Determination of Crystal Axes in Semimetallic T'-MoTe2 by Polarized Raman Spectroscopy

Abstract

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Distorted octahedral T′ phase of MoTe2 has recently attracted significant interest due to its predicted topological states and novel charge transport properties. Here, we report a nondestructive method for determining the crystal orientation of few-layer T′-MoTe2 flakes by polarized Raman spectroscopy. The experimentally observed Raman modes are assigned to eigenmodes of vibrations predicted by density functional theory calculations. Polarized Raman measurements reveal four distinct types of angle-dependent intensity variations. From group theory, it can be deduced that the intensity of the Bg mode reaches a maximum in the (Formula presented.) configuration when the polarization vector of the incident light is either parallel or orthogonal to the metal–metal zigzag chain direction. The intensity variation of the Bg mode cannot be used to unambiguously determine the crystal orientation. Using electron diffraction analysis, it is demonstrated that the intensity of the Ag mode at around 162 cm−1 reaches a maximum when the polarization vector of the incident light is parallel to the metal–metal chain direction in the (Formula presented.) configuration. Furthermore, a simple method is proposed for identifying crystal orientation in nonpolarized Raman spectroscopy.