Optical Evidence of Interfacial Strain-Induced Ferroelectric Tuning and Enhancement in CuInPS via Ferroelectric Substrate.

The precise domain control in ferroelectric CuInPS (CIPS) remains challenging. A promising approach is by interfacing CIPS with the ferroelectric layer, but interface-driven ferroelectricity tunning mechanism remains unclear. Here, the demonstration of interfacial strain-induced ferroelectric tuning and enhancement in CIPS via ferroelectric substrate is reported by photoluminescence (PL) spectroscopy, combined with piezoresponse force microscopy (PFM) and density functional theory (DFT) calculations. PFM studies show that thin CIPS flakes form the same domain as that of ferroelectric PbZrTiO (PZT) and P(VDF-TrFE) films, suggesting enhanced polar alignment in CIPS via ferroelectric substrate. PL analyses show that a significant redshift occurs for PL emission of CIPS on ferroelectric substrate compared with that on conventional substrate, revealing interface tensile strain-induced lattice change in CIPS, as further confirmed by DFT calculation. By analyzing PL spectra of monolayer MoS on CIPS/PZT, the polarization of CIPS is evidenced to be anti-aligned with that of ferroelectric substrate. In situ, temperature-dependent PL studies show that thin CIPS on ferroelectric substrate exhibits enhanced Curie temperature of higher than 200 °C. This study not only provides an effective material strategy to engineer the ferroelectric properties of CIPS but also offers a simple optical method to reveal interface-driven ferroelectricity modulation mechanism in CIPS.