Macroscopic Approach to Plasma Polymerization Using the Concept of Energy Density

The film growth and the properties of plasma polymers are determined by gas phase and surface reactions. In order to gain more insights and to optimize plasma polymerization processes, some assumptions can be made that allow a macroscopic approach. Therefore, a concept was developed based on the energy input both into the gas phase (plasma) and during film growth (surface) that helps to distinguish between predominating gas phase or surface processes. Different experimental series using gas mixtures of C2H4 with CO2 or N-2/H-2 were performed at different power inputs W and gas flow rates F. Thereby, the same range of specific energy input W/F can be maintained at different ion bombardment to the substrate. The results indicate that changes in film growth were initiated by plasma chemical processes for CO2/C2H4 discharges (scavenger effects), while the obtained drop in deposition rate at high energy input values for N-2/H-2/C2H4 is caused by the energy dissipated in the film during growth pointing towards a threshold energy for chemical sputtering.