Near-Field Imaging of Free Carriers in ZnO Nanowires with a Scanning Probe Tip Made of Heavily Doped Germanium

Although scattering-type scanning near-field infrared microscopy can provide access to key parameters of nanomaterials, presently it is performed with unoptimized gold-coated cantilever probes, mainly due to their commercial availability. This work demonstrates that heavily doped germanium, with a midinfrared plasma frequency, is also a good choice for such probes. The peculiarities of IR plasmonic resonances of doped semiconductor nanostructures are highlighted with the aid of multiple-scattering models. This development in coating-free monolithic tips for scanning-probe microscopy could facilitate a lot of nanotechnology research, particularly in plasmonics and photonics.