[9406][9407][9408][9409][9410] adsorption the contribution of double-layer charging may be removed via background subtraction where the background is estimated from the same voltammetric response prior to the onset of the faradaic current. This eliminates the need for additional experiments to determine the contribution of double-layer capacitance.Furthermore, the potential of semiintegral analysis to determine surface concentration in the presence of fast surface phenomena suggests that its use may be extended to other areas of electrochemical interest. The thin-layer model discussed herein is one such example which can be extended to the study of thin films where the concentration of redox species within the film is affected by partitioning into or out of the film. Of interest would be the use of semiintegral analysis for the identification and quantitation of strong adsorption involving more complex isotherms which take into consideration interactions between adsorbed species, and the use of semiintegration analysis for kinetic and mechanistic studies in the presence of weak adsorption and thin films.
Acknowledgment.The spatial monitoring of ion diffusion into an ultrathin film sample was demonstrated by our depth profiling method using variable observation angle fluorescence spectroscopy under normal incidence conditions. A 143-nm-thick LB multilayer model sample was prepared in which the fluorophore rhodamine B was homogeneously distributed in each layer. The model sample was then immersed into an aqueous solution of sodium tungstate, where the tungstate ion diffused into it and r e a d with rhodamine B to form a nofluorescent complex. Because of this chemical quenching effect, the homogeneous concentration distribution of rhodamine B was changed by the tungstate ion diffusion. Changes in concentration depth profiles of rhodamine B with diffusion time were measured by the variable observation angle fluorescence depth profiling method based on the reciprocal theory, which has a spatial resolution of the monolayer thickness level in the depth direction. As a result, the diffusion behavior of tungstate ion was monitored, and its diffusion coefficient in LB multilayers was obtained as (1.2 -1.7)x 10-l' cm2/s.