Nanostructuring of titanium oxide thin film by UV femtosecond laser beam: From one spot to large surfaces

•Different nanostructure morphologies were generated on non-stoichiometric titanium oxide thin films.•The free-surface energy minimization mechanism is proposed to explain the nanostructures formation.•Micro-nanostructuring of a large homogeneous surface was performed at relatively low fluences. Surface structuring of titanium oxide thin films by a UV femtosecond laser beam (266nm, 100fs) is presented in this paper. Without using laser scanning, the results show the formation of regular dots and laser induced periodic surface structures (LIPSS) with a period close to that of the beam wavelength. These nanostructures seem to be due to free-surface energy minimization. Furthermore, laser irradiation of large homogeneous surfaces by laser scan (5×5mm2) showed more exotic surface morphologies, ranging from regular dots and low spatial frequency LIPSS to microstructures that are completely controlled by the laser fluence and the number of shots. Typically 2D circular dots of 100nm diameter with two distinct periods (260 and 130nm) are achieved under a very low fluence of 15mJ/cm2 after 13000 shots.