Effects of Ammonia Addition on Thermal Chemical Vapor Deposition Rates and Microstructures of Carbon Films.

When ammonia is added in methane to form carbon films using thermal chemical vapor deposition, effects of the ammonia/methane ratio on the deposition rate and microstructures of carbon films are investigated. Meanwhile, effects of the deposition temperature, working pressure, and residence time on the deposition rate are also considered. Experimental results indicate that as the ammonia/methane rate increases, the deposition rate of carbon films decreases, and also, the ordered degree, nano-crystallite size, and sp² carbon atoms of carbon films increase. Nevertheless, if the deposition temperature, working pressure, and residence time increase, the deposition rate of carbon films increases. The relationship between the deposition rate and deposition process parameters is formulated. The deposition process is controlled by the process to create mono-carbon and bi-carbon species in carbon films. Moreover, one mono-nitrogen will suppress about three mono-carbons to form carbon films. Few nitrogen and hydrogen atoms are incorporated into carbon films. The activation energy (= 507 kJ/mole) of carbon deposition is related to the activation energies of methane and ammonia dissociation. If the working pressure is smaller than a threshold value (= 30 kPa) or the residence time is shorter than a threshold value (= 1.5 s), no film is formed. [ABSTRACT FROM AUTHOR]