Atomically Clean van der Waals Interfaces for Reliable Remote Epitaxy of Complex-Oxide Membranes

Recent developments in graphene-based remote epitaxy and layer transfer techniques allow for generating a wide range of freestanding complex-oxide membranes with high-crystallinity including perovskite, spinel, and garnet. Such single-crystalline complex-oxide membranes can be easily stacked to form unique material systems, where structurally and chemically incompatible materials are interfaced with each other. Thus, material spectrum can be greatly expanded to explore new physical phenomena by creating the artificial heterostructures as well as to enhance material properties by avoiding the substrate clamping effect. However, graphene transfer – a typical graphene formation process on the growth substrates – inevitably introduces a significant number of unwanted defects such as wrinkles, holes, process residues, and interfacial contamination, which could disturb remote interaction between the substrate and epitaxial layer through graphene and thereby reduce crystal quality and exfoliation yield of membranes. Here, we propose a direct synthesis of two-dimensional (2D) material on the epitaxial substrates of complex-oxides including MgAl₂O₄ (MAO) and Gd₃Ga₅O₁₂ (GGG) to demonstrate reliable remote epitaxy of spinel CoFe₂O₄ (CFO) and garnet Y₃Fe₅O₁₂ (YIG) respectively via defect-free 2D interlayer. Atomically clean van der Waals (vdW) interfaces created by a direct growth of 2D material onto growth substrates offer an ideal platform for high-throughput production of single-crystalline complex-oxide membranes and efficient manipulation of physical properties at well-defined heterointerfaces.