Chemical Vapor Deposition of Graphene Nanomaterials on Copper and Gold Using Brominated Polycyclic Aromatic Hydrocarbons

Two-dimensional (2D) graphene and one-dimensional (1D) graphene nanoribbons (GNRs) are atomically thin carbon-based multifunctional materials that show great promise for applications ranging from quantum computing to membrane technologies for water remediation arising from their remarkable physical and electronic properties. The complementary development of chemical vapor deposition (CVD) methods introduces a scalable route to produce large-area films of these carbon nanomaterials on the surface of coinage metal catalysts, such as Cu and Au, that drive the self-organized growth of extended structures from molecular building blocks. This study investigates the efficacy of brominated, polycyclic aromatic hydrocarbons (BrPAHs) as molecular precursors for graphene nanomaterials on Cu through a surface-assisted Ullmann coupling reaction. We demonstrate that high-quality graphene grows at 1000ºC under conventional low-pressure CVD configurations. However, deposition at lower temperatures to form extended GNR networks does not yield macroscopic 2D films due to surface-bound Br by-products that inhibit covalent coupling. X-ray photoelectron spectroscopy (XPS) measurements determine that Br remains on the Cu surface until 400ºC. By adopting a confined CVD configuration to alter the growth kinetics, it is possible to fabricate networks of covalently bonded nanomaterials by first self-assembling Br-embedded carbon structures at 230ºC and then post-annealing to 400C to transform the material into 2D GNR networks. Raman spectroscopic measurements capture the drastic transformation of the material before and after the dehalogenation of the Cu surface. Additionally, we demonstrate a method to grow covalently linked GNR networks on Au thin films, using the same molecular precursor by tuning the pressure during deposition. Fabricating GNR field effect transistors (FETs) from the films enables the characterization of their electronic and optoelectronic properties and identification of the charge carrier transport mechanism. The covalently bound GNR networks are transferred over 550 nm-diameter pores to form freestanding films that function as a preliminary membrane. Our findings report the first successful method to grow GNR-derived films on Cu foils by CVD and 2D networks of chevron GNRs on Au capable of forming freestanding membranes