Microsecond Electron Drift Observed by Band-Pass Kelvin Probe Force Microscopy

Carrier drift in materials critically influences the performance of devices, such as transistors, solar cells, and lithium-ion batteries. While many advanced Kelvin Probe Force Microscopy (KPFM) techniques have been developed for characterizing ionic drift, visually observing electron drift is challenging. This difficulty arises because electrons drift much faster than ions but are more susceptible to instrumental noise, necessitating methods with higher spatiotemporal resolution and improved signal-to-noise ratios. Here, we introduce a band-pass Kelvin Probe Force Microscopy (BP-KPFM) method that employs the frequency spectrum analysis of probe deflection along with a custom band-pass algorithm. This technique achieves precise quantitative measurements of potential with nanometer spatial and microsecond temporal resolution, capturing the dynamic and inhomogeneous process of electron drift at an average velocity of 1.4 ± 0.1 nm/μs. The BP-KPFM method can be applied broadly to study fast charge transport processes in advanced information and energy devices.