Excitonic Resonance Raman features of magnetron sputtered WSe₂

In this study, magnetron pulsed DC and DC/ RF sputtered tungsten diselenide (WSe₂) thin film, grown anisotropically along its c-plane as measured by XRD, studied using Raman spectroscopy at several excitation energies including 1.57 eV, 2.33 eV, and 2.86 eV will be presented. The characteristic WSe₂ phonon modes of E_2g¹ and A_1g at ~247 cm­^-1 and ~251 cm^-1 were resolved using linearly polarized backscattered Raman configuration. Circularly polarized Raman is also used to verify and resolve E_2g¹ and A_1g peaks. Under a specific laser irradiation wavelength of 785 nm (1.57 eV), a new Raman peak E_1g appeared at ~176 cm^-1 and exhibited excitation energy dependence. Resonance with exciton energy A leads to this E_1g Raman active but forbidden peaks to be observed in backscattered Raman configuration, suggesting broken selection rules in the crystal. Also, second-order phonon mode intensity is enhanced, and A_1g mode selectively improved with 1.57 eV excitation, which is close A exciton energy. At B exciton energy, Raman peak at 310 cm^-1 appeared, which is Raman inactive. These features in the Raman spectrum are interpreted as the strong resonance with exciton energies. This study addressed the fundamental fingerprint of excitonic resonance Raman phonon modes in layered transition metal dichalcogenides.