Strain and structure heterogeneity in MoS 2 atomic layers grown by chemical vapour deposition

Monolayer molybdenum disulfide (MoS₂) has attracted tremendous attention due to its promising applications in high-performance field-effect transistors, phototransistors, spintronic devices and nonlinear optics. The enhanced photoluminescence effect in monolayer MoS₂ was discovered and, as a strong tool, was employed for strain and defect analysis in MoS₂. Recently, large-size monolayer MoS₂ has been produced by chemical vapour deposition, but has not yet been fully explored. Here we systematically characterize chemical vapour deposition-grown MoS₂ by photoluminescence spectroscopy and mapping and demonstrate non-uniform strain in single-crystalline monolayer MoS₂ and strain-induced bandgap engineering. We also evaluate the effective strain transferred from polymer substrates to MoS₂ by three-dimensional finite element analysis. Furthermore, our work demonstrates that photoluminescence mapping can be used as a non-contact approach for quick identification of grain boundaries in MoS₂.