Abstract
Tungsten ditelluride (WTe2), a layered transition-metal dichalcogenide (TMD), has recently demonstrated an extremely large magnetoresistance effect, which is unique among TMDs. This fascinating feature seems to be correlated with its special electronic structure. Here, we report the observation of 6 Raman peaks corresponding to the , , , , and phonons, from the 33 Raman-active modes predicted for WTe2. This provides direct evidence to distinguish the space group of WTe2 from those of other TMDs. Moreover, the Raman evolution of WTe2 from bulk to monolayer is clearly revealed. It is interesting to find that the mode, centered at ~109.8 cm−1, is forbidden in a monolayer, which may be attributable to the transition of the point group from C2v (bulk) to C2h (monolayer). Our work characterizes all observed Raman peaks in the bulk and few-layer samples and provides a route to study the physical properties of two-dimensional WTe2.
Highlights
Transition-metal dichalcogenides (TMDs) of the MX2 type, where M refers to Mo and W, and X refers to S, Se and
The basic structure of bulk MX2 comprises two-dimensional (2D) X-M-X layers stacked through Van der Waals forces
Mono- and few-layer MX2 can be fabricated by the mechanical exfoliation method[8]
Summary
33 Raman vibrations are predicted by group theory, only 6 Raman peaks were observed in our experiments. We calculated the Raman intensities and spectrum (green curve in Fig. 2a) to verify the phonon modes corresponding to the observed Raman peaks. When we state that one mode is “forbidden”, it means that this Raman mode is prevented from observing by group theory or unable to exist on account of the DFPT calculation, while “vanish” means a Raman mode is active in theory, but in a certain configuration its intensity is too weak to observe due to the specific parameters in its. This equation makes it easy to undersfmvotearornydLdesasmtshedaerellaIteInv:raimtslhuoietenrsAoeop1t6fhyaaeonafddntedhApeeb19Anvmd24aenomnidscoeheds,eowa.npThpthihleeeaestrlhpadeesuceAeirf1i8tccoomvntaohflideugieeursarlapoatrpfigoaeea,nrbc.sIavdnnaudltuehceetosicnaiatntsshedleaotrRhfgeaLemaAvsaa1e8lnrumteIe,oontdfhseobe.rvAsTa1ohn6feiasrtnhhedeeissAAad1198us,imemAtooi16ldaiaertnssedwvffeeAirtch1y9t
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