Electrochemical investigation of copper oxide films formed by oxygen plasma treatment

Linear potential sweep voltammetry was used to characterize the copper oxides grown on a metal substrate when exposed to a low pressure inductively coupled oxygen plasma. This study confirms the formation of a precursor oxide CuxO (x > 4), two copper(I) oxides Cu2-xO and Cu3O2 and copper(II) oxide CuO. The electrochemical reduction curve of CuxO is characterized in aqueous solution (pH 9.2) by a minor peak near -0.5 V vs SCE while the two Cu(I) oxides present one reduction peak at -0.8 V vs SCE and cannot be electrochemically separated; CuO is reduced to Cu(I) at -0.65 V vs SCE. The reduction potentials of the copper(I) and copper(II) oxides vary with the oxide layer thickness which increases with the time of exposure to the plasma and the injected electric power and decreases as the distance between the sample and the 1st coil increases for given treatment parameters. In addition, a mechanism is proposed for the reduction of thin films containing the copper(I) and copper(II) oxides formed after plasma treatment.