Materials Chemistry and Physics 130 (2011) 1380–1386 Contents lists available at SciVerse ScienceDirect Materials Chemistry and Physics jo u rn al hom epage : www.elsevier.com/locate/matchemphys Effects of the anion in glycine-containing electrolytes on the mechanical properties of electrodeposited Co–Ni films E. Pellicer a,∗ , S. Pané b , K.M. Sivaraman b , O. Ergeneman b , S. Suri ˜ nach a , M.D. Baró a , B.J. Nelson b , J. Sort c a Departament de Física, Facultat de Ciències, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain b Institute of Robotics and Intelligent Systems (IRIS), ETH Zurich, CH-8092 Zurich, Switzerland c Institució Catalana de Recerca i Estudis Avanc ¸ ats (ICREA) and Departament de Física, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain a r t i c l e i n f o Article history: Received 20 January 2011 Received in revised form 23 August 2011 Accepted 12 September 2011 Keywords: B. Coatings C. Nanoindentation D. Mechanical properties D. Wear a b s t r a c t Tailoring of the mechanical properties (e.g., hardness, Young’s modulus or wear characteristics) of Co–Ni electrodeposits has been accomplished by changing the anion (sulphate versus chloride ions) in glycine-containing solutions at 80 ◦ C, while maintaining all the other electroplating conditions unal- tered. Galvanostatic deposition on metalized silicon substrates at 5–40 mA cm -2 produced well adherent Co–Ni films with varying surface finish, chemical composition (50–83 wt% Co), morphology and structure. The deposition from chloride salts yielded matte grey, cobalt-rich Co–Ni films with hexagonal close- packed structure and crystallite sizes around 65–85 nm. Films obtained under the same electrodeposition conditions from sulphate salts were Ni-rich, displayed smoother surfaces and smaller crystallite sizes (30–40 nm) belonging mainly to the face-centered cubic phase. The crystallite size played a key role on the mechanical properties of the films, while the composition and the phase percentage had little effect. It is thus demonstrated that the nature of the anion induces a large tunability both in the microstructure and mechanical properties of the deposits. In particular, the nanoindentation hardness could be varied between 1.6 and 7.1 GPa, while the Young’s modulus ranged between 122 and 181 GPa. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Studies on the electrodeposition of iron-group metals (Ni, Co and Fe) and their alloys have focused mainly on their soft mag- netic properties for use in microelectromechanical system (MEMS) technologies [1–3]. Compared to physical deposition methods, electrodeposition has a competitive edge for growing both thick or thin films and nanostructures due to its cost-effectiveness and ease of operation [4]. Electrodeposited cobalt–nickel (Co–Ni) alloy films have found a role in this field due to the large tunability in their electrochemical and physical properties, including the magnetic behavior, depending on the composition and microstructure [5,6]. Co–Ni alloys can be electroplated from a variety of salts (sulpha- mate, chloride, sulphates), eventually including a complexing agent (citrate has been the most commonly utilized) [7]. Deposition of Co–Ni is classified as anomalous, which means that cobalt, the less noble metal, is preferentially deposited [8]. As a consequence, the Co/Ni ratio in the deposits is higher than the [Co(II)]/[(Ni(II)] ratio in solution. Although the relationship between the composition, temperature, and pH of the baths and the applied electrodepo- sition parameters with the chemical composition, morphology, ∗ Corresponding author. Tel.: +34 93 581 14 01; fax: +34 93 581 21 55. E-mail address: Eva.Pellicer.icn@uab.cat (E. Pellicer). microstructure and magnetic behavior of the deposits has been investigated, literature regarding their mechanical response is lim- ited. While enhancement of the magnetic properties of Co–Ni is certainly important, other characteristics relevant to material pro- cessing and the end application should also be optimized. The tribological interactions of a magnetic material with its surround- ings are important in MEMS devices with sliding contacts involved [9]. For example, in ultra-high density magnetic recording systems, the hardness of writers used should match the hardness of the insu- lator to avoid pole recession during head lapping. The ability of the head to survive plastic deformation in the event of a contact must also be taken into account [1]. A very low surface roughness is also desired to minimize the probability of tribological problems occurring during operation. For instance, minimum roughness and internal stress coupled to high hardness are essential in electrode- posited Co–Ni microstructures used as metallic micro-moulds in the fabrication of microlens arrays [10]. In this work, the mechanical properties of Co–Ni films deposited from glycine-containing solutions have been investigated using nanoindentation. The results reveal that the chemical nature of the anion (sulphate and chloride) plays a key role in determining the composition, microstructure and, in particular, the crystallite size of the films. A series of structurally graded Co–Ni deposits (i.e., featuring different face-centered cubic, fcc, and hexagonal close- packed, hcp, phase percentages, and different crystallite sizes) have 0254-0584/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2011.09.032