In situ atomic force microscopy studies of the deposition of cerium oxide films on regularly corrugated surfaces

In situ atomic force microscopy (AFM) has been employed to study the electrodeposition of cerium oxide onto a gold substrate, characterized by regular triangular corrugations (of base length 400-500 nm, and height 10-20 nm) as well as microscopic steps and pits on individual corrugation surfaces. The substrate surface provides macroscopic and microscopic physical shields for the deposit nuclei against the lateral force of the scanning AFM tip while allowing sufficient resolution. The deposition is revealed to proceed through a novel mechanism in which nuclei form from a precursor gel mass produced at the electrode-electrolyte interface during deposition. Occurrence of the gel is supported by transient smearing of in situ AFM images and material transport by the scanning tip to the border regions of the imaging site and subsequent retention there. Gel formation is inherent to the deposition rather than owing to a particular substrate morphology or control conditions. The nucleation mechanism is seen from an induction period for deposition, emergence, and growth of fine deposit grains, and prolonged absence of deposition on particular local areas where initial nuclei are removed. Gel formation is achieved rapidly within 10-20 s, where subsequent nucleation from the gel is comparatively slow, requiring up to several minutes. Nucleation from a gel rather than direct deposition, is also the mechanism for bulk deposition on the cerium oxide phase already deposited. (C) 1999 The Electrochemical Society. S0013-4651(98)05-088-5. All rights reserved.