Gold Nanoparticle Multilayers; Rectification of Quantized Charging Even in the Presence of Hard Electrolyte Anions

摘要

Quantized capacitance charging of monolayer-protected gold nanoparticles (Au MFCs) can be rectified by hydrophobic electrolyte anions in aqueous solutions when the particles are immobilized on electrode surfaces forming monolayers.~1 These unique rectification behaviors are interpreted on the basis of a Randies equivalent circuit where the electrode interfacial capacitance consists of two components, one for the collective contribution of surface-immobilized MFC nanocapacitors and the other accounting for the interparticle void.~2 These interesting single electron-transfer characters demonstrate that these nanoscale entities can be used as building blocks for the fabrication of next-generation, nanoscale electronic devices.In this work, we focus on the electrochemistry of self-assembled multilayers of gold nanoparticles in aqueous solutions which also exhibit rectified quantized capacitance charging characteristics, even in the absence of hydrophobic anions, in contrast to those with nanoparticle monolayers. Gold nanoparticle multilayers were prepared by the following procedure. A polycrys-talline gold disk (sealed in glass tubing; gold disk area 0.61 mm~2) was used as the working electrode. Prior to use, the gold electrode was cleaned by a procedure described previously.~2 Briefly, the gold electrode was first polished with 0.05 um alumina slurries, followed successively by sonication in dilute nitric acid, sulfu-ric acid, and nanopure water. The electrode was then subjected to electrochemical etching by rapid potential sweep (10 V/s) in 0.10 M H_2SO_4 within the potential range of +1.2 to -0.2 V for 5 min. After this, the electrode was rinsed with copious amounts of nanopure water and ethanol, and then dried in a gentle stream of ultrahigh-purity nitrogen. The resulting gold electrode was dipped into a dichloromethane solution containing n-hexanethiolate-protected gold particle (AuC6, core diameter ca. 1.6 nm) at a concentration of 1 mg/mL. The electrode was quickly pulled out and blow-dried by N_2. The gold electrode, with multilayers of AuC6 particles, was used as a working electrode in the electrochemical measurements. In a typical experiment, 10-20 layers of particles were deposited on the electrode surface as estimated by voltammetric measurements (vide infra).