Researchers have used a technique similar to MRI to track the movement of individual atoms in real time as they cluster together to form two-dimensional materials, which are a single atomic layer thick.
The results, reported in the journal Physical Review Letters, could be used to design new types of materials and quantum technology devices.
The University of Cambridge researchers have recorded the atoms’ motion at speeds eight orders of magnitude too fast for conventional microscopes.
Two-dimensional materials, such as graphene, have the potential to improve the performance of existing and new devices due to their unique properties, such as excellent conductivity and strength.
Two-dimensional materials have a wide variety of potential applications, from biosensing and drug delivery to quantum information and quantum computing.
However, for two-dimensional materials to reach their full potential, their properties must be refined through a controlled growth process.
These materials normally form as atoms ‘jump’ on a supporting substrate until they attach to a growing cluster.By being able to monitor this process, scientists gain much more control over the finished materials
. However, for most materials, this process is so rapid and at such high temperatures that it can only be tracked using snapshots of a frozen surface, capturing a single moment rather than the entire process.
“This technique is not new, but has never been used in this way to measure the growth of a two-dimensional material.” – Nadav Avidor
Now researchers at the University of Cambridge have been monitoring the entire process in real time, at temperatures comparable to those in the industry.
The researchers used a technique known as “helium spin echo” developed in Cambridge over the past 15 years.
The technique has similarities to magnetic resonance imaging (MRI), but uses a beam of helium atoms to ‘illuminate’ a target surface, similar to light sources in everyday microscopes.
“This technique allows us to perform MRI-like experiments while the atoms are scattering,” said Dr. Nadav Avidor of the Cavendish Laboratory in Cambridge, the paper’s senior author.
“If you think of a light source that shines photons on a sample while those photons come back into your eye, you can see what is happening in the sample.” Instead of photons, Avidor and his colleagues use helium atoms to observe what is happening on the surface of the sample.
The interaction of the helium with atoms on the surface allows the motion of the surface species to be deduced. Using a test sample of oxygen atoms moving across the surface of ruthenium metal, the researchers recorded the spontaneous breaking and formation of oxygen clusters, only a few atoms in size, and the atoms rapidly diffusing between the clusters.
“This technique is not new, but has never been used in this way to measure the growth of a two-dimensional material,” said Avidor. “If you look back at the history of spectroscopy, light-based probes have revolutionized how we see the world, and the next step – electron-based probes – allowed us to see even more.
“We are now taking it a step further, towards atomic-based probes, allowing us to observe more phenomena on an atomic scale. In addition to its usefulness in designing and manufacturing future materials and devices, I am curious what else we will see.”