SCANNING-TUNNELING-MICROSCOPY FRACTAL CHARACTERIZATION OF POLY(O-TOLUIDINE) FILMS PRODUCED ELECTROCHEMICALLY ON POLYFACETED GOLD SINGLE-CRYSTAL SPHERES

The topography evolution of a poly(o-toiuidine) layer (the object) ele ctrodeposited on a polyfaceted Au single crystal from 0.5 M H2SO4 + 0. 65 M o-toluidine aqueous solution at 25 degrees C has been studied com bining nanometer scale ex-situ scanning tunneling microscopy and elect rochemical techniques. A thin polymer layer structure consists of nodu lar elements following the substrate topography, whereas a thick polym er structure corresponds to a rather disordered structure made up of a gglomerates formed by nodular elements with average diameter size d(s) congruent to 15 nm. In contrast to the former one, this structure is independent of the substrate topography. For thick layers xi, the root -mean-square roughness of the polymer coating, and L(s), the scan leng th, fulfill a xi proportional to L(alpha) relationship with alpha = 0. 33 +/- 0.05 for L(s) > d(s) and alpha = 0.85 +/- 0.05 for L(s) < d(s). Accordingly, the polymer layer surface behaves as a self-affine fract al. For L(s) > d(s) the value of alpha agrees with that predicted for moving interfaces generated by the Eden model, whereas for L(s) < d(s) the value of alpha approaches that expected from an Euclidean surface . The topographic analysis of these polymer layers can be related to t he kinetics of electrochemical reactions at polymer-coated Au electrod es.