New research by engineers at the University of Illinois combines atomic-scale experiments with computational modeling to determine how much energy is required to bend multilayer graphene ̵
Graphene – a single layer of carbon atoms that is arranged in a lattice – is the strongest material in the world and so thin that it is flexible, the researchers said. It is considered one of the key components of future technologies.
Most of the current research on graphene is aimed at the development of nanoscale electronic devices. Researchers say, however, that many technologies – from stretchable electronics to tiny robots that are so small that they can not be seen with the naked eye – require an understanding of the mechanics of graphene, especially the way it bends and bends, to exploit its potential.
"The flexural rigidity of a material is one of its most basic mechanical properties," said Edmund Han, a student and co-author of Materials Science and Engineering. "Although we have been studying graphene for two decades, we still need to solve this fundamental property, because different research groups have found different answers that span orders of magnitude."
The team discovered why earlier research efforts disagreed. "They either bent the material slightly or bent it hard," said Jaehyung Yu, a student of mechanical engineering and engineering and co-author of the study. "But we've found that graphs behave differently in these two situations: bending a multilayer graph a little bit more like a stiff plate or a piece of wood, bending it like a pile of paper Atomic layers can slip past each other. "
" The exciting thing about this work is that it shows that, although everyone else disagreed, everyone was right, "said Arend van der Zande, a professor of engineering and study co-author. "Each group measured something different, and what we discovered is a model to explain all the differences by showing how they are all related by different degrees of bending."
To make the curved graph, Yu made single hexagonal atomic layers of boron nitride, another 2D material, in atomic increments, then stamped the graph over it. Using a focused ion beam, Han cut a disk of material and used an electron microscope to image the atomic structure to see where the individual graphene layers were.
Subsequently, the team developed a series of equations and simulations to calculate the bending stiffness based on the shape of the graphene bend.
By draping multiple layers of graphene over a single-to-five-atom step, the researchers created a controlled and precise method to measure how the material bends over the step in various configurations.
There are two types of forces involved in bending graphene, "said Pinshane Huang, Professor of Materials Science and Engineering and study author." Adhesion or the attraction of atoms on the surface attempts to pull the material down , The stiffer the material, the more it will try to jump up again to resist its adhesion. The form in which the graphene takes the atomic steps "encodes all information about the stiffness of the material."
The study systematically controlled exactly how much the material flexed and how the properties of the graphene changed.
"As we studied graphene that was bent in varying amounts, we could see the transition from one regime to another, from rigid to flexible, and from sheet to sheet," said the professor of engineering and engineering, Elif Ertekin, who led the part of computer modeling research. "We built models on an atomic scale to show that it could cause the layers to slip over each other, and when we had that idea, we could confirm the slip between each layer using the electron microscope."  The new results have implications for the development of machines that are small and flexible enough to interact with cells or biological material.
"Cells can change their shape and react to their environment, and if we want to move towards microrobots or systems that have the capabilities of biological systems, we need electronic systems that can change their shape and are also very soft" said van der Zande. "By exploiting the interlayer slip, we have shown that graphene can be orders of magnitude softer than traditional materials of the same thickness."
Graphene is both 3-D and 2-D
Edmund Han et al., Ultrasoft-Mediated Bending in Multilayer Graphene, Nature Materials (2019). DOI: 10.1038 / s41563-019-0529-7
Graphene: The more you bend it, the softer it gets (2019, 14th November)
retrieved on November 14, 2019
This document is subject to copyright. Apart from any fair dealings for the purpose of private learning or research, no
Part may be reproduced without written permission. The content is for informational purposes only.