(Invited) Electrodeposition of In and Ga from Non-Aqueous Electrolytes

Abstract

Indium and gallium are metals whose applications have increased during the last decades. Both metals are primarily used in the form of binary, tertiary or quaternary (semi)conductor compounds in integrated circuits, photovoltaics, liquid crystal display devices, lasers and light-emitting diodes.In the past, the electrodeposition of indium and gallium has been investigated from both aqueous and non-aqueous electrolytes. Due to the negative standard reduction potentials of the two metals (E°In(III)/In(0) = −0.34 V and E°Ga(III)/Ga(0) = −0.53 V), their electrodeposition from aqueous electrolytes is hampered. This is especially true for gallium. In this talk, the electrodeposition of indium and gallium was investigated from several organic solvents. The investigated electrolytes are 1,2-dimethoxyethane (DME), polyethylene glycol (PEG), dimethyl sulfoxide (DMSO), and acetonitrile, containing chloride, bistriflimide, or methanesulfonate-based indium or gallium precursors.The electrochemistry and the electrodeposition of indium and gallium was studied using various electrochemical methods in combination with quartz crystal microbalance (QCM) and rotating (ring) disk electrodes. DMSO-based electrolytes enabled the electrodeposition of indium at room temperature and above its melting point (159.6 °C), while DME electrolytes gave rise to gallium electrodeposits composed of small liquid gallium spheres (Fig 1). In all the investigated electrolytes, the formation of intermediate monovalent indium(I) or gallium(I) species during reduction and oxidation was demonstrated. These species are unstable and react away via disproportionation reactions. Yet, it was found that the extent of their formation and their stability depends on the nature of the electrolyte. In addition, the electrodeposition of indium antimonide (InSb) films and eutectic gallium indium (EGaIn) liquid metal lines and patterns will be discussed, as well as the electrochemical synthesis of spherical indium nanoparticles.