Copper oxides: kinetics of formation and semiconducting properties. Part II. Copper single crystals

The anodic formation of Cu(I) and Cu(II) oxides on (100), (110), and (111) single crystals of copper in deoxygenated 0.1 M KOH was examined by voltammetry, chronoamperometry, and chronopotentiometry with a synchronous registration of photocurrent and photopotential, in situ spectroscopy of photocurrent, as well as SEM measurements. The transition from polycrystalline samples to single crystals inhibits the copper corrosion by the traces of dissolved oxygen. Cu(I) and Cu(II) oxides on copper single crystals are p-type semiconductors independent of the route of their formation (corrosion or anodic oxidation). The kinetic regularities of Cu(I) oxide formation and some structure-sensitive properties slightly change depending on the face of single crystal copper. The coefficient of optical absorption, space charge region, and band gap, which is equal to 2.2 +/- 0.1 eV for indirect optical transitions, hardly changed. The interrelation between the state of oxide/metal boundary and the structure-sensitive properties of Cu2O allow us to assume that the anodic formation of Cu(I) oxide occurs via the primary electrochemical reaction. The lack of a similar interrelation for Cu(II) oxide points to the secondary mechanism of oxide formation via the stages of copper dissolution, the oversaturation of a near-electrode layer, and the precipitation of oxidation products.