The properties of diamond-like carbon layers deposited onto SiO 2 aerogel

Abstract

Possible production of an SiO 2 aerogel coated with diamond-like carbon (DLC) by the r.f. decomposition of methane is presented. The r.f. decomposition of methane seems to be the most convenient method for the production of superhard carbon coating on silica aerogels. Aerogels are new materials obtained by removing solvent from gels under supercritical conditions. They are usually transparent, highly porous with very low density. Other unique properties such as a low heat transfer coefficient, low sound velocity, refractive index close to that of air, high purity, and easy doping by different inorganic and organic substances make their applications very promising in electronics, ceramics, catalysts and other fields. However, silica aerogels are problematic because they are brittle. The silica gel was obtained by hydrolysis and condensation of tetraethoxysilan. A two-step method was used. One set of gel samples was heated in the autoclave filled with alcohol and decompressed isothermally after reaching the critical point of the solvent. Another set was subjected to supercritical extraction of alcohol by carbon dioxide followed by isothermal decompression at a temperature higher than the critical temperature of CO 2 (304.2 K). In the processes described transparent aerogels of density 104–115 kg m -3 were obtained. In the paper the influence of DLC coating on the mechanical strength of the DLC-SiO 2 aerogel system is presented. The DLC layer was deposited onto two surfaces of an aerogel plate by r.f. plasma chemical vapour deposition. The DLC films are very hard and resistant to acids and bases. DLC, which is semitransparent for mass transfer, is a good material for sensors. Together with the aerogel substrate the DLC film creates a structure which is very promising for electronics.