Cu3+ Ion Evaluation and O2− Vacancy Identification in CuO Nanofibers by XPS

Cu3+-like species and oxygen vacancies (Vₒ) in electrospun CuO nanofibers were identified by X-ray photoelectron spectroscopy (XPS) via Cu 2p3/2 and O 1s core-level spectra. Nanobeam electron diffraction (NBD) revealed a Cu3+-related superlattice. The geometrical topofactor method corroborated the chemical composition of samples thermally treated at 600 °C (CuO600) and 700 °C (CuO700). Bulk CuO served as a comparison. XPS peak fitting of the Cu 2p and O 1s regions used an SVSC-type background and a two-parameter Tougaard function. X-ray diffraction (XRD) confirmed the presence of tenorite and cuprite phases. Crystallite size was estimated using the Rietveld method; values ranged from 20.59 ± 0.06 nm to 31.06 ± 0.06 nm. High-resolution transmission electron microscopy (HR-TEM) produced sizes of 14.98 ± 0.34 nm and 36.10 ± 0.94 nm, highlighting the distinction between diffraction domains and physical particle dimensions. Cu3+-like species and oxygen vacancies modulate the nanofibers’ electronic structure, which is relevant to electronic applications.