LIMITATIONS OF ELECTROCHEMICAL METHODS FOR SURFACE ANALYSIS AT SMALL FRACTALITY SCALES

Based on solid arguments, it was demonstrated that: (i) the fractality scale detected during electrochemical measurements depends only on the yardstick length, i.e., the diffusion layer width, and not on the size of the diffusing electroactive species; (ii) Fractal analysis cannot be performed by electrochemical methods at scales smaller than 100 nm, since the thickness of Helmholtz double layer is comparable with the diffusion layer width, and the diffusion layer width cannot be assumed to act as yardstick length. Indeed, it should be taken into account that the yardstick length is equal to "diffusion layer width + Helmholtz double layer." On the other hand, thin diffusion layers on rough surfaces lead to 3D diffusion; thus, the fundamental electrochemistry is no longer valid. In general, fractal analyses by electrochemical methods has severe limitations, which should be taken into account before applying it for different cases. In other words, surface analysis by this approach just senses microscale roughness, and ignores nanostructure.