Is all epitaxy on mica van der Waals epitaxy?

Abstract

Epitaxy on layered substrates, for example, mica, manifests different characteristic from that on non-layered substrates, which is demonstrated to be the fantastic road towards high-quality functional films. To date, van der Waals epitaxy has been generally accepted as the mechanism to describe the interaction between layered substrate and epilayer. However, some experimental evidences also revealed that pure van der Waals interaction was not sufficient for long-range ordering nucleation. In this work, we provide unambiguous evidence demonstrating that the epitaxy on mica is not always the van der Waals type. Detailed studies on the interface microscopic structure and strain release process of ZnO epitaxial films indicate a new epitaxy mode on fluorphlogopite mica substrate. ZnO epitaxial films on fluorphlogopite mica substrates with superior crystal quality and excellent optical property are obtained. The improved epitaxy of ZnO film is ascribed to compliant substrate epitaxy rather than van der Waals epitaxy. It is anticipated that this epitaxy mechanism provides a low-cost reusable-substrate method for high-quality functional films and flexible device application.