Phonon Properties of Few-Layer Crystals of Quasi-One-Dimensional ZrS3 and ZrSe3

The frequencies of Raman active modes of few-layer ZrS3 and ZrSe3 and their dependence on the number of layers have been investigated by Raman scattering spectroscopy and first-principles calculations. We find a considerable downshift of the frequency of the Ag3 mode with decreasing the number of layers, and a slight downshift of the Ag5 mode. The same frequency shifts are reproduced by the calculations with remarkable accuracy. We explain the difference in the frequency shifts of the Ag3 and Ag5 modes in terms of intrachain, interchain, and interlayer force constants in simple one-dimensional lattice models. We thus show that the large shift of the Ag3 mode reflects the quasi-one-dimensional structure of ZrS3 and ZrSe3, which does not exist in the more widely studied two-dimensional materials.