Oct 14, 2008
Ink-jet printable copper nanoparticles
Ink-jet printing of metal nanoparticles for conductive metal patterns has attracted great interest because current fabrication techniques like vapor deposition are very expensive. Silver and gold nanoparticles are used for ink-jet formulations because they are good electrical conductors and they do not show oxidation problems.
Potential applications for printable electronics are RFID tags (radio frequency identification), which require costs of around 1 cent per unit if they are broadly applied. Therefore, regarding the high material price of silver and gold, something that still remains to be solved is cost reduction.
Due to its good electrical conductivity, copper is a promising candidate as an alternative material. But a disadvantage of non-noble metal nanoparticles, such as copper, is their tendency to oxidize spontaneously when they get in contact with ambient air.
In a study recently published in Nanotechnology it was demonstrated how copper nanoparticles could be tuned air-stable. The nanoparticles were synthesized by flame-spray synthesis and in combination with a simple in situ functionalization step, graphene bi and trilayers could be deposited on the individual spherical copper nanoparticles. The graphene shells act as a barrier for oxidation and make the metal nanopowder air-stable allowing easy handling at ambient conditions. By using these nanopowders, a stable nanocolloid was prepared and printed on a flexible polymer substrate. Without any additional treatment the resulting as-printed copper patterns exhibited electrical conductivity as shown by operating light-emitting diodes (see figure).
The electrical performance of the present material is still lower than the theoretical performance of bulk copper, but by conducting further investigations, including a sintering or densification step of the printed patterns, it is believed that the conductivity can be improved.
About the author
Norman A Luechinger and Evagelos K Athanassiou are PhD students in the group of Prof. Stark at the Institute for Chemical and Bioengineering at ETH Zurich. Wendelin J Stark is professor of the Functional Materials Laboratory at the Institute for Chemical and Bioengineering at ETH Zurich.