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

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. Sm-Co NWs/NTs are electrocrystallized into alumina pores at low/high potential. Nucleation and diffusional growth mechanisms during co-deposition are described. The deposition potential and the pore radius are key parameters in the process. Diffusional field at pore mouth changes from lineal to radial during deposition. At high negative potential and large pore diameter NTs form due to H 2 evolution.