Islands of monolayer vacancies can be generated on transition metal surfaces by ion bombardment of samples
held at elevated temperature. Our experiments show that the average size of the monolayer vacancy islands
can be varied in a controlled manner from 3 to 30 nm by adjusting the sample temperature. We also demonstrate
that monolayer vacancy islands can be used as two-dimensional nanometer-scale catalytic “reaction vessels.”
The reactants are confined to the reaction vessels by energetic barriers to adsorbate diffusion across the atomic
steps that form the walls of the vessels. Reaction vessels with diameters of ∼3 nm can accommodate only a
small number of reactant molecules (e.g., a maximum of 28 ethylene molecules can be adsorbed in an area
with a diameter of 3.3 nm on a Pt(111) surface). Reactions whose products or rates depend on the number
of reactant molecules that are available can be controlled using these reaction vessels. This is demonstrated
for the particular example of carbon particles that are formed from the dehydrogenation of mono-olefins on
Pt.
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