An Angle-Resolved, Polarized Raman Methodology to Calibrate Lattice Plane Orientations in 2D Materials

Two-dimensional (2D) materials typically have heterogeneous electronic and magnetic structures that host quantum phenomena, often reflecting the direction-dependent properties of the material. Angle-resolved, polarized Raman spectroscopy is a highly controllable method of optically characterizing the lattice plane symmetry of quantum material phonons (and other related quasiparticles) with a high spatial resolution limited by the diffraction limit of the excitation laser. Here, we present a methodology that uses a 180-backscatter geometry in a Raman microscope system combined with precise polarization control; two pairs of halfwave plates (HWP), and polarizers. We utilize a polarimeter to characterize the rotation-dependent ellipticity and orientation of the incident HWP. We exploit the symmetric E_g and asymmetry A_1g phonons of isotropic molybdenum disulfide (MoS₂) to configure the mapping combinations of HWPs that select parallel and perpendicular polarization. We validate this protocol against anisotropic materials of known crystalline planes of silicon (Si) and lithium niobate (LiNbO₃). Repeating this protocol with four different laser excitation wavelengths, we calibrate the HWP to characterize various 2D anisotropic materials such as black phosphorus, bismuth selenide (Bi₂Se₃), rhenium disulfide (ReS₂), and tungsten ditelluride (WTe₂). Modifying the configuration of the HWP with a quarter waveplate (QWP), we also investigate the helicity-resolved Raman scatter of these 2D anisotropic materials. The outcomes of this study will be used to establish quantitative Raman-based metrics on polarization Raman spectroscopy for documentary standards within ISO.