Angle-Resolved Polarized Raman Study of Layered Cr2Se3

The polarization-resolved Raman spectra of two-dimensional Cr₂Se₃ synthesized via chemical vapor deposition (CVD) and chemical vapor transport (CVT) techniques were investigated in detail. The samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). A distinct polarization dependence was observed in the Raman intensity of all the Cr-Cr, Cr-Se, and Se-Se modes in both samples. The observed angle-dependent Raman intensities of each peak could be related to the crystal structure-specific Raman tensor. XRD results of the bulk Cr₂Se₃ sample synthesized via CVT confirm its trigonal crystal structure, and the Raman peaks can be fitted using the Raman tensors for the 𝐴_𝑔 and 𝐸_𝑔 modes for both the parallel and crossed polarizations. However, for the Cr₂Se₃ samples directly grown on Si/SiO₂ substrates by CVD, it was necessary to assume the triclinic crystal structure in order to explain the polarized Raman dependence of all the peaks in both parallel and crossed polarization directions. This is the first experimental result suggesting the existence of triclinic Cr₂Se₃ crystal structure, which has been theoretically predicted in the Materials Project database.