Temperature and Thickness Dependent Raman scattering of Ferrelectric CuInP₂Se₆

Two-dimensional (2D) van der Waals materials with ferroelectric properties are promising platforms for studying long-range dipole ordering in the 2D limit. CuInP₂Se₆ (CIPSe) is a van der Waals material known to exhibit ferroelectricity in its bulk form, making it an ideal candidate for investigating the effects of dimensionality reduction on this phenomenon. The temperature window for the ferroelectric transition is broad, between 250 – 230 K, below which mixed anti-ferroelectric/ferroelectric (AFE/FE) domains can be found. These effects are directly measurable through temperature-dependent changes in the frequencies, intensities, widths and number of Raman modes. In this study, we mechanically exfoliated single crystals of CIPSe onto Si/SiO₂ substrates and conducted temperature-dependent Raman measurements (80 – 300 K) on thin flakes with varying thicknesses.We observe several Raman modes that show clear changes in peak shape, frequency, and width as a function of temperature. We further discuss the thermal evolution of these phonon modes in the vicinity of the FE transitions. as a function of flake thickness.