Engineers treat printed graphene with lasers

RESEARCHERS have developed a method of treating printed graphene with lasers to enable paper-based electronics in sensors and other technologies.

A team from Iowa State University, US has been investigating methods of securing the graphene to paper surfaces without damaging them. The honeycomb structure of one-atom thick graphene allows it to be a great conductor of heat and electricity.

Recent projects that used inkjet printers to print multi-layer graphene circuits and electrodes showed the potential for use in flexible, wearable and low-cost electronics. However, once printed, the graphene had to be treated further using chemicals or temperatures between 200–400°C to improve the electrical conductivity to make it sufficiently conductive for electronics and sensors, thereby chemically destroying or burning the paper or polymer bases.

The team used a pulsed-laser process to treat the graphene. They found the technique was able to improve the electrical conductivity and did not damage the paper, polymers or other fragile printing surfaces.

The team achieved this by developing 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 graphene flakes. The process increases electrical conductivity by more than a thousand times.

Suprem Das, an Iowa State postdoctoral research associate in mechanical engineering, said: “The laser works with a rapid pulse of high-energy photons that do not destroy the graphene or the substrate. They heat locally.”

Localised laser processing also changes the shape and structure of the printed graphene from a flat surface to one with raised 3D nanostructures. The rough and ridged structure increases the electrochemical reactivity of the graphene, making it useful for chemical and biological sensors.

Jonathan Claussen, assistant professor at Iowa State, said: “The breakthrough of this project is transforming the inkjet-printed graphene into a conductive material capable of being used in new applications.” Such applications might include paper circuit boards, sensors with biological applications, energy storage systems, electrical conducting components, and paper-based electronics.

Claussen told The Chemical Engineer the printing and laser processes can be scaled up for roll-to-roll manufacturing of electronics. He said this could lead to a high yield, low-cost environment for graphene-based electronics production.

He added that next step will be to focus on developing specific commercial products using this technology in the field of disposable and wearable biosensors. For example the graphene could be printed onto sticking plaster or temporary tattoo paper, so that the biosensor is stuck to the skin and monitors chemical analytes in sweat. He also imagines the technology could be incorporated in a wide range of applications that require low-cost and disposable electronics.

The Iowa State Research Foundation has filed for a patent on the technology.

Nanoscale, DOI: http://doi.org/bqb8