Hydrothermal–electrochemical growth of heterogeneous ZnO: Co films

Abstract

This study demonstrates the preparation of heterogeneous ZnO: Co nanostructures via hydrothermal–electrochemical deposition at 130 °C and −1.1 V (vs Ag/AgCl (satd)) in dimethyl sulfoxide (DMSO)–H2O mixture. Under the stated conditions, ZnO: Co nanostructures grow preferentially along (002) direction. Strength of directional growth progressively increases with the increasing concentration of Co(II) in the deposition bath. Films are composed of hexagonal Wurtzite ZnO, metallic cobalt, and mixed cobalt oxide on the surface and cobalt(II) oxide in deeper levels. Increasing the Co(II) concentration in the deposition bath results in different morphological features as well as phase separation. Platelets, sponge-like structures, cobalt-rich spheres, microislands of cobalt-rich spheres which are interconnected by ZnO network can be synthesized by adjusting [Co(II)]: [Zn(II)] ratio. Growth mechanisms giving rise to these particular structures, surface morphology, crystal structure, phase purity, chemical binding characteristics, and optical properties of the deposits are discussed in detail.