High Speed Mapping of Surface Charge Dynamics via Sparse Scanning Kelvin Probe Force Microscopy

Unraveling local dynamic charge processes is vital for progress in diverse fields, from microelectronics to energy storage. This relies on the ability to map charge carrier motion across multiple length- and timescales and understanding how these processes interact with the inherent material heterogeneities. Towards addressing this challenge, we introduce high-speed Sparse Scanning Kelvin Probe Force Microscopy (SS-KPFM), which combines sparse spiral scanning and image reconstruction via Gaussian process optimization. SS-KPFM enables sub-second imaging rates (3.3 fps) of nanoscale charge dynamics, representing several orders of magnitude improvement over traditional KPFM methods. Bridging this improved spatiotemporal resolution with macroscale device measurements, we demonstrate the applicability of this approach by visualizing electrochemically mediated diffusion of mobile surface ions on a LaAlO₃/SrTiO₃ planar device, processes which are known to impact band-alignment and charge-transfer dynamics at such heterointerfaces. Additionally, we track oxygen vacancy diffusion generated under a biased tip, at the single grain level in polycrystalline TiO₂. Temperature-dependent measurements reveal a charge diffusion activation energy of 0.18 eV, in good agreement with previously reported values and backed up here by further modelling. Together, these findings highlight the effectiveness and versatility of our method in understanding ionic charge carrier motion in microelectronics or nanoscale material systems.