Laser-induced surface oxidation of (Ni/Ti)/Si system with picosecond laser pulses

The surface oxidation of Ni/Ti bilayer, deposited on silicon substrate, affected by picosecond Nd: YAG laser radiation has been investigated. Fluence close to the target ablation threshold and multi-pulse laser irradiation regime were applied. Changes in the chemical composition of the formed surface oxide layer were studied by Elastic Recoil Detection Analysis (ERDA) and X-ray photoelectron spectroscopy (XPS). Morphological features analysis, at the oxide surface layer, was monitored, too. Laser modification as-deposited (Ni/Ti)/Si sample with 10 pulses induces a progressed interaction between Ni and Ti layers with the initial surface oxidation and formation of NiTi alloy phase. Progressed intermixing of components was achieved for the irradiation with 50 and more pulses, when all components were quite uniformly distributed to a depth of about 80 nm. An oxide layer was formed at the surface, with the specific combination of the oxide phases depending on the number of accumulated pulses. Changes in the morphological characteristics are reflected in the increase of the mean surface roughness and the generation of a certain number of cavities. These features are decreased with increasing number of pulses, caused by the surface melting and a pronounced mobility of the materials.