High-speed mapping of surface charge dynamics using sparse scanning Kelvin probe force microscopy

Abstract

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, which combines sparse scanning and image reconstruction. This approach is shown to enable sub-second imaging (>3 frames per second) of nanoscale charge dynamics, representing several orders of magnitude improvement over traditional Kelvin probe force microscopy imaging rates. Bridging this improved spatiotemporal resolution with macroscale device measurements, we successfully visualize electrochemically mediated diffusion of mobile surface ions on a LaAlO3/SrTiO3 planar device. Such processes are known to impact band-alignment and charge-transfer dynamics at these heterointerfaces. Furthermore, we monitor the diffusion of oxygen vacancies at the single grain level in polycrystalline TiO2. Through temperature-dependent measurements, we identify a charge diffusion activation energy of 0.18 eV, in good agreement with previously reported values and confirmed by DFT calculations. Together, these findings highlight the effectiveness and versatility of our method in understanding ionic charge carrier motion in microelectronics or nanoscale material systems.

Accelerated Nano-Optical Imaging through Sparse Sampling

“…The acceleration of the measurements has important implications, as SNOM measurements are prone to drift in piezo steering, excitation laser pointing and steering, and tip quality degradation in the time scale that it takes to collect traditional raster scans. Therefore, increases in the speed enabled by GP regression-aided spiral scanning can uncover features that have been hidden by system drift …”

“…Therefore, increases in the speed enabled by GP regressionaided spiral scanning can uncover features that have been hidden by system drift. 56 As mentioned above, the implementation of sparse sampling is the first step toward more advanced data acquisition techniques. The first logical progression of our technique is toward accelerated nano-Fourier transform infrared measurements from three-dimensional sparsely sampled data (two spatial dimensions and one spectral dimension).…”