Structure and non-equilibrium phase diagram of the co-sputtered and post-annealed Co–ZnO system

X-ray diffraction, magnetic measurement and electron microscopic studies on co-sputtered Zn1−xCoxO single crystalline films showed the solubility limit to be about x = 0.58. An increase of Co greater than 0.58 resulted in the growth of Co rods elongated in the growth direction in a matrix of ZnCoO solid solution at a substrate temperature of 673 K. Above a substrate temperature of 873 K, the ZnCo2O4 spinel phase rather than the Co metal phase was seen. Annealing of as-sputtered films with a single phase of Zn1−xCoxO in air led to the decomposition of a two-phase structure of Zn1−xCoxO wurtzite and ZnCo2O4 spinel and the decrease of the solubility limit of Co in ZnO to about x = 0.2.