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Resolving the Valence of Iron Oxides by Resonant Photoemission Spectroscopy

Chen, Hao ; Liu, Yun ; Zhang, Hexin ; Zhao, Shengdi ; Liu, Haishan ; Girotto, Gustavo Z LU orcid ; Nemsak, Slavomir and Salmeron, Miquel (2025) In The Journal of Physical Chemistry Letters 16. p.10975-10981
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... (More)

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).

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publishing date
type
Contribution to journal
publication status
published
in
The Journal of Physical Chemistry Letters
volume
16
pages
7 pages
publisher
The American Chemical Society (ACS)
external identifiers
  • pmid:41084831
ISSN
1948-7185
DOI
10.1021/acs.jpclett.5c02103
language
English
LU publication?
no
id
48e4d959-ad4f-4b14-a6a7-a53d33bdc541
date added to LUP
2025-10-17 12:29:10
date last changed
2025-10-23 15:33:41
@article{48e4d959-ad4f-4b14-a6a7-a53d33bdc541,
  abstract     = {{<p>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). </p>}},
  author       = {{Chen, Hao and Liu, Yun and Zhang, Hexin and Zhao, Shengdi and Liu, Haishan and Girotto, Gustavo Z and Nemsak, Slavomir and Salmeron, Miquel}},
  issn         = {{1948-7185}},
  language     = {{eng}},
  month        = {{10}},
  pages        = {{10975--10981}},
  publisher    = {{The American Chemical Society (ACS)}},
  series       = {{The Journal of Physical Chemistry Letters}},
  title        = {{Resolving the Valence of Iron Oxides by Resonant Photoemission Spectroscopy}},
  url          = {{http://dx.doi.org/10.1021/acs.jpclett.5c02103}},
  doi          = {{10.1021/acs.jpclett.5c02103}},
  volume       = {{16}},
  year         = {{2025}},
}