Surface diffusion of atoms is an important phenomenon in areas of materials processing such as thin-film growth and sintering. Self-diffusion (that is, diffusion of the atoms of which the surface is comprised) has been much studied on clean metal and semiconductor surfaces1,2. But in most cases of practical interest the diffusion happens on surfaces partly covered by atoms and molecules adsorbed from the gas phase. Adsorbed hydrogen atoms are known to be capable of both promoting and inhibiting self-diffusion3,4,5,6,7, offering the prospect of using adsorbed gases to control growth or sintering processes8,9,10,11. Here we derive mechanistic insights into this effect from observations, using the scanning tunnelling microscope, of hydrogen-promoted self-diffusion of platinum on the Pt(110) surface. We see an activated Pt–H complex which has a diffusivity enhanced by a factor of 500 at room temperature, relative to the other Pt adatoms. Our density-functional calculations indicate that the Pt–H complex consists of a hydrogen atom trapped on top of a platinum atom, and that the bound hydrogen atom decreases the diffusion barrier.
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We thank P. R. Rasmussen, T. R. Linderoth and B. Kasemo for discussions. This work was supported by the Danish National Research Foundation through the Center for Atomic-scale Materials Physics (CAMP), and by the VELUX and the Knud Højgaard foundations.
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