Intrinsic High-Order Ionic Layered Superlattices in 2D DJ-Phase Oxide Perovskites

2D layered materials have emerged as promising materials due to their attractive physical properties[1]. In addition, the vast variety of promising 2D material candidates, including graphene, h-BN, TMCs, MAXenes, and nanosheet family, and the ability to realize heterostructures with a high degree of freedom provides us huge opportunities freeing up the structural design of functional devices and their material combinations. These attractive properties offer tremendous possibilities to expand the functionalities of 2D material-based devices for various future applications.[1]<br/>In this sense, novel 2D layered materials are always welcome. Recently, layered oxide perovskites have gained huge attention by means of their high stability and tunability. Additionally, an oxide perovskite monolayer was successfully exfoliated by ion-exchange methods from Dion-Jacobson (DJ) phase (A^’A_n-1B_nX_3n+1) bulk perovskite crystals, immersing themselves into the world of 2D materials. Innately, perovskite materials are highly tunable in their compositions. Not only that, as well as other 2D layered materials, low-dimensional perovskite layers are expected to exhibit novel physics, which means that exploring their intrinsic material properties is highly demanded.[2]<br/>In this presentation, we will introduce unprecedented intrinsic high-order ionic layered superlattices in 2D DJ-phase oxide perovskites. We have confirmed that these exfoliated 2D DJ perovskite layers are compatible with the conventional 2D vdW platform by successfully picking them up with the PDMS stamp which has been conventionally used in the field of 2D vdW materials. Owing to the design freedom of the vdW platform, we could fabricate vertical junction devices with 2D DJ-phase oxide perovskite Sr₂Nb₃O₁₀ flakes employing graphene (Gr) electrodes which are known to be suitable for investigating intrinsic properties of materials due to their passive nature. From the systematic measurement of electronic properties of the vertical junction devices, the intrinsic high-order ionic layered superlattices in few-layer SNO flakes could be found. During the ion-exchange process for exfoliation, there will always be few-layer flakes that are not fully exfoliated. Thus, this a few-layer SNO flake (HSNO) has alternative layers composed of positively charged proton layers (H⁺) and negatively charged SNO layers (Sr₂Nb₃O₁₀^-) forming ionic layered superlattices. These superlattices can introduce quantum wells along the z-axis, resulting in the resonance tunneling through the quantum wells formed through the vertical junction and huge charge trapping in the energy well structures. Additionally, unprecedented memristor devices and artificial synaptic devices will be shown as potential applications by virtue of quantum wells and their charge trapping behavior from the intrinsic ionic superlattices. We believe that our results pave the way for understanding emerging 2D layered DJ oxide perovskite materials.<br/><br/>Ref<br/>[1] K. Cho et al. ACS Nano, 13, 9, 9713-9734<br/>[2] A. C. Ricciardulli et al. Nat. Mater. 2021, 20, 1325-1336