First-principles investigation of dominant strain axes in chemical vapor deposition grown monolayer MoS2

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 MoS2 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 MoS2 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 MoS2 monolayers is primarily uniaxial. In addition, uniaxial strain computations show a break in K and K′ 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 MoS2 monolayers fabricated with chemical vapor deposition is nonuniformly biaxial.