Chemical Vapor Deposition of Large-area 2D Hexagonal Diamond

Hexagonal diamond, or lonsdaleite, is an allotrope of sp³ carbon with a hexagonal lattice that has only been prepared in bulk form with thickness above micrometer level. Here we report the first synthesis of uniform hexagonal diamond nanometer-thick films, to our knowledge, in large area (> 10 μm) by chemical vapor deposition. Using atomic force microscopy, we demonstrated that the film is uniform with thickness of < 0.9 nm. X-ray photoelectron spectroscopy and Raman spectroscopy indicate that the film consists primarily of sp³ bonded carbon in diamond crystal structure with minimal sp² bonding. The hexagonal structure was also confirmed with selected area diffraction performed in a transmission electron microscope. We demonstrated that the diamond film has a high elastic modulus comparable to graphene prepared by chemical vapor deposition.