Single-Electron Charging Features of Larger,Dodecanethiol-Protected Gold Nanoclusters:Electrochemical and Scanning Tunneling Microscopy Studies

摘要

In this report,we demonstrate the single-electron charging features of larger-sized (ca.3.72 nm) Au nanoclusters protected with dodecanethiol [approximate composition,Au_(1415)(RS)328] using combined electrochemical and scanning tunneling microscopic (STM) studies.In particular,these nanoclusters show a highly populated single-electron charging peak in voltammetric experiments,where the calculated capacitance is in good agreement with the experimentally obtained value of 1.6 aF.In comparison to the voltammetric studies,STM measurements over a single Au particle on the highly oriented pyrolytic graphite surface reveal nonlinear current-voltage (I-V) characteristics with a large central gap,signifying single-electron-transfer features.The I-V results demonstrate a clear Coulomb blockade effect with a central gap of around 0.2 eV,which is in good agreement with the orthodox theory for the double barrier tunnel junction system.The standard heterogeneous electron-transfer rate constant estimated from impedance measurements is found to be of 7.97 x 10~(-6) cm centre dot s~(-1),suggesting that the process is very sluggish.Furthermore,diffusion coefficient (D_c) values calculated from chronoamperometry and impedance measurements are in good agreement with theoretically calculated values using the modified Stokes-Einstein equation.The electron-transfer rate constant estimated from cyclic voltammograms of adsorbed monolayer protected Au nanoclusters is found to be about 2 s~(-1),which is slower than that reported for its smaller analogues.