Synthesis and characterization of Co/ZnO nanocomposites: towards new perspectives offered by metal/piezoelectric composite materials

Abstract A new type of composite material, consisting of metallic cobalt nanoparticles dispersed within a piezoelectric ZnO matrix has been elaborated by a sol–gel process. Cobalt and zinc salt solutions with a cobalt to zinc atomic ratio equal to 0.1 have been spin-coated onto fused quartz substrates and films of 400 nm thickness have been obtained. An annealing of the as-deposited film in air above 500 °C has allowed ZnO to be well-crystallized and (0 0 2) oriented. Further heat treatments, in reducing atmosphere, were necessary to obtain the cobalt metal. ZnO being sensitive to reduction, such reducing heat treatments have been performed in a mild reducing atmosphere (H2/H2O) at a temperature not exceeding 450 °C. It is possible in such conditions to obtain Co00.1/ZnO thin films in which Co is metallic and ZnO is (0 0 2) oriented. The size of the cobalt particles depends on the temperature of the treatment in air prior to the reduction.