Optical Properties of Two-Dimensional Islands of Tungsten Disulfide (WS2)

The paper presents the results of investigation of the optical and structural properties for tungsten disulfide (WS2) islands using atomic force microscopy (AFM), Raman scattering, and photoluminescence (PL). The morphology and local composition as well as oxidation induced changes in the WS2 islands were investigated. Micro- Raman and micro-PL spectra reveal the fundamental vibrational end exciton modes in WS2 islands, respectively. The intensity distribution maps of the phonon and exciton modes are discussed. The frequency dependences for the fundamental vibrational modes (A 1g and E2g) in WS2 islands on their thickness is obtained. A low-frequency shift of the E2g mode and a high-frequency shift of the A 1g mode with increasing the number of layers are reported. A shift in the PL peak energy position and changes in intensity induced by defects in the WS2 islands are observed. It is suggested that the shift of the PL energy, apparently, can be associated with the sample oxidation.