Expeditious low-temperature sintering of copper nanoparticles with thin defective carbon shells

The realization of air-stable nanoparticles, well-formulated nanoinks, and conductive patterns based on copper is a great challenge in low-cost and large-area flexible printed electronics. This work reports the synthesis of a conductively interconnected copper structure via thermal sintering of copper inks at a low temperature for a short period of time, with the help of thin defective carbon shells coated onto the copper nanoparticles. Air-stable copper/carbon core/shell nanoparticles (typical size similar to 23 nm, shell thickness similar to 1.0 nm) are prepared by means of an electric explosion of wires. Gaseous oxidation of the carbon shells with a defective structure occurs at 180 degrees C, impacting the choice of organic solvents as well as the sintering conditions to create a crucial neck formation. Isothermal oxidation and reduction treatment at 200 degrees C for only about 10 min yields an oxide-free copper network structure with an electrical resistivity of 25.1 mu Omega cm (14.0 mu Omega cm at 250 degrees C). Finally, conductive copper line patterns are achieved down to a 50 mu m width with an excellent printing resolution (standard deviation similar to 4.0%) onto a polyimide substrate using screen printing of the optimized inks.