Raman scattering

Raman spectroscopy

Materials science

Chromatography

Trion

Atomic physics

Photoluminescence

Laser

Physics

Nanotechnology

Exciton

Optics

Molecular physics

Superconductivity

Condensed matter physics

Analytical Chemistry (journal)

Monolayer

Chemistry

Quasiparticle

Optoelectronics

Journal of Raman Spectroscopy

Bound quasiparticles, negatively charged trions and neutral excitons, are associated with the direct optical transitions at the K-points of the Brillouin zone for monolayer MoS$_2$. The change in the carrier concentration, surrounding dielectric constant and defect concentration can modulate the photoluminescence and Raman spectra. Here we show that exposing the monolayer MoS$_2$ in air to a modest laser intensity for a brief period of time enhances simultaneously the photoluminescence (PL) intensity associated with both trions and excitons, together with $\sim$ 3 to 5 times increase of the Raman intensity of first and second order modes. The simultaneous increase of PL from trions and excitons cannot be understood based only on known-scenario of depletion of electron concentration in MoS$_2$ by adsorption of O$_2$ and H$_2$O molecules. This is explained by laser induced healing of defect states resulting in reduction of non-radiative Auger processes. This laser healing is corroborated by an observed increase of intensity of both the first order and second order 2LA(M) Raman modes by a factor of $\sim$ 3 to 5. The A$_{1g}$ mode hardens by $\sim$ 1.4 cm$^{-1}$ whereas the E$^1_{2g}$ mode softens by $\sim$ 1 cm$^{-1}$. The second order 2LA(M) Raman mode at $\sim$ 440 cm$^{-1}$ shows an increase in wavenumber by $\sim$ 8 cm$^{-1}$ with laser exposure. These changes are a combined effect of change in electron concentrations and oxygen-induced lattice displacements.

Enhanced Raman and photoluminescence response in monolayer MoS<sub>2</sub> due to laser healing of defects

Enhanced Raman and photoluminescence response in monolayer MoS2 due to laser healing of defects

Enhanced Raman and photoluminescence response in monolayer MoS₂ due to laser healing of defects