We have designed a new apparatus, an electrochemical SFA, for measuring the forces between symmetric gold electrode surfaces under electrochemical potential control. The surface separation was determined by two-beam (twin-path) interferometry. The potential was applied to the gold surfaces (working electrode) in 1mM aqueous KClO4 using Ag/AgCl as the reference and Pt as the counter electrode. We observed the van der Waals attraction and the double layer repulsion which decreased with the increasing potential from -0.1 to 0.2V (vs. Ag/AgCl).
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