Alloy Electrodeposition

摘要

Alloy electrodeposition was first developed in the 1840s at nearly the same time as metal deposition, with brass coatings being an early commercial application. Despite this long history, alloy electrodeposition continues to attract attention; the majority of the electrodepo-sition-related articles published by The Electrochemical Society are on alloys. The enduring interest in alloy electrodeposition is tied to the wide range and tunability of physical properties one can achieve by varying alloy composition. As a result, most high-value-added applications of electrodeposition involve alloys, with the notable exception of copper interconnects for integrated circuits. For example, in the emerging field of nano- and microelectromechanical systems (NEMS/MEMS), alloying is key for achieving materials that are sufficiently strong to withstand grueling mechanical and environmental demands.~1 Other recent examples of alloy electrodeposition from the Journal and Letters include lithium-ion secondary battery anodes, magnetic recording materials, solder bumps, and catalysts for direct methanol fuel cells. The purpose of this tutorial is to provide non-expert practitioners of the art a flavor for the science, engineering, and issues that underpin and rationalize alloy electrodeposition. Electrodeposition involves the reduction of precursor metal ions and/or metal ion complexes from solution at a conductive substrate. (Chemical reductants are used as the source of electrons in electroless deposition.) At a minimum, an alloy electrodeposition process requires an electrolyte with two or more reducible metal ions, a conductive substrate, a counter electrode, a power supply, and a container to hold the electrolyte and electrodes. This simplicity accounts for the appeal of electrodeposition, but may also lead one to neglect some basic controls needed to ensure reproducibility. As we describe below, good alloy electrode-position also requires a means for reproducibly mixing the electrolyte, some consideration of cell geometry, and, like all electrodeposition processes, careful substrate preparation.