The electroadsorption on columnar Au electrodes (substrate) of pyridine from x M pyridine + 0.1 M HClO4 and x M pyridine + 0.1 M KClO4 aqueous solutions (10 -3 e x e 10 -2 ), at constant potential and 298 K, was studied using voltammetry, chronocoulometry, and ac impedance combined with scanning tunneling microscopy to characterize the substrate topography. For a constant pyridine concentration (c), the degree of surface coverage by pyridine adsorbate (θ) diminished as R was increased. The θ vs c plots, irrespective of R, were interpreted by a Frumkin adsorption isotherm including a constant standard adsorption free energy. The evaluation of adsorption isotherms reflects the existence of an excluded volume effect, which can be related to a barrier effect due to adsorbates at nanometer size pore entrances.

The roughness relaxation of thin columnar Au electrodeposits at constant potential and 25°C in 0.05 M NaF, 0.05 M KC1 and 0.05 M K,SO, has been studied. These measurements were taken in the -0.6 to 0.8 V (vs Hg/Hg,SO, reference electrode) potential range. The kinetic data were obtained from the roughness factor decay over 5 ~10~ s. The value of the surface diffusion coefficient D, of Au atoms was derived from the roughness decay law at constant potential and PH. At any potential, the value of D, increases in the order NaF < K,SO, < KCl. This sequence correlates with the specific adsorption of anions on Au. In K,SO, and NaF solutions, as the electroformation of AuOH species takes place, the effect of SO:-and F-ions is no longer observed. In contrast, in 0.05 M KCI solution, the value of D, increases steadily as the applied potential is increased positively. INTRODUCIIONSurface roughness relaxation phenomena on metals in the range 273-325 K offer the possibility of deriving quantitative information about the mobility of surface atoms either in vacua or at metal-aqueous solution interfaces [l-3].

No abstract