Survey of Raman Spectroscopy and Fabry–Pérot Interference in Thin Flakes of 2H-MoS2, 1T-TaS2, 1T’-MoTe2, Td-WTe2, and α-MoO3

We report here a comprehensive study of thickness-dependent Raman measurements at the wavelength of 532 nm of five ultrathin van der Waals materials, namely, 2H-MoS2, 1T-TaS2, 1T'-MoTe2, Td-WTe2, and α-MoO3, and interpret using Fabry–Pérot (F–P) interferences. We point out the importance of extinction coefficient k for F–P phenomena, which together with optical contrast are stronger for materials characterized by low k values. Conducted simulations indicate that in first approximation, one can expect enhancement of the Raman signal from regions of low optical contrast. Additionally, we find also that for the 532 nm light, the tellurides have a higher absorption coefficient than the sulfides. Moreover, we observe edge states amplified by plasmonic effects in the trench formed in the tear of a MoS2 flake. Finally, we show that laser irradiation of MoTe2 and WTe2 can lead to generation of metallic tellurium. This result is an alternative explanation to many recent reports claiming a transition in MoTe2 from 1T' to Td phase.