Tracking charge dynamics by high speed and time resolved Kelvin Probe Force Microscopy

L. Collins
Oak Ridge National Laboratory,
United States

Keywords: charge dynamics, Kelvin probe force microscopy, energy materials


The understanding of charge dynamics and electrochemical processes is integral to the progression of materials and devices, including batteries, fuel cells, and bioelectronics to name but a few. Nonetheless, analyzing electronic, ionic, and electrochemical processes across varying time and length scales poses significant difficulties. Kelvin probe force microscopy (KPFM) offers high spatial resolution, essential for exploring critical material heterogeneities such as grain boundaries, domain walls, and interfaces. However, KPFM's limited imaging speed curtails its efficacy in studying dynamic/kinetic processes. This presentation will introduce two potential solutions: time resolved KPFM and high-speed imaging KPFM. Time-resolved KPFM, inclusive of G-Mode KPFM (1,2,3), can examine rapid, repeatable events from milliseconds to sub-microseconds and even nanoseconds. These methods have proven particularly beneficial for the spatiotemporal characterization of bias or photogenerated charge carriers, which will be demonstrated in this presentation with various hybrid perovskite solar cell materials. However, when probing non-cyclo-stationary or irreversible occurrences like structural modifications or chemical reactions—for instance, the formation of a solid-electrolyte interface layer in a battery—a unique approach is required. In response, we've developed high-speed KPFM imaging, incorporating sparse spiral scanning and image reconstruction via Gaussian processing. We show that spiral scan KPFM (SS-KPFM (4)) allows imaging at approximately 3-4 images per second, ideal for capturing slowers process within the 100s millisecond - minutes range. The presentation will exhibit the usefulness of this approach for the spatiotemporal characterization of several energy-related materials by SS-KPFM, including charge dynamics at a LaAlO3/SrTiO3 planar device and charge diffusion dynamics in polycrystalline TiO2 thin films. 1. Collins, L., et al. (2017). Breaking the Time Barrier in Kelvin Probe Force Microscopy: Fast Free Force Reconstruction Using the G-Mode Platform. ACS Nano, 11, 8717-8729. 2. Giridharagopal, R., et al. (2019). Time-resolved electrical scanning probe microscopy of layered perovskites reveals spatial variations in photoinduced ionic and electronic carrier motion. ACS Nano, 13(3), 2812-2821. 3. Collins, L., et al. (2020). Correlation of Spatiotemporal Dynamics of Polarization and Charge Transport in Blended Hybrid Organic–Inorganic Perovskites on Macro-and Nanoscales. ACS Applied Materials & Interfaces, 12(13), 15380-15388. 4. Checa, M., et al. (2023). High Speed Mapping of Surface Charge Dynamics via Spiral Scanning Kelvin Probe Force Microscopy. Nature Communications, 14, 7196.