Iron resonant photoemission spectroscopy on anodized hematite points to electron hole doping during anodization.
Anodization of α-Fe(2)O(3) (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.
Laboratory for High Performance Ceramics, Empa. Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland. artur.braun@alumni.ethz.ch
Artur
A
Braun
Qianli
Q
Chen
Dorota
D
Flak
Giuseppino
G
Fortunato
Krisztina
K
Gajda-Schrantz
Michael
M
Grätzel
Thomas
T
Graule
Jinghua
J
Guo
Tzu-Wen
TW
Huang
Zhi
Z
Liu
Anastasiya V
AV
Popelo
Kevin
K
Sivula
Hiroki
H
Wadati
Pradeep P
PP
Wyss
Liang
L
Zhang
Junfa
J
Zhu