Nanoengineers have found that using lasers can improve the electrical conductivity of graphene circuits without degrading the delicate material they’re printed on.
“The laser works with a rapid pulse of high-energy photons that do not destroy the graphene or the substrate.”
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. For example, “Could we make graphene at scales large enough for glucose sensors?” asks Suprem Das, a postdoctoral research associate in mechanical engineering at Iowa State University and an associate of the US Department of Energy’s Ames Laboratory.
But there were problems with the existing technology. Once printed, the graphene had to be treated to improve electrical conductivity and device performance. That usually meant high temperatures or chemicals—both could degrade flexible or disposable printing surfaces such as plastic films or even paper.
Let’s use lasers
Das and Jonathan Claussen came up with the idea of using lasers to treat the graphene. Claussen, an Iowa State assistant professor of mechanical engineering and an Ames Laboratory associate, worked with Gary Cheng, an associate professor at Purdue University’s School of Industrial Engineering, to develop and test the idea.
And it worked: They found 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 commercialize and scale-up the manufacturing of graphene,” Claussen says. “The breakthrough of this project is transforming the inkjet-printed graphene into a conductive material capable of being used in new applications.”
Those applications could include sensors with biological applications, energy storage systems, electrical conducting components, and even paper-based electronics.
‘They bombard locally’
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,” Das says. “They heat locally. They bombard locally. They process locally.”
That localized, 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 write 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 findings appear in the journal Nanoscale. The National Institute of Food and Agriculture of the US Department of Agriculture, the Roy J. Carver Charitable Trust, and Iowa State’s College of Engineering and department of mechanical engineering support the work.
The Iowa State Research Foundation Inc. has filed for a patent on the technology.
Source: Iowa State University