Abstract
Ruthenium is electrodeposited for the first time from a deep eutectic solvent based electrolyte composed of ethylene glycol and choline chloride in 1:2 molar ratio. Deposition is found to effectively occur upon addition of sulfamic acid to the Ru(III) containing deep eutectic solvent. The main consequence of the presence of sulfamic acid, as evidenced by the electrochemical characterization performed, is the oxidation of Ru(III) to Ru(IV). Consequently, Ru electroreduction is demonstrated to take place from the tetravalent state. Optimized plating conditions are able to yield uniform and crack-free Ru coatings up to 800 nm thickness. No oxides or other notable secondary phases can be individuated in the obtained metallic layers. Morphological and electrical properties of the layers obtained are comparable with Ru coatings deposited from sputtering and suggest possible applications in the electronics field as barrier layers for interdiffusion.
Highlights
Ruthenium, a transition metal belonging to the same group of platinum,[1] is used nowadays in many different industrial applications: decorative and corrosion resistant coatings, wear protection for electrical contacts[2,3] and interdiffusion barrier layers.[4,5] interesting catalytic properties have been demonstrated for this bright white metal both in its metallic form[6] and as oxide.[7]
Ru deposition optimization.—Initially, galvanostatic ruthenium electrodeposition was attempted from a mixture of Choline chloride (ChCl)/ethylene glycol (EG) and 40 mM RuCl3
Copper was used as substrate and current density was varied over a broad range, but no reproducible ruthenium plating was achieved
Summary
A transition metal belonging to the same group of platinum,[1] is used nowadays in many different industrial applications: decorative and corrosion resistant coatings, wear protection for electrical contacts[2,3] and interdiffusion barrier layers.[4,5] interesting catalytic properties have been demonstrated for this bright white metal both in its metallic form[6] and as oxide.[7]. Ruthenium electrodeposition typically takes place from aqueous sulfamate based electrolytes containing the metal in the form of a bridged complex known as μ-nitridobisaquatetrachlororuthenate [Ru2(μ-N)(H2O)2Cl8].14–16 Deposition from these baths is characterized by a good cathodic efficiency (exceeding 90%) and by crack-free deposits up to 1–2 μm thickness. The aim of the present paper is the investigation of ruthenium electrodeposition from a DES obtained mixing choline chloride and ethylene glycol in 1:2 molar ratio This DES, belonging to the class III and commercially known as ethaline, is characterized by interesting physical and chemical properties and it constitutes a good electrolyte for the deposition of many metals. RuCl3 in different amounts (20 or 40 mM) was added to form the plating solution, which
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