Self-assembled monolayers (SAMs) of

organothiols on metal surfaces have attracted enormous

attention in recent years owing to their ease-ofpreparation,

long-term stability, and controllable surface

chemical functionality. The understanding of the

molecular packing of SAMs is important for the

interpretation of fundamental studies and for the

development of practical applications. SAMs of aromatic

compounds with two ligands (like mercaptopyridine,

bipyridine and pyridine-carboxylic acids) on gold are

receiving a strong interest in bioelectrochemistry due to

their functionality in order to facilitate direct electron

transfer of metalloproteins such as cytochrome c [1] as

well as the possibility of interacting via the π-system [2].

In this paper, potentiodynamic and potentiostatic

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 COObonded)

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.

References

[1] T. Sawaguchi, F. Mizutani, S. Yoshimoto, I.

Taniguchi, Electrochim. Acta 45 (2000) 2861.

[2] W. Azzam, C. Fuxen, A. Birkner, H.T. Rong, M.

[2] W. Azzam, C. Fuxen, A. Birkner, H.T. Rong, M.

Buck, C. Wöll, Langmuir 19 (2003) 4958.