New research by University of Illinois engineers combines atomic testing with computer modeling to determine how much energy is needed to bend a multilayer graphene – a question that has eluded scientists since graphene was first isolated. The findings were reported in the journal Materials of Nature on November 11, 2019.
Graphene – a single layer of atoms and carbon arranged in a living room – is the strongest material in the world and This skin is flexible, the researchers said. It is considered one of the key components of future technologies.
"What makes this work so interesting is that even though everyone disagrees, they are all right." – Arend van der Zande, Professor of Mechanical Science and Engineering
Most current research on graphene targets the development of nanoscale electronic devices. However, researchers say many technologies – from scattered electronics to small robots that they can't see with the naked eye – require an understanding of the mechanics of graphene, especially if how flexible it is and bend it, to unlock their potential.
"The bending stiffness of a material is one of the major mechanical properties of this material," says Edmund Han, a graduate student in science and engineering and study co-author . "Although we have been studying graphene for two years, we still have to solve this very important property. The reason is that different research groups have different answers." encompasses the orders of greatness. ”
The team discovered why previous research efforts disagree. "Either they bend the material a little or bend it a lot," says Jaehyung Yu, a mechanical engineering and engineering graduate student and study co-auth or. "But we found that graphene behaves differently in these two situations. When you bend a multilayer graphene a little, it acts like a hard plate or a piece of wood. When you bend it, it acts like a stack of papers on which atomic layers can pass through each other. "
" What is interesting about this work is that it is shown that even though everyone disagrees, they are all right, "says Arend van der Zande, a professor of mechanical science and engineering and study co-author. "Each group has a different dimension. Our findings are a model to explain all disagreements by showing how they are all interrelated through different degrees of bending."
"Because we study graphene that is bent by different values, we have seen the transition from one regime to another, from durable to flexible and from plate to sheet behavior. "- Elif Ertekin, Professional Science and Technical Technology
To produce bent graphene, Yu produced individual atomic layers of hexagonal boron nitride, another 2D material, in atomic-scale steps , then stamped graphene on top. Using a focused ion beam, Han cut a slice of material and imaging the atomic structure with an electron microscope to see where each graphene layer was sitting.
The team then developed a set of equations and simulations to calculate bending stiffness using graphene bend shape.
By drilling multiple layers of graphene at a step of only one to five atoms high, the researchers created a controlled and accurate way of measuring how the material would bend in step in different arrangements.
"In this simple structure, there are two types of forces involved in bending graphene," says Pinshane Huang, a professor of science and engineering and study co-author. "The adhesive, or the attraction of atoms to the surface, tries to pull the material in. The more material it holds, the more it tries to pop up, it stops pulling the adhesive. atoms include all information on the stiffness of the material. ”
The study systematically controlled exactly how much material was bent and how the properties of graphene changed.
" we studied graphene bending of different values, we saw the transition from one regime to another, from rigid to flexible and from plate to sheet behavior, "says mechanical science and engineering professor Elif Ertekin, who heads the computer modeling portion of the research. "We have built atomic-scale models to show that the most probable cause for this is the individual layer a y can be slippery on each other. When we came up with this idea, we used electron microscopy to confirm the slip between individual layers. ”
The new results have implications for the production of machines that are small and flexible enough for cells or biological materials. , the researchers said.
"Cells can change shape and respond to their environment, and if we want to move in the direction of microrobots or systems capable of biological systems, we need to have electronic systems that can change of their shape and become soft as well, "van der Zande said. "By exploiting the interlayer slip, we have shown that graphene can be orders of magnitude softer than conventional materials of the same thickness." 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, Materials of Nature .
DOI: 10.1038 / s41563-019-0529-7
The National Science Foundation, through the Illinois Materials Research Center, supported this research.