Electrochemical Deposition of Biferrocene Derivative-Attached Gold Nanoparticles and the Morphology of the Formed Film

The electrodeposition phenomenon of octyl thiolate-stabilized gold nanoparticles with a 2.3 ± 0.5 nm core diameter modified with biferrocene-terminated alkanethiolates on their surface (Aun−BFc) has been investigated using cyclic voltammetry, STM and AFM morphological observation, and electrochemical quartz crystal microbalance (EQCM) of the deposited Aun−BFc film. Consecutive potential scans causing two-step one-electron oxidation of the biferrocene units of Aun−BFc in CH2Cl2 electrolyte solution produce the adhesive Aun−BFc film on electrode surface. The deposition rate is lower for the biferrocene derivative on one particle θBFc with a smaller modification number and a kind of electrolyte anion: ClO4- ∼ BF4- ≫ PF6-. The STM and AFM images have revealed that the thickness of the Aun−BFc film grows gradually by increasing the number of cyclic scans, forming many monolayer-level domains with ca. 80 nm diameter of the assembled Aun−BFcs. The average interparticle spacing of neighboring Aun−BFcs in the film is 7.5 nm, which is longer than the estimated diameter of whole Aun−BFc species (5.9 nm). Analysis of boron in the film electrodeposited in Bu4NBF4−CH2Cl2 by the prompt γ-ray neutron activation (PGA) method shows that the BF4- ion is incorporated in the film. EQCM measurement suggests that not only ions but also the included CH2Cl2 solvent molecules in the film are moved in and out reversibly in a potential range of E0‘2 of Aun−BFc. These results indicate that the formation of ionic lattice including Aun−BFc2+ and counterion is accompanied by the exclusion of CH2Cl2 solvent molecules among the particles in the initial deposition process.