Thin films: Small 10/2010

The cover picture shows the mechanics of the tearing of a ribbon from a single-layer graphene sheet attached to an adhesive substrate, simulated using molecular dynamics with a first-principles-based reactive force field. The overlay shows the torn part of the sheet and the resulting rough edges at the atomic scale largely consist of characteristic armchair surface termination. The underlying color plot shows the out-of-plane deformation in the section of the sheet still attached to the substrate. The concentrated region of large deformation (red and blue color) right below the tearing flap in contrast to zero deformation in regions away from the flap (green color) causes large shear stresses, leading to shear rupture in the sheet. The tearing results in the formation of tapered nanoribbons, where the tapering angle can be controlled by adhesion strength to the substrate and number of graphene layers torn off. Considering graphene as a model 2D material, experiments, atomistic simulation, and theory provide fundamental insight into the energetics of tearing that can be extended to other 2D nanoscale thin films attached to substrates. For more information, please read the Full Paper “Tearing Graphene Sheets From Adhesive Substrates Produces Tapered Nanoribbons” by M. J. Buehler et al., beginning on page 1108.