Morphology, hardness, wettability and free surface energy of various copper surfaces

This paper aims to analyze wettability and the free surface energy of various copper surfaces. The Cu deposits produced galvanostatically from the basic sulphate electrolytes without and with an addition of levelling and brightening additives, and cold-rolled (c-r) Cu simultaneously used as the cathode in Cu electrodeposition processes have been investigated. Hardness of electrolytically produced Cu deposits was also determined. The wettability and the free surface energy of Cu surfaces were examined applying the OWRK (Owens–Wendt–Rabel–Kaelble) method, while morphology and hardness characterization of the surfaces was done by atomic force microscope (AFM) and Vickers microindentation, respectively. The surface roughness obtained by AFM software was used as a parameter for comparison of a state of various Cu surfaces. The Jönsson-Hogmark composite hardness model was used to determine the absolute hardness of Cu electrodeposits, and the obtained values of 1.509 GPa for microcrystalline (mc) deposit obtained from the basic sulphate electrolyte and 1.130 GPa for the nanocrystalline (nc) deposit obtained from the electrolyte containing levelling/brightening additives were in excellent agreement with those found in literature for copper. The surface roughness of Cu increased in the row: nc (30.84 nm) < c-r (83.22 nm) < mc (129.3 nm), causing the change of a state of Cu surfaces from hydrophilic to hydrophobic. Analysis of tensile and yield strengths of Cu surfaces computed from microhardness data, and the free surface energy values determined by the OWRK method also indicated on the strong correlation between a roughness and these properties of Cu surfaces.