Control size, nanometer-scale, reaction vessels in two dimensions

Islands of monolayer vacancies can be generated on transition metal surface s by ion bombardment of samples held at elevated temperature. Our experimen ts show that the average size of the monolayer vacancy islands can be varie d in a controlled manner from 3 to 30 nm by adjusting the sample temperatur e. We also demonstrate that monolayer vacancy islands can be used as two-di mensional nanometer-scale catalytic "reaction vessels." The reactants are c onfined to the reaction vessels by energetic barriers to adsorbate diffusio n across the atomic steps that form the walls of the vessels. Reaction vess els with diameters of similar to3 nm can accommodate only a small number of reactant molecules (e.g., a maximum of 28 ethylene molecules can be adsorb ed in an area with a diameter of 3.3 nm on a Pt(lll) surface). Reactions wh ose products or rates depend on the number of reactant molecules that are a vailable can be controlled using these reaction vessels. This is demonstrat ed for the particular example of carbon particles that are formed from the dehydrogenation of mono-olefins on Pt.