Researchers from AMBER, the SFI Research Centre for Advanced Materials and BioEngineering Research, the School of Physics and the CRANN Institute, at Trinity College Dublin, have helped to discover a relationship between the size and thickness of flakes of two-dimensional, “2D”, materials. This may have significant consequences for the viability and roll-out of mass-produced nanotechnology based on these extremely thin, exotic particles. The findings of the research provides new opportunities for rapidly identifying industrially mass-producible 2D materials, which are promising candidates for a range of applications such as solar cell and laser technology, high-power capacitors, medical bio-sensing, and chemical catalysis, and even next-generation computing and data storage.
The research published in the prestigious American Chemical Society journal ACS Nano involved the creation and detailed analysis of graphene, the famously strong and thin 2D material, in addition to ten more recently discovered 2D materials. The team, including Profs. Coleman and O’Regan at Trinity College Dublin, combined experimental and theoretical techniques to identify a common trend among the 2D flakes that relates their face area to their thickness. The team were able to determine that, on average, whenever the thickness doubles, the face area also quadruples. This newly-found characteristic trend was observed across very different 2D materials made from a wide range of chemical elements.
The team discovered this remarkably simple rule in the context of 2D flakes made by immersing ordinary 3D materials into a mechanically vibrated liquid. This process, known as liquid-phase exfoliation, has been pioneered by Prof. Jonathan Coleman, School of Physics and AMBER principal investigator at Trinity College Dublin. As it is relatively simple, inexpensive, and widely-applicable, this technique is a leading contender for the large-scale industrial roll-out of 2D material fabrication. Finding out which 3D parent materials will produce many large-but-thin 2D flakes when processed in this way, the study shows, can be predicted by comparing how tough the 3D parent is when you try to stretch it in two different directions. This provides a very useful, easy-to-use indicator to help in the selection of 2D materials applicable to consumer devices and nanotechnology.
The theory that Prof. O’Regan and Coleman have developed fully explains the new rule that has emerged from the comprehensive, eleven-material data set generated and analysed in a novel approach developed by their collaborator and paper lead-author Dr Claudia Backes and her team at the Chair of Applied Physical Chemistry at the University of Heidelberg. It is further bolstered by state-of-the-art quantum-mechanical supercomputer simulations performed on the materials by the group of Prof. Nicola Marzari at EPFL, in Switzerland. The data from these simulations enabled the two researchers at Trinity College Dublin to theoretically connect a 2D flake’s shape and its toughness, for the first time. Essentially, their new theory proposes that energy must be equally shared out when the faces and edges of new 2D flakes are made, due to a principle called equipartition.
“This work was extremely exciting to carry out,” says theoretician Prof. David O’Regan, “because we were seeing the trends emerge from the experimental data in real time, at the same time that we were developing the model. It’s ideal when theory and experiment can work in tandem like that.” Looking forward to the next steps, O’Regan remarked “Now that we can explain the data accurately, we will start to make predictions. Based on a quick desktop simulation of a solid, we can suggest whether or not its 2D analogue will form nice thin flakes. This could speed up the discovery of viable 2D materials, and lower its cost.”
Link to the ACS Nano paper: https://pubs.acs.org/doi/10.1021/acsnano.9b02234
Figure reprinted with permission from ACS Nano 2019 13, 6, 7050-7061. Copyright 2019 American Chemical Society.