Role of machining and exposure conditions on the surface chemistry modification of femtosecond laser-machined copper surfaces

We systematically investigate (i) how the surface chemistry of Cu substrates is altered by femtosecond laser machining LIPSS in different atmospheres and (ii) the impact of subsequent exposure conditions on the surface chemistry of Cu substrates laser-machined in an inert Ar atmosphere. All experiments were conducted by carefully avoiding exposure to uncontrolled conditions until the completion of the XPS analysis. We confirmed that hydroxyl groups present on the oxide surface significantly contribute to the chemisorption of carbonaceous species. Samples maintained in humid atmospheres presented a superior surface carbon content. In carrying out these experiments, we found that laser machining in Ar humidified with a lauric acid-ethanol solution provided the highest C/Cu ratio, while the lowest C/Cu ratio was observed for the sample machined in the inert Ar environment. We confirmed that the decomposition of CO2 into carbon stands less favored for our given exposure conditions (20 °C & 150 °C), and that CO2 effectively acts inert like Ar. Our experiments with acetylene demonstrate the significance of identifying a more reactive carbonaceous gas that contributes non-polar carbon to a laser-machined surface. Furthermore, immersing a laser-machined sample in a carbon-rich solution (lauric acid-ethanol solution) maximizes surface carbon content.