Year: 2025
Type: article
Abstract: Precisely determining the oxidation states of metal cations within variable-valence transition metal oxides remains a significant challenge, yet it is crucial for understanding and predicting the properties of these technologically important materials. Iron oxides, in particular, exhibit a remarkable diversity of electronic structures due to the variable valence states of iron (Fe 2+ and Fe 3+ ). A quantitative analysis using conventional X-ray photoelectron spectroscopy (XPS) is challenging because of the strong overlap of the Fe 2p XPS peaks from different oxidation states. In this study, we show how this problem can be resolved using Resonant Photoemission Spectroscopy (ResPES), which unambiguously distinguishes Fe oxidation states and spectroscopically estimates the composition ratio of Fe cation valence states in the complex Fe oxides. We demonstrate this in the model case of a FeO 2 monolayer film on Pt(111), showing that the FeO 2 film consists of an equal mixture of Fe 2+ and Fe 3+ cations, yielding an average valence of +2.5, contrary to the +3 valence proposed based on density functional theory (DFT).
Authors: Hao Chen, Yun Liu, Hexin Zhang, Shengdi Zhao, Haishan Liu, Gustavo Z. Girotto, Slavomir Nemsak, Miquel Salmeron
Institutions: Lawrence Berkeley National Laboratory, Chinese Academy of Sciences, Institute of Urban Environment, Xiamen University, Collaborative Innovation Center of Chemistry for Energy Materials, University of Chinese Academy of Sciences, University of California, Riverside, Advanced Light Source
Language: English
Subfield: Surfaces, Coatings and Films
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W4415169110