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

Abstract

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.

Flexoelectric engineering of van der Waals ferroelectric CuInP 2 S 6

“…Nevertheless, field-driven ionic migration often causes erratic and damaging switching of CIPS (3), which is highly undesirable for device applications. Hence, alternative switching mechanisms have to be developed, for example, using electric field induced by ion adsorption (27). In this work, we abandon electric field altogether and explore the prospect of mechanical switching of CIPS instead via flexoelectric effect (14,(28)(29)(30)(31)(32)(33).…”

Electric-Field-Induced Room-Temperature Antiferroelectric–Ferroelectric Phase Transition in van der Waals Layered GeSe

“…Two-dimensional (2D) materials with atomic thickness and distinctive electronic structure have attracted considerable interest due to their emerging physical properties and promising applications to replace the conventional microelectronics. − Ranging from 2D metals to insulators, the trend continues with the recent addition of ferroelectric (FE) materials in the 2D material family. − Although 2D ferroelectricity had been predicted in a number of van der Waals (vdW) 2D systems in the past decade, only a few 2D room-temperature FE materials, for example, CuInP 2 S 6 , − In 2 Se 3 , − d1T-MoTe 2 , SnSe, and WTe 2 , , have been experimentally verified so far. Compared with 2D FEs, investigations on antiferroelectric (AFE) 2D materials are still desired.…”

Large-Scale Domain Engineering in Two-Dimensional Ferroelectric CuInP2S6 via Giant Flexoelectric Effect

“…Atomically thin van der Waals (vdW) crystals provide the opportunity to explore ferroelectricity at the two-dimensional (2D) limit which is a long-sought goal in conventional bulk ferroelectrics due to the constrain of critical size effect . Experimentally, a series of 2D ferroelectrics with intrinsic either in-plane or out-of-plane electric polarization have been verified, such as the SnTe family, − NbOX 2 family, CuInP 2 S 6 , − α-In 2 Se 3 , − Bi 2 O 2 Se, , and d1 T -MoTe 2 . Along with the atomic thickness, vdW material also offers the layer degree of freedom that leads to the emergence of sliding ferroelectricity induced by interlayer translation. − The rich 2D ferroelectricity found in vdW crystals therefore provides the potential to revolutionize future electronic applications with exotic functions. − …”