Resonance-Enhanced Terahertz Nanoscopy Probes

Near-field nanoscopy at terahertz (THz) frequencies is uniquely placed to probe a multitude of physical phenomena at the nanoscale. However, at THz frequencies, the scattering efficiency of standard near-field probes is poor, limiting the sensitivity and, hence, resolution of the technique. Here, we propose and demonstrate tunable resonant scattering from metal tips that allow us to overcome this limitation. Tips supporting a λ/2 dipolar resonance in the THz range are fabricated from indium metal directly on the tine of a quartz tuning fork. We observe enhancement of the THz scattering efficiency at the resonance frequency with a Q-factor of ∼2-3. These tips enable a subwavelength spatial resolution better than 100 nm. We support the experimentally observed enhancement using a numerical model. The enhanced scattering efficiency afforded by the resonant indium tips can enable the probing of new phenomena, such as plasmons in two-dimensional materials, that have proven difficult to observe thus far.