Substrate-free gas-phase synthesis of diamond powder by CO 2 laser pyrolysis of C 2H 4

Abstract

Diamond powders with grain diameters up to 0.3 μm were obtained by CO 2-laser-induced decomposition of C 2 H 4 and mixtures of C 2 H 4- H 2- SiH 4 at low pressures and temperatures in a gas flow reactor. Solid products were produced in a yellow- to orange-coloured flame (500– 550 °C) and collected in filters. The product contained polyaromatic species, high molecular polymers, graphite, amorphous carbon and spherical diamond particles. Several diamond particle populations, with mean diameters of 6.2–122 nm were observed by transmission electron microscopy. Both diamond modifications, cubic and hexagonal, were identified by electron diffraction. Hydrogen-free pyrolysis of pure ethylene produced diamond of high purity (no diffraction rings of graphite detectable).