Structure–properties relationship in reactively sputtered Ag–Cu–O films

Abstract

Ag–Cu–O films were deposited on glass substrates by pulsed dc sputtering of a silver–copper target (Ag50Cu50) in reactive Ar–O2 mixtures. The film chemical composition was estimated by x-ray energy dispersive spectrometry and the structure was studied by x-ray diffraction (XRD). Optical properties (reflectance and transmittance) and room temperature electrical resistivity were evaluated using spectrophotometry and the four point probe method, respectively. Since silver atoms are less reactive versus oxygen than copper ones, the increase in the oxygen flow rate introduced into the deposition chamber induced the preferential oxidation of sputtered copper atoms. XRD analysis showed that the structure of the deposited films can be divided into three domains. At low oxygen flow rate, the films were biphased (metallic silver-based solid solution and crystalline copper-based oxide). At intermediate oxygen flow rate, the films were x-ray amorphous (grain size lower than 2 nm). At high oxygen flow rate, the films contained a crystalline silver–copper oxide phase and a crystalline unknown phase. Thanks to the absorption band of silver in the UV range, reflectance measurements were used to show the occurrence of metallic silver phase in the films. It was shown that the chemical environment of silver atoms in the x-ray amorphous region evolved from metallic to oxide when the oxygen flow rate increased. Transmittance evolution versus the oxygen flow rate were well correlated with that of the electrical resistivity. The evolution of Ag–Cu–O film properties was discussed in connection with the structure and chemical composition.