Nucleation and growth mechanisms in Cu-Co films

Abstract

Nucleation and growth mechanisms in Co, Cu, and CoxCu100-x single films, and in CoxCu100-x/Cu bilayers, electrodeposited on Cu70Zn30 brass substrates, are studied by the constant potential technique. The recorded current-time transients (CTTs) are rather complex, and they extend for long times. Co, Cu, and CoxCu100-x alloys electrocrystallize onto brass, undergoing a process with more than a single maximum during the CTTs, as if two or more consecutive nucleation steps were present. The first stage of electrocrystallization in Co and CoxCu100-x films involves 3D instantaneous nucleation, but then, at long times, a progressive nucleation regime predominates. CTTs in Cu/brass and in Cu/CoxCu100-x/brass bilayers are well fitted by a 2DP progressive nucleation process at the initial stage, while for longer growing times a transition to a 3DP regime is observed, in which film growth becomes controlled by adatoms incorporation to the lattice. Film morphologies observed by SEM are consistent with these growth mechanisms. XRD results indicate that pure Co layers are hcp phase, while Cu and Cu-Co layers have an fcc lattice. Films are soft ferromagnetic, with an "in-plane" magnetization easy axis; there is evidence of crystallographic texture, which should be responsible for the higher coercivity observed in the "out-of-plane" configuration, with the applied field perpendicular to the film plane.