Self-oscillatory mode of plasma polymerization of benzene vapor-nitrogen mixture in a capacitively coupled radiofrequency discharge

The nonmonotonic dependence of the polymerization rate in the capacitively coupled radiofrequency discharge in a benzene vapor-nitrogen mixture on the total gas pressure at constant flow rate, geometry, and discharge power was revealed. Following an abrupt increase in the rate of growth of the polymer film at P > 45 Pa, the behavior of polymerization changes at P = 60 Pa: the rate of film growth decreases down to virtually zero and the formation of powder is observed. The further increase of pressure up to 80 Pa results in slow growth of the film and simultaneous formation of the powder. The abrupt change of the polymerization mode is accompanied by the appearance of self-oscillations of the integral intensity of the discharge emission and by a change in the chemical composition of the plasma. It was shown that the change of the polymerization mechanism is responsible for the appearance of self-oscillations