Excitonic features in WS2 nanotubes revealed by photoacoustic spectroscopy

Abstract

Photoacoustic spectroscopy (PAS) is an absorption-like method that is particularly suitable for materials that strongly absorb or scatter light and are therefore difficult to investigate using conventional reflectance or transmittance measurements. However, its capability to provide quantitative information on the optical and thermal properties of complex nanostructured transition metal dichalcogenides has remained largely underexplored. Here, we demonstrate that randomly oriented WS2 nanotubes (NTs) assembled into cube-shaped structures are well suited for investigation by PAS, as they produce a high intensity signal and exhibit excitonic features from a material that is difficult to investigate using conventional absorption-based techniques. From the spectral analysis, we determined the effective energy of the direct bandgap of 2.08 ± 0.01 eV and the effective A exciton binding energy of 80 ± 3 meV for the WS2 NTs. Moreover, we estimated the effective thermal conductivity of the NTs at 7.5 ± 2.2 W m−1 K−1. These findings highlight that PAS enables quantitative determination of both optical and thermal parameters in nanostructured materials that are challenging to characterize using conventional absorption-like techniques, thereby extending the applicability of PAS to complex transition metal dichalcogenide architectures.