Synthesis of functional nitride membranes using sacrificial water-soluble BaO layers

Transition metal nitrides (TMNs) exhibit fascinating physical properties that show great potential in future device applications. Stacking two-dimensional TMNs with other functional materials with different orientations and symmetries requires separating epitaxial TMNs from the growth substrates. However, the lattice constants of TMNs are incompatible with those of most sacrificial layers, resulting to a great challenge in fabricating high-quality single-crystalline TMN membranes. In this study, we report the application of a water-soluble BaO sacrificial layer as a general method for creating freestanding TMN membranes. Using CrN as an example, the relatively small lattice mismatch and identical cubic structure between BaO and CrN ensure the formation of heterostructures. We directly observe the planar atomic structure and correlate its electronic state with its intrinsic transport properties using millimeter-size CrN membrane. Our research enables the fabrication of freestanding TMN membranes and transfers them to arbitrary substrates. By integrating TMN membranes with other materials will stimulate further studies in the emergent phenomena at heterointerfaces.