Electrocrystallization of Tetrathiafulvalene Charge-Transfer Salt Nanorods on Gold Nanoparticle Seeds

This paper describes electrochemical synthesis of nanorods of tetrathiafulvalene (TTF) charge-transfer salt on gold nanoparticle (GNP) seeds. The seed-mediated process was monitored by cyclic voltammetry, AFM, and field-emission SEM. The electrodeposition of GNPs (nucleation seeds) on highly oriented pyrolytic graphite (HOPG) electrodes was studied as a function of the electrolytic conditions. The GNP size increases with increasing HAuCl4 concentration and decreasing applied overpotential. A morphological transition from quasi-spherical particles to dendritic aggregates occurs when the HAuCl4 concentration increases from 0.5 to 1 mM. The electrocrystallization of (TTF)Br0.76 on the GNP-decorated HOPG was investigated as a function of TTF concentration and GNP morphology. We observed a preferential nucleation of (TTF)Br0.76 on the GNP seed. The seed-mediated (TTF)Br0.76 crystals display a confined crystal morphology in comparison to those nucleated on bare HOPG. (TTF)Br0.76 nanorods as small as 7 nm in height were nucleated on GNPs of 20 nm in height. We also observed preferential nucleation of (TTF)Br0.76 on high-energy facets rather than on the most prominent face of the GNP. The nanoconfinement effect is attributed to the local curvature of the GNP seed that imposes an interfacial strain, thus limiting the cross-sectional dimension of the ensuing (TTF)Br0.76 crystal. This study contributes to the understanding of electrocrystallization at the nanoscale and a solution-based method to incorporate nanorods on nanopatterns and nanodevices.