The Ultrahigh-Rate Growth of Nanotwinned Copper Induced by Thiol Organic Additives

Incorporation of high-density coherent twin boundaries into copper grains can improve the physicochemical properties of copper. However, the scheme to synthesize such an attractive structure by high-speed direct-current electrodeposition is not adequately understood. Here we provide the first report for a facile strategy to induce the growth of nanotwinned copper grains with adding sufficient amount of the thiol organic molecule and discover that columnar nanotwinned copper can actually be deposited at an average growth rate up to 130 nm·s ⁻¹ via the direct-current electroplating. We confirm that the Cu ⁺ concentration during the cupric ion reduction is crucial in the mechanism of twin formation. The high coverage of thiol-chloride bridges greatly accelerates the Cu ²⁺ /Cu ⁺ reduction rate and promote the quantity and stability of Cu ⁺ intermediates during electrodeposition. The concentrated thiol-chloride-Cu ⁺ intermediates at the cathode surface/vicinity enable the formation of high-density nucleation sites for copper deposition and reduce the interfacial energy via stress releasing, leading to the formation of the nanotwinned structure. Ultimately, transformation into the microstructure with large columnar grains filled with high-density twin boundaries becomes the most thermodynamically favorable path for copper nucleation and growth.