Cuprite, paramelaconite and tenorite films deposited by reactive magnetron sputtering

Copper oxides films (Cu2O, Cu4O3 and CuO) have been deposited by magnetron sputtering of a copper target in various Ar–O2 reactive mixtures. The films are characterized by X-ray diffraction, scanning electron microscopy, four-point probe method and UV-Vis spectrometry. The three defined compounds in the CuO binary system can be deposited by varying the oxygen flow rate introduced into the reactor. All the films are crystallized with a mean crystal size ranging from 10 to about 35 nm. They are highly resistive and present a direct optical band gap higher than 2 eV. The application of a bias voltage during the deposition phase modifies the texture of the Cu2O films and also induces a preferential resputtering of oxygen from the Cu4O3 ones. This resputtering phenomenon leads firstly to the occurrence of the cuprite phase mixed with the paramelaconite one and secondly to the amorphisation of the films. Finally, the thermal stability in air of cuprite, paramelaconite and tenorite films has been investigated. The results show that the stability of Cu2O and Cu4O3 films in air is influenced by the thickness and/or the texture of the films. Tenorite films with a low optical band gap (1.71 eV) can be formed after air annealing at 350 °C of an unbiased cuprite film.