We describe the preparation of long (> 1.0 µm) nanocrystallites of an electronically conductive organic charge transfer salt, tetrathiafulvalene bromide, that are narrowly dispersed in diameter. Our method involves the size-selective electrocrystallization of this salt on platinum catalyst particles supported on a graphite surface according to the reaction:

These platinum particles, ranging in diameter from 70 nm to 1.3 µm, were prepared by electrodeposition. The electrocrystallization of tetrathiofulvalene bromide ((TTF)Br_x ) from a dimethyl acetamide (DMAC) solution was then carried out at this nanostructured surface. (TTF)Br_x nanocrystals having widths in the range from 30 nm to 600 nm and aspect ratios of 20 or more were formed at the platinum nanoparticles on these surfaces by the electrochemical oxidation of TTF in bromide-containing electrolyte according to the reaction:

Figure 1. Scanning electron microscope (SEM) images of HOPG electrode surfaces following the electrodeposition of platinum nanoparticles (a) and the electrocrystallation of tetrathiafulvalene bromide on a platinum nanoparticle-covered graphite surface (b).

Figure 3. (Left) SEM images of four TTF(Br) crystallites and the platinum nanoparticles on which they nucleated. (Right) Plot of TTF(Br) crystallite width as a function of the diameter of the platinum particle on which nucleation occurred for 107 crystallites. The error bars in this plot estimate the precision with which the dimensions of particles and crystallites could be measured.

Figure 3. a. An ensemble of platinum nanoparticles following the electrocrystallization of TTF(Br); a single TTF(Br) crystallite has nucleated on one of the particles within this ensemble. TTF(Br) crystallites are not observed immediately adjacent to platinum particles on the surface. b. Schematic representation of the Òexclusion zoneÓ (in gray) surrounding platinum catalyst particles for the ensemble shown in (a). The positions of TTF(Br) crystallites on the graphite surface are marked by black dots.