Geometric artefact suppressed surface potential measurements

Abstract

Due to the finite scanning probe microscopy (SPM) tip radius and the resulting geometricconvolution between the tip and the sample surface, nano-resolution surface potential (SP)or electric force measurement (EFM) cannot be free from topographic artefacts. Forconventional Kelvin probe microscopy (KPM), only the first harmonic component of the tiposcillation signal (either oscillation amplitude for amplitude-modulated AM-KPM orfrequency shift for frequency-modulated FM-KPM) induced by the applied acvoltage is typically used. However, the first harmonic signal depends not only ontip–sample potential difference, but also on the capacitance gradient (AM-KPM) or thesecond-order gradient (FM-KPM), the main cause of topographical artefacts. Since thesecond-order harmonic component is proportional only to the capacitance gradient orsecond-order gradient, we are able to extract true potential difference signals,free of geometric artefacts, by dividing the first- and second-order harmonics.Surface potential mapping on an equipotential surface verifies that this alternativemethod significantly reduces the magnitude of topological artefacts. In addition,adoption of the proposed imaging method reduces the dependence of the measuredpotential on the tip–sample separation by more than an order of magnitude.