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Iron Resonant Photoemission Spectroscopy on Anodized Hematite Points to Electron Hole Doping during Anodization

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Braun Artur, Chen Qianli, Flak Dorota, Fortunato Giuseppino, Gajda-Schrantz Krisztina, Graetzel Michael, Graule Thomas, Guo Jinghua, Huang Tzu-Wen, Liu Zhi, Popelo Anastasiya V., Sivula Kevin, Wadati Hiroki, Wyss Pradeep P., Zhang Liang, Zhu Junfa,
Project Fundamental Aspects of Photocatalysis and Photoelectrochemistry / Basic Research Instrumentation for Functional Characterization
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Original article (peer-reviewed)

Journal CHEMPHYSCHEM
Volume (Issue) 13(12, SI)
Page(s) 2937 - 2944
Title of proceedings CHEMPHYSCHEM
DOI 10.1002/cphc.201200074

Abstract

Anodization of a-Fe2O3 (hematite) electrodes in alkaline electrolyte under constant potential conditions the electrode surface in a way that an additional current wave occurs in the cyclic voltammogram. The energy position of this current wave is closely below the potential of the anodization treatment. Continued cycling or exchanging of the electrolyte causes depletion of this new feature. The O 1s and Fe 2p core-level X-ray photoelectron spectra (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectra of such conditioned hematite exhibit a chemical shift towards higher binding energies, in line with the general perception that anodization generates oxide species with dielectric properties. The valence band XPS and particularly the iron resonant valence band photoemission spectra, however, are shifted towards the opposite direction, that is, towards the Fermi energy, suggesting that hole doping on hematite has taken place during anodization. Quantitative analysis of the Fe 2p resonant valence band photoemission spectra shows that the spectra obtained at the Fe 2p absorption threshold are shifted by virtually the same energy as the anodization potential towards the Fermi energy. The tentative interpretation of this observation is that anodization forms a surface film on the hematite that is specific to the anodization potential.
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