Most industrial chemicals are the products of catalysis. A catalyst’s efficacy depends not only on its ability to facilitate and accelerate reactions but also on its ability to mix with reactants and spread, which, on a surface, is determined by lateral diffusion. Despite the importance of surface diffusion, researchers have yet to observe and understand all its basic atomic-scale dynamics.

Early diffusion studies focused on clean or sparsely populated surfaces with quick diffusion rates. But when the density of atoms increases or there are two or more different species on the surface, as is often the case in industrial processes, diffusion becomes more complicated. Intuitively, one expects higher density and the presence of other particles to slow down diffusion as the adsorbed species get in each other’s way. But that doesn’t have to be the case.

Joost Wintterlin of the Ludwig-Maximilians University Munich and his colleagues have taken a step...

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