  Electrochemical oxidation of hematite ({\alpha}-Fe2O3) nano-particulate films
at 600 mV vs. Ag+/AgCl reference in KOH electrolyte forms a species at the
hematite surface which causes a new transition in the upper Hubbard band
between the Fe(3d)-O(2p) state region and the Fe(4sp)-O(2p) region, as
evidenced by oxygen near edge x-ray absorption fine structure (NEXAFS) spectra.
The electrochemical origin of this transition suggests that it is related with
a surface state. This transition, not known for pristine {\alpha}-Fe2O3 is at
about the same x-ray energy, where pristine 1% Si doped Si:Fe2O3 has such
transition. Occurrence of this state coincides with the onset of an oxidative
dark current wave at around 535 mV - a potential range, where the tunneling
exchange current has been previously reported to increase by three orders of
magnitude with the valence band and the transfer coefficient by a factor of 10.
Oxidation to only 200 mV does not form such extra NEXAFS feature, supporting
that a critical electrochemical potential between 200 and 600 mV is necessary
to change the electronic structure of the iron oxide at the surface. Decrease
of the surface roughness, as suggested by visual inspection, profilometry and
x-ray reflectivity, points to faceting as potential structural origin of the
surface state.
