Diffuse layer properties of thiol-modified gold electrodes probed by direct force measurements

Area of Science:

• Electrochemistry
• Surface Science
• Nanotechnology

Background:

• Understanding diffuse layer properties is crucial for electrochemical applications.
• Gold electrodes modified with self-assembled monolayers (SAMs) offer tunable surface characteristics.
• Direct force measurements provide a unique approach to probe interfacial phenomena.

Purpose of the Study:

• To determine diffuse layer properties of modified gold electrodes using direct force measurements.
• To investigate the influence of SAM thickness and terminal functional groups on electrode properties.
• To quantitatively describe interaction force profiles and correlate them with electrochemical parameters.

Main Methods:

• Utilized atomic force microscopy (AFM) with a colloidal probe for direct force measurements.
• Modified gold electrodes with self-assembled monolayers (SAMs) of varying thickness and functional groups.
• Applied potentiostatic control to the gold electrodes during measurements.
• Fitted interaction force profiles to nonlinear Poisson-Boltzmann equation solutions, incorporating charge regulation.

Main Results:

• Accurate quantitative description of force profiles was achieved by considering charge regulation.
• Diffuse layer potentials were determined and studied in relation to the applied electrode potential.
• Capacitance and potential of zero charge (pzc) of SAMs were successfully measured.
• SAM capacitance correlated with monolayer thickness and crystalline structure.
• Distinct pzc differences were observed for different functional groups, linked to their dipole moments.

Conclusions:

• Direct force measurements offer a reliable method to characterize modified gold electrodes.
• SAM properties like capacitance and pzc are significantly influenced by monolayer structure and terminal groups.
• The findings align with classical electrochemical techniques and ion adsorption theories, with reduced effects compared to bare gold.