Tracking Charge Dynamics by High Speed and Time Resolved Kelvin Probe Force Microscopy

Understanding charge dynamics and electrochemical processes is crucial for advancing a wide range of materials and devices, including batteries, fuel cells, and bioelectronics. However, investigating electronic, ionic, and electrochemical phenomena across diverse time and length scales remains a significant challenge. Kelvin probe force microscopy (KPFM), with its high spatial resolution, is instrumental in probing key material features such as grain boundaries, domain walls, and interfaces. Despite its capabilities, KPFM's limited imaging speed restricts its effectiveness in studying dynamic processes. This presentation introduces two promising solutions: time-resolved KPFM and high-speed KPFM imaging. Time-resolved KPFM, including G-Mode KPFM (1,2,3), can capture rapid, fully reversible dynamics within timescales ranging from milliseconds to nanoseconds. These techniques are especially useful for the spatiotemporal analysis of bias-induced or photogenerated charge carriers, which will be demonstrated using various hybrid perovskite solar cell materials.
For non-cyclo-stationary or irreversible processes, such as structural transformations or chemical reactions—like the formation of a solid-electrolyte interface in batteries—a different approach is needed. To address this, we have developed high-speed KPFM imaging, leveraging sparse spiral scanning and image reconstruction through Gaussian processing. Spiral scan KPFM (SS-KPFM (4)) enables imaging at approximately 3-4 frames per second, making it suitable for capturing slower processes occurring over hundreds of milliseconds to minutes. This presentation will showcase the application of SS-KPFM for spatiotemporal characterization of energy-relevant materials, including charge dynamics in a LaAlO3/SrTiO3 planar device and charge diffusion in polycrystalline TiO2 thin films.

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