TiO2 films prepared by sol-gel route are active photocatalysts for the oxid
ation of organics in photoelectrochemical cells. The as-grown films for pho
tocatalysis applications and those exposed to Ar+ or H-2(+)-Ar+ ion bombard
ment are characterized by different spectroscopic methods, such as X-ray di
ffraction (XRD), atomic force microscopy (AFM), UV-vis transmittance, photo
thermal deflection spectroscopy (PDS) and X-ray photoelectron spectroscopy
(XPS), as well as by conductance. This material has defects associated with
oxygen vacancies produced during the sample preparation which support nond
issociative adsorption of Oz when films are exposed to air. Charge transfer
from reduced Ti species to adsorbed dioxygen leads to Ti-O-2(-) surface co
mplexes that are partially removed by heating at 200 degreesC, and fully re
moved after 30 min ion bombardment. By comparison with the relatively well-
understood structural defects of bombarded TiO2 we arise to a quite complet
e structural model of the as grown material which corresponds to an amorpho
us semiconductor possessing relative low disorder and density of states as
compared with a pure amorphous material. These TiO2 films are modeled as lo
w size crystalline domain embedded in an amorphous matrix whose electronic
structure exhibit exponential band tails and a narrow band close to the con
duction band. The latter is fully or partially occupied depending on the pr
esence of adsorbed electron scavengers such as dioxygen.