Abstract: Quantized capacitance charging was observed for octanethiolate self-assembled monolayer protected gold clusters(C₈AuMPC) self-assembled on a gold electrode surface. The result from differential pulse voltammetry(DPV) shows that four pairs of well-defined quantized capacitance charging peaks appeared within the potential range from -0.8 V to +0.8 V. Electrochemical impedance spectra(EIS) of the monolayer protected clusters(MPC) modified electrode show that the electrode interfaces with adsorbed MPC consisted of two components, namely, the electrode-MPC interface and the MPC-solution interface. The interfacial capacitances of the electrode-MPC interface(C_DL1) and the MPC-solution interface(C_DL2) almost had no change near the potential of zero charge(ca.-0.2 V), then C_DL1 and C_DL2 both changed along with increasing or decreasing the electrode potentials. Quantized capacitance charging of MPC was further theoretically analyzed by using the theory of Coulomb blockade in normal metal two tunnel junctions, confirming that EIS method was an effective method for studying quantized capacitance charging of MPC. In addition, the effect of the electroactive species-ferrocene on quantized capacitance charging of C₈AuMPC was studied. The results show that the electroactive species in the solution almost made no contribution to the electron transfer of the MPC-solution interface, which mostly occurred between the nanoparticles.

Key words: Self-assembling of gold nanoparticles, Quantized capacitance charging, Electrochemical impedance spectrum(EIS), Interfacial structure