Angle-/temperature-dependence of Raman scattering in layered NbSe3 crystal

Distinguishing the lattice vibrational modes of different Raman peaks and further studying the temperature-dependent behaviour of the different Raman modes are fundamental subjects for Raman spectroscopy of single crystal. Herein, we conducted a comprehensive study of angle- and temperature-dependant Raman scattering behaviour in high-crystalline NbSe3 layers prepared by chemical vapour transport method. The polarization experiments performed on NbSe3’s (100) crystal surface revealed that the Raman peaks could be clearly identified as Ag and Bg vibrational modes, indicating significantly anisotropic structure. Meanwhile, the effect of charge density wave (CDW) transition on the lattice vibrational behaviour was studied by investigating temperature-dependent Raman scattering spectra above and below the CDW transition temperature. It was observed that Raman shifts versus temperature for the four prominent Raman peaks of NbSe3 which belonged to Ag vibrational mode exhibited linear softening behaviour as the temperature increased from 83k to 293k. The temperature coefficient of Raman peaks fitted by Grüneisen model further confirmed the anharmonicity of the lattice in NbSe3 crystal, suggesting that the changes of ionic positions across the CDW transition has small effect on its Raman scattering behaviour.