From Auto-Kirigami to Drumheads: Suspended, Self-Tearing, and Strained Graphene Nanostructures Formed by Nanoindentation

Nanoindentation of substrate-supported graphene can produce auto-kirigami (AK) structures: spontaneously folded and extended self-tearing nanoribbons up to several micrometers in length. However, the mechanisms governing their formation and yield are poorly understood. Here, we study graphene AK through statistical analysis of high-throughput experiments involving hundreds-fold arrays of indents on highly uniform regions of exfoliated monolayer and bilayer graphene, with no applied oscillation (in contrast with prior work). Post-mortem atomic force microscopy analysis reveals a baseline AK formation rate of 13-61% for monolayers and 0-17% for bilayers depending on inter-indent pitch. Force-distance curves of each type of nanostructure showed no appreciable differences. Moreover, graphene can remain intact after indentation, permitting formation of unbroken graphene suspended over or conformed within indents. Inter-indent pitch affects the absolute and relative formation rates of these nanostructures, attributed to indentation-induced tensile graphene strain. This advances the understanding of mechanisms for controlled formation of nanostructures, including twisted bilayers of graphene and other van der Waals materials.