New laser-treated printed graphene may lead to paper electronics

In an advance that may lead to low-cost paper-based electronics, scientists, including one of Indian-origin, have developed a new laser treatment that allows printed graphene circuits to be used even on fragile surfaces.

Graphene, often touted as a wonder material, is great at conducting electricity and heat. It is strong and stable.

However, researchers have struggled to move beyond tiny lab samples for studying its material properties to larger pieces for real-world applications.

Recent projects that used inkjet printers to print multi-layer graphene circuits and electrodes had the engineers thinking about using it for flexible, wearable and low-cost electronics.

But there were problems with the existing technology. Once printed, the graphene needs to be treated to improve electrical conductivity and device performance.

That requires high temperatures or chemicals - both of which degrade flexible or disposable printing surfaces such as plastic films or paper.

Suprem Das, postdoctoral research associate and Jonathan Claussen, assistant professor at Iowa State University in the US came up with the idea of using lasers to treat graphene.

Researchers found that treating inkjet-printed, multi-layer graphene electric circuits and electrodes with a pulsed-laser process improves electrical conductivity without damaging paper, polymers or other fragile printing surfaces.

"This creates a way to commercialise and scale-up the manufacturing of graphene," Claussen said.

"The breakthrough of this project is transforming the inkjet-printed graphene into a conductive material capable of being used in new applications," Claussen said Those applications could include sensors with biological applications, energy storage systems, electrical conducting components and even paper-based electronics.

To make all that possible, the engineers developed computer-controlled laser technology that selectively irradiates inkjet-printed graphene oxide.

The treatment removes ink binders and reduces graphene oxide to graphene - physically stitching together millions of tiny graphene flakes. The process makes electrical conductivity more than a thousand times better.

"The laser works with a rapid pulse of high-energy photons that do not destroy the graphene or the substrate," said Das, who is 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 3D structures are like tiny petals rising from the surface, researchers said. The rough and ridged structure increases the electrochemical reactivity of the graphene, making it useful for chemical and biological sensors.

The findings were published in the journal Nanoscale.