Laser-induced structural and composition modification of multilayered Ni/Ti thin film in air and liquids

Abstract

The interaction of an Er, Yb, Cr-glass laser, operating at 1540 nm wavelength and a pulse duration of 40 ns, with Ni/Ti multilayer thin films has been studied. Five (Ni/Ti) bilayers deposited by DC ion sputtering on Si(100) wafers to a total thickness of about 180 nm were treated with laser fluences of about 6.4 and 8.8 J cm(-2). Single and multi-pulse laser irradiation was done at normal incidence in air, water and ethanol ambients. The composition and surface morphology were monitored by particle-induced x-ray emission, Rutherford backscattering spectrometry (RBS), scanning electron microscopy and profilometry. Most of the absorbed laser energy was rapidly transformed into heat, producing intensive modifications of composition and morphology on the target surface. The results show an increase in surface roughness, formation of parallel periodic surface structures, appearance of hydrodynamic features and ablation of surface material. RBS analysis revealed that laser modification induced inter-mixing between the components of individual Ni and Ti layers, with indications of the formation of NiTi intermetallic compounds. An interesting finding is the morphological changes dominant in the Si substrate, whereas the Ni/Ti multilayer structure has mainly undergone changes in the chemical composition.