For the first time, chemists have taken before-and-after photographs of molecules involved in a chemical reaction. The pictures show how individual carbon atoms - and the chemical bonds between them - rearranged on a metal surface.
The researchers took their pictures with an atomic force microscope (AFM), which works rather like a record player. It has a probe with an incredibly sharp metal tip - and that has a single molecule of carbon monoxide stuck to it. As the oxygen atom moves across the surface, it jogs up and down in response to the electrons spread around the molecule being studied. That jiggling is detected by a laser bouncing off the top of the probe, and converted into an image.
IBM scientists first used this technique in 2009, to image a very simple carbon molecule called pentacene. In the latest research, led by Felix Fischer at the University of California, Berkeley, the scientists have used the technique to understand how a chemical reaction works. Chemists usually have to infer these mechanisms through indirect techniques: infrared spectroscopy reveals the presence of chemical bonds that absorb certain frequencies of light, for example. Using AFM, you can see directly what has happened to the atoms, in pictures that look like textbook diagrams of carbon-based molecules.
Fischer's team started with a zig-zag molecule made of three benzene rings joined together with more carbon atoms, and stuck it to a silver surface. They cooled it to 4K (-269°C) with liquid helium to take the 'before' snapshot - warmed it up to 90°C to run the reaction - then cooled it again to take the 'after' photo.
The scientists are now using the technique to help build precisely-tailored forms of graphene - an atom-thin honeycomb of carbon atoms that has been the darling of materials science for the past decade, because of its incredible strength, flexibility, and electrical properties. It could also show how reactions happen on catalytic metal surfaces, they suggest.