Nanostructures which retain both: surface plasmons (SP) and excitons; hold a great promise for the nanoscale integration of photonics and electronics in opto-electrical devices. Here nano-imaging was used in order to study the properties of SP and exciton in an individual WS2 nanotube. The surface waves were detected and imaged in real space in the visible light range using a scattering-type scanning near-field optical microscope (s-SNOM) (Fig. 1). The standing wave appears with specific incident light polarization and is induced by interference between the tip-excited wave and its reflection from the nanotube. This interaction leads to periodic modulation of tip-scattered infrared radiation which then measured by the detector. It was noted that the standing wave’s wavelength is varying with the number of crystal layers in the inorganic nanotube (INT). The measured dispersion of waves is appearing to be governed by the INT diameter.
The WS2 nanotubes are prepared in high temperature gas phase reaction which often resulted in strain related defects, mixture of phases and more. These structural variations are strongly affecting the optical properties of the INT. Using a balanced detection scheme together with acusto-optic-tunable filter (AOTF) and a supercontinuum laser source, the extinction spectrum of individual WS2 nanotube was observed for the first time (Fig. 2). Furthermore, this method provides a unique tool for studying the influence of phase mixture and structural defects on the optical properties of a single WS2 nanotube.
