Unit-Cell-Thick Oxide Synthesis by Film-Based Scavenging

With the influx of flexible electronics as well as the emergence or prediction of unique phenomena in two-dimensional forms of materials, epitaxy at weakly coupled interfaces is gaining momentum as a feasible technique to develop nanostructured and two-dimensional materials. The weak substrate–film chemical interaction expected in this method of epitaxy has been believed to be crucial in enabling not only the formation of sharp heterostructures but also the mechanical exfoliation of the epilayer. In this report, we unravel an unconventional understanding of epitaxy at weakly coupled interfaces, entailing ions of the van der Waals substrate being scavenged by the growing film, resulting in the formation of a distinct and uniform unit-cell-thick interfacial layer. Using a layered Dion–Jacobson perovskite as the substrate and VO₂ as the growing epilayer, we show that VO₂ scavenges ions from the substrate and forms an epitaxial vanadate compound. Additionally, the crystal anisotropy of the substrate significantly modifies the energy landscape for diffusion of ions and leads to the creation of a unit-cell-thick epitaxial Aurivillius phase at the interface, predicted to exhibit the ferroelectric Rashba–Dresselhaus effect. The scavenging effect, interfaced with an anisotropic low-dimensional substrate, opens a new window to develop two-dimensional flexible components for future electronics.