Conformal deposition of RuO₂ on Cu via a galvanic cementation reaction

We develop a seedless wet chemical process to deposit uniform RuO₂ on a Cu substrate. Our approach entails the synthesis of volatile RuO₄ colloids in a pH 9 aqueous solution from the oxidation of RuCl₅ ²⁻ by ClO⁻, followed by a galvanic cementation reaction in which the Cu undergoes a mild oxidation in conjunction with the reduction of RuO₄ to produce a dense and conformal RuO₂ thin film on the Cu surface. The nature for the chemical reactions and constituents involved are investigated by UV-Vis, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy. Both as-deposited and annealed RuO₂ films are characterized by scanning electron microscope and X-ray diffractometer. The as-deposited RuO₂ film, with a thickness of 199 nm, reveals an amorphous structure and after an Ar annealing, becomes crystalline in rutile phase. In between the RuO₂ and Cu, there are presence of CuO from the displacement cementation reaction, and Cu₂O from the parasitic Cu corrosion as expected from the Pourbaix diagram. These Cu oxides, with a thickness of 330 nm, provide sufficient adhesive bonding between RuO₂ and Cu.