2.2.1. Electrochemistry

SAMs can be characterized by a range of methods, among which electrochemical methods have been widely reported [59]. Electrochemical methods involve cyclic (CV) and linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS). CV of non-redox active SAMs, i.e., capacitive voltammetry, generally shows decreased double-layer capacitance after SAM adsorption on a metal surface. LSV and CV records the irreversible reductive (and oxidative) desorption of SAMs at a negative (or positive) potential. Reductive desorption is well suited to evaluating the surface coverage and the thermodynamic stability of the SAM Au-S units. The shape and position of the desorption peaks are sensitive to the crystalline surface structure and the SAM species. EIS can disentangle the ET resistance from the mass transfer or diffusion resistance. As noted, the ET resistance increases with increasing chain length because of the increased tunneling distance [63]. Electrochemical quartz crystal microbalance (EQCM) is an in situ technique, allowing real-time monitoring of the SAM adsorption process with high sensitivity to the mass changes on the electrode [59].
