Fabricating nanostructured TiO₂ by femtosecond laser irradiating titanium

many materials including titanium. Laser structuring of titanium surfaces has been investigated for a variety of applications, including biocompatibility and solar energy harvesting. We use femtosecond laser irradiation of titanium to create nanometer scale laser-induced periodic surface structures and study the influence of atmospheric composition on these surface structures. Altering the gas composition and pressure does not change the surface morphology, but it does impact the chemical composition of the surface. We demonstrate that irradiation of titanium in oxygen containing atmospheres forms a highly stable surface layer of nanostructured amorphous titanium dioxide (TiO₂). We find that the resulting surface structures do not depend on gas chemical composition and pressure, which is in contrast to earlier work using nanosecond pulses.

In addition, we present a novel method for femtosecond-laser doping of TiO₂ for above bandgap absorptance by irradiating titanium metal in the presence of oxygen and dopants. With a bandgap of 3.2 eV for the anatase crystalline phase, TiO₂ most strongly absorbs in the UV range (λ < 387 nm). However, doping with metals and nitrogen has been shown to create intermediate states in the bandgap. We present compositional data from x-ray photoelectron and Raman spectroscopy and structural data from scanning electron microscopy.

In conclusion, we form nanostructured and doped TiO₂ and non-stoichiometric TiN films by femtosecond laser irradiation in controlled atmospheres. We show that oxygen and nitrogen incorporation occurs in these films when the laser fluence exceeds the ablation threshold. Our research offers an innovative approach using laser scanning techniques to alter the surface and structure of TiO₂ to generate new materials with applications in biomedical devices and for visible-light watersplitting.