Apr 13 2021
Using a method similar to magnetic resonance imaging (MRI), scientists have tracked the real-time movement of individual atoms as they combine together to create 2D materials, which have a thickness of just one atom.
2D materials. Image Credit: Seagul from Pixabay.
Published in the Physical Review Letters journal, the results could be used for designing new kinds of materials as well as quantum technology devices. The team from the University of Cambridge recorded the atom movements at speeds that are eight orders of magnitude too quick for traditional microscopes.
Graphene and other similar 2D materials are capable of enhancing the performance of new and existing devices because of their special properties, like excellent strength and conductivity.
Such 2D materials have a broad range of promising applications, ranging from drug delivery and bio-sensing to quantum computing and quantum information. But to reach their full potential, the properties of these 2D materials had to be further adjusted via a regulated growth process.
Such materials are typically formed as atoms 'jump' onto a supporting substrate until they bind to an increasing cluster.
The ability to track this process offers investigators relatively more control over the final materials.
But for the majority of the materials, a process like this occurs so rapidly and at such increased temperatures that it can only be tracked by using images of a frozen surface, recording a single moment instead of the entire process.
Scientists from the University of Cambridge have now monitored the whole process in real-time, at temperatures that were similar to those employed in the industry.
The investigators employed a method called 'helium spin-echo,' which has been designed in Cambridge over the past 15 years. While this method is similar to MRI, it utilizes a beam of helium atoms to 'illuminate' the surface of a target, analogous to light sources used in day-to-day microscopes.
Using this technique, we can do MRI-like experiments on the fly as the atoms scatter. If you think of a light source that shines photons on a sample, as those photons come back to your eye, you can see what happens in the sample.
Dr Nadav Avidor, Study Senior Author and Cavendish Laboratory, University of Cambridge
But instead of using photons, Avidor and his collaborators used helium atoms to see what exactly happens on the sample surface. The interaction between helium and atoms at the surface helps infer the movement of the surface species.
The investigators used a test specimen of oxygen atoms moving on the ruthenium metal surface and captured the spontaneous breakdown and formation of clusters of oxygen, which measure only a few atoms in size, and also recorded the atoms that rapidly diffuse between the oxygen clusters.
This technique isn’t a new one, but it’s never been used in this way, to measure the growth of a two-dimensional material. If you look back on the history of spectroscopy, light-based probes revolutionised how we see the world, and the next step – electron-based probes—allowed us to see even more.
Dr Nadav Avidor, Study Senior Author and Cavendish Laboratory, University of Cambridge
“We’re now going another step beyond that, to atom-based probes, allowing us to observe more atomic scale phenomena. Besides its usefulness in the design and manufacture of future materials and devices, I’m excited to find out what else we’ll be able to see,” concluded Dr Avidor.
The study was performed in the Cambridge Atom Scattering Centre and funded by the Engineering and Physical Sciences Research Council (EPSRC).
Journal Reference:
Kelsall, J., et al. (2021) Ultrafast diffusion at the onset of growth: O=Ru(0001). Physical Review Letters. doi.org/10.1103/PhysRevLett.126.155901.