Raman-scattering measurements and first-principles calculations of strain-induced phonon shifts in monolayer MoS2
The effect of strain on the phonon modes of monolayer and few-layer MoS${}_{2}$ has been investigated by observing the strain-induced shifts of the Raman-active modes. Uniaxial strain was applied to a sample of thin-layer MoS${}_{2}$ sandwiched between two layers of optically transparent polymer. The resulting band shifts of the ${E}_{2g}^{1}$ ($\ensuremath{\sim}$$385.3\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$) and ${A}_{1g}$ ($\ensuremath{\sim}$$402.4\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$) Raman modes were found to be small but observable. First-principles plane-wave calculations based on density functional perturbation theory were used to determine the Gr\"uneisen parameters for the ${E}_{1g}$, ${E}_{2g}^{1}$, ${A}_{1g}$, and ${A}_{2u}$ modes and predict the experimentally observed band shifts for the monolayer material. The polymer--MoS${}_{2}$ interface is found to remain intact through several strain cycles. As an emerging 2D material with potential in future nanoelectronics, these results have important consequences for the incorporation of thin-layer MoS${}_{2}$ into devices.