Electrodeposition of metallic Cu from CuCl gas source transported into ionic liquid in a vacuum

The authors propose a new electrochemical process combined with vapor-phase deposition. In this process, an ionic liquid (IL) layer of ∼20-μm thickness is used as the electrolyte and then coated on a patterned electrode substrate. The desired source material to electro-deposit is then introduced into the IL layer by vapor deposition in a vacuum under the control of applied electrode potential. In this work, the authors have demonstrated that metallic Cu was electrodeposited in IL by depositing CuCl from the gas phase. At negative electrode potentials versus Cu, CuCl was able to be reduced to metallic Cu, while CuCl remained as-deposited at positive electrode potentials versus Cu. The current density during the electrodeposition was found to strongly correlate with the vapor deposition rate of CuCl at an electrode potential of -0.7 V versus Cu. This suggests that the rate-limiting step in this overpotential region was the vapor deposition rate of CuCl. The rate could then be used to directly modulate the size and density of metallic Cu crystal grains.