Selective synthesis of diamond and CNT nanostructures directly on stainless steel substrates

Without surface pretreatment or applying additional interlayer, diamond films have been directly synthesized on an Fe–25Cr–5Al steel substrate by a hot filament chemical vapor deposition method from an H2-1vol.% CH4 gas mixture. Due to an effective removal of intermediate graphite phase from the diamond–steel interface, the coated diamond films were continuous and adherent well to the steel substrate. Aligned conical diamond structures were also achieved on this steel substrate by negatively biasing the substrate holder and inducing a glow discharge. The deposition behavior of carbon on Fe–Cr–Ni steel substrate was different. A graphite-rich carbon film incorporated with diamond particles grew in the absence of biasing, then aligned carbon nanotube bundles were formed in the presence of negative biasing and glow discharge. The different deposition behavior of carbon on the two kinds of steel substrates was addressed in terms of the effect of their chemical compositions.

Research Highlights
► Without surface pre-treatment or buffer layer, a selective synthesis of diamond or CNTs is directly realized on steel substrates.
► Alloying element Al shows a unique role in growing adherent diamond nanostructures directly on steels.
► The films and the underlying steel substrates are characterized by synchrotron XAS to reveal the fundamental growth mechanism.