Enhanced Dielectric Screening and Photoluminescence from Nanopillar-Strained MoS₂ Nanosheets: Implications for Strain Funneling in Optoelectronic Applications

Abstract

Nonuniform strain on multilayer transition-metal dichalcogenide (TMDC) nanosheets is an exciting path toward practical optoelectronic devices, as it combines the advantages of localized control of optical and electronic properties with ease of fabrication. However, the weaker photoluminescence (PL) due to their indirect nature poses a challenge to their application. Here, we demonstrate extraordinary enhancement of PL from multilayer MoS2 nanosheets under nonuniform strain generated by nanopillars. We observe charge and exciton funneling to the pillar strain apex. The screening from the increased exciton and charge density lowers the exciton binding energy and renormalizes the band gap. Hence, we attribute the dramatic increase in PL to dissociation of bound excitons to free electron–hole pairs, showing that nonuniform strain on TMDC nanosheets can effectively manipulate the nature of light–matter interaction in these atomically thin materials for application in novel strain-engineered optoelectronics.

Charge Separation in Monolayer WSe2 by Strain Engineering: Implications for Strain-Induced Diode Action

“…Spatially varying strain in 2D TMDCs bends the band structure and generates a spatial bandgap gradient, thus offering exciton funneling and trion drift . Work utilizing a strain gradient includes both static straining devices, e.g., micro/nano pillars, wrinkled substrate, and dynamic straining devices, e.g., piezoelectric actuators, , atomic force microscopy tips, , nanogap, and MEMS devices . Moreover, exciton funneling in TMDCs may lead to critical densities for droplet formation and strong PL enhancement (e.g., MoS 2 , WS 2 , and WSe 2 ).…”

Charge Mobility and Strain Engineering in Two-Step MS-Grown MoS2/Seed Layer Heterointerface and Photo-Excitation Mechanism

“…The exciton binding energy in semiconductor films is changed by screening the Coulomb interaction and modifying the electron–electron interaction. This PL enhancement can also be attributed to the direct transition of the dissociated free electron–hole pairs at the K-point. − At the same time, the screening of increased exciton and charge density lowers the exciton binding energy and renormalizes the emission peak of A. Moreover, the strain can provide extra screening, further reduce exciton binding energy, and release electron–hole pairs .…”

“…This PL enhancement can also be attributed to the direct transition of the dissociated free electron–hole pairs at the K-point. − At the same time, the screening of increased exciton and charge density lowers the exciton binding energy and renormalizes the emission peak of A. Moreover, the strain can provide extra screening, further reduce exciton binding energy, and release electron–hole pairs . In contrast to MoS 2 on the Si substrate, the A exciton emission of MoS 2 is blue-shifted on the metal Ag and semiconductor (ZnO, Al 2 O 3 ) substrates, which corresponds to its luminescence enhancement.…”

Improved Ordering of Quasi-Two-Dimensional MoS2 via an Amorphous-to-Crystal Transition Initiated from Amorphous Sulfur-Rich MoS2+x

“…Two-dimensional (2D) transition-metal dichalcogenides (TMDCs) have demonstrated a very strong application potential in many areas depending on the form of the crystalline phase. Flat and large single-layer crystals have been used for the fabrication of optoelectronics and sensors, − while standing flakes, nanoparticles, and thin films have shown their potential in applications such as photocurrent generation, − photocatalytic degradation of organic pollutants, , electrocatalytic evolution of hydrogen − and energy, , and data storage. , An urgent task in the application of TMDCs is therefore the development of synthesis techniques for the growth of well-defined crystals with a controlled number of layers over large areas.…”