Effect of oxidation time on structural, optical and electrical properties of mixed copper oxides nanocrystallites

Mixed nanocrystalline copper oxides were prepared from pre-sputtered copper films at 500 °C for various oxidation times. Mixed orthorhombic Cu64O and monoclinic CuO phases with CuO phase ration varied from 57.8 to 90.8% were obtained upon varying the oxidation time from 1 to 3 h. SEM observations revealed the nanocrystallites morphologies for the oxidized films. The film oxidized for 1 h have sizes in the range 39-69 nm and more coalescent nanocrystallites, with diameters in the ranges 45-157 nm and 47-251 nm, were observed for the films oxidized for 2 h and 3 h, respectively. The optical transmittance and reflectance as well as the optical constants were found to vary strongly with the variation of oxidation time. The optical band gap decreases from 2.58 to 2.49 eV with increasing oxidation time from 1 to 3 h. Semiconducting behavior and two distinct activation energies were reported for the films. The obtained results of the mixed copper oxides varied in a wide range which may find applications in optoelectronic devices.