Low temperature electrochemical deposition of highly active elements

Electrochemical methods are attractive for thin film deposition due to their simplicity, conformal and high rate deposition, the ability to easily make multilayers of different composition, ease of scale-up to large surface areas, and applicability to wide variety of different shapes and surface geometries. However, many elements from periodic table of commercial importance are too active to be electrodeposited from aqueous solution. Recent advances are briefly reviewed for room temperature methods for electrochemical deposition, including electrodeposition from ionic liquids, electrodeposition from organic solvents, combined electrodeposition and precipitation on liquid metal cathodes, and galvanic deposition. Recent studies of electrodeposition from ionic liquids include deposition of thick (40 μm) Al coatings on high-strength steel screws in a manufacturing environment; deposition of continuous Si, Ta and Nb coatings; and numerous interesting mechanistic studies. Recent studies of electrodeposition from organic solvents include Al coatings from the AlCl3-dimethylsulfone electrolyte, which demonstrate that additives can be employed to suppress impurity incorporation and to improve the deposit quality, and thick (5-7 μm) and continuous Si coatings from SiCl4 in acetonitrile. Galvanic deposition of Ti, Mo and Si coatings onto Al alloys has recently been reported, which is potentially much simpler and less expensive than electrodeposition from ionic liquids and organic solvents, but has complications associated with substrate consumption and coating adhesion.