Coating and active surface of Ni-Zn alloys studied by atomic force microscopy

The topology analysis of a real material surface undertaken here runs into a new approach of the active surface parameter, S-u, based on the scaling behaviour of the interface width. w. This approach is experimentally illustrated from the Coating of a copper substrate with 2 mum-thick Ni-Zn alloy electodeposits investigated varying their growth rate, r, located below 0.50 mum/s. The imaging of their surface by atomic force microscopy (AFM) enables the following of their Hurst exponent, a, and their correlation length, L-c, versus r. It is shown that their interface growth may proceed from the Kardar-Parisi-Zhang (KPZ) dynamics, the restricted surface diffusion effect increasing with the increase of r. Both, alpha and L-c stabilise from a critical rate r(c)' = 0.16 mum/s. The study evidences a peculiar surface microstructure of the Ni-Zn alloy favourable to catalytic activity at another critical point r(c)" = 0.08 mum/s which corresponds to a Ni (80 at.%)-rich specimen leading to the maximal active surface obtained S-a = 132 nm. (C) 2001 Published by Elsevier Science B.V.