Adlayer Adsorption Film Monolayers

For the same reason, Ru(OOOl) modihcation by Pt monolayer islands results in a pronounced promotion of the CO oxidation reaction at potentials above 0.55 V, which on unmodified Ru(OOOl) electrodes proceeds only with very low reaction rates. The onset potential for the CO oxidation reaction, however, is not measurably affected by the presence of the Pt islands, indicating that they do not modify the inherent reactivity of the O/OH adlayer on the Ru sites adjacent to the Pt islands. At potentials between the onset potential and a bending point in the j-E curves, COad oxidation proceeds mainly by dissociative H2O formation/ OHad formation at the interface between the Ru(OOOl) substrate and Pt islands, and subsequent reaction between OHad and COad- The Pt islands promote homo-lytic H2O dissociation, and thus accelerate the reaction. At potentials anodic of the bending point, where the current increases steeply, H2O adsorption/OHad formation and COad oxidation are proposed to proceed on the Pt monolayer islands. The lower onset potential for CO oxidation in the presence of second-layer Pt islands compared with monolayer island-modified Ru(OOOl) is assigned to the stronger bonding of a double-layer Pt film (more facile OHad formation). 

Fig. 7 High-resolution in situ STM images showing the structure of inhibiting BTAH films on Cu(lOO) at different BTAH coverages, (a) Chainlike structures at submonolayer coverages (350 A X 350 A) (b) close-packed arrangement in the completed chemisorbed BTAH monolayer (100 A X 100 A) (c) model of the BTAH adsorption geometry in the close-packed monolayer phase [rectangles in (d) and (c) indicate the surface unit cell of the BTAH adlayer] and (d) disordered polymeric chains in the Cu(l)BTA multilayer phase (300 A x 300 A) [22, 24, 25).

Modification of a snbstrate snrface by spontaneous adsorption (24), now more commonly referred to as self-assembly, is one of the most utilized modification pathways. These films are typically bound to the snbstrate by chanisorption however, intermolecular forces within the film are also important Chemisorption is the strong adsorption of a molecule onto a snrface throngh the spontaneous formation of a chemical bond (1). This chemical bond forms between a fnnctional group in the molecule and a site on the electtode. Monomolecular layers prepared by chemisorption are known as self-assembled monolayers (SAMs). These adlayers can be used to impart the desired function to the electrode directly, or can serve as a foundation for more complex electrode architectures. 

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