Tuning the structure and preferred orientation in reactively sputtered copper oxide thin films.

Binary copper oxide (Cu 2 O, Cu 4 O 3 and CuO) thin films have been selectively deposited on glass and silicon substrates by magnetron sputtering at room temperature from a metallic copper target in various Ar–O 2 reactive mixtures. The influence of oxygen flow rate and total pressure on the film structure and its preferred orientation has been studied. A schematic deposition diagram, which describes the film structure as a function of O 2 flow rate and total pressure, is depicted by combining X-ray diffraction and Raman spectrometry. The oxygen flow rate process windows for Cu 2 O or Cu 4 O 3 single phase synthesis are narrow, while that for CuO is wider. Between two single phase domains, biphase films are systematically deposited. It is found that the deposition total pressure is a relevant parameter to control the texture and the morphology of pure Cu 2 O and Cu 4 O 3 films. Low total pressure favors the growth of planes with high surface energy ((1 0 0) for Cu 2 O and (1 0 1) for Cu 4 O 3 ) parallel to the substrate. On the other hand, high total pressure facilitates the growth of planes with low surface energy ((1 1 1) for Cu 2 O and (1 0 0) for Cu 4 O 3 ). The oxygen flow rate is effective to control the preferred orientation of CuO thin films that evolves from 〈1 1 1〉 to 1 ¯   1   1 with the increase of oxygen flow rate. These results are supported by transmission electron microscopy observation in cross section. [ABSTRACT FROM AUTHOR]