Cu³⁺-like species and oxygen vacancies (Vₒ) in electrospun CuO nanofibers were identified by X-ray photoelectron spectroscopy (XPS) via Cu 2p^3/2 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.

The presence of Cu³⁺ cations and oxygen vacancies (VO) in the electrospun CuO nanofibers was identified by X-ray photoelectron spectroscopy (XPS) from the Cu 2p₃/₂ and O 1s core-level spectra, respectively. A Cu³⁺-related superlattice was observed using nano-beam electron diffraction (NBD). The chemical composition of the two samples thermally treated at 600 °C (CuO600) and 700 °C (CuO700) was further corroborated using the geometrical topofactor method. For comparison, bulk CuO was also analyzed. XPS peak fitting of the Cu 2p and O 1s regions was performed using an SVSC-type background and two-parameter Tougaard function. X-ray diffraction (XRD) confirmed the presence of the tenorite and cuprite phases and enabled crystallite size estimation (FullProf). The average crystallite size ranged from 20.59 ± 0.06 nm to 31.06 ± 0.06 nm, in good agreement with High Resolution Transmission Electron Microscope, HR-TEM, measurements (14.98 ± 0.34 nm and 36.10 ± 0.94 nm). Therefore, we identify that Cu³⁺ and oxygen vacancies in these nanofibers plays a crucial role in optimizing their future applications in the electronic and catalytic fields.