Fe-Pt thin-film alloys have been grown by electrodeposition at potentials positive to that required to deposit elemental Fe. X-ray diffraction studies indicate the formation of fine grained face centered cubic alloys, while Rutherford backscattering spectrscopy and energy-dispersive X-ray spectroscopy reveal substantial incorporation of oxygen in the FePt deposits. The Fe-Pt codeposition process is driven by the negative enthalpy associated with alloy formation. The experimentally determined relationship between alloy composition and the iron group underpotential was found to be in reasonable agreement with free energy calculations for the binary alloy system, based on thermochemical data.There is currently considerable interest in FePt as a high-density perpendicular recording medium, due to the high magnetocrystalline anisotropy of the L1 0 phase. The significant challenges of achieving an appropriately oriented L1 0 phase, while maintaining the required grain ͑or particle͒ size of less than 5 nm, remain unsolved, despite considerable effort. 1-3 FePt has attracted additional interest due to its shape-memory properties, and Invar effects, both of potential utility in microelectromechanical systems ͑MEMS͒. 4 In addition to these useful physical properties Fe-Pt and related alloys have potential application as CO-tolerant electrocatalyst in polymer electrolyte fuel cells. 5,6 In all the above applications, process control during synthesis is of central importance.A variety of means have been used to produce Fe-Pt and similar alloys ranging from vacuum methods like MBE and sputtering 2,3,7,8 to electrodepositon 9-13 of thin films or fine particle production by solution phase chemical reduction. 1,14-16 One particular advantage of electrochemical methods is the ability to easily specify and control the supersaturation while monitoring its effect on growth kinetics.Herein we examine the factors affecting alloy composition during electrodeposition from an aqueous electrolyte containing chlorocomplexes of platinum and iron. Traditional alloy deposition studies largely focus on growth in the overpotential domain. 17 In this case, the composition is controlled by the relative rate of reduction of the constituents occurring in a potential regime where both species can be deposited in their elemental form. The desired differential activity, required for a particular alloy composition, is achieved by judicious choice of component concentrations and complex forming ligands. In contrast, in this study the use of the free energy of alloy formation to control alloy composition is demonstrated.The thermodynamic basis for alloy formation is well established. In fact, high temperature electrochemical potential ͑emf͒ measurements have contributed significantly toward the understanding of phase equilibria and the construction of phase diagrams. A necessary condition for binary alloy A 1Ϫx B x formation is equality of the electrochemical potential of the respective constituentswhere E i is the Nernst potential given by ͓2͔The free e...

The kinetics of the oxygen reduction reaction (ORR) on a series of electrodeposited normalPt100−xnormalNix and normalPt100−xnormalCox alloy films were examined in comparison to electrodeposited Pt and mechanically polished polycrystalline Pt. The alloys were electrodeposited at potentials positive of that required to grow the pure iron group metal. The growth process is ascribed to strong bonding enthalpy between Pt and the iron group metals that can be envisioned as iron-group underpotential deposition (upd) on Pt surface sites coupled with ongoing Pt overpotential electrodeposition. Rotating disk electrode measurements of the ORR kinetics, normalized for the H upd electroactive area, indicate a ∼1.9 to 2.7-fold catalytic enhancement on normalPt100−xnormalCox and normalPt100−xnormalNix, when x is in the range of 25–35, as compared to electrodeposited Pt films grown under similar conditions. An even greater ORR enhancement factor, between 3 and 4.8, was noted for dealloyed transition metal-rich (x75) films. Different schemes for integrating the electrodeposition (and dealloying) process into the fabrication of fuel cell membrane electrode array are also briefly discussed.

Electrochemical codeposition of a series of face-centered cubic Ni x Pt 1−x alloys is demonstrated ͑0.1 Ͻ x Ͻ 0.95͒. The alloy composition is a monotonic function of potential. The Pt-rich Ni x Pt 1−x alloys are formed at potentials positive to that required to deposit elemental Ni. Codeposition is ascribed to the negative enthalpy of Ni x Pt 1−x alloy formation that proceeds via a Ni underpotential deposition reaction in concert with Pt deposition. Interestingly, this process occurs at higher Ni underpotentials than anticipated based on extrapolated literature data from thermochemical measurements and ab initio calculations of alloy formation. In contrast, Ni-rich Ni x Pt 1−x alloys are produced at Ni overpotentials although the films are formed under conditions where pure Ni deposition is otherwise kinetically hindered. The alloy composition corresponding to the transition from underpotential to overpotential deposition is a function of the PtCl 4 /NiCl 2 electrolyte composition. The films were found to be bright and specular over the full range of compositions studied ͑grain size Ͻ10 nm͒. Atomic force microscopy yielded root-mean-square roughness values on the order of 5 nm for Ni-rich deposits up to 2.5 m thick.

We have carried out an extensive search for credible evidence to support the existence of a ballistic magnetoresistance ͑BMR͒ effect in magnetic nanocontacts. We have investigated both thin-film and thin-wire geometries for both mechanically formed and electrodeposited nanocontacts. We find no systematic differences between mechanically formed and electrodeposited nanocontacts. The samples we have investigated include mechanical contacts between ferromagnetic wires, electrodeposited nanocontacts between ferromagnetic wires, ferromagnetic nanocontacts electrodeposited on Cu wires, nanocontacts electrodeposited between ferromagnetic films anchored on wafers, ferromagnetic nanocontacts electrodeposited on Cu films anchored on wafers, nanocontacts between two ferromagnetic films connected by a pinhole through an insulating film, and nanocontacts formed by focused ion-beam etching. In none of these samples did we find credible evidence for a BMR effect. However, we did find a number of artifacts due to magnetostrictive, magnetostatic, and magnetomechanical effects that can mimic BMR.

This work presents experiments and theory describing a mechanism for how brighteners in electrolytes function. The mechanism involves change of local coverage of a deposition rate-enhancing catalyst adsorbed on the surface through change of local surface area during growth as well as accumulation and consumption. A first-order perturbation analysis shows the surface is stable against growth of perturbations for all wavelengths below a critical value that is deposition-condition dependent. The model predictions are shown to be consistent with the experimental results.Roughness evolution during electrodeposition is a subject of wide-ranging scientific and technical interest. Experience has shown that metal ion depletion at the interface is usually associated with destabilization of planar growth fronts. This has been explained by Mullins-Sekerka morphological stability theory which examines system response to small perturbations from steady-state growth conditions. Typically, a sinusoidal variation of surface height is imposed on the flat surface, and the resulting time evolution, to first order in the amplitude of the perturbation, is analyzed. 1,2 A positive growth rate reflects instability while a negative value results in attenuation of the perturbation; the former yields a rough surface while the latter case gives a smooth interface. This type of analysis has been widely applied to study phase transformations ranging from solidification, 1,2 to additive-free electroplating, 3-11 and chemical vapor deposition. 12,13 In contrast to the destabilizing influence of the reactant gradient, it is known that capillarity, adatom diffusion, and reaction kinetics dampen, and even stabilize the system, particularly at shorter wavelengths.An important aspect of electroplating practice involves the use of electrolyte additives to generate smooth, optically bright films. In certain instances, additives even allow the leveling of undesired surface imperfections by inducing preferential deposition at the bottom of features such as scratches. The traditional leveling mechanism behind this process is the existence of a concentration gradient of the inhibiting additive that results in lower deposition of the inhibitor, with associated decreasing inhibition of the metal deposition, the farther down one goes in the defect. 14-17 It is generally known that electrolytes that otherwise deposit at equal rates on all surfaces can be induced to deposit preferentially at the bottoms of polishing scratches and other surface imperfections through the addition of deposition-rate inhibiting additives.It is generally recognized that the traditional leveling mechanism will not affect deposition substantially when the dimensions of the defect are orders of magnitude smaller than the thickness of the boundary layer responsible for the concentration gradient. For optically relevant dimensions that are only a fraction of 1 m and a typical boundary layer thickness of 100 m, the appropriateness of such a model becomes questionable. For this reason, el...

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The electrodeposition of Pt100−xCux alloys is demonstrated using an electrolyte comprised of 1 mol/L normalH2SO4 , 0.001 mol/L normalK2PtCl4 , and 0.1 mol/L CuSO4 . Film growth proceeds by facile Cu underpotential deposition occurring in parallel with Pt overpotential deposition, with the latter controlling the overall rate of alloy deposition. Pt and Pt100−xCux depositions are monitored in real time using an electrochemical quartz crystal microbalance. Pt deposition from 1 mol/L normalH2SO4+0.001mol/LnormalK2PtCl4 is diffusion limited at potentials below −0.150 V saturated sulfate electrode and occurs with close to 100% current efficiency. In the added presence of CuSO4 , Pt100−xCux alloy deposition occurs, supported by the exothermic enthalpy of mixing. Monitoring the steady-state mass/charge ratio enables the composition of the growing film to be evaluated with submonolayer precision. For a given potential, the film composition so determined is in excellent agreement with the alloy composition determined for 1μm thick films using a combination of ex situ methods. The potential dependence of the alloy composition is described by an asymmetric regular solution model with an extremum for alloying enthalpy of −18.9±0.2kJ/mol .