Influence of re-deposited nanoparticles on the surface elemental composition of femtosecond laser machined copper surfaces

Abstract

Nanoparticles re-deposited during the laser machining process have been suspected to modify the intrinsic surface chemistry of machined metallic surfaces. However, only very few studies have focused on elucidating their effect. In this work, under two different machining conditions (laboratory air & controlled humid air), we fabricated laser-induced periodic surface structures, LIPSS, on polished Cu surfaces with three different amounts of re-deposited Cu nanoparticles to quantify how re-deposited Cu nanoparticles affect the surface chemistry of the machined samples. In carrying out these experiments, we demonstrate that the re-deposition of nanoparticles during laser machining is affected by the volume of the laser machining environment, which impacts the surface chemistry of laser-machined surfaces. Our results indicate that evacuation of the vacuum chamber before and after laser machining using a vacuum scroll pump did not affect the adsorption of carbonaceous molecules. Further, we present the effect of removing re-deposited nanoparticles through ultrasonic cleaning on the surface chemistry of the test surface. The cleaning exposes the LIPSS surface entirely to airborne carbonaceous species, resulting in a more significant increase in the total surface carbon content. Finally, we evaluated the quality of the nanoparticles generated during laser machining by assessing their stability to provide a first insight into the utility of those nanoparticles.