From Bulk to Monolayer MoS₂: Evolution of Raman Scattering

Abstract

Molybdenum disulfide (MoS2) is systematically studied using Raman spectroscopy with ultraviolet and visible laser lines. It is shown that only the Raman frequencies of $ E_{2{\rm g}}^1 $ and $ A_{{\rm 1g}}^{} $ peaks vary monotonously with the layer number of ultrathin MoS2 flakes, while intensities or widths of the peaks vary arbitrarily. The coupling between electronic transitions and phonons are found to become weaker when the layer number of MoS2 decreases, attributed to the increased electronic transition energies or elongated intralayer atomic bonds in ultrathin MoS2. The asymmetric Raman peak at 454 cm−1, which has been regarded as the overtone of longitudinal optical M phonons in bulk MoS2, is actually a combinational band involving a longitudinal acoustic mode (LA(M)) and an optical mode ($ A_{{\rm 2u}}^{} $). Our findings suggest a clear evolution of the coupling between electronic transition and phonon when MoS2 is scaled down from three‐ to two‐dimensional geometry.

A novel and facile method for detecting the lattice orientation of MoS 2 tribological surface using the SPSA process

“…As shown in Fig. 1(c) and 1(f), the distances between the E 2g 1 mode and A 1g mode are 24.3 and 18.1 cm −1 , which agree well with the previous results in the literature [24], indicating that the two samples are four-layer and monolayer nanosheets (For sample-1, Raman spectroscopy was performed on the regions with a lower height.) After the thicknesses of the samples were confirmed, lateral force microscopy (LFM) was subsequently performed on the relatively flat regions of the sample surfaces to obtain atomic images and atomic-scale friction information.…”

Atomic layer deposition on 2D transition metal chalcogenides: layer dependent reactivity and seeding with organic ad-layers

“…28 The out-of-plane Raman active vibration of MoS 2 at 405-410 cm À1 has previously been shown to shift with layer number and doping. 29 A shift with layer number is expectedly observed as shown in Fig. 4a but no further shift upon Al 2 O 3 deposition occurs as shown in Fig.…”

Spectroscopic Signatures of AA′ and AB Stacking of Chemical Vapor Deposited Bilayer MoS2

“…27 For MoS 2 atomic layers, Raman spectroscopy shows a clear evolution trend of A 1g and E 2g 1 peak positions with layer thickness. 10,28 As layer thickness increases, the A 1g peak position blue shifts while the E 2g 1 peak red shifts. 10,28 Compared with the first-order process in normal Raman scattering, resonance Raman scattering enhances the possibility of higher-order Raman scattering resulting in enriched spectral information.…”

“…Interactions between MoS 2 layers as well as the specific stacking order can significantly modify their electrical, 9 optical, 3 and vibrational properties. 10 The specific spinÀorbit-based behavior depends sensitively on crystal symmetry, as elucidated by many theoretical studies. 4,11 Robust valley polarization is assured by the lack of centrosymmetry in all monolayer TMDs as well as bilayer ones with AB stacking.…”