THE PROPERTIES OF DIAMOND-LIKE CARBON LAYERS DEPOSITED ONTO SIO2 AEROGEL

Possible production of an SiO2 aerogel coated with diamond-like carbon (DLC) by the r.f. decomposition of methane is presented. The r.f. dec omposition of methane seems to be the most convenient method for the p roduction of superhard carbon coating on silica aerogels. Aerogels are new materials obtained by removing solvent from gels under supercriti cal conditions. They are usually transparent, highly porous with very low density. Other unique properties such as a low heat transfer coeff icient, low sound velocity, refractive index close to that of air, hig h purity, and easy doping by different inorganic and organic substance s make their applications very promising in electronics, ceramics, cat alysts and other fields. However, silica aerogels are problematic beca use they are brittle. The silica gel was obtained by hydrolysis and co ndensation of tetraethoxysilan. A two-step method was used. One set of gel samples was heated in the autoclave filled with alcohol and decom pressed isothermally after reaching the critical point of the solvent. Another set was subjected to supercritical extraction of alcohol by c arbon dioxide followed by isothermal decompression at a temperature hi gher than the critical temperature of CO2 (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-SiO2 aerogel system is presented. The DLC layer was deposi ted onto two surfaces of an aerogel plate by r.f. plasma chemical vapo ur deposition. The DLC films are very hard and resistant to acids and bases. DLC, which is semitransparent for mass transfer, is a good mate rial for sensors. Together with the aerogel substrate the DLC film cre ates a structure which is very promising for electronics.