Electronic properties of MoSe2 nanowrinkles.

Mechanical deformations, either spontaneously occurring during sample preparation or purposely induced in their nanoscale manipulation, drastically affect the electronic and optical properties of transition metal dichalcogenide monolayers. In this first-principles work based on density-functional theory, we shed light on the interplay among strain, curvature, and electronic structure of MoSe2 nanowrinkles. We analyze their structural properties highlighting the effects of coexisting local domains of tensile and compressive strain in the same system. By contrasting the band structures of the nanowrinkles against counterparts obtained for flat monolayers subject to the same amount of strain, we clarify that the specific features of the former, such as the moderate variation of the band-gap size and its persisting direct nature, are ruled by curvature rather than strain. The analysis of the wave-function distribution indicates strain-dependent localization of the frontier states in the conduction region while in the valence, the sensitivity to strain is much less pronounced. The discussion about transport properties, based on inspection of the effective masses, reveals excellent perspectives for these systems as active components for (opto)electronic devices.

Quantum Dots in Transition Metal Dichalcogenides Induced by Atomic-Scale Deformations.

Single-photon emission from monolayer transition metal dichalcogenides requires the existence of localized, atom-like states within the extended material. Here, we predict from first-principles the existence of quantum dots around atomic-scale protrusions, which result from substrate roughness or particles trapped between layers. Using density functional theory, we find such deformations to give rise to local membrane stretching and curvature, which lead to the emergence of gap states. Having enhanced outer-surface localization, they are prone to mixing with states pertaining to chalcogen vacancies and adsorbates. If the deformation is sharp, the conduction band minimum furthermore assumes atomic and valley-mixed character, potentially enabling quantum light emission. When such structural defects are arranged in an array, the new states couple to form energetically separated sub-bands, holding promise for intriguing superlattice dynamics. All of the observed features are shown to be closely linked to elastic, deformation-induced intra- and intervalley scattering processes.