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• Artifact-free Surface Potential Imaging

Artifact-free Surface Potential Imaging

Due to the finite scanning probe microscopy (SPM) tip radius and resulting geometric convolution between tip and sample surface, nano-resolution surface potential (SP) or electric force measurement (EFM) cannot be free from topographic artifacts. Here, we present a method that suppresses image features caused by surface variations by modifying conventional Kelvin probe microscopy (KPM).

For conventional KPM, only the first harmonic component of tip oscillation signal (either oscillation amplitude for AM-KPM or frequency shift for FM-KPM) induced by applied AC voltage has been used. However, the first harmonic signal depends not only on tip-sample potential difference but also capacitance gradient (AM-KPM) or second order gradient (FM-KPM), the main cause of topographical artifacts. By using the second harmonic component, which is proportional only to the capacitance gradient or second order gradient, we are able to extract true potential difference signal, free of geometric artifacts by dividing first and second order harmonics.

Surface potential mapping on an equipotential surface verifies that this new method reduces the magnitude of topological artifacts significantly. Besides, tip-sample separation dependency of measured potential was diminished by more than 10 times.

Figure 1: Conventional and modified KPM Setup

Figure 2: Significant artifact suppression using the modified KPM