Direct Probing of Electrical Double Layers by Scanning Electrochemical Potential Microscopy

We report the direct experimental measurement of electrical double layer profiles on metallic (Pt foil) and insulator (SiO2 on Si) surfaces in a dilute electrolyte with no added redox mediator by scanning electrochemical potential microscopy (SECPM). An important consideration in these measurements is fabrication of the probe (tip), and experimental details are given for the reproducible preparation of suitable polyethylene-coated PtIr nanoelectrodes. A small amount of silver was electrodeposited on these tips to stabilize them for sensitive potentiometric measurements. A Pt foil surface and an oxide-grown Si(100) wafer in 10 μM KCl were approached to record the potential distribution in the vicinity of the surface. The advantages and limitations of SECPM are compared to conventional current-sensing techniques.