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The more you bend it, the softer it is



November 13, 2019

(News from NanoverkNew research by University of Illinois engineers combines atomic-scale experimentation with computer modeling to determine how much energy is needed to bend multilayer graphene – a question left by scientists since the first isolation of graphene.

The findings are reported in the journal Natural materials ("Ultrasoft Sliding Interface in Graphic Sliding").

Graphene – the only layer of carbon atoms deployed in a grid – is the strongest material in the world and so thin that it is flexible, researchers say. It is considered one of the key ingredients of future technologies.Curve Illustration in Biller GrafenCurve Illustration in Biller Grafen. (Graphic: Blanka Janicek, Pincan Huang Lab)

Most of the current graphene research is aimed at developing nano-scale electronic devices. However, researchers say many technologies – from stretching electronics to tiny robots so small that they cannot be seen with the naked eye – require an understanding of graphene mechanics, especially how they flex and bend, to unlock their potential.

"The stiffness of the material bends is one of its most basic mechanical properties," said Edmund Hahn, a graduate student and co-author of studies in science and engineering. "Even though we have been studying graphs for two decades, we still do not have to settle this fundamental property. The reason is that different research groups have come up with different answers that include orders of magnitude. "

The team discovered why previous research efforts disagreed. "They either bent the material a little bit or bent it a lot," said Ehjeung Shu, a graduate of mechanical engineering and engineering and a study co-author. "But we found that graphene behaves differently in these two situations. When you bend a bit with multilayer graphene, it acts more like a solid plate or piece of wood. When you bend a lot, it acts like paper stacks where the atomic layers can slide one next to each other. "

"What is exciting about this work is that it shows that while not everyone disagreed, they were actually correct," said Arend van der Zande, a professor of mechanical science and engineering and co-author of studies. “Each group measured something different. What we found is a model that explains all the disagreements by showing how they are all linked together through different degrees of bending. "

To make the graphene bent, Hu invented individual atomic layers of hexagonal boron nitride, another 2D material, in atomic-scale steps, and then sealed the graphene upwards. Using the focused ion beam, Ian cut a piece of material and displayed the atomic structure with an electron microscope to see where each layer of graphene sits.

The team then developed a set of equations and simulations to calculate the bending stiffness using the graphene bending form.

By drilling multiple layers of graphene in a step of only one to five atoms, the researchers developed a controlled and precise way of measuring how the material would bend over the step in different configurations.

"In this simple structure, there are two types of forces involved in bending graphene," said Pynshan Huang, professor of materials science and engineering and co-author of the study. "The adhesion, or the attraction of atoms on the surface, tries to tear the material down. The harder the material, the more it will try to appear back, as opposed to pulling adhesion. the hardness of the material. "

The study systematically controlled exactly how the material bent and how the properties of the graphene changed.

"Because we were studying graphene sloping in different quantities, we were able to see the transition from one regime to another, from rigid to flexible, and taken to the plate," said mechanical science and engineering professor Elif Ertekin, who led the modeling section of research computers. "We have built atomic scale models to show that the reason that can happen is that individual layers can slide over each other. Once we had this idea, we were able to use an electron microscope to confirm sliding between individual layers ".

The new results have implications for creating machines that are small and flexible enough to communicate with cells or biological material, the researchers said.

"Cells can change shape and respond to their environment, and if we want to move in the direction of microbes or systems that have the capabilities of biological systems, we need to have electronic systems that can change their shape and be very soft. , "Said van der Zand. "By utilizing the sliding of the interlayer, we have shown that graphene can be smaller in size than conventional materials of the same thickness."


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