Signatures of Bright‑To‑Dark Exciton Conversion in Corrugated Mos2 Monolayers

In this study, we investigated the effect of periodic uniaxial strains on electron and phonon transports of MoS 2 monolayers on a periodically corrugated sapphire surface. Micro-Raman, polarized photoluminescence and second harmonic generation results shows the anisotropy of the corrugation-induced strain in both single- and polycrystalline MoS 2 monolayers. AFM topography measurements show periodically-rippled surfaces of the MoS 2 in the nanometre scale. The application of the periodic strain produces two major effects on the band structure of MoS 2 monolayers: modulations on the band gap anisotropy and removal of the degeneracy of K points in the Brillouin zone. The degeneracy lifting enables an electron spin-flip scattering process that can convert a formerly bright exciton to a dark exciton. Our results demonstrate the ability to control both the bandgap and exciton character in monolayer MoS 2 via periodic strains imposed by corrugated sapphire substrates. The bright-to-dark excitons conversion in photovoltaic devices can boast longer lifetimes than their bright exciton counterparts so they can be more efficiently collected by external electrodes. The strain-induced conversion of the bright-to-dark excitons makes the hybrid MoS 2 /corrugated sapphire structure an interesting platform for future photovoltaic applications