In situ growth of large-scale and ultrathin carbon nitride films shield common metal substrates from corrosion and oxidation

A centimeter-size carbon nitride (CN) film, with nanoscale thickness, is in situ deposited on various metals through the thermal condensation of melamine, achieving broad and uniform coverage, without any pre- and post-treatments. As the temperature rises, the nitrogen content in the film increases, leading to the part of CN to transform into g-C₃N₄. Benefit from higher Gibbs adsorption free energies of g-C₃N₄ with Cl^- and O₂ in aqueous environment, a 30 nm CN film deposited at 475 ℃ with large g-C₃N₄ network, minimal segregation and low internal stress enables pure metals and alloys to achieve over 90 % protection efficiency.