THE FORMATION OF CU2O LAYERS ON CU AND THEIR ELECTROCHEMICAL AND PHOTOELECTROCHEMICAL PROPERTIES

Cu2O films up to 30 nm have been formed on Cu2O passivating layers on Cu by cathodic reduction of (CuO2)2- in 5 M KOH solutions. These films grow linearly with time. At E > 0.2 V they may be partially oxidized to Cu(II) oxide which grows according to a high field mechanism. With XPS a Cu2O composition is found for the cathodically formed films and a Cu(II) oxide overlayer at E > 0.2 V with large amounts of hydroxide. Only negative photocurrents are obtained. The results follow best a simple semiconductor model with p-type Cu2O. The band gap of Cu2O decreases slightly with the oxide thickness and fits well the data of passive oxides and the crystalline material. The flat-band potential equals the value of the passive film. The Cu(I)/Cu(II) duplex layer yields a much more positive flat-band potential, which is a consequence of the potential drop at the interfaces between both oxides and the Cu(II) oxide and the electrolyte. © 1990.