Photonic van der Waals integration from 2D materials to 3D nanomembranes

The integration of functional nanomaterials and heterostructures with photonic architectures has laid the foundation for important photonic and optoelectronic applications. The advent of epitaxy and layer lift-off techniques has enabled a wide spectrum of two-dimensional materials and three-dimensional single-crystalline freestanding thin films with diverse optical functionalities, featuring van der Waals (vdW) interfaces suitable for photonic vdW integration. Physical assembly leveraging vdW interactions eliminates the constraints of epitaxial lattice-matching, introducing unprecedented freedom to combine dissimilar materials with appealing optoelectronic properties but radically distinct crystal structures. Various prefabricated vdW building blocks can be combined in novel hetero-integrated photonic architectures and hybrid vdW heterostructures to prototype new devices and explore exotic nanophotonic phenomena at mixed-dimensional vdW interfaces. The ultrathin nature of these freestanding nanomembranes also enables flexible and lightweight photonic devices for low-cost wearable and multifunctional health-care applications. In this Review, we survey the recent progress in photonic nanomembranes with vdW interfaces, discussing a broad range of delaminated freestanding nanomembranes from film preparation to device implementation. We also analyse the remaining challenges and highlight emerging opportunities for advanced vdW hetero-integration.