van der Waals Epitaxy of Lead Monoxide and Application as a Virtual Substrate for Oxide Membranes

We report the successful growth of epitaxial layers of van der Waals (vdW) lead oxide (PbO) polymorphs on different substrates, via pulsed laser deposition. A thin layer of vdW α-PbO (∼5 nm) was subsequently used as a virtual substrate to grow thin films of perovskites BaTiO3, SrTiO3, and the spinel CoFe2O4. For some of these layers, the crystal quality or functionality was comparable to direct epitaxy on single-crystal oxide substrates. Notably, films with a larger lattice parameter underwent spontaneous and spatially uniform spalling within days of growth, remaining structurally intact, or were easily exfoliated and transferred using the tape method. This work establishes PbO as a promising virtual substrate for the fabrication of freestanding oxide membranes via vdW epitaxy, offering advantages over conventional sacrificial-layer methods.