Photocatalytic Response of Flash-Lamp-Annealed Titanium Oxide Films Produced by Oblique-Angle Deposition

We report the photocatalytic (PC) response of titanium oxide (TiO<i>_x</i>) films grown by reactive DC magnetron sputtering under oblique-angle-deposition (OAD) and subjected to post-deposition flash-lamp-annealing (FLA). Under ballistic growth conditions, OAD yields TiO<i>_x</i> films with either compact or inclined columnar structure as the deposition incidence angle (<i>α</i>) with respect to the substrate normal varies from zero to grazing. On the one hand, films produced for <i>α</i> ≤ 45° display a compact and opaque structure comprising the formation of nanocrystalline cubic titanium monoxide (<i>c</i>-TiO) phase. On the other hand, films grown at larger <i>α</i> (≥60°) display tilted columns with amorphous structure, yielding highly porous films and an increased transparency for <i>α</i> > 75°. For TiO<i>_x</i> films grown at large <i>α</i>, FLA induces phase transformation to nanocrystalline anatase from the amorphous state. In contrast to <i>as-grown</i> samples, FLA samples display PC activity as assessed by bleaching of methyl orange dye. The best PC performance is attained for an intermediate situation (<i>α</i> = 60-75°) between compact and columnar structures. The obtained photoactivity is discussed in terms of the different microstructures obtained by OAD and posterior phase formation upon FLA.