Detection of injected charges by Kelvin probe and multimode electrostatic force microscopy

Electrical charges were injected into a PMMA electret by applying a voltage pulse between tip and sample. The charge pattern was detected by Kelvin probe force microscopy (KFM) and multimode electrostatic force microscopy (MM-EFM) under ambient conditions. In MM-EFM topography and surface potential can be obtained simultaneously because different frequencies are used to demodulate the corresponding signals. Both techniques provide a comparable resolution. MM-EFM is a single pass technique and thus offers twice the imaging speed of KFM under ambient conditions.