Nucleation and Growth Mechanisms of Bimetallic Sm-Co Nanowires and Nanotubes

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Nucleation and growth mechanisms of bimetallic Sm-Co magnetic nanowires and nanotubes, electrocrystallizing into hard anodic alumina templates, are described. Nanowires are produced at two overpotentials −0.9 V and −3 V, into templates with pore diameters of 20 nm and 40 nm; for larger pores, 200 nm in diameter, nanowires result at −0,9 V while at −3 V nanotubes form. The electrodeposition process mainly develops under diffusional control, with the current monotonically decreasing with time. Experimental current/time curves are described by suitable models adapted to bimetallic phases, considering successive stages in the pore filling process. In membranes with small pore diameter, a linear diffusion zone ahead the growing nanowire surface allows to apply a modified Cottrell equation. Models based on recessed microelectrodes behaviour are proposed, considering the overlap of diffusion zones at the porous mouth. For large pore diameter (>100 nm), current transitory is described by a 1D model for nanowires grown at −0.9 V, while a new expression is derived for nanotubes developing at −3 V, where the hydrogen evolution provides an important contribution to the mechanism. The mechanisms proposed are consistent with nanowires´ and nanotubes´ morphology details observed in SEM images.