Hexagonal Graphene 'Onion Rings' (IMAGE) Rice University Caption Structural models of hexagonal graphene "onion rings" show a layer of graphene, a single-atom-thick sheet of carbon, atop a set of concentric nanoribbons. The ribbons grow by chemical vapor deposition in a high-pressure, hydrogen-rich atmosphere. Credit Yuanyue Liu/Rice University Usage Restrictions For news reporting purpose only. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.