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

摘要

The surface stress associated with the underpotential deposition (upd) of lead on (11 l)-textured Au is examined, using the wafer curvature method, in acidic perchlorate supporting electrolyte. The surface stress is correlated to theta, the fractional Pb coverage, by independent nanogravimetric measurements using an electrochemical quartz crystal nanobalance (EQNB). The gravimetric results are similar to the data found in the literature, showing an electrosorption valency of 2 and the formation of a hexagonal close-packed monolayer of Pb. The complete Pb monolayer causes an overall compressive surface stress change of about -1.2 N m~(-1). The stress-coverage curve can be divided into two linear regions separated by a plateau. The region at low to intermediate coverage is caused by the formation of Au-Pb bonds which decrease the charge density and reduce the tensile surface stress inherent to the clean Au surface. In the second linear region at high coverage, the Pb adlayer compresses and behaves as a free-standing elastic film with a biaxial modulus close to that for Pb (111) in the bulk. The plateau that separates these two linear regions corresponds to the stress relaxation "hump" that appears in the stress-potential curve. This stress relaxation is attributed to island coalescence.