Underpotential Deposition of Tl on (111)-Textured Au: In Situ Stress and Nanogravimetric Measurements

The surface stress associated with the underpotential deposition (upd) of thallium (Tl) on (111)-textured Au is examined, using the wafer curvature method in acidic perchlorate supporting electrolyte. The process is also examined by independent nanogravimetric measurements using an electrochemical quartz crystal nanobalance (EQCN). We observe a sweep rate dependence for both the individual voltammetric waves and stress response, which we attribute to kinetically controlled surface alloying that occurs only it low coverage. Similar behavior has been reported for Pb upd on (111)-textured Au, hut the kinetics for Tl considerably slower and are very sensitive to the defect density of the Au(111) surface. At high coverage. a full Tl monolayer is formed; however. a dealloying step is required prior to completion of the monolayer. The stress hump that is coincident with the last voltammetric wave appears to he caused by the formation and removal of the surface alloy. This is confirmed by long-term potentiostatic pulsing experiments.