Crystalline monolayer graphdiyne synthesized in the MXene interlayer space

Graphdiyne (GDY) is an artificial carbon allotrope that is conceptually similar to graphene but composed of sp- and sp2-hybridized carbon atoms. Monolayer GDY (ML-GDY) is predicted to be an ideal two-dimensional (2D) semiconductor material with a wide range of applications. However, its preparation has not been achieved experimentally due to difficulties with synthesis. Here, we report that in-situ polymerization of hexaethynylbenzene within the sub-nanometer interlayer space of MXene can effectively prevent out-of-plane growth or vertical stacking of the material, resulting in crystalline ML-GDY. The subsequent exfoliation process successfully yields free-standing GDY monolayers with micrometer-scale lateral dimensions. The fabrication of field-effect transistor on free-standing ML-GDY makes the first measurement of its electronic properties possible. The measured electrical conductivity (5.1×103 S m-1) and carrier mobility (231.4 cm2 V−1 s−1) at room temperature are remarkably higher than those of the previously reported multilayer GDY materials. The space-constrained synthesis using layered crystals as templates provides a new strategy for preparing 2D materials with precisely controlled layer numbers and long-range structural order.