3-DIMENSIONAL MONOLAYERS - NANOMETER-SIZED ELECTRODES OF ALKANETHIOLATE-STABILIZED GOLD CLUSTER MOLECULES

Rotated disk electrode voltammetry is described for CH2Cl2 solutions o f cluster molecules with nanometersized gold cores and stabilizing lig and shells consisting of mixed monolayers of octanethiolate and omega- ferrocenyloctanethiolate ligands in molar ratios ranging from 2:1 to 2 4:1. Voltammograms for the cluster molecules exhibit a ferrocene oxida tion wave with a limiting current that is under hydrodynamic mass tran sport control. The current-potential curves preceding (''prewave'') an d following (''postwave'') the ferrocene wave, which are ideally flat, are decidedly sloped. The Delta i/Delta E slopes are proportional to the square root of electrode rotation rate, i.e., are also under hydro dynamic control. The Delta i/Delta E slopes are due to the charging of the electrical double layers of the cluster molecules, showing them t o act as diffusing, molecule-sized ''nanoelectrodes''. A theoretical a nalysis is presented of the transport control of the double layer char ging. Possible reasons that the values of the cluster molecule capacit ance (per unit surface area Of cluster molecule, which entails use of models for the shape of the Au core of the cluster) are somewhat large r than the literature expectation for octanethiolate monolayers on fla t gold surfaces are discussed. The tiny capacitances of the cluster mo lecules means that changing their charges by small potential increment s can require an average of less than a single electron per cluster mo lecule.