Unambiguous determination of crystal orientation in black phosphorus by angle-resolved polarized Raman spectroscopy

Abstract

Angle-resolved polarization Raman spectroscopy (ARPRS) is widely used to determine the crystal orientations of anisotropic layered materials (ALMs), which is an essential step to study all anisotropic properties of them....

Anomalous polarization pattern evolution of Raman modes in few-layer ReS2 by angle-resolved polarized Raman spectroscopy

“…Why do the ARPRS patterns of different modes change with the thickness, especially for the out-of-plane vibration modes? Several explanations are proposed, such as the phase effects induced by external interference in Fresnel formula 23 and thickness-dependent birefringence. 20,31 Firstly, the external interference usually happens in thick samples in the scale of λ /4 of the incident laser, which is used to explain the thickness dependence of Raman modes as thick as 180 nm in BP.…”

“…20,31 Firstly, the external interference usually happens in thick samples in the scale of λ /4 of the incident laser, which is used to explain the thickness dependence of Raman modes as thick as 180 nm in BP. 16,23 Due to the interference from the interface, Raman intensity will change periodically with the thickness, which could result in the ARPRS pattern change. However, in our experiment, the thickest ReS 2 flake is ∼12 nm in thickness, which is far thinner than the λ /4 of the excitation light.…”

“…22 This extrinsic interference effect has been observed clearly in BP recently. 23,24 The third “phase” is from the phase difference between the elements of Raman tensors, which is related to the derivative of the imaginary part of the dielectric element ε ij . 10,12 However, it is still unclear how these “phases” contribute to the ARPRS with the change of layers, especially in the distorted ARPRS patterns.…”

“…The most studied anisotropic 2D material is BP, which usually contains three nonzero elements in Raman tensor due to the orthorhombic structure ( D 2h point group), 16 so that the crystal orientation along the zig-zag or arm-chair direction can be determined by ARPRS unambiguously. 23 Besides, several other anisotropic materials with orthorhombic lattice structures such as SnSe 25 and Ta 2 NiS 5 26 have also been studied, in which A g Raman tensors just contain 3 non-zero elements with the maximum Raman intensity along the arm-chair direction. Few non-zero elements in these materials make the ARPRS analysis simple and easy to determine the crystal orientation.…”

Anisotropic Optical and Vibrational Properties of GeS

“…Due to the observed behavior of different peaks, we can assume that (i) the polarization properties of the B 2 1g mode can be used to determine the crystallographic axes in GeS, but without attribution the zigzag and armchair directions; (ii) the variation of the polarization axis of the A 3 g as a function of the excitation energy suggests that the electron-phonon coupling may change the A 3 g polarization axis (see the work in [32] for details); and (iii) due to 2-fold symmetries of the polarization properties (except for 1.96 eV) and the almost fixed polarization axis of the A 4 g mode, its polarization properties are good to identify the zigzag and armchair crystallographic directions. Note that the observed influence of the excitation energies on the axes and shape of polarization properties of phonon modes is very similar to those reported for different anisotropic layered materials, e.g., BP, ReS 2 , ReSe 2 , SnSe 1−x S x [6,9,[32][33][34]. Moreover, as the effect of thickness on the polarization properties of different modes in BP has been reported [6,33], the outline of further research on thin layers of GeS seems to be clear.…”