Compositional Control in Electrodeposited Co x Pt1 − x Films

Electrochemical co-deposition of Co x Pt 1 - x alloys is demonstrated at potentials positive to that required to deposit elemental cobalt (underpotential, or "induced," co-deposition). Co-deposition is attributed to the negative enthalpy of Co x Pt 1 - x alloy formation. A regular solid-solution model is used to describe the dependence of the film composition on the deposition potential. X-ray diffraction of films grown on Cu(100)∥Si(100), as well as poly- Au∥SiO 2 ∥Si, reveal the formation of a randomly oriented Co x Pt 1 - x face-centered cubic alloy for x > 0.3. A transition to the hexagonal close-packed phase is evident at higher cobalt concentrations (x > 0.9).