Morphology-induced spectral modification of self-assembled WS2 pyramids

Due to their unique optical properties, including stable and chiral excitons, two-dimensional transition metal dichalcogenites hold the promise of applications in nanophotonics. Chemical vapor deposition techniques offer a platform to fabricate and design nanostructures with diverse geometries. However, the more exotic the grown nanogeometry, the less is known about its optical response. We have fabricated tungsten disulphide nanostructures with geometries ranging from monolayers to dented pyramids. The dented pyramids exhibit a strongly reduced photoluminescence with respect to horizontally layered tungsten disulphide, facilitating the study of their clear Raman signal in more detail. Excited resonantly, the dented pyramids exhibit a great number of higher-order phononic resonances. In contrast to monolayers, the spectral features of the optical response of the pyramids are position dependent. Differences in peak intensity, peak ratio and spectral peak positions reveal local variations in the atomic structure of the dented pyramids crater and sides. We characterize the position-dependent optical response of dented tungsten disulphide pyramids and attribute this to growth-induced nanogeometry. Thereby we open the way for producing tunable nanophotonic devices with applications ranging from opto-electronics to non-linear optics.