The topologically nontrivial and chemically functional distorted octahedral (T') transition-metal dichalcogenides (TMDCs) are a type of layered semimetal that has attracted significant recent attention. However, the properties of monolayer (1L) T'-TMDC, a fundamental unit of the system, are still largely unknown due to rapid sample degradation in air. Here we report that well-protected 1L CVD T'-MoTe2 exhibits sharp and robust intrinsic Raman bands, with intensities about 1 order of magnitude stronger than those from bulk T'-MoTe2. The high-quality samples enabled us to reveal the set of all nine even-parity zone-center optical phonons, providing reliable fingerprints for the previously elusive crystal. By performing light polarization and crystal orientation resolved scattering analysis, we can effectively distinguish the intrinsic modes from Te-metalloid-like modes A (∼122 cm-1) and B (∼141 cm-1), which are related to the sample degradation. Our studies offer a powerful nondestructive method for assessing sample quality and for monitoring sample degradation in situ, representing a solid advance in understanding the fundamental properties of 1L-T'-TMDCs.
Keywords: Raman scattering; anisotropy; crystal quality; monolayer T′ molybdenum ditelluride; topological insulator; transition-metal dichalcogenide.