Simultaneous growth of diamond thin films and carbon nanotubes at temperatures ⩽550 °C

Diamond thin films (on silicon wafers) and carbon nanotubes (CNTs) (on Inconel plates) were simultaneously synthesized at temperatures ⩽550 °C without any additional catalyst. The synthesis was achieved in a microwave plasma enhanced chemical vapor deposition (CVD) reactor with graphite etching in a gas mixture of hydrogen and methane. The substrate stage consisted of an Inconel 600 plate and a stainless steel plate separated by a 53 mm long quartz tube. Silicon wafers were placed on the stainless steel plate located at the upper part of the substrate stage, while Inconel plates were placed at the lower part of the substrate stage. During the deposition, the substrates were heated only by the plasma and the substrate temperature was controlled by the applied microwave power, which ranged from 350 W to 950 W. The backside temperatures of Si wafers ranged from 290 °C to 550 °C, higher than the corresponding temperatures of Inconel 600, which ranged from 220 °C to 350 °C. The Raman spectroscopic and electron microscopic results show that the thin films deposited on Si consist of well faceted polycrystalline diamond, and that the black soot deposited on Inconel plates is composed of multiwall carbon nanotubes as long as one millimeter.