(TTF)Br crystallites that nucleate and grow on platinum particles exhibit widths that are linearly related to the diameter of the platinum particles on which they grow. Populations of long (TTF)Br crystallites having a predetermined width can be prepared by electrodeposition onto surfaces covered with size-monodispersed platinum catalyst particles. The Figure shows an SEM image of a (TTF)Br nanocrystallite grown on a cluster of Pt particles.