Room-temperature ferroelectricity in two-dimensional materials offer a potential route for developing atomic-scale functional devices beyond Moore's law.However, as a key for the technology implementations of ferroelectrics in electronics, the controllable generation of uniform domains remains challenging in two-dimensional ferroelectrics at current stage because domain engineering through an external electric field at 2D limit inevitably leads to large leakage current and material break-down. Here, we demonstrate a voltage-free method, the flexoelectric effect, to artificially generate largescale stripe domains in two-dimensional ferroelectric CuInP2S6 with single domain lateral size at the scale of several hundred microns. With giant strain gradients (~10 6 m -1 ) at nanoscale, we mechanically switch the out-of-plane polarization in ultrathin CuInP2S6. The flexoelectric control of ferroelectric polarization is understood with a distorted Landau-Ginzburg-Devonshire double well model as evidenced by the shifted ferroelectric hysteresis loops and the first-principle calculations. Through substrate mechanical strain engineering, the stripe domain density is controllable. Our results not only highlight the potential of developing van der Waals ferroelectrics-based memories but also offer the opportunity to study ferroelectric domain physics in two-dimensional materials.

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With the advent of the post Moore era, modern electronics require further device miniaturization of all electronic components, particularly ferroelectric memories, due to the need for massive data storage. This demand stimulates the exploration of robust switchable ferroelectric polarizations at the atomic scale. In this scenario, van der Waals ferroelectrics have recently gained increasing attention because of their stable layered structure at nanometer thickness, offering the opportunity to realize two‐dimensional ferroelectricity that is long‐sought in conventional thin film ferroelectrics. In this review, recent advancements are summarized in layered ferroelectrics with highlights of the fundamentals of intrinsic two‐dimensional ferroelectricity, the emergence of artificial stacking ferroelectricity, and related protype devices with exotic functions. In addition, the unique polarization control in van der Waals ferroelectrics is discussed. Although great challenges remain unsolved, these studies undoubtedly advance the integration of 2D ferroelectrics in electronics.

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Room-temperature ferroelectricity in two-dimensional materials offer a potential route for developing atomic-scale functional devices beyond Moore’s law. However, as a key for the technology implementations of ferroelectrics in electronics, the controllable generation of uniform domains remains challenging in two-dimensional ferroelectrics at current stage because domain engineering through an external electric field at 2D limit inevitably leads to large leakage current and material break-down. Here, we demonstrate a voltage-free method, the flexoelectric effect, to artificially generate large-scale stripe domains in two-dimensional ferroelectric CuInP2S6 with single domain lateral size at the scale of several hundred microns. With giant strain gradients (~106 m−1) at nanoscale, we mechanically switch the out-of-plane polarization in ultrathin CuInP2S6. The flexoelectric control of ferroelectric polarization is understood with a distorted Landau-Ginzburg-Devonshire double well model as evidenced by the shifted ferroelectric hysteresis loops and the first-principle calculations. Through substrate mechanical strain engineering, the stripe domain density is controllable. Our results not only highlight the potential of developing van der Waals ferroelectrics-based memories but also offer the opportunity to study ferroelectric domain physics in two-dimensional materials.

The title compound, C10H13NO3, crystallizes with two molecules in the asymmetric unit. Molecules related by an a‐axis translation are stacked over each other, bound by π–π interactions with a perpendicular distance of 3.455 Å. Molecules in adjacent stacks are linked to each other through N—H...O hydrogen bonds.