An IR CO2 laser operating at room temperature can turn cheap polymer into multilayer graphene with heightened electrical conductivity and capacitance. Researchers at Rice University say their one-step laser-induced graphene (LIG) process could enable rapid, roll-to-roll manufacturing of nanoelectronics. “This will be good for items people can relate to: clothing and wearable electronics like smartwatches that configure to your smartphone,” said professor Dr. James Tour. The Rice University mascot is produced on a flexible polyimide sheet by burning a graphene foam pattern into it with a laser. The scale bar is 1 mm. Images courtesy of the Tour Group/Rice University. The technique works by converting sp3-carbon atoms into sp2-carbon atoms through pulsed laser irradiation. The resulting LIG is porous and about 20-µm thick. Because the laser does not cut all the way through, it remains attached to the flexible polyimide substrate. Typically, graphene has a hexagonal molecular structure, being composed of interconnected six-atom carbon rings. LIG is made up of overlapping flakes of five-, six- and seven-atom carbon rings. These defects allow LIG, unlike typical graphene, the ability to trap electrons and store a charge. “Theoretical methods and density functional computations allowed us to look inside the electronic energy states’ organization,” said professor Dr. Boris Yakobson. “What we discovered is that the very low density of available states — which is crucial for the layer capacitance — increases dramatically, due to various topological defects, mainly pentagonal and heptagonal rings. The fact that highly defective graphene performs so well is a freebie, a gift from nature.” A scanning electron microscope image of laser-induced graphene foam. The scale bar for the main image is 10 µm; the bar for the inset is 1 µm. The best results showed capacitance of more than 4 mF/cm2 and power density of about 9 mW/cm2, comparable to other carbon-based microsupercapacitors. Degradation was negligible after as many as 9000 charge-discharge cycles. Funding came from the U.S. Air Force Office of Scientific Research and its Multidisciplinary University Research Initiative (MURI), the Office of Naval Research MURI, the National Center for Research Resources, the National Science Foundation Partnerships for Research and Education in Materials and the National Institute on Minority Health and Health Disparities, part of the National Institutes of Health. The work was published in Nature Communications (doi:10.1038/ncomms6714). For more information, visit www.rice.edu.
CO2 Laser Sources