Nanopatterned films of Co3O4 nanopetals

Abstract Hierarchical transition metal oxide nanostructures are promising materials in the field of catalysis. Physical vapor deposition of a Co film on a mask of self-ordered nanospheres has been used to obtain a 2D-ordered array of Co metallic nanostructures. Then, oxidizing annealing in specific conditions resulted in the progressive oxidation of Co to Co3O4, with the concomitant growth of nanopetals out of the free surface of the deposited film. In this way hexagonal arrays of nanotriangles or of nanodomes decorated with nanopetals have been obtained. X-ray Absorption Spectroscopy shows that the extent of Co oxidation depends on nanostructuring, being the oxidation of nanotriangle and nanodome arrays more rapid than the one of a flat film produced in the same deposition. X-ray diffraction and Scanning Electron Microscopy show that for long annealing time the sample morphology is preserved, and the only crystalline phase is Co3O4.