Peak-fitting of Cu 2p photoemission spectra in Cu0, Cu1+, and Cu2+ oxides: A method for discriminating Cu0 from Cu1

• Published in: Applied surface science Vol. 622; p. 156960
• Main Authors: Torres-Ochoa, Jorge Alejandro, Cabrera-German, Dagoberto, Cortazar-Martinez, Orlando, Bravo-Sanchez, Mariela, Gomez-Sosa, Gustavo, Herrera-Gomez, Alberto
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.06.2023
• Subjects: Active background approach; Block Approach; Copper; Oxides; Peak-fitting; Shirley Background; X-ray photoelectron spectroscopy; XPS; Peak-fitting; Block Approach; Oxides; XPS; Active background approach; Copper; Shirley Background; X-ray photoelectron spectroscopy
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2023.156960

[Display omitted] •Discerning the identical Cu0 and Cu1+ via the Lorentzian width of the Cu 2p1/2 line.•Lorentzian width of the Cu 2p1/2 line can be used to estimate the proportion of Cu1+.•Early stages of oxidation of metallic copper surface; Cu0, Cu1+ and Cu2+ coexist.•Block-Approach allows for accurate fitting of metal and oxide signals in Cu 2p.•Peak-fitting parameters for improved fitting of Cu2+ in quantitative XPS. The photoemission spectra of Cu 2p are one of the most studied. Its analysis is especially challenging because, among others, the peaks for Cu0 and Cu1+ overlap, and Cu1+ and Cu2+ coexist under many conditions. The chemical state determination of metallic copper and the initial oxidation mechanism of copper require state-of-the-art peak fitting analysis and background modeling. This work presents a detailed and quantitative analysis of the Cu 2p photoemission spectra for a metallic ultra-thin film and the initial oxidation stages. Additionally, annealed films at 200 °C for up to 5 min were analyzed to assess the full oxidation of the copper oxides and assert the validity of the proposed peak-fitting procedures. For the initial oxidation, it was possible to accurately identify Cu1+ and Cu2+ states and, alongside, quantify the corresponding O 1s species, resulting in compositions close to stoichiometric values. Using the active background, it was possible to achieve close reproduction of all the photoemission spectra; three coexisting copper species were resolved during the fitting procedure. An accurate peak-fitting analysis allowed for quantifying the relative proportion of Cu1+ to Cu0 states despite their strong overlap.