On the composition depth profile of electrodeposited Fe–Co–Ni alloys

Depth profile of electrodeposited Fe–Co–Ni alloys was measured using secondary neutral mass spectrometry with the reverse sputtering direction. A spontaneous near-substrate composition modulation was found for each sample studied. The initial deposit is very rich in Fe, which decays due to the depletion of the electrolyte in the vicinity of the cathode surface. The near-substrate modulation pattern can be elucidated by taking into account the mutual deposition preference of the iron-group metals and the mass transport of the ions in the solution. The composition fluctuations of Fe and Co at distances larger than 100 nm from the substrate are strictly correlated. Composition fluctuations beyond the near-substrate zone are attributed to the instability of the depleted electrolyte layer in the vicinity of the cathode. A critical analysis of earlier depth profile data for electrodeposited Fe–Co–Ni samples is also given.