Polarized Raman study of large built-in strain in monolayer WS₂ grown on Au/W substrate

Strain plays a crucial role in the energy landscape of atomically thin two-dimensional materials. Here, we report polarized Raman results of WS₂ monolayers having either rough or wrinkled surface morphologies. For rough WS₂, the E^′ phonon intensity exhibits polar behavior that deviates from the Raman polarization selection rules. Furthermore, with the formation of wrinkles on the WS₂ surface, the E^′ phonon splits into E^′− and E^′+ phonons. Polar plots of the E^′− and E^′+ phonon intensities as a function of polarization angle θ show that both phonons have strong polar dependence with orthogonal characteristics in their polarized intensity profiles: the E^′− phonon intensity is maximum when the E^′+ phonon intensity is diminished, and vice versa. Our result demonstrates that built-in strain in low-dimensional materials can be quantitatively identified by polarized Raman studies and further provides a useful strategy to achieve better device performance for which strain engineering is required.