Monolayer thin films, materials chemistry

As outlined above, the electrochemical properties of this redox species are strongly pH-dependent and this behavior can be used to illustrate the supramolecular nature of the interaction between the polymer backbone and the pendent redox center. The cyclic voltammetry data shown in Figure 4.17 are obtained at pH = 0, where the polymer has an open structure and the free pyridine units are protonated (pKa(PVP) = 3.3). The cyclic voltammograms obtained for the same experiment carried out at pH 5.7 are shown in Figure 4.18. At this pH, the polymer backbone is not protonated and upon aquation of the metal center the layer becomes redox-inactive, since protons are involved in this redox process. This interaction between the redox center and the polymer backbone is typical for these types of materials. Such an interaction is of fundamental importance for the electrochemical behavior of these layers and highlights the supramolecular principles which control the chemistry of thin films of these redox-active polymers. Finally, it is important to note that the photophysical properties of polymer films are very similar to those observed in solution. Since the layer thickness is much more than that of a monolayer, deactivation by the solid substrate is not observed. 

The plateau of the adsorption isotherm indicates the concentration(s) at which all adsorption sites for the adsorbing species are occupied, in surface chemistry terms the fractional surface coverage of the substrate by the adsorbate is unity. Such a specimen provides an ideal opportunity to probe the interfecial chemistry of adhesion directly using what is sometimes referred to as the thin film approach. As the layer of organic material, such as adhesive, is very thin (as a result of monolayer coverage) the contribution of interfacial chemistry at the interface will be maximized in the resultant XPS or ToF-SIMS spectrum. For this reason, the construction of adsorption isotherms is often used as a precursor to direct interphase analysis in this manner. 

The purpose of this chapter is to review recent progress in surface structural characterization of select oxide films, with particular emphasis on systems that are sensitive to some of the problems listed above. By thin , we mean a few monolayers up to -1000 A. We take the approach of addressing the issues of oxidation chemistry, either during or after film formation, and lattice and symmetry mismatch with the substrate. We examine representative case studies that illustrate the materials issues listed above. It is assumed that the reader is... 

Doblhofer K (1994) Thin polymer films on electrodes a physicochemical approach. In Lipkowsld J, Ross PN (eds) The electrochemistry of novel materials. VCH, Weinheim, p 141 Murray RW (1992) Molecular design of electrode surfaces. John Wiley, New York Burgmayer P, Murray RW (1986) Polymer film covered electrodes. In Skotheim TA (ed) Handbook of conducting polymers. Marcel Dekker, New York, p 507 FinMea HO (1996) Electrochemistry of organized monolayers of thiols and related molecules on electrodes. In Bard AJ, Rubinstein I (eds) Electroanalytical chemistry, vol 19. Marcel Dekker, New York, p 109... 

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