The phrase "single atom" refers to an individual, tiny particle that cannot be broken down into any smaller parts. It is the smallest unit of a chemical element and is extremely small. Full definition
In addition to the unique energetic properties of single atoms, the CO2 conversation reaction was facilitated by the interaction of the nickel atoms with a surrounding sheet of graphene. (sciencedaily.com)
Instead of noble metal nanoparticles, they used single atoms of nickel. (sciencedaily.com)
This opens up the possibility of constructing extremely sensitive sensors with the ability to detect single atoms with light. (sciencedaily.com)