Synthesis of oxidation-resistant core–shell copper nanoparticles

We present a simple method to synthesize non-oxidizable copper nanoparticles surrounded by copper formate. The formation of the core–shell nanoparticles was achieved via surface reaction induced by the injection of formic acid on the preformed core particles. High resolution transmission electron microscopy revealed that copper particles with a diameter of 77 nm are conformally surrounded by a 5 nm thick layer of copper formate, which prevents oxidation of the copper. This non-metallic shell was readily reduced to Cu during low temperature annealing without leaving behind organic residues, resulting in highly conductive films with a resistivity of 13.5 μΩ cm after annealing at 250 °C for 1 h in nitrogen. Time- and temperature-dependent sheet resistance measurements demonstrated that the resistivity of the core–shell nanoparticle films will double after exposure to an ambient atmosphere at room temperature for 27 years. Our core–shell Cu nanoparticles are a promising and cost-effective alternative to silver nanoparticles for the efficient production of printed conductors with enhanced chemical stability.