Understanding the atomic-scale contrast in Kelvin Probe Force Microscopy

TL;DR

This paper investigates the atomic-scale contrast in Kelvin probe force microscopy through atomistic simulations and experimental comparisons, revealing that contrast arises from ion polarization effects rather than surface potential magnitude.

Contribution

It provides a detailed numerical analysis linking atomic-scale KPFM contrast to ion polarization mechanisms, aligning with experimental results.

Findings

Atomic-scale CPD reflects ionic crystal periodicity.

Contrast is due to ion polarization, not surface potential magnitude.

Simulation results agree with experimental observations.

Abstract

A numerical analysis of the origin of the atomic-scale contrast in Kelvin probe force microscopy (KPFM) is presented. Atomistic simulations of the tip-sample interaction force field have been combined with a non-contact Atomic Force Microscope/KPFM simulator. The implementation mimics recent experimental results on the (001) surface of a bulk alkali halide crystal for which simultaneous atomic-scale topographical and Contact Potential Difference (CPD) contrasts were reported. The local CPD does reflect the periodicity of the ionic crystal, but not the magnitude of its Madelung surface potential. The imaging mechanism relies on the induced polarization of the ions at the tip-surface interface owing to the modulation of the applied bias voltage. Our findings are in excellent agreement with previous theoretical expectations and experimental observations.