Auto-Kirigami: How to Make Graphene Perform Acrobatics
We present an exploration of auto-kirigami (AK), where a nanoscale mechanical probe is used to trigger the self-assembly of stacked multilayer structures of graphene and other 2D materials with lateral dimensions up to micrometers in size. AK exploits the atomic-scale thickness, high out-of-plane flexibility, significant self-adhesion, and ultralow intrinsic friction of 2D materials. In AK, graphene ribbons spontaneously fold, tear, taper, and propagate by sliding over an underlying graphene host sheet. By scanning with a nanoscale atomic force microscope (AFM) tip, we controllably trigger AK formation in graphene by using applied contact forces, or by using electrochemical etching combined with applied contact forces. From this we observe clear shape anisotropy of the AK structures, and quantization of the AK propagation direction. These effects are explained by using continuum mechanics and atomistic modeling to explain the relationship between AK tearing angles, AFM cutting directions, friction anisotropy, and graphene’s lattice orientation. From this, we propose a method to fabricate stacked graphene with pre-determined interlayer twist angles via tip-induced shear, offering potential applications in semiconductors, twistronics, and beyond.
Bio: Robert Carpick is the John Henry Towne Professor of Mechanical Engineering and Applied Mechanics at the University of Pennsylvania. He studies nanotribology, nanomechanics, scanning probes, and mechanochemistry. He is a recipient of numerous awards including the AVS Nanotechnology Recognition Award and the Midwest Mechanics Speakership. He is a Fellow of several societies including the ASME, the American Physical Society, the Materials Research Society, and the Society of Tribologists and Lubrication Engineers. He holds 10 patents, has authored over 220 journal publications, and is co-author of the textbook “Tribology on the Small Scale”. He received his B.Sc. (University of Toronto, 1991), his Ph.D. (University of California at Berkeley, 1997) in physics and was a postdoctoral researcher at Sandia National Laboratory. He served as MEAM department chair from 2011-2019.