Observation of Moiré Patterns in Twisted Stacks of Bilayer Perovskite Oxide Nanomembranes with Various Lattice Symmetries

Abstract

The design and fabrication of novel quantum devices in which exotic phenomena arise from moiréphysics have sparked a new race of conceptualization and creation of artificial lattice structures. This interest is further extended to the research on thin-film transition metal oxides, with the goal of synthesizing twisted layers of perovskite oxides concurrently revealing moirélandscapes. By utilizing a sacrificial-layer-based approach, we show that such high-quality twisted bilayer oxide nanomembrane structures can be achieved. We observe atomicscale distinct moirépatterns directly formed with different twist angles, and the symmetry-inequivalent nanomembranes can be stacked together to constitute new complex moiréconfigurations. This study paves the way to the construction of higher-order artificial oxide heterostructures based on different materials/symmetries and provides the materials foundation for investigating moire-related electronic effects in an expanded selection of twisted oxide thin films.

A 2D ferroelectric vortex lattice in twisted BaTiO3 freestanding layers

“…Extending the exploration to artificial twisted stacks of ionically bonded transition metal oxides, however, has been hampered by the difficulty to isolate these systems in freestanding form. The recent reports on the fabrication of freestanding single crystalline oxide thin films [29][30][31], which can be handled in a way similar to van der Waals 2D materials, open up the possibility of stacking freestanding layers with arbitrary twist angles [32,33] and thus design completely novel strain patterns. To our knowledge, this approach to induce strain landscapes spatially varying at the nanoscale in complex oxides has not been reported so far.…”

Research progress of applications of freestanding single crystal oxide thin film

“…3.6.2 自支撑单晶氧化物薄膜的堆叠整合 将具有不同材料和取向的自支撑氧化物薄膜组装成具有异质界面的人工堆 叠技术，长期以来一直是新物理效应研究以及新型电子器件开发的基础，例如二 维材料的范德瓦尔斯异质结构 [126] 道电子，能给氧化物提供新的自由度，产生丰富的奇异相 [127] 。受此启发，Li 等 [38] 将自支撑 STO 与 CGO 以特定扭曲角交替堆叠，证实了通过控制堆叠顺序以 及具有原子尖锐界面的组成层之间的扭曲角来定制氧化物堆叠(图 14(d-e))，并且 观察到扭转角相关的氧离子的示踪扩散系数(图 14(f))。Shen 等 [129] 通过扭转两层 STO 外延薄膜观察到不同扭转角直接形成的原子级的不同莫尔图案(图 14(g-h))。 上述方法开辟了用于制造人工 3D 氧化物堆叠异质结构的途径，为开发具备复 杂氧化物晶体结构与奇异功能的氧化物异质结提供了指导。 图 14 自支撑单晶氧化物薄膜的堆叠整合。 (a) CFO/PMN-PT 膜异质结构的横截面 TEM 图像 [17] ；(b) 由交流磁场强度诱导的 PMN-PT(δVME)两端的感应电压 [17] ；(c) 在室温下测量的 CFO 膜，YIG 膜和 CFO/YIG 异质结构的面外磁滞回曲线 [17] ；(d) 扭曲角为 45°、100°的 CGO/CGO 双层与 STO/STO 双层薄膜的光学显微镜图像 [38] ； (e) 10°扭转角堆叠的 STO/STO 界面的原子分辨率 ADF-STEM 图像 [38] ；(f) STO/STO 异质结氧离子的示踪扩散系数(D*)与 扭转角的关系 [38] ；(g) 硅片上以 24°扭转角堆叠 STO 膜的光学图像与示意图 [129] ；(h) tBL-STO 薄膜的莫尔条纹 HRTEM 图像和 FFT 晶格分析 [129] 。 Fig. 14.…”

“…Stacking and twisting of freestanding single crystal oxide films. (a) Cross-sectional TEM image of the CFO/PMN-PT heterostructure [17] ; (b) The induced voltage across the PMN-PT(δVME) induced by the AC magnetic field [17] ; (c) Out-of-plane magnetization curves of CFO, YIG, and CFO/YIG heterostructures at room temperature [17] ; (d) Optical microscope images of CGO/CGO bilayer and STO/STO bilayer films with a twist angle of 45° and 100° [ 38] ; (e) Atomic resolution ADF-STEM image of STO/STO interface stacked at 10° twist angle [38] ; (f) The dependence of oxygen ions tracer diffusion coefficient (D*) and twist angle of STO/STO heterostructure [38] ; (g) Optical images and schematics of STO films stacked at a 24° twist angle on silicon wafers [129] ; (h) Moiré stripes of tBL-STO film analysis of HRTEM images and different Moiré lattices [129] .…”

Redistributing the Electronic States of 2D‐Covalent Organic Frameworks for Electrochemical Energy Applications

“…b) Schematic illustration of the synthesis procedure of STO Moiré lattice (inset: Representation of STO Moiré lattice), c) HRTEM images of STO Moiré lattice patterns, Reproduced with permission. [ 181 ] Copyright 2022, American Chemical Society. d) Representation of BP‐COF/hBN/Cu(111) Moiré lattice, e) Scanning tunneling microscopy (STM) images of BP‐COF/Au(111) and BP‐COF/hBN/Cu(111), f) d I /dV point spectra for unoccupied states in BP‐COF/hBN/Cu(111) and BP‐COF/Au(111) (inset: Representation of the lateral view of BP‐COF/hBN/Cu(111) and BP‐COF/Au(111)).…”

“…Figure 15b represents a typical synthesis procedure for Moiré patterns on bilayer perovskite oxide SrTiO 3 (STO) twisted at various angles. [ 181 ] Hi‐resolution TEM (HRTEM) images in Figure 15c of STO show the interface of the bilayers with different orientation of 2D Moiré lattice structures.…”