Structural, vibrational and electronic properties of CuO nanoparticles synthesized via exploding wire technique

The study of mixed phase Cu/Cu2O/CuO nanoparticles synthesized by Exploding Wire Technique has been recently reported by us. Aiming to achieve single phase CuO nanoparticles, the mixed phase Cu/Cu2O/CuO nanoparticles were subjected to annealing at different temperature and time durations in oxygen environment. In this article, we discussed two samples; two phase Cu2O/CuO and single phase pure CuO nanoparticles obtained by annealing at 500 degrees C and 900 degrees C for 10 h. Rietveld refinement and Williamson-Hall analyses revealed formation of pure phase of CuO at 900 degrees C with an average crsytallite size of 27.6 nm. Irregular shape of nanoparticles with average size of 8 nm was observed by Transmission Electron Microscopy. Selected Area Electron Diffraction pattern matches with standard interplanar distance of CuO. Fourier Transform Infrared and Micro-Raman (mu R) spectra exhibit broadening of vibrational modes; indicative of pure phase CuO at 900 degrees C. Extensive X-ray Photoelectron Spectroscopy analysis revealed that the percentage contributions of Cu1+ and oxygen vacancy (V-O) decreases whereas; Cu2+ and interstitial oxygen (O-1) enhances on increasing the annealing temperature from 500 degrees C to 900 degrees C and thus, resulting the pure phase formation of CuO nanoparticles. Notably, through our analyses we propose an electronic band structure diagram on the basis of valance band maximum, as obtained by XPS and the band gap energy as estimated via UV-visible spectroscopy for mixed phase of Cu2O/CuO (1.6 +/- 0.02 eV) and pure phase of CuO (1.3 +/- 0.02 eV) nanoparticles.