Johnson, Tawfick advance moire pattern research
Two-dimensional materials, such as graphene, are a relatively new class of materials whose beneficial properties are still not fully understood by researchers. It has recently been observed that when sheets of these materials are stacked, they create a type of defect that can alter the material properties. These defects are caused by the interference pattern, also known as the moire pattern, between the layers.
“Any kind of grid pattern that is aligned on top of another grid pattern can form a moire pattern,” said Professor Harley Johnson, who has been awarded an NSF grant, along with Assistant Professor Sameh Tawfick, for the project, “Moire Patterns and the Mechanics of Defects and Interfaces in 2D Materials.”
These patterns can occur when two thin layers of a material with periodic structure, such as shear fabric or window screens, are layered atop one another. In electronics, these patterns can be observed when one takes a photo of an LED screen with a phone camera.
Researchers have been seeing these patterns in numerous studies of these two-dimensional materials, but they could not determine what they were or what effect they have. Johnson and Tawfick’s project is based on the realization that these patterns can be described by conventional theories, such as Taylor’s dislocation theory. Johnson and his team are working on computer-based simulations of the moire patterns, while Tawfick’s research group is working on nano-scale measurements and experimental mechanics.
While a major motivation for this project is to understand moire patterns in 2D materials, the researchers are also focused on the mechanical properties that come about because of the moire patterns. A greater understanding of the various properties could affect the development of new lubricants and coatings and in creating impact-resistant materials.
One property affected by moire patterns is the material’s friction. “It’s been shown that at certain twist angles, because of the moire, you can get really low friction between the sheets,” said Johnson.
The project also includes an outreach program in collaboration with the School of Art + Design, due to the visual nature of patterns. The collaborators hope to bring engineering and art students together to create activities for engineering camps that will get K-12 students thinking about how these patterns can be used as objects of art. They aim to bridge the gap between fine arts and engineering and introduce more students to STEM disciplines.