The different elements found in nature each have their distinct isotopes. For carbon, there are 99 atoms of the lighter stable carbon isotope 12C for each 13C atom, which has one more neutron in its nucleus. Apart from this natural variation, materials can be grown from isotope-enriched chemicals. This allows scientists to study how the atoms arrange into solids, for example to improve their synthesis. Yet, most traditional techniques to measure the isotope ratio require the decomposition of the material or are limited to a resolution of hundreds of nanometers, obscuring important details.
Although atoms in graphene can be “seen” by shooting electrons through the material in what is called transmission electron microscopy, different isotopes can appear identical.
The results show that atomic-resolution electron microscopes can distinguish between different isotopes of carbon. Although the method was now demonstrated only for graphene, it can in principle be extended for other two-dimensional materials, and the researchers have a patent pending on this invention. “Modern microscopes already allow us to resolve all atomic distances in solids and to see which chemical elements compose them. Now we can add isotopes to the list”, Jani Kotakoski concludes.
Funding from the Austrian Science Fund (FWF), the Wiener Wissenschafts-, Forschungs- und Technologiefonds (WWTF), and the European Research Council (ERC) directly contributed to enabling the research.