Bimetal Nanocube Siding

By adjusting the rate at which silver nitrate is added to a solution containing palladium nanocubes, materials scientists can precisely control whether silver atoms stick to and grow on one, three, or all six sides of the cubes (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201107061). Such bimetallic nanocrystals are of interest for their use in photonics and as tandem catalysts. At slow AgNO₃ addition rates, Younan Xia of Washington University in St. Louis and coworkers obtained palladium nanocubes with silver attached to one side. At moderate rates, silver deposited on three adjacent sides of the cubes, and at fast rates, silver formed a shell around the palladium cubes by adhering to all six sides. Xia says this deposition selectivity occurs because of supply and demand: At slow AgNO₃ addition rates, the concentration of silver is so low that nucleation and growth are limited to one side of the cubes. At moderate rates, the nucleation can spread to adjacent sides, and at fast rates, it’s unlimited. Bimetallic nanocrystals may be fabricated by other methods, Xia says, but this one is the first to “precisely control the sites at which heterogeneous nucleation and growth are initiated.” The approach should be applicable to other bimetallic systems, he adds.