Electrochimica Acta 56 (2010) 483–490 Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta Electrochemical investigation of electrodeposited Fe–Pd alloy thin films M. Rezaei, M. Ghorbani ∗ , A. Dolati Department of Materials Science and Engineering, Sharif University of Technology, Azadi Ave., P.O. Box 11155-9466, Tehran, Iran article info Article history: Received 10 July 2010 Received in revised form 6 September 2010 Accepted 7 September 2010 Available online 16 September 2010 Keywords: Fe–Pd alloy Electrodeposition Kinetic Diffusion-controlled process Nucleation and growth mechanism abstract In the present study, the electrodeposition of Fe, Pd and Fe–Pd alloys, in alkaline solutions, has been investigated. Using ammonium hydroxide and trisodium citrate as the complexing agents, it has been shown that the co-deposition of Fe and Pd is achieved due to diminishing the difference between the reduction potentials of these two metals. Cyclic voltammetry results clearly show that the electrodepo- sition processes are diffusion-controlled and the diffusion coefficients of Fe 2+ and Pd 2+ are 1.11 × 10 -6 and 2.19 × 10 -5 cm 2 s -1 , respectively. The step potential experiments reveal that nucleation mechanism is instantaneous with a typical three-dimensional (3D) growth. At low overpotentials, addition of Pd 2+ to Fe 2+ solution leads to a dramatic reduction in the number of nucleation sites, due to this fact that at such overpotentials, the electrodeposition behavior of Pd 2+ governs on the overall process. The analysis of chemical composition of the electrodeposited films and the number of nucleation sites indicate that at higher overpotential, Fe 2+ is deposited preferentially, thus the electrodeposition of iron–palladium alloys was classified as an anomalous co-deposition. © 2010 Elsevier Ltd. All rights reserved. 1. Introduction Fe–Pd thin films have many potential applications due to their specific chemical composition. Shape memory properties at alloys including 28–31 at.% Pd [1–6] and high magnetic anisotropy at about 50 at.% Pd [7–13] make them as promising materi- als for microelectromechanical systems (MEMS). Moreover, invar anomalies (30–35 at.% Pd) [14,15] and catalytic properties of palladium-rich thin films (including high hydrogen absorption capacity [16–18] and dechlorination of organic compounds [19,20]) can be considered as reasons of increased attention to the Fe–Pd thin films. Different methods have been proposed to synthesize Fe–Pd thin films; including electron-beam evaporation and sputter- ing [15,21,22], melt spinning [5,23], arc melting [3–5,12] and electrodeposition [6–9,24]. Among these techniques the electrode- position is more desirable both economically and practically [8,9]. There are some reports on the electrodeposition of Fe–Pd alloys in ammonium citrate [8,24], ammonium tartrate [6,9] and sulfos- alicylic acid solutions [7,16]. Although all of the electrolytes are effective to co-deposition of Fe–Pd alloys, it is difficult to achieve a wide range of chemical composition of the thin layers with- out varying the electrolyte composition [8,16]. In addition, most studies on electrodeposition of Fe–Pd alloys have been dedicated to investigation of their physical properties whereas their depo- ∗ Corresponding author. Tel.: +98 21 66165219; fax: +98 21 66005717. E-mail address: ghorbani@sharif.edu (M. Ghorbani). sition process from electrochemical point of view has been less attended. Characterization of alloy electrodeposition is useful to recognize the relation between thin films properties and the mechanism of electrodeposition [25,26]. Therefore, the need of a comprehensive study with a focus on the mechanism of Fe–Pd alloy electrodepo- sition seems to be essential. The aim of present study is to develop a stable electrolyte to achieve a wide range of Fe–Pd alloy thin films. Moreover, cyclic voltammetry and chronoamperometry techniques were applied to study the mechanism of the electrodeposition process. The effect of cathodic potential on overpotential deposition (OPD) and also on the number of nucleation sites has been investigated. 2. Experimental 2.1. Materials Electrolytes were prepared using analytical grade of FeSO 4 ·7H 2 O and PdCl 2 as the parent metal ions with the dif- ferent concentrations ratio. NH 4 OH and Na 3 C 6 H 5 O 7 ·2H 2 O were used as the complexing agents for palladium and iron ions, respectively. H 3 BO 3 and (NH 4 ) 2 SO 4 were utilized as additive and supporting electrolyte. The chemical compositions of the solutions are listed in Table 1. The pH of the electrolytes was adjusted to 8 using ammonia solution. At such levels of pH, hydrogen evolution on the cathode surface is not an issue of concern. The working electrode was a copper wire with surface area about 1 cm 2 and roughness less than 20 nm. The counter electrode was a 316L 0013-4686/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2010.09.022