Dimensional changes of alpha-type nickel hydrous oxide, alpha-Ni(OH)(2)(hyd), films electrodeposited on the basal plane of highly oriented pyrolytic graphite, HOPG(bp), electrodes, have been monitored by in situ by atomic force microscopy (AFM) in 1 M KOH as a function of the applied potential. Freshly prepared alpha-Ni(OH)(2)(hyd) films were found to consist of conformal sections covered by large numbers of distinctly bright, globular-type features (0.25 mu m average diameter), separated by sharply defined crevices. Upon oxidation, the width of the crevices, W-c, increased, whereas the distances between any two globular features, i and j, within a specific section, r(ij), decreased. A statistical analysis involving more than 100 pairs of features from different sections of independent films showed that the relative decrease in r(ij), induced by the nominal full oxidation of the film, r(ij)(ox)/r(ij)(red), is remarkably constant, 0.06 +/- 0.01, and independent of the magnitude of r(ij). Plots of W-c obtained from linear AFM scans along an axis normal to the crevice as a function of the extent of oxidation of the films revealed, within the time scale of the experiments, a marked hysteresis between the oxidation and subsequent reduction process.