Determination of the thickness and orientation of few-layer tungsten ditelluride using polarized Raman spectroscopy

TL;DR

This study develops a polarized Raman spectroscopy method combined with electron diffraction to accurately determine the thickness and orientation of few-layer tungsten ditelluride, revealing polarization-dependent Raman features.

Contribution

The paper introduces a reliable, non-destructive technique for measuring the thickness and crystallographic orientation of WTe2 using polarization-sensitive Raman spectroscopy.

Findings

Raman peak separation at ~90 cm-1 and 80-86 cm-1 correlates with thickness.

Polarization dependence of A1 modes indicates crystallographic orientation.

Raman polarization behaviors vary with excitation wavelength and thickness.

Abstract

Orthorhombic tungsten ditelluride (WTe2), with a distorted 1T structure, exhibits a large magnetoresistance that depends on the orientation, and its electrical characteristics changes rom semimetallic to insulating as the thickness decreases. Through polarized Raman spectroscopy in combination with transmission electron diffraction, we establish a reliable method to determine the thickness and crystallographic orientation of few-layer WTe2. The Raman spectrum shows a pronounced dependence on the polarization of the excitation laser. We found that the separation between two Raman peaks at ~90 cm-1 and at 80-86 cm-1, depending on thickness, is a reliable fingerprint for determination of the thickness. For determination of the crystallographic orientation, the polarization dependence of the A1 modes, measured with the 632.8-nm excitation, turns out to be the most reliable. We also discovered that the polarization behaviors of some of the Raman peaks depend on the excitation wavelength as well as thickness, indicating a close interplay between the band structure and anisotropic Raman scattering cross section.