A New Subcritical Nanostructure of Graphene—Crinkle-Ruga Structure and Its Novel Properties

Here, we report an experimental characterization of a new subcritical graphene nanostructure termed a crinkle ruga. Multilayer graphene forms crinkles as a periodic mode of buckling if the ratio of periodic buckling span to thickness is smaller than a critical value. Otherwise, it forms wrinkles. The crinkles have sawtooth-shaped profiles with their faces perfectly flat and the tips of the peaks and valleys highly curved. Our AFM measurements show that the width of the curvature focusing band at the tip is very narrow, e.g. smaller than 16 nm for a 6o crinkle, indicating a strong influence of flexoelectric coupling in crinkle formation. We also found that concavity or convexity of crinkle tips, i.e. parity of the crinkle, can be controlled. Due to the flexoelectric coupling, the concave tip at the crinkle valley is positively charged, and the convex tip at the crinkle peak negatively charged. In addition, here, we demonstrate that the charges at the crinkle tips can attract macromolecules in adsorption experiments. We show linearly-aligned adsorption of C60 along crinkle valleys on an HOPG surface. In another experiment, we exhibit period-doubled adsorption of lambda DNA on an HOPG surface, possibly caused by ion kinetics involved in the DNA adsorption along the crinkle valleys.