Grid (IMAGE) Penn State Caption A grain boundary forms when graphene growth advances past an apex on a conical bump, where the curvature resembles that on a sphere; it terminates at the foot of the bump, where curvature is saddle-like. Credit Crespi, Penn State Usage Restrictions Non commercial use 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.