Splitting of monolayer out-of-planeA1′Raman mode in few-layerWS2

Abstract

We present Raman measurements of mono-and few-layer WS2. We study the monolayer A 1 mode around 420 cm −1 and its evolution with the number of layers. We show that with increasing layer number there is an increasing number of possible vibrational patterns for the out-of-plane Raman mode: in N -layer WS2 there are N Γ-point phonons evolving from the A 1 monolayer mode. For an excitation energy close to resonance with the A excitonic transition energy, we were able to observe all of these N components, irrespective of their Raman activity. Density functional theory calculations support the experimental findings and make it possible to attribute the modes to their respective symmetries. The findings described here are of general importance for all other phonon modes in WS2 and other layered transition metal dichalcogenide systems in the few layer regime.

Growth of WS2 flakes on Ti3C2Tx Mxene Using Vapor Transportation Routine

“…As the most distinguishable feature, the intensity of A 1g peak subsequently decreases from LT1 to LT5. This agrees well with previous reports, and can be attributed to the decreasing layer thickness [25,26]. The shift of A 1g peak can also be used to determine the layer thickness [25,26].…”

“…This agrees well with previous reports, and can be attributed to the decreasing layer thickness [25,26]. The shift of A 1g peak can also be used to determine the layer thickness [25,26]. The A 1g Raman peaks of flakes T1-T5 collected at LT1-LT5 are plotted in Figure S3a.…”

“…The obtained peak positions are shown in Figure S3b. For thick layer flake T1, the peak position of A 1g is 419.2 cm −1 , corresponding to the peak position of thick layer [25,26]. For flakes T2 and T3, the A 1g peak shifts to 418.5 and 418 cm −1 , indicating trilayer and bilayer of these two flakes [25,26], respectively.…”

“…For flakes T2 and T3, the A 1g peak shifts to 418.5 and 418 cm −1 , indicating trilayer and bilayer of these two flakes [25,26], respectively. The average peak position of T4, T5, and 1 L flake deposition without mxene is 416.9 cm −1 , confirming the 1 L characteristic of these three flakes [25,26].…”

Gate‐Tunable Resonant Raman Spectroscopy of Bilayer MoS2

“…Davydov splitting is more pronounced at resonance, which is consistent with previous reports on WS 2 and MoTe 2 . [17,30] In the moderate/heavy electron doping region when there is no splitting, increases of V tg causes A 1g mode to blue-shifts when excitation wavelength is 612.2 nm while red-shifts when 632.9 nm is used.…”