Tailoring the etchability of aluminium foil by laser interference metallurgy

During the last decades, different surface patterning techniques have been developed to produce structures in the nano/submicron scale, Laser Interference Metallurgy (LIMET) being one of them. LIMET allows the production of direct periodic arrays over large areas by using the interference of several laser beams. This technique is an attractive tool to improve the etching process of anode aluminium during the manufacturing of high-voltage aluminium capacitors, where aluminium foils are etched so as to develop a high surface area thereby achieving the maximum possible capacitance. The aim of this work was to develop a method for controlling the pit-site distribution during the etching process of aluminium foil. For this purpose, the mechanism that governs the surface patterning of metals and the physical/chemical changes induced by LIMET were investigated. It was demonstrated that the main forces producing the periodic structures on metallic surfaces are surface-tension-driven flow and recoil pressure. Moreover, the impact on aluminium etchability of ordered local oxidation and incorporation of small quantities of Pb and Cu was studied. It was found that periodic surface activation and/or passivation improve the pit distribution of the exposed aluminium. In all systems studied, the etching process followed the ordered array generated by laser interference. Finally, 3D quantitative characterisation of etched structures was performed using FIB tomography.