The impact of local heating on the oxidation process of cobalt nanowires

The process of oxidation of cobalt (Co) nanowires leading to the formation of different oxides (CoO an Co₃O₄) was investigated. The transition from CoO to Co₃O₄ was studied by X-ray diffraction analysis and Raman spectroscopy techniques. Only Co₃O₄ reflexes were detected in the X-ray diffraction patterns after annealing nanowires at 360°C, which confirms the complete conversion to cobalt tetroxide. A similar result was observed upon exposure to laser radiation, where local heating induced by the laser also led to the transition from CoO to Co₃O₄. Two Raman spectra of cobalt tetroxide were demonstrated with a relative shift of 20 cm^-1 depending on the degree of crystallization at different excitation laser powers.