Fabrication and characterization of dual sputtered Pd–Cu alloy films for hydrogen separation membranes H.T. Hoang a, * , H.D. Tong a , F.C. Gielens b , H.V. Jansen a , M.C. Elwenspoek a a Transducer Science and Technology Group, MESA + Research Institute, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands b Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands Received 2 April 2003; accepted 9 June 2003 Abstract In this paper, submicron thin Pd– Cu alloy films are deposited using a dual sputtering technique, which allows a high composition control of the layer. The composition, surface morphology and phase structure of the sputtered layers are investigated by energy-dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffractiometry (XRD). For example, the XRD data prove that the Pd– Cu layers are an alloy of Pd and Cu. Subsequently, the characterized Pd – Cu alloy layers are deposited on a silicon support structure to create a 750-nm thin Pd – Cu membrane for hydrogen separation. The reported membrane obtained a high flux of 1.6 mol H 2 /m 2 s at a temperature of 725 K, while the selectivity is at least 500 for H 2 /He. D 2003 Published by Elsevier B.V. Keywords: Dual sputtering; Pd – Cu alloy layers; Support structures; Pd – Cu alloy membranes; Hydrogen separation 1. Introduction The increased demand for hydrogen in recent years has led to a revival of interest in methods for separation and purification of hydrogen from gas mixtures in many sectors such as petroleum refining, petrochemical and semiconduc- tor processing, as well as in new energy-related applications such as clean fuel for fuel cells and vehicles [1–3]. Metal membranes with high perm selectivity for hydro- gen and good thermal, chemical, and mechanical properties are widely being used. From these metals, palladium (Pd) is predominantly used because of its high hydrogen perme- ability and compatibility with other gases in mixtures [4–6]. However, pure Pd membranes suffer from embrittlement due to the a- to h-phase transition during hydrogen absorp- tion, which often causes a destruction of the membrane structure [7–9]. They also suffer from poisoning due to hydrogen sulfide, sulfur contaminants and carbon monox- ide. For these reasons, Pd membranes have been alloyed with other metals such as silver (Ag), copper (Cu), gold (Au) or nickel (Ni). Among these membrane alloys, Pd–Ag is commonly used due to its high permeability of hydrogen and reduction of embrittlement [10–12]. Also, Pd–Cu membranes have been reported to have high resistance to hydrogen sulfide and sulfurous constituents in gas mixtures while maintain- ing a desirable set of properties [13,14]. Up to now, many deposition methods have been devel- oped to fabricate Pd–Cu composite membranes including electroless plating, electrodeposition, chemical vapor depo- sition (CVD) and sputtering [15–17]. Among these meth- ods, sputtering is a simple process with a high deposition rate and giving high purity layers [9,18]. This paper focuses on the fabrication of Pd–Cu alloy thin films with high composition control using the dual sputtering technique. Afterward, several characterization techniques like energy-dispersive spectrometry (EDS), X- ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffractiometry (XRD) are used to investigate the microstructure and surface morphology of layers. The optimized Pd–Cu alloy is subsequently deposited on a micromachined support structure to realize a Pd–Cu membrane to separate hydrogen from a gas mixture. 0167-577X/$ - see front matter D 2003 Published by Elsevier B.V. doi:10.1016/S0167-577X(03)00539-1 * Corresponding author. Tel.: +31-53-4894423; fax: +31-53-4893343. E-mail address: h.t.hoang@el.utwente.nl (H.T. Hoang). www.elsevier.com/locate/matlet Materials Letters 58 (2004) 525 – 528