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This study investigates the growth of mono- and few-layer MoS$_2$ on SiO$_2$ substrates using room-temperature pulsed laser deposition (PLD), highlighting the sensitivity of its vibrational and excitonic properties to layer number and structural disorder. Multiwavelength Raman spectroscopy is employed to track the evolution of Raman-shift differences and defect density as a function of deposition laser pulses, revealing significant insights into symmetry-dependent exciton-phonon coupling. The findings not only validate PLD as a suitable method for fabricating two-dimensional MoS$_2$ but also elucidate the impact of growth-induced defects on excitonic interactions, contrasting with mechanically exfoliated samples.
Symmetry-dependent exciton-phonon coupling in MoS$_2$ reveals how growth-induced defects can dramatically alter optical properties.
Molybdenum disulfide (MoS$_2$) is a semiconductor whose vibrational and excitonic properties are highly sensitive to layer number and structural disorder. We demonstrate the growth of MoS$_2$ monolayers on inert, electronics-compatible SiO$_2$ substrates using room-temperature pulsed laser deposition (PLD). Control of the process parameters enables tuning from monolayer to multilayer films, which we investigate by multiwavelength Raman spectroscopy. The evolution of the Raman-shift difference between the $E_{2g}^{1}$ and $A_{1g}$ modes, combined with an assessment of defect density, tracks film growth as a function of the number of deposition laser pulses. Although excitonic effects strongly influence the optical response of two-dimensional transition-metal dichalcogenides, experimental reports of symmetry-selective exciton-phonon coupling remain limited. We provide experimental evidence of symmetry-dependent exciton-phonon coupling in PLD-grown monolayer MoS$_2$. Specifically, we observe modulation of the resonant behaviour of the out-of-plane $A_{1g}$ and in-plane $E_{2g}^{1}$ modes, related to their different coupling to A excitons, predominantly derived from Mo $d_{z^2}$ orbitals, and C excitons, characterized by mixed orbital contributions from Mo $d_{z^2}$ and S $p_x$ and $p_y$ states. Comparison with mechanically exfoliated monolayers reveals the role of growth-induced defects in modulating these interactions. These findings establish room-temperature PLD as a viable approach for growing two-dimensional MoS$_2$ on inert, electronics-compatible substrates and provide insight into the interplay between excitonic resonances and growth-induced disorder in two-dimensional MoS$_2$.
