Characterization of particulates and coatings created in a 13.56 MHz radiofrequency methane plasma

Carbon particulates and a-C:H films were synthetized from pure CH4 by a radio-frequency (13.56 MHz) plasma enhanced chemical vapor deposition technique. Two powder families appear in the plasma: white spherical particulates created in the discharge and brown particulates coming from the flaking of the coating growing on the biased electrode. The two kinds of particulates have been characterized by scanning electron microscopy (SEM). The collected white particulates always have diameters in the range 0.2–0.8 μm. Infrared and Raman spectroscopies are employed to determine the local microstructure both of the particulates and the coatings for different methane pressures (93–146 Pa) and different incident rf powers (40–120 W). The observed absorption peaks with frequencies lower than 3000 cm−1 reveal a preponderance of sp3 carbon sites and indicate the formation of polymer-like hydrocarbon nanoparticles and films.