Nanoscale strain induced effects on the optoelectronic properties of monolayer transition metal dichalcogenides.

We perform simulations and scanning tunneling spectroscopic (STS) studies of the strain effects on the optoelectronic properties of monolayer TMDC materials MS₂, where M = Mo and W. We use molecular dynamics to simulate the strain effect on MS₂ by relaxing a (60x60) nm2 monolayer MS₂ sheet on top of a 2.5 nm radius semi-sphere gold nanoparticle. We find that the strain tensor component εxy changes between the top S-layer (positive) and bottom S-layer (negative), indicating the top S-layer experiences an effective stretching force whereas the bottom S-layer is compressed. For STS studies, high quality monolayer MoS₂ single crystals with areas to 200x200nm² are synthesized by CVD and transferred to Si substrates with triangular arrays of nanostructures. Nanostructures are ~20nm in size with a lattice constant of ~400nm. Spatially resolved STS studies on the LDOS in MS₂ are carried out to investigate spatial variations resulting from strain and temperature evolution of the local electronic bandgap. Using a variable-wavelength light source, circularly polarized light is also applied to the sample under STS studies, and the spatially resolved LDOS in strained MS₂ are investigated as a function of temperature, optical wavelength and polarization.This work is supported by NSF and ARO