Low-Frequency Raman Modes and Electronic Excitations In Atomically Thin MoS2 Crystals

Abstract

Atomically thin MoS${}_2$ crystals have been recognized as a quasi-2D semiconductor with remarkable physics properties. This letter reports our Raman scattering measurements on multilayer and monolayer MoS${}_2$, especially in the low-frequency range ($<$50 cm${}^{-1}$). We find two low-frequency Raman modes with contrasting thickness dependence. With increasing the number of MoS${}_2$ layers, one shows a significant increase in frequency while the other decreases following a 1/N (N denotes layer-number) trend. With the aid of first-principle calculations we assign the former as the shear mode $E_{2g}^2$ and the latter as the compression vibrational mode. The opposite evolution of the two modes with thickness demonstrates novel vibrational modes in atomically thin crystal as well as a new and more precise way to characterize thickness of atomically thin MoS${}_2$ films. In addition, we observe a broad feature around 38 cm${}^{-1}$ (~5 meV) which is visible only under near-resonance excitation and pinned at the fixed energy independent of thickness. We interpret the feature as an electronic Raman scattering associated with the spin-orbit coupling induced splitting in conduction band at K points in their Brillouin zone.

5 pages, 4 figures

References in corpus (4)

• Two Dimensional Atomic Crystals
• Anomalous Lattice Vibrations of Single and Few-Layer MoS2
• Raman spectroscopy of the interlayer shear mode in few-layer MoS2 flakes
• Layer number determination in graphene using out-of-plane vibrations

Cited by in corpus (40)

• Phonon and Raman scattering of two-dimensional transition metal dichalcogenides from monolayer, multilayer to bulk material
• Three-band tight-binding model for monolayers of group-VIB transition metal dichalcogenides
• Lattice dynamics in mono- and few-layer sheets of WS2 and WSe2
• Shear and Layer Breathing Modes in Multilayer MoS2
• Lattice Vibrational Modes and Phonon Thermal Conductivity of Monolayer MoS2
• Anomalously Robust Valley Polarization and Valley Coherence in Bilayer WS2
• Observation of interlayer phonon modes in van der Waals heterostructures
• Interlayer electronic hybridization leads to exceptional thickness-dependent vibrational properties in few-layer black phosphorus
• Raman vibrational spectra of bulk to monolayer ReS2 with lower symmetry
• Splitting of interlayer shear modes and photon energy dependent anisotropic Raman response in $N$-layer ReSe${}_2$ and ReS${}_2$
• Coupling and stacking order of ReS2 atomic layers revealed by ultralow-frequency Raman spectroscopy
• Mapping of Low-Frequency Raman Modes in CVD-Grown Transition Metal Dichalcogenides: Layer Number, Stacking Orientation and Resonant Effects
• Anomalous excitonic resonance Raman effects in few-layer MoS2
• Multiwavelength excitation Raman Scattering Analysis of bulk and 2 dimensional MoS2: Vibrational properties of atomically thin MoS2 layers
• Unified description of the optical phonon modes in $N$-layer MoTe${}_2$
• Hall and field-effect mobilities in few layered $p$-WSe${}_2$ field-effect transistors
• Anomalous Frequency Trends in MoS2 Thin Films Attributed to Surface Effects
• A direct comparison of CVD-grown and exfoliated MoS2 using optical spectroscopy
• A Comprehensive Multiphonon Spectral Analysis in MoS2
• Newly observed first-order resonant Raman modes in few-layer MoS${}_2$
• Anharmonic phonons in few layer MoS${}_2$: Raman spectroscopy of ultra low energy compression and shear modes
• Splitting of the monolayer out-of-plane A'1 Raman mode in few-layer WS2
• Temperature-activated layer-breathing vibrations in few-layer graphene
• Ultralow-frequency collective compression mode and strong interlayer coupling in multilayer black phosphorus
• Stacking-Dependent Interlayer Phonons in 3R and 2H MoS${}_2$
• Stacking-dependent shear modes in trilayer graphene
• Interlayer bond polarizability model for stacking-dependent low-frequency Raman scattering in layered materials
• Interlayer Coupling in Two-Dimensional Semiconductor Materials
• Excitonic Resonance Effects and Davydov Splitting in Circularly Polarized Raman Spectra of Few-Layer WSe2
• Electron-phonon and phonon-phonon anharmonic interactions in 2H-MoX2 (X=S, Te): A comprehensive Resonant Raman study
• Simultaneous Generation of Direct- and Indirect-Gap Photoluminescence in Multilayer MoS2 Bubbles
• Rigid-layer Raman-active modes in $N$-layer Transition Metal Dichalcogenides: interlayer force constants and hyperspectral Raman imaging
• Phonon Modes in Single-Walled Molybdenum Disulphide (MoS2) Nanotubes: Lattice Dynamics Calculation and Molecular Dynamics Simulation
• Suppression of the Shear Raman Mode in Defective Bilayer MoS2
• Stacking sequence determines Raman intensities of observed interlayer shear modes in 2D layered materials - A general bond polarizability model
• Giant Shear Displacement by Light-Induced Raman Force in Bilayer Graphene
• Insights into vibrational and electronic properties of MoS${}_2$ using Raman, photoluminescence and transport studies
• Vacuum gauge from ultrathin MoS2 transistor
• Light-induced shear phonon splitting and instability in bilayer graphene
• Uniaxial Strain-Induced Electronic Properties Alteration of MoS${}_2$ Monolayer