New research from University of Illinois engineers combines atomic-level experiments with computer modeling to determine how much energy is needed to bend multilayer graphene – a question Scientists escaped since graphene was first isolated. The results were published in the journal Nature Materials of November 11, 2019.
Graphene – a single layer of carbon atoms arranged in a lattice – is the world's strongest and thinnest material flexible, the researchers said. It is considered as one of the key components of future technologies.
"The exciting thing about this work is that it shows that although everyone else disagreed, they were all right." – Arend van der Zande, Professor of Mechanical Science and Engineering
Most recent research on graphene targets the development of nanoscale electronic devices. Researchers say, however, that many technologies – from elastic 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 realize 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 dealing with graphene for two decades, we still have to resolve this fundamental property. The reason for this is that different research groups have found different answers that span orders of magnitude.
The team discovered why previous research efforts did not agree. "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. "However, we have found that graphs behave differently in these two situations. If you bend multilayer graphene a little, it looks more like a stiff plate or a piece of wood. If you bend it hard, it behaves like a pile of paper on which the atomic layers can slide past each other. "
" The exciting thing about this work is that it shows that although everyone else disagreed, in fact, all were right, "said Arend van der Zande, professor of engineering and co-author of the study." Each group measured something What we have discovered is a model to explain all the differences by showing how they all interact with each other through different degrees of bending. "
" Since we studied graphene that was bent in different amounts, We were able to see the transition from one regime to another, from rigid to flexible, and from sheet to sheet. "- Elif Ertekin, Professor of Mechanical Engineering
To make the curved graph, Yu made single atomic layers of hexagonal boron nitride, one other 2D material, at an atomic scale steps, then graphene over the top., cut with a focused ion beam Han took a disk of material and used an electron microscope to visualize the atomic structure to see where the individual graphene layers were.
Subsequently, the team developed a set 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.
In this simple structure, there are two types of forces involved in bending graphene, "said Pinshane Huang, a professor of materials science and engineering and co-author of the study. "Adhesion or attraction of atoms on the surface tries to pull the material down. The stiffer the material, the more it tries to retract to withstand the adhesive force. The form in which the graphene takes 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.
"Because we studied graphene To varying degrees, we were able to observe 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 is the part of Conducted research on computer modeling. "We built models on an atomic scale to show that it may cause the layers to slip over each other. After having this idea, we were able to 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. 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 also be very soft, "said van der Zande. "By utilizing interlayer slip, we have shown that the graphene can be orders of magnitude softer than traditional materials of the same thickness."
Reference: "Ultrasoft slip-shifted bending in a few layers of graphene" by Edmund Han, Jaehyung Yu, Emil Annevelink, Jangyup Son, Dongyun A. Kang, Kenji Watanabe, Takashi Taniguchi, Elif Ertekin, Pinshane Y. Huang, and Arend M. van der Zande, November 11, 2019, Nature Materials .
DOI: 10.1038 / s41563-019-0529-7
The National Science Foundation supported this research through the Illinois Materials Research Center.