Plasma Polymerization at Atmospheric Pressure with a New Type of DBD Reactor for Combinatorial Studies: Classification of Precursor Concentration Dependencies

Design and first applications of a new kind of reactor for plasma treatments or plasma-assisted chemical vapor deposition (PACVD) processes based on dielectric barrier discharges (DBD) at atmospheric pressure are presented. Inserting a combination of two modules, gradient mixer and homogenizer, into the gas-supply line, the DBD module can be fed by a laminar gas flow featuring a concentration gradient of the precursor or another relevant gas species, oriented perpendicular to the flow direction. The generation of surfaces with a controlled gradient of physico-chemical properties by DBD-based PACVD or by surface modification is thus made possible. The new reactor concept is tested using plasma polymerization of hexamethyldisiloxane, tetramethylsilane, trans-2-hexene-1-al, and glycidyl methacrylate, respectively. Main focus of the work is laid on the influence of precursor concentrations, varied along the y direction, on film thickness profiles along the gas flow direction, d(x). It is shown that two different types of d(x, y) behavior can be distinguished, depending on the roles played by metastable atoms or molecules of the carrier gas. A third type is observed when surface polymerization is dominating.