Size effects in cupric oxide nanocrystals, synthesized using a novel electrochemical route, having average diameters of about 4 and 6 nm, are probed by x-ray photoelectron spectroscopy. Cu—O bond ionicity was found to increase with reduction in nanocrystallite size. Formation of pure CuO phase was confirmed from x-ray diffraction, infrared spectrophotometry and photoelectron spectroscopy. This report also disproves the earlier conjecture that nanometer sized CuO phase is unstable below 25 nm.

• Received 2 August 1999

DOI:https://doi.org/10.1103/PhysRevB.61.11093