Modification of Ti/Zr multilayer by femtosecond laser pulses

Femtosecond laser texturing holds promise for the surface modification of materials, due to a wide application to all materials; the possibility of getting a wide variety of structures with micro- and nano-scaled features; and a fast, repeatable and contactless process. Laser processing is unique method, which allows production of active surface with formation of the desired oxide, creation of nano/micro textures and change wettability of the surface. Due to excellent mechanical properties and moderate biocompatibility, Ti/Zr multi- layer thin films, as novel nanolayered composites were deposited by ion sputtering on Si substrate. Subsequently, the Ti/Zr thin films were irradiated by femtosecond laser pulses in air to induce the following modifications: (i) mixing of components within the thin film structures, (ii) formation of ultrathin oxide layer at the irradiated surfaces, and (iii) structuring of the surface arrays in form of ripple structure. The main focus of this experimental study was examined different surface motives with nano- and micrometre features. For this purpose, the modifications of Ti/Zr multilayers were included forma- tion of spots, lines and surfaces with different pulse energy, scanning speed i.e. number of pulses, z-distance. Laser-induced spots are composed of concentric circles, where the number of circles in individual spots is increased with increasing pulse energy. Maxi- mum depth in the centre of spots and total roughness are gradually rising with pulse energy, but heights between ablated layers in these spots does not match with the thick- ness of layers, but these deviations are not significant. Lines and surfaces were scanned with different scanning rate, the conditions for formation of well-defined LSFL (low spa- tial frequency LIPSS) are determined. The periodic structures at high scanning rate (3 mm/s) are mainly formed on the multilayer thin film. However, the degree of ablation becomes higher at the lowest rate (0.5 mm/s) where