In this paper, potentiodynamic and potentiostatic methods combined with electrochemical impedance spectroscopy (EIS) measurements as well as the ellipsometric characterisation are used in order to compare the adsorption of aromatic molecules in a wide range of conditions. Cyclic voltammetry allows obtaining the potential regions of stability and desorption of the layers.
Preparation of monolayers of mercaptopyridine (N or S-bonded) and isonicotinic acid (N or COO-bonded) on monocrystalline and polycrystalline gold surfaces as well as pyridine and mercaptopyridine on nickel, is reported. The influence of temperature, pH of dipping solution and time of dipping in the electrical and optical properties of the adsorbed layers, is analysed. For nickel, different cathodic pre-treatments in acidic and alkaline solutions were applied before the adsorption in order to electroreduce the spontaneous oxide layer
The impedance characteristics of these systems are discussed in terms of ideal and non-ideal circuit networks. The elements are associated with electrical analogs of the corresponding physical and chemical processes taking place at the interfaces. The kinetics of electron transfer for redox couples as well as the impedance response was employed in order to obtain information on the compactness of the layers.
Ellipsometric results indicate that the cathodic pre-treatments are effective for reducing the nickel oxide as well as indicate the adsorption of pyridine.
STM images are employed for obtaining the structural characteristics of the self-assembled layers as well as the changes with potential.
