolecules in this spectral range which holds potential for highly sensitive analyses. In this work, we present a detailed overview of our current research on THz biosensing, focusing on the development and analysis of THz biosensors based on frequency selective surfaces (FSS) for two different measurement scenarios: i) label-free, highly sensitive and selective analysis of dried biomolecules, and ii) sensitive and selective analysis in an aqueous environment. With our carefully designed THz biosensor for measurements in the dry state, we were able to indirectly measure tumor-marker MIA RNA in a concentration as low as 1.55 × 10−12 mol/L, without the need for biochemical amplification. Our biosensor with substrate-integrated microfluidics for terahertz measurements in an aqueous environment is validated by simulations, showing that the resonance feature in the frequency response of our sensor is maintained even for measurements in water.