XPS spectral analysis for a multiple oxide comprising NiO, TiO2, and NiTiO3

• Published in: Applied surface science 2020-10, Vol.526, p.146729, Article 146729
• Main Authors: Sakamoto, Kota, Hayashi, Fumio, Sato, Kazuyoshi, Hirano, Mitsuhiro, Ohtsu, Naofumi
• Format: Article
• Language: English
• Subjects: Accurate quantification; Angle-resolved XPS; Nickel titanate; Nickel titanium; Principal component analysis; X-ray photoelectron spectroscopy
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2020.146729

[Display omitted] •Principal component analysis (PCA) was conducted to analyze XPS spectra comprising NiO, TiO2, and NiTiO3.•The PCA could provide the accurate ratio of NiTiO3 and NiO from the complex-shaped Ni 2p spectra.•The PCA results of Ti 2p spectra inaccurately predicted the ratio of NiTiO3 and TiO2.•The values calculated from Ti 2p spectra showed good linear collation with the corresponding theoretical values.•The accurate results could be obtained using the measured linear correlation. XPS spectra collected from a mixture of NiO, TiO2, and NiTiO3 cannot be analyzed using a standard curve-fitting method; thus, principal component analysis (PCA) was conducted to accurately determine the ratio of various oxides in the mixture. Model samples comprising NiO, TiO2, and NiTiO3 exhibited a complex-shaped Ni 2p spectrum with a satellite peak, from which the atomic ratio of NiO and NiTiO3 could be accurately quantified using the PCA. In contrast, the Ti 2p spectrum exhibited a symmetric shape despite comprising both NiTiO3 and TiO2 states; thus, the PCA results predicted the ratio inaccurately. However, the PCA results showed linear correlation with the theoretical values over an entire range. Thus, accurate ratios were obtained using a calibration curve. The PCA procedure for multiple oxides was applied to angle-resolved XPS spectra for thermally oxidized nickel titanium alloy. The results revealed the in-depth distribution of NiO, TiO2, and NiTiO3 on the surface of the alloy.