Electrodeposition of Biferrocene Derivative-Attached Gold Nanoparticles:  Solvent Effects and Lithographic Assembly

The solvent effects of electro-oxidative deposition of octyl thiolate-stabilized gold nanoparticles with 2.3 ± 0.5 nm core diameter modified with biferrocene-terminated alkanethiolates on their surface (Aun-BFc) were investigated using cyclic voltammetry, UV−vis spectroscopy, scanning tunneling microscopy (STM), and electrochemical quartz crystal microbalance (EQCM) techniques. Consecutive potential scans causing two-step one-electron oxidation of the biferrocene units of Aun-BFc in 0.1 M Bu4NClO4−organic solvent [CH2Cl2, tetrahydrofuran (THF), toluene + acetonitrile (toluene/MeCN; 2:1 v/v)] solution under Ar produced the adhesive Aun-BFc film on an electrode. The deposition rate was higher in the order THF > toluene/MeCN > CH2Cl2. The STM images indicated that the films prepared in CH2Cl2 or THF were likely to form domains with ∼80 and 170 nm diameters of the assembled Aun-BFc's, respectively, as contrast particles were randomly connected in the film deposited in toluene/MeCN. The experimental results all suggested that the electrodeposition process was considerably influenced by solvent properties: the degree of assistance of the chemical reaction of BFc units and the affinity for the charged Aun-BFc's. By utilizing scanning electrochemical microscopy (SECM), we constructed dot- and line-shape lithographic assemblies of Aun-BFc particles at a resolution of ∼50−100 μm.