Temperature-Dependent Low-Frequency Raman Modes in CVD-Grown Monolayer MoS₂

Low-frequency Raman modes of two-dimensional (2D) layered materials originate from interlayer interactions and are usually seen in bilayer (2L) or thicker layered samples, whereas they are absent in monolayer (1L) samples. Herein, temperature-dependent low-frequency Raman bands at ∼23 and ∼40 cm–1, corresponding to shear force (S) and layer breathing (LB) modes, respectively, are observed on 1L MoS2 samples grown by a chemical vapor deposition (CVD) method. These two modes exhibit decreasing intensity as the temperature is lowered from 373 to 240 K, while they totally disappear at temperature <240 K. Angle-resolved polarization Raman spectra (ARPRS) measurements reveal that these two modes exhibit Raman polarization behaviors similar to those of 2L MoS2. These results greatly enrich the knowledge of 1L MoS2 and benefit the understanding of its physical properties.