SCANNING ELECTROCHEMICAL MICROSCOPY .22. EXAMINATION OF THIN SOLID FILMS OF AGBR - ION DIFFUSION IN THE FILM AND HETEROGENEOUS KINETICS AT THE FILM SOLUTION INTERFACE

A new approach to the characterization of thin solid films, based on t he use of the scanning electrochemical microscope (SECM), is described . Parameters of interest, e.g., the heterogenous rate constant for a c hemical. reaction at the film/solution interface and the diffusion coe fficient of species inside the film, can be determined from the SECM a pproach curves. The analysis of the SECM current-distance curves also provides information about the spatial localization of a chemical (or electrochemical) reaction (i.e., at the substrate/film vs the film/sol ution interface). Silver bromide films electrodeposited on a silver su bstrate were used as a model experimental system to test this method, with determination of the diffusion coefficient of bromide ion in the AgBr layer (5.6 x 10(-7) cm2/s) and the heterogenous rate constant for the reaction of AgBr with hexaammineruthenium(II) (0.082 cm/s). The l atter reaction occurs at a film/solution interface, in contrast with t he electroreduction of tris(2,2'-bipyridyl)osmium(II) which occurs at the silver substrate surface via diffusion through pores in the AgBr f ilm rather than at the highly resistive AgBr/solution interface.