Raman fingerprint of semi-metal WTe2 from bulk to monolayer

TL;DR

This study identifies specific Raman peaks of WTe2 from bulk to monolayer, revealing structural and electronic insights, including a forbidden mode in monolayer, advancing understanding of this layered TMD's properties.

Contribution

It provides the first detailed Raman spectral characterization of WTe2 from bulk to monolayer, clarifying its vibrational modes and symmetry changes during exfoliation.

Findings

Six Raman peaks identified, confirming WTe2's unique electronic structure.

The A2^4 mode becomes forbidden in monolayer, indicating symmetry change.

Raman evolution from bulk to monolayer is clearly demonstrated.

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 A_2^4, A_1^9, A_1^8, A_1^6, A_1^5 and A_1^2 phonons, from the 33 Raman-active modes predicted for WTe2. This provides direct evidence to distinguish the space group of WTe2 from that of other TMDs. Moreover, the Raman evolution of WTe2 from bulk to monolayer is clearly revealed. It is interesting to find that the A_2^4 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.