Thickness dependence of domain size in 2D ferroelectric CuInP2S6 nanoflakes

Abstract

Two-dimensional (2D) ferroelectrics refer to those ferroelectrics with layered structure and weak interlayer interactions (e.g., van de Waals interlayer coupling). A number of basic physical issues in the framework of ferroelectricity deserve clarifications, and one of them is the size effect regarding the dependence of ferroelectricity on material thickness. In this work, we investigate the ferroelectric domain structures of 2D ferroelectric CuInP2S6 nanoflakes attached on heavily doped Si wafers and polarization switching using the piezoresponse force microscopy. While the domain structure shows highly irregular morphology and 180° domain walls, the statistics on domain size (diameter) W and nanoflake thickness d demonstrates the remarkable thickness dependence of domain size, illustrated by the shrinking domain size from 630 nm to 75 nm with decreasing thickness d from ∼130 nm to ∼11 nm. This dependence fits the Landau-Lifshitz-Kittel (LLK) scaling law with the scaling exponent of ∼0.65, slightly larger than 0.5 for 3D ferroelectrics. It is suggested that the size effect in terms of the LLK scaling law does not show an essential difference between the 2D and 3D ferroelectric systems.

A gate-programmable van der Waals metal-ferroelectric-semiconductor memory

“…2b, exhibiting hysteresis loops with asymmetric coercivity fields biased toward positive voltage. Such biased polarizationswitching fields are also seen in previous reports [27][28][29]. We notice that for Cr/CuInP 2 S 6 /FLG devices, there is no distinct resistive switching behaviour in the diffusive regime, as shown in Supplementary Figure S6.…”

Van der Waals layered ferroelectric CuInP2S6: Physical properties and device applications

“…CIPS nanoflakes of different thicknesses were exfoliated and placed on heavily doped Si substrates, and the temperaturedependent surface potential changes (ΔV) were detected by using Kelvin probe force microscopy (KPFM). Their study demonstrates that CIPS remains pyroelectric down to a few nanometers, even for bilayer, which breaks the reported critical limit for ferroelectricity [13,34,69]. Pyroelectric currents of CIPS nanoflakes under varying temperature were measured using Bruker Peakforce TUNA modulus with a conductive probe (Fig.…”

“…10a-c). A quantitative study was performed recently by Chen and coworkers [34]. What they found is a deviation of the domain scaling from the classic LLK law, with an exponent about 0.65 instead of 0.5 (Fig.…”

“…d, Scaling of the domain width with respect to flake thickness as derived from (a-c). e, Domain scaling results from another study [34].…”

“…The unusual crystal structure and ferroelectric order endow CIPS with intriguing characteristics and rich physics, which attract much interest in the past few years. [13,23,[29][30][31][32][33][34][35][36][37][38][39][40][41].…”