Graphene has many properties that researchers would love to use in various applications. It is strong and stable and conducts both heat and electricity extremely well. Based on carbon, graphene has a honeycomb structure and is only an atom thick. Researchers using it do however struggle with obtaining larger pieces for real world applications, as opposed to miniature lab samples used for studying its material properties. Researchers in Jonathan Claussen’s lab at Iowa State University have been trying to find ways to utilize graphene’s amazing properties in sensors and other technologies.
Following successful results by using inkjet printers to print multi-layer graphene circuits and electrodes, engineers started looking at how they could use graphene for flexible, wearable and low-cost electronics. Suprem Das, an Iowa State postdoctoral research associate in mechanical engineering and an associate of the U.S. Department of Energy’s Ames Laboratory, wondered if it were possible to make graphene in large enough quantities so it could be used for glucose sensors.
The existing technology has a number of drawbacks. The graphene has to be treated to improve device performance and electrical conductivity after it has been printed. That is normally done with chemicals, high temperatures or both. Disposable printing surfaces such as paper or plastic films degrades under these conditions and loses flexibility. Das and Claussen experimented with using lasers to treat the graphene. Claussen, an Iowa State assistant professor of mechanical engineering and an Ames Laboratory associate, collaborated with Gary Cheng, an associate professor at Purdue University’s School of Industrial Engineering, to prove the concept.
The experiment worked. Electrical conductivity is improved when using a pulsed laser process to treat inkjet-printed, multi-layer graphene electrodes and electric circuits. Polymers, paper or other fragile printing surfaces are not damaged by this process. Claussen notes that graphene manufacturing can now be increased and the material will become easy to commercialize. A spinoff of the research is that a new conductive material that can be used in many new applications has effectively been created. Possible new applications includes paper-based electronics, electrical conducting components, sensors with biological applications and energy storage systems.
To achieve this breakthrough, the engineers utilized laser technology that is computer controlled and selectively treats inkjet-printed graphene oxide. This method removes ink binders and reduces graphene oxide to graphene. The result is that millions of tiny graphene flakes are effectively stitched together. Electrical conductivity of the graphene is improved by more than a thousand times. Das explained that the laser uses a rapid pulse of high-energy photons that does everything locally – heating, bombarding and processing. As a result, the graphene or substrate is not affected or destroyed.
The localized laser processing has another side effect. The shape and structure of the printed graphene is changed from a flat surface to one with 3-D nanostructures that are raised. The 3-D structures can be compared to tiny petals rising from the surface and improves the electrochemical reactivity of the graphene. Biological and chemical sensors can now be manufactured from the rough and ridged structure.
Claussen and his team of nano-engineers write that all of this could move graphene to commercial applications. Numerous disposable, low-cost graphene-based applications including paper-based electronics with graphene circuits and electrochemical electrodes for medical devices, fuel cells, sensors and biosensors can now be created.
The full study was published in the journal Nanoscale.