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.