Combined Ion Conductance and Atomic Force Microscope for Fast Simultaneous Topographical and Surface Charge Imaging

Area of Science:

• Surface science
• Nanotechnology
• Electrochemistry

Background:

• Accurate characterization of surface charge and topography is crucial for understanding interfacial phenomena.
• Conventional methods for probing local surface charges, such as using glass nanopipettes, face limitations in sensitivity and stability, particularly in low ionic strength electrolytes.
• Atomic Force Microscopy (AFM) provides high-resolution topographical imaging but lacks direct, sensitive charge mapping capabilities.

Purpose of the Study:

• To develop and demonstrate an advanced approach for simultaneous and independent submicroscale imaging of local surface charge and topography.
• To enhance the sensitivity and speed of charge mapping, especially in challenging conditions like low ionic strength solutions.
• To investigate the physical limits of high-speed scanning for charge and topography imaging.

Main Methods:

• Utilizing microchanneled cantilevers, known as FluidFM nanopipette probes, for simultaneous ion current and force measurements.
• Employing ion current rectification through a 300 nm nanopipette opening to probe electrical double layer properties.
• Integrating FluidFM's force sensing for precise vertical positioning and topography imaging, analogous to AFM contact mode.

Main Results:

• Achieved simultaneous and independent imaging of topographical and surface charge at high scanning rates (thousands of pixels per second), exceeding previous methods by two orders of magnitude.
• Demonstrated high positioning accuracy comparable to standard AFM, without compromising simultaneous charge mapping.
• Successfully probed local surface charges in electrolytes with low ionic strength (below 10 mM) with enhanced sensitivity and stability.
• Identified the physical limitations of high-speed scanning, governed by ion redistribution dynamics in surface-induced rectification.

Conclusions:

• The FluidFM nanopipette probe offers a powerful and rapid platform for simultaneous topographical and surface charge imaging.
• This technique significantly improves the ability to study electrical double layers and surface charges, particularly in low ionic strength environments.
• The high-speed capabilities open new avenues for real-time analysis of interfacial dynamics and material characterization.