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 mu Omega cm after annealing at 250 degrees 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.