Numerical Correction of In Situ AFM-SECM Measurements

Area of Science:

• Electrochemistry
• Surface Science
• Microscopy

Background:

• Mass-transport-limited catalysis and membrane transport rely on concentration profiles near active surfaces.
• Scanning electrochemical microscopy (SECM) measures these profiles but its tip can distort diffusion and alter surface chemistry.
• Accurate characterization of surface features requires accounting for and removing tip-induced distortions.

Purpose of the Study:

• To quantify the distortion of concentration profiles caused by SECM tip geometry.
• To develop a method for analytically removing tip effects to reveal intrinsic surface properties.
• To compare the distortion introduced by different AFM-SECM tip geometries.

Main Methods:

• Atomic force microscopy-based SECM (AFM-SECM) was used to collect approach curves over PTFE and gold electrode surfaces.
• Finite element method (FEM) modeling was employed to inversely fit the experimental approach curves.
• Kinetic and geometric tip parameters were derived to characterize tip-induced diffusion hindrance.

Main Results:

• Tip presence can increase local concentration by up to 120% at one tip radius above the surface.
• The tip compresses the concentration field vertically, with distortion proportional to surface feature size and tip separation.
• Conical AFM-SECM tips cause less concentration distortion than disk-shaped tips due to their geometry.

Conclusions:

• Analytical removal of tip effects using AFM-SECM and FEM modeling allows for accurate estimation of intrinsic concentration profiles and reaction properties.
• Understanding and correcting for tip-induced distortions is crucial for precise electrochemical surface characterization.
• Tip geometry significantly impacts measurement fidelity, with conical tips offering improved accuracy.