Atmospheric-Pressure Flame Vapor Deposition of Nanocrystalline Diamonds over Large Areas

Nanocrystalline diamonds (NCDs) are one of the many carbon allotropes that have attracted great attention for the advancement of many technologies, owing to their superior mechanical, thermal, and optical properties. Yet, their synthesis must be improved for availability at low costs and their widespread application. Here, we report the atmospheric-pressure flame vapor deposition (FVD) synthesis of NCD particles and thin films over an area of more than 28 cm2 using methane-hydrogen-air flat flames. Notably, the FVD method unlocks new conditions for diamond growth beyond the previously considered diamond-growth region of the C-H-O phase diagram. Additionally, we demonstrate that the FVD growth of NCDs can be facilely controlled by tuning the reactant gas composition, substrate material, seeding density, and external electric bias. Overall, with the low cost and simplicity for operation without the need of vacuum, this atmospheric-pressure FVD approach will offer new opportunities to facilitate the scaling-up of diamond synthesis.