In situ stress measurements during aluminum deposition from AlCl3-EtMeImCl ionic liquid

In situ stress measurements were made during aluminum electrodeposition from Lewis acidic aluminum chloride-1-ethyl-3-methylimidazolium chloride (AlCl3-EtMeImCl) using the wafer curvature method. The underpotential deposition of Al on (111)-textured Cu shows a stress response that is consistent with a two-step process where the first step involves the desorption of AlCl4- from the Cu surface. This results in a tensile surface stress which is consistent with adsorbate-induced stress models that appear in the literature. The tensile stress is eliminated when the full incommensurate monolayer of aluminum is formed. On (111)-textured Au, the full Al monolayer results in a tensile stress that can be attributed to both lattice misfit and Al-Au alloying. The bulk deposition of Al on (111)-textured Au appears to be governed by Stranski-Krastanov three-dimensional growth. Initially a compressive stress is observed that we attribute to capillarity effects. This is followed by a rapid increase in tensile stress that is consistent with nuclei coalescence and grain boundary formation. In this region of nucleation and growth, the total stress is the superposition of both stress mechanisms and each is dependent on the deposition potential.