Spatial and spectral mode mapping of a dielectric nanodot by broadband interferometric homodyne scanning near-field spectroscopy

Abstract

We investigate the optical properties of nanostructures of antimony sulfide (Sb2S3), a direct-bandgapsemiconductor material that has recently sparked considerable interest as a thin film solar cell absorber.Fabrication from a nanoparticle ink solution and two- and three-dimensional nanostructuring with patternsizes down to 50 nm have recently been demonstrated. Insight into the yet unknown nanoscopic opticalproperties of these nanostructures is highly desired for their future applications in nanophotonics. Weimplement a spectrally broadband scattering-type near-field optical spectroscopy technique to study individualSb2S3nanodots with a 20-nm spatial resolution, covering the range from 700 to 900 nm. We show that inthis below-bandgap range, the Sb2S3nanostructures act as high-refractive-index, low-loss waveguideswith mode profiles close to those of idealized cylindrical waveguides, despite a considerable structuraldisorder. In combination with their high above-bandgap absorption, this makes them promising candidatesfor applications as dielectric metamaterials, specifically for ultrafast photoswitching.