Ion adsorption-induced reversible polarization switching of a van der Waals layered ferroelectric

Solid-liquid interface is a key concept of many research fields, enabling numerous physical phenomena and practical applications. For example, electrode-electrolyte interfaces with electric double layers have been widely used in energy storage and regulating physical properties of functional materials. Creating a specific interface allows emergent functionalities and effects. Here, we show the artificial control of ferroelectric-liquid interfacial structures to switch polarization states reversibly in a van der Waals layered ferroelectric CuInP2S6 (CIPS). We discover that upward and downward polarization states can be induced by spontaneous physical adsorption of dodecylbenzenesulphonate anions and N,N-diethyl-N-methyl-N-(2-methoxyethyl)-ammonium cations, respectively, at the ferroelectric-liquid interface. This distinctive approach circumvents the structural damage of CIPS caused by Cu-ion conductivity during electrical switching process. Moreover, the polarized state features super-long retention time (>1 year). The interplay between ferroelectric dipoles and adsorbed organic ions has been studied systematically by comparative experiments and first-principles calculations. Such ion adsorption-induced reversible polarization switching in a van der Waals ferroelectric enriches the functionalities of solid-liquid interfaces, offering opportunities for liquid-controlled two-dimensional ferroelectric-based devices. Whether it is possible to achieve polarization inversion in a ferroelectric without any energy consumption is an open question. Here, the authors demonstrate an energy-free approach to control the polarization state of CuInP2S6, a typical room-temperature van der Waals layered ferroelectric.

Automated summary

This study demonstrates the reversible polarization switching in a van der Waals ferroelectric by controlling the ferroelectric-liquid interface structure. By inducing upward and downward polarization states through physical adsorption of organic ions at the ferroelectric-liquid interface, this approach offers opportunities for liquid-controlled two-dimensional ferroelectric-based devices with super-long retention time.