Strain-dependent luminescence and piezoelectricity in monolayer transition metal dichalcogenides

Abstract

The modification of optical and electronic properties of transition metal dichalcogenides via mechanical deformation has been widely studied. Their ability to withstand large deformations before rupture has enabled large tunability of the bandgap, and further, the spatially varying strain has been shown to control the spatial distribution of the bandgap and lead to effects such as carrier funneling. Monolayer transition metal dichalcogenides exhibit a significant piezoelectric effect that could couple to a spatially inhomogeneous strain distribution to influence electronic and optical behavior. We investigate both experimentally and theoretically an example case of photoluminescence in structures with a strain distribution similar to that employed in single-photon emitters but generated here via nanoindentation. Using a mechanical model for strain induced by nanoindentation, we show that piezoelectricity can result in charge densities reaching 1012 e/cm2 and can generate electrostatic potential variations on the order of ±0.1 V across the suspended monolayer. We analyze the implications of these results for luminescence and exciton transport in monolayer transition metal dichalcogenides with spatially varying strain.

Spatial Control of 2D Nanomaterial Electronic Properties Using Chiral Light Beams

“…For the simulated linearly polarized Gaussian beam, the optical momentum flux points only out-of-plane in the direction of light propagation (Figure a). This qualitatively replicates the effects achieved by a physical push of monolayer WS 2 , for instance, similar to that generated by AFM tips in contact mode . For LG beams, the optical momentum flux density still has a significant out-of-plane component, but in addition there is an in-plane shear force, corresponding to the azimuthal component of the momentum flux (Figure b).…”

“…This effect is most pronounced for the exfoliated sample, with the PL spectra returning to close to its initial line shape after 2 hours (Figure S11). Previous work has demonstrated that the X 0 component red shifts and the T/X 0 intensity ratio increases with strain caused by out-of-plane deformations, such as wrinkles . Due to the faster relaxation times displayed by WS 2 samples compared to graphene, wrinkling cannot be monitored directly with AFM and Raman mapping.…”

“…Previous work has demonstrated that the X 0 component red shifts and the T/ X 0 intensity ratio increases with strain caused by out-of-plane deformations, such as wrinkles. 41 Due to the faster relaxation times displayed by WS 2 samples compared to graphene, wrinkling cannot be monitored directly with AFM and Raman mapping. The residual spectral changes after switching back from LG to Gaussian beams rules out the possibility of an electronic origin of the effect.…”

Optical Strain Engineering Enables Dynamic Spatial Control of 2D Nanomaterial Properties

“…This qualitatively replicates the effects achieved by a physical push of monolayer WS2, for instance, similar to that generated by AFM tips in contact mode. 43 For LG beams, the optical momentum flux density still has a significant out-of-plane component, but in addition there is an in-plane shear force, corresponding to the azimuthal component of the momentum flux (Fig. 5d).…”

“…Previous work has demonstrated that the X 0 component red shifts and the T/X 0 intensity ratio increases with strain caused by out-of-plane deformations, such as wrinkles. 43 Due to the faster relaxation times displayed by WS2 samples compared to graphene, wrinkling cannot be monitored directly with AFM and Raman mapping. The residual spectral changes after switching back from LG to Gaussian beams rules out the possibility of an electronic origin of the effect.…”