Treating graphene right: pulsed laser process improves conductivity

Graphene is considered something of a wonder material: the carbon honeycomb is just one atom thick, it’s great at conducting electricity and heat, and it’s strong and stable. But researchers have struggled to move beyond tiny lab samples for studying its material properties to larger pieces for real-world applications.

Recent projects have used inkjet printers to print multilayer graphene circuits and electrodes, but there were problems with the existing technology. Once printed, graphene had to be treated to improve electrical conductivity and device performance. But that usually meant high temperatures or chemicals — both of which could degrade flexible or disposable printing surfaces such as plastic films or paper.

Iowa State University researchers came up with the idea of treating the graphene using lasers. They collaborated with an associate professor at Purdue University to develop and test the idea.

And it worked: they found treating inkjet-printed, multilayer graphene circuits and electrodes with a pulsed laser process improves electrical conductivity without damaging paper, polymers or other fragile printing surfaces.

“This creates a great way to commercialise and scale up the manufacturing of graphene,” said Jonathan Claussen, an Iowa State assistant professor of mechanical engineering.

“The laser works with a rapid pulse of high-energy photons that do not destroy the graphene or the substrate. They heat locally. They bombard locally. They process locally,” said Suprem Das, an Iowa State postdoctoral research associate in mechanical engineering and an associate of the US Department of Energy’s Ames Laboratory.

That localised, laser processing also changes the shape and structure of the printed graphene from a flat surface to one with raised, 3D nanostructures. The engineers say the 3D structures are like tiny petals rising from the surface. The rough and ridged structure increases the electrochemical reactivity of the graphene, making it useful for chemical and biological sensors.

All of that, according to Claussen’s team of nanoengineers, could move graphene to commercial applications.

“This work paves the way for not only paper-based electronics with graphene circuits,” the researchers wrote in their paper, “it enables the creation of low-cost and disposable graphene-based electrochemical electrodes for myriad applications including sensors, biosensors, fuel cells and (medical) devices.”

The researchers’ findings are featured on the front cover of issue 35 of the journal Nanoscale.