IN-SITU ATOMIC-FORCE MICROSCOPY STUDIES OF ELECTRODEPOSITION MECHANISM OF CERIUM OXIDE-FILMS - NUCLEATION AND GROWTH OUT OF A GEL MASS PRECURSOR

In situ atomic force microscopy (AFM) of the electrochemical depositio n of cerium oxide coatings is presented for the first time. The AFM im ages and the tip-deposit interaction, observed during early stages of deposition, demonstrate clearly the presence of a transitional gel sta te of the depositing material between the preceding solution-dispersed state and the subsequent solid state. The deposition is shown to occu r through a nucleation and growth mechanism in which microscopic nucle i crystallized out from this intermediate gel mass serve as the growth centres of the new phase. Among the successive steps of the overall p rocess, including reactants discharge at the electrode surface, and ma ss transfers to and from it, the nucleation and growth process is the rate-determining step. (C) 1997 Elsevier Science Ltd.