Abstract
Exquisite control of the electrodeposition of metal films and coatings is critical to a number of high technology and manufacturing industries, delivering functionality as diverse as anti-corrosion and anti-wear coatings, electronic device interconnects and energy storage. The frequent involvement of more than one metal motivates the capability to control, maintain and monitor spatial disposition of the component metals, whether as multilayers, alloys or composites. Here we investigate the deposition, evolution and dissolution of single and two-component metal layers involving Ag, Cu, and Sn on Au substrates immersed in the deep eutectic solvent (DES) Ethaline. During galvanostatically controlled stripping of the metals from two-component systems the potential signature in simultaneous thickness electrochemical potential (STEP) measurements provides identification of the dissolving metal; coulometric assay of deposition efficiency is an additional outcome. When combined with quartz crystal microbalance (QCM) frequency responses, the mass change : charge ratio provides oxidation state data; this is significant for Cu in the high chloride environment provided by Ethaline. The spatial distribution (solvent penetration and external roughness) of multiple components in bilayer systems is provided by specular neutron reflectivity (NR). Significantly, the use of the recently established event mode capability shortens the observational timescale of the NR measurements by an order of magnitude, permitting dynamic in situ observations on practically useful timescales. Ag,Cu bilayers of both spatial configurations give identical STEP signatures indicating that, despite the extremely low layer porosity, thermodynamic constraints (rather than spatial accessibility) dictate reactivity; thus, surprisingly, Cu dissolves first in both instances. Sn penetrates the Au electrode on the timescale of deposition; this can be prevented by interposing a layer of either Ag or Cu.
Highlights
Faraday Discussions͘ZŽďĞƌƚ,ŝůůŵĂŶϭΎZŽďĞƌƚĂƌŬĞƌϮZŽďĞƌƚDĂůŐůŝĞƐŚϯsŝƌŐŝŶŝĂ͘&ĞƌƌĞŝƌĂκ ŵŵĂ:͘ZWĂůŝŶϭZĂĐŚĞůD^ĂƉƐƚĞĂĚϭŵŵĂ>͘^ŵŝƚŚρEŝŶĂͲ:ƵůŝĂŶĞ^ƚĞŝŶŬĞϯ ĞŝĐĞƐƚĞƌ hŶŝǀĞƌƐŝƚLJ ZŽĂĚ.
ΎŽƌƌĞƐƉŽŶĚŝŶŐĂƵƚŚŽƌĞŵĂŝůĂƌŚϳΛůĞĂĐƵŬ ϭĎƐƚƌĂĐƚ džƋƵŝƐŝƚĞĐŽŶƚƌŽůŽĨƚŚĞĞůĞĐƚƌŽĚĞƉŽƐŝƚŝŽŶŽĨŵĞƚĂůĨŝůŵƐĂŶĚĐŽĂƚŝŶŐƐŝƐĐƌŝƚŝĐĂůƚŽĂŶƵŵďĞƌ ŽĨŚŝŐŚƚĞĐŚŶŽůŽŐLJĂŶĚŵĂŶƵĨĂĐƚƵƌŝŶŐŝŶĚƵƐƚƌŝĞƐĚĞůŝǀĞƌŝŶŐĨƵŶĐƚŝŽŶĂůŝƚLJĂƐĚŝǀĞƌƐĞĂƐĂŶƚŝͲ ĐŽƌƌŽƐŝŽŶ ĂŶĚ ĂŶƚŝͲǁĞĂƌ ĐŽĂƚŝŶŐƐ ĞůĞĐƚƌŽŶŝĐ ĚĞǀŝĐĞ ŝŶƚĞƌĐŽŶŶĞĐƚƐ ĂŶĚ ĞŶĞƌŐLJ ƐƚŽƌĂŐĞ dŚĞ ĨƌĞƋƵĞŶƚŝŶǀŽůǀĞŵĞŶƚŽĨŵŽƌĞƚŚĂŶŽŶĞŵĞƚĂůŵŽƚŝǀĂƚĞƐƚŚĞĐĂƉĂďŝůŝƚLJƚŽĐŽŶƚƌŽůŵĂŝŶƚĂŝŶ ĂŶĚ ŵŽŶŝƚŽƌ ƐƉĂƚŝĂů ĚŝƐƉŽƐŝƚŝŽŶ ŽĨ ƚŚĞ ĐŽŵƉŽŶĞŶƚ ŵĞƚĂůƐ ǁŚĞƚŚĞƌ ĂƐ ŵƵůƚŝůĂLJĞƌƐ ĂůůŽLJƐ Žƌ ĐŽŵƉŽƐŝƚĞƐ,ĞƌĞǁĞŝŶǀĞƐƚŝŐĂƚĞƚŚĞĚĞƉŽƐŝƚŝŽŶĞǀŽůƵƚŝŽŶĂŶĚĚŝƐƐŽůƵƚŝŽŶŽĨƐŝŶŐůĞĂŶĚƚǁŽͲ ĐŽŵƉŽŶĞŶƚ ŵĞƚĂů ůĂLJĞƌƐ ŝŶǀŽůǀŝŶŐ Ő Ƶ ĂŶĚ ^Ŷ ŽŶ Ƶ ƐƵďƐƚƌĂƚĞƐ ŝŵŵĞƌƐĞĚ ŝŶ ƚŚĞ ĚĞĞƉ ĞƵƚĞĐƚŝĐ ƐŽůǀĞŶƚ ;^Ϳ ƚŚĂůŝŶĞ ƵƌŝŶŐ ŐĂůǀĂŶŽƐƚĂƚŝĐĂůůLJ ĐŽŶƚƌŽůůĞĚ ƐƚƌŝƉƉŝŶŐ ŽĨ ƚŚĞ ŵĞƚĂůƐ ĨƌŽŵ ƚǁŽͲĐŽŵƉŽŶĞŶƚ ƐLJƐƚĞŵƐ ƚŚĞ ƉŽƚĞŶƚŝĂů ƐŝŐŶĂƚƵƌĞ ŝŶ ƐŝŵƵůƚĂŶĞŽƵƐ ƚŚŝĐŬŶĞƐƐ ĞůĞĐƚƌŽĐŚĞŵŝĐĂů ƉŽƚĞŶƚŝĂů ;^dWͿ ŵĞĂƐƵƌĞŵĞŶƚƐ ƉƌŽǀŝĚĞƐ ŝĚĞŶƚŝĨŝĐĂƚŝŽŶ ŽĨ ƚŚĞ ĚŝƐƐŽůǀŝŶŐ ŵĞƚĂůĐŽƵůŽŵĞƚƌŝĐĂƐƐĂLJŽĨĚĞƉŽƐŝƚŝŽŶĞĨĨŝĐŝĞŶĐLJŝƐĂŶĂĚĚŝƚŝŽŶĂůŽƵƚĐŽŵĞtŚĞŶĐŽŵďŝŶĞĚ ǁŝƚŚƋƵĂƌƚnjĐƌLJƐƚĂůŵŝĐƌŽďĂůĂŶĐĞ;YDͿĨƌĞƋƵĞŶĐLJƌĞƐƉŽŶƐĞƐƚŚĞŵĂƐƐĐŚĂŶŐĞĐŚĂƌŐĞƌĂƚŝŽ ƉƌŽǀŝĚĞƐ ŽdžŝĚĂƚŝŽŶ ƐƚĂƚĞ ĚĂƚĂ ƚŚŝƐ ŝƐ ƐŝŐŶŝĨŝĐĂŶƚ ĨŽƌ Ƶ ŝŶ ƚŚĞ ŚŝŐŚ ĐŚůŽƌŝĚĞ ĞŶǀŝƌŽŶŵĞŶƚ ƉƌŽǀŝĚĞĚ ďLJ ƚŚĂůŝŶĞ dŚĞ ƐƉĂƚŝĂů ĚŝƐƚƌŝďƵƚŝŽŶ ;ƐŽůǀĞŶƚ ƉĞŶĞƚƌĂƚŝŽŶ ĂŶĚ ĞdžƚĞƌŶĂů ƌŽƵŐŚŶĞƐƐͿ ŽĨŵƵůƚŝƉůĞĐŽŵƉŽŶĞŶƚƐŝŶďŝůĂLJĞƌƐLJƐƚĞŵƐŝƐƉƌŽǀŝĚĞĚďLJƐƉĞĐƵůĂƌŶĞƵƚƌŽŶƌĞĨůĞĐƚŝǀŝƚLJ;EZͿ ^ŝŐŶŝĨŝĐĂŶƚůLJ ƚŚĞ ƵƐĞ ŽĨ ƌĞĐĞŶƚůLJ ĞƐƚĂďůŝƐŚĞĚ ĞǀĞŶƚ ŵŽĚĞ ĐĂƉĂďŝůŝƚLJ ƐŚŽƌƚĞŶƐ ƚŚĞ ŽďƐĞƌǀĂƚŝŽŶĂů ƚŝŵĞƐĐĂůĞ ŽĨ ƚŚĞ EZ ŵĞĂƐƵƌĞŵĞŶƚƐ ďLJ ĂŶ ŽƌĚĞƌ ŽĨ ŵĂŐŶŝƚƵĚĞ ƉĞƌŵŝƚƚŝŶŐ ĚLJŶĂŵŝĐ ŝŶ ƐŝƚƵ ŽďƐĞƌǀĂƚŝŽŶƐ ŽŶ ƉƌĂĐƚŝĐĂůůLJ ƵƐĞĨƵů ƚŝŵĞƐĐĂůĞƐ ŐƵ ďŝůĂLJĞƌƐ ŽĨ ďŽƚŚ ƐƉĂƚŝĂů ĐŽŶĨŝŐƵƌĂƚŝŽŶƐŐŝǀĞŝĚĞŶƚŝĐĂů^dWƐŝŐŶĂƚƵƌĞƐŝŶĚŝĐĂƚŝŶŐƚŚĂƚĚĞƐƉŝƚĞƚŚĞĞdžƚƌĞŵĞůLJůŽǁůĂLJĞƌ ƉŽƌŽƐŝƚLJ ƚŚĞƌŵŽĚLJŶĂŵŝĐ ĐŽŶƐƚƌĂŝŶƚƐ ;ƌĂƚŚĞƌ ƚŚĂŶ ƐƉĂƚŝĂů ĂĐĐĞƐƐŝďŝůŝƚLJͿ ĚŝĐƚĂƚĞ ƌĞĂĐƚŝǀŝƚLJ ƚŚƵƐƐƵƌƉƌŝƐŝŶŐůLJƵĚŝƐƐŽůǀĞƐĨŝƌƐƚŝŶďŽƚŚŝŶƐƚĂŶĐĞƐ^ŶƉĞŶĞƚƌĂƚĞƐƚŚĞƵĞůĞĐƚƌŽĚĞŽŶƚŚĞ ƚŝŵĞƐĐĂůĞŽĨĚĞƉŽƐŝƚŝŽŶƚŚŝƐĐĂŶďĞƉƌĞǀĞŶƚĞĚďLJŝŶƚĞƌƉŽƐŝŶŐĂůĂLJĞƌŽĨĞŝƚŚĞƌŐŽƌƵ.
^Ɛ ĂƌĞ ƐLJƐƚĞŵƐ ĨŽƌŵĞĚ ĨƌŽŵ ĞƵƚĞĐƚŝĐ ŵŝdžƚƵƌĞƐ ŽĨ ƌƆŶƐƚĞĚ Žƌ >ĞǁŝƐ ĂĐŝĚƐ ĂŶĚ ďĂƐĞƐ ƚLJƉŝĐĂůůLJ ŵŝdžƚƵƌĞƐ ŽĨ ƚŚĞ ƐĂůƚ ĐŚŽůŝŶĞ ĐŚůŽƌŝĚĞ ǁŝƚŚ ƐŵĂůů ŚLJĚƌŽŐĞŶ ďŽŶĚŝŶŐ ŵŽůĞĐƵůĞƐ ƐƵĐŚ ĂƐ ĞƚŚLJůĞŶĞ ŐůLJĐŽů Žƌ ƵƌĞĂ ϳ ^ ďĂƐĞĚ ĞůĞĐƚƌŽůLJƚĞƐ ŚĂǀĞ ďĞĞŶ ƵƐĞĚ ĨŽƌ ƚŚĞ ĞůĞĐƚƌŽĚĞƉŽƐŝƚŝŽŶŽĨĂǁŝĚĞƌĂŶŐĞŽĨŵĞƚĂůĂŶĚĂůůŽLJĐŽĂƚŝŶŐƐŝŶĐůƵĚŝŶŐƵΘε^ŶϭϬϭϭ͕ϭϮŶ ϭϯ ϭκ ƌϭρ ϭς ŶͬEŝ ϭϳ ĂŶĚ Ŷͬ^Ŷ ϭΘ dŚĞƐĞ ^ ĞůĞĐƚƌŽůLJƚĞ ŵĞĚŝĂ ŽĨĨĞƌ ƉƌŽƐƉĞĐƚŝǀĞ ŝŵƉƌŽǀĞŵĞŶƚƐ ŝŶ ƉƌŽĐĞƐƐ ĐŽŶƚƌŽůͬĞĨĨŝĐŝĞŶĐLJ ĞŶǀŝƌŽŶŵĞŶƚĂů ƐƵƐƚĂŝŶĂďŝůŝƚLJͬŝŵƉĂĐƚ ĂŶĚ ĨƵŶĐƚŝŽŶĂůŝƚLJ ĂƐ ǁĞůů ĂƐ ŐŝǀŝŶŐ ĂĐĐĞƐƐ ƚŽ ƌĞĂĐƚŝǀĞ ŵĞƚĂů ĚĞƉŽƐŝƚŝŽŶ ŶŽƚ ƉƌĞǀŝŽƵƐůLJ ƉŽƐƐŝďůĞ ;ĨŽƌĞdžĂŵƉůĞůͿ,ŽǁĞǀĞƌĚƵĞƚŽƚŚĞĨƵŶĚĂŵĞŶƚĂůĚŝĨĨĞƌĞŶĐĞƐďĞƚǁĞĞŶŵŽůĞĐƵůĂƌƐŽůǀĞŶƚƐ ůŝŬĞǁĂƚĞƌĂŶĚ/>Ɛͬ^ƐƚŚĞƌĞĂƌĞƐŝŐŶŝĨŝĐĂŶƚĚŝƐƉĂƌŝƚŝĞƐŝŶƚŚĞǁĂLJŵĞƚĂůĨŝůŵƐŶƵĐůĞĂƚĞĂŶĚ ŐƌŽǁŽŶƐƵƌĨĂĐĞƐϭεdŚŝƐƉƌĞƐĞŶƚƐŝŶƚĞůůĞĐƚƵĂůĂŶĚƉƌĂĐƚŝĐĂůĐŚĂůůĞŶŐĞƐŝŶŽƌĚĞƌƚŽďĞĂďůĞƚŽ ƵŶĚĞƌƐƚĂŶĚ ĂŶĚ ĐŽŶƚƌŽů ƚŚĞ ĐŽĂƚŝŶŐ ƉƌŽĐĞƐƐĞƐ ĂŶĚ ĞdžƉůŽŝƚ ƚŚĞ ƉŽƚĞŶƚŝĂů ďĞŶĞĨŝƚƐ ŽĨ ƚŚĞƐĞ ŵĞĚŝĂ tĞ ŚĂǀĞ ďĞĞŶ ĞŶŐĂŐĞĚ ŝŶ ƚŚĞ ƐƚƵĚLJ ŽĨ ĞůĞĐƚƌŽůLJƚŝĐ ŵĞƚĂů ĚĞƉŽƐŝƚŝŽŶ ĂŶĚ ĚŝƐƐŽůƵƚŝŽŶ ŝŶ ^ ŵĞĚŝĂ ǁŝƚŚ ƉĂƌƚŝĐƵůĂƌ ƌĞůĂƚŝŽŶ ƚŽ ƉŽƚĞŶƚŝĂů ĂƉƉůŝĐĂƚŝŽŶƐ ŝŶ ƚŚĞ ĞůĞĐƚƌŽŶŝĐƐ ŵĂŶƵĨĂĐƚƵƌŝŶŐ ƐĞĐƚŽƌƐϮϬ ,ĞƌĞ ŝƚ ŝƐ ŝŵƉŽƌƚĂŶƚ ƚŽ ďĞ ĂďůĞ ƚŽ ĐŽŶƚƌŽů ĂŶĚ ƉƌĞĚŝĐƚ ƌĂƚĞ ŽĨ ĚĞƉŽƐŝƚŝŽŶ ŽĨ ƚŚĞ ŵĞƚĂůĂƐǁĞůůĂƐƚŽĂĐŚŝĞǀĞƚĂƌŐĞƚǀĂůƵĞƐŽĨƐƵƌĨĂĐĞƌŽƵŐŚŶĞƐƐĂŶĚĐŽŚĞƌĞŶƚĚĞŶƐĞĐŽĂƚŝŶŐƐ DŽŶŝƚŽƌŝŶŐ ƐƵƌĨĂĐĞ ƌŽƵŐŚŶĞƐƐ Ĩŝůŵ ƚŚŝĐŬŶĞƐƐ ;ďŽƚŚ Ăƚ ƚŚĞ ŶĂŶŽŵĞƚƌĞ ƐĐĂůĞͿ ĂŶĚ ĚĞŶƐŝƚLJ κ.
Summary
͘ZŽďĞƌƚ,ŝůůŵĂŶϭΎZŽďĞƌƚĂƌŬĞƌϮZŽďĞƌƚDĂůŐůŝĞƐŚϯsŝƌŐŝŶŝĂ͘&ĞƌƌĞŝƌĂκ ŵŵĂ:͘ZWĂůŝŶϭZĂĐŚĞůD^ĂƉƐƚĞĂĚϭŵŵĂ>͘^ŵŝƚŚρEŝŶĂͲ:ƵůŝĂŶĞ^ƚĞŝŶŬĞϯ ĞŝĐĞƐƚĞƌ hŶŝǀĞƌƐŝƚLJ ZŽĂĚ.
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