Electron-Phonon Interaction and Double-Resonance Raman Studies in Monolayer WS2

Atomically thin layers of 2D WS2 offer a realization of novel valley-selective electronics and power-efficient optoelectronic device fabrication due to large spin splitting at the top of the valence band and high quantum efficiency. However, the synthesis of the large-area monolayer WS2 film through chemical vapor deposition (CVD) method is in a rudimentary stage. Here we report a modified CVD method to synthesize high-crystalline monolayer WS2 (1L) with uniform size distribution over a large area. The intensity of the second-order Raman modes in 1L WS2 is enhanced, particularly the overtone of the acoustic mode LA(M), when the excitation wavelength is in the vicinity of B exciton. The variation in the intensity profile of the first-order Raman modes for 1L and bulk WS2 in (laser-energy-dependent) resonant Raman scattering processes is discussed within the third-order perturbation theory.