XPS and SIMS study of aluminium native oxide modifications induced by Q-switched Nd :YAG laser treatment

Abstract

During laser cleaning of aluminium in ambient atmosphere, modifications of the metal surface can be induced by transient thermal effects. This work aims to characterize the modification of the aluminium oxide layer on pure aluminium for a wide range of power per area using a Q-switched Nd :YAG (1064 nm) laser with two pulse durations, 10 and 180 ns. Experiments were carried out with single laser shots in ambient air at fluences (e.g. energy per area) below the ablation regime. For 10-ns pulses with fluences between 0.7 and 1.7 J/cm2, X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) revealed thermal oxidation with an increase of the oxide-layer thickness for 0.7–1.3 J/cm2. Above a threshold at about 1.3 J/cm2 the oxide thickness decreased. The Mixing Roughness Model was used for the SIMS depth profile. For 180-ns pulses with fluences between 2.1 and 4.3 J/cm2, and therefore much lower power per area than with the 10 ns pulses, XPS showed a variation of surface composition with a different behaviour for 2.1–2.9 J/cm2 compared to 3.1–4.3 J/cm2. However, no significant changes of the average thickness of the oxide layer were found.