On the use of atomic force microscopy and scaling analysis to quantify the roughness of zinc electrodeposits produced from an industrial acid sulfate electrolyte containing glue

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The morphology and roughness of zinc electrodeposits produced on an aluminum cathode from an industrial acid sulfate electrolyte have been characterized with scanning electron microscopy (SEM), atomic force microscopy (AFM), and scaling analysis. SEM and AFM images provided a topographical view of the deposit, while scaling analysis was used to determine the mechanism of surface growth and to quantify surface characteristics including the root-mean-squared (rms) roughness and periodicity. For an electrolyte with a fixed composition of additives, both the rms roughness and the width of the surface features increased with deposition time and the mechanism of surface growth was dominated by surface diffusion. However, when the deposition time was fixed but the concentration of glue in the electrolyte was increased between 3 and 60 mg L−1, a marked change in the deposition mechanism was observed. Here, small elevations in glue had minimal influence on the rms roughness but reduced the width of surface features thereby producing rougher deposits. At glue concentrations above 30 mg L−1, the scaling analysis plot changed considerably and corresponded to samples with two distinct deposit morphologies on a single surface, an observation that was not apparent from the SEM images alone. The features include large zinc islands with numerous small zinc features on their surfaces, which indicate competing mechanisms of nucleation and surface diffusion, respectively. The results show that scaling analysis offers complementary information to SEM characterization and can render additional information on the mechanism of zinc deposition under industrial conditions.