First-principles investigation of dominant strain axes in chemical vapor deposition grown monolayer ${\mathrm{MoS}}_2$

Transition metal dichalcogenides have been proven to be highly tunable and versatile materials that show promise in electronics applications. Chemical vapor deposition as a monolayer growth method is scalable for mass production and can reliably yield sample sizes larger than those from mechanical exfoliation. Characterizing defect concentrations of chemical vapor deposition grown ${\mathrm{MoS}}_2$ to rapidly evaluate sample quality is possible through Raman spectroscopy, though this method can prove difficult due to strain interference in the monolayer Raman scattering signals. In this paper, first-principles density functional theory phonon and mode-Grüneisen parameter calculations are compared with experimentally derived mode-Grüneisen values to better characterize the sample strain on chemical vapor deposition grown ${\mathrm{MoS}}_2$ monolayers. We show that mode-Grüneisen parameter computations performed assuming a uniaxial straining direction match more closely with experimental findings than calculations performed assuming uniform biaxial strain, suggesting that substrate-sample strain for the grown ${\mathrm{MoS}}_2$ monolayers is primarily uniaxial. In addition, uniaxial strain computations show a break in K and $K^{\prime }$ reciprocal point symmetry, which accounts for a reduction in the intensity of double-resonant Raman processes observed in experimental data, reinforcing the assumption that strain on ${\mathrm{MoS}}_2$ monolayers fabricated with chemical vapor deposition is nonuniformly biaxial.