On the reactivity of silver electrodes in a chlorine radiofrequency plasma - Plasma oxidation vs. thermal oxidation

The plasma-electrochemical growth of an ion-conducting film by the oxidation of a metal in an electronegative plasma is investigated and compared with results from thermal oxidation. As model system we studied the oxidation kinetics of silver electrodes in a Cl-2 rf plasma. The electrochemical control of the reaction by external currents through the product layer using the plasma as a fluid electrode was achieved. Both potentiostatic and galvanostatic control of the reaction was applied. The morphology of the product layer and its temporal evolution was investigated using SEM, A formation of silver chloride surface patterns in the oxidation pro-cess takes place if a simple stability criterion is not fulfilled. Specific surface morphologies were found under different experimental conditions. The morphology of the product layer is influenced by the external electric current and the substrate temperature. The influence of the plasma phase on the thermodynamics and kinetics of the oxidation process is discussed. The role of excited plasma species, the electrical charging of the surface and radiation from the plasma are taken into account.