Researchers at Iowa State University Jonathan Claussen Labs, who like to call themselves nano-engineers, are always looking for ways to use graphene and its amazing properties in their sensors and other technologies.
Graphene is a magical material: this carbon honeycomb structure is only one atom thick. It has good electrical and thermal conductivity; it is strong and stable. But researchers have been struggling with pushing small samples of labs used to study material properties to bigger pieces that can be used in practical applications.
The recent project to print multilayer graphene circuits and electrodes with inkjet printers has led engineers to consider using it for low-cost flexible, wearable electronics. For example, "Can we make graphene that's big enough for a glucose sensor?" Suprem Das asked. He is a postdoctoral research assistant in mechanical engineering at Iowa State University and an assistant at the Ames Laboratory at the U.S. Department of Energy.
However, existing technologies have some problems. After graphene has been printed, it must be processed to improve conductivity and device performance. This usually means high temperatures or chemicals - both of which can degrade the flexible or disposable printing surface such as plastic film or paper.
Iowa State University engineers are developing practical, low-cost graphene applications.
Das and Claussen came up with the idea of ​​using laser to process graphene. Claussen, an assistant professor of mechanical engineering at Iowa State University and an Ames lab assistant, developed and experimented with Gary Cheng, associate professor of industrial engineering at Purdue University.
The results prove to be viable: they found that pulsed laser processing of ink-jet printed multilayer graphene circuits and electrodes increases conductivity without damaging paper, polymers or other delicate printed surfaces.
"This will create a way to commercialize and scale graphene production," Claussen said.
The study is published on the cover of the 35 issue of Nanoscale magazine. Claussen and Cheng are correspondence authors and Das is the lead author. Other co-authors from Iowa State University include Allison Cargill, John Hondred and Shaowei Ding, graduate students in mechanical engineering. Other co-authors from Purdue University include Qiong Nian and Mojib Saei, graduate students in industrial engineering.
Two major funds have funded the project and related research: a three-year grant of funded by the USDA National Institute of Food and Agriculture and a three-year grant from Roy J. Carver Charitable Trust. Iowa State University Engineering and Mechanical Engineering also funded the study.
The Iowa State University Research Foundation company has applied for a patent for the technology.
"The breakthrough of this project is to convert ink-jet printed graphene into a conductive material that can be used for new applications," Claussen said.
These applications may include sensors for biological applications, energy storage systems, conductive elements, and even paper-based electronics.
To make it all possible, engineers have developed computer-controlled laser technology that selectively irradiates inkjet-printed graphene oxide. This process removes the ink binder and reduces the graphene oxide on the graphene - physically splicing millions of small graphene sheets. The process increased conductivity by more than a thousand times.
"The laser uses a fast pulse of high-energy photons that does not damage graphene or the substrate," Das said. "They are heated locally, they are partially bombed and they are handled locally."
The localized laser processing also transforms the shape and structure of printed graphene from a flat surface into a raised three-dimensional nanostructure. Engineers say the three-dimensional structure is like tiny petals rising from the surface. Rough ridged structure increases the electrochemical reactivity of graphene, making it useful for both chemical and biological sensors.
According to the team of nano-engineers at Claussen, all of this will make graphene commercially available.
"This work not only paves the way for paper-based electronics with graphene circuits," the researchers wrote in their paper: "It also makes it possible to include sensors, biosensors, fuel cells and (medical ) Devices and other countless applications of low-cost disposable graphene-based electrodes possible.
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