Anomalous twin boundaries in two dimensional materials
Journal: Nature Communications
Publication Date: 05 September, 2018
Surprises found in graphene folds
Researchers at The University of Manchester have discovered how to predict the microstructural features that will be present when bending van der Waals (vdW) materials, depending on the thickness of the material and the angle it is bent to. While characterising deformed microstructures in graphite, hBN and MoSe2 using atomic resolution scanning transmission electron microscopy we observed that special angle “twin” boundaries form for particular bending conditions. Unlike in conventional metals, ceramics and even in text book examples, in vdW materials the energy is minimised by twin boundaries being delocalised over several nanometers. The research also finds that there is a critical thickness below which twin boundaries are not formed. The synthesis of 2D materials from their bulk crystals often relies on a poorly understood process by which a bulk material is repeatedly cleaved via shear forces. This research goes some way to explain why exfoliation (liquid phase or scotch tape) produces many sheets of material >30 basal planes thick, and yet comparatively few below this. In addition, these vdW twin defects can induce changes in layer stacking, and hence in the optical behaviour of the crystals, which could be harnessed for optoelectronic applications.
- A single layer of graphene is incredibly easy to fold without breaking, making the material a great candidate for flexible electronics and wearable technology
- Not all two dimensional (2D) materials are as flexible as graphene – generally 2D materials are harder to bend as they get thicker and have more complicated atomic structures
- 2D and vdW materials can exist with the atomic planes layered together in different ways and these different stacking sequences can change the properties of the material
- A twin boundary is where the crystals on either side of a plane are mirror images of each other.
- Twin boundaries can form as a result of tensile or thermal stress and often effect the resulting properties of the material.
- Institute of Textiles and Clothing, Polytechnic University, Hung Hom, Hong Kong
- Center for Multidimensional Carbon Materials, Institute for Basic Science (IBS-CMCM)/School of Material Science and Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Korea
- National Graphene Institute