Intermodulation electrostatic force microscopy for imaging surface photo-voltage

TL;DR

This paper introduces an intermodulation electrostatic force microscopy technique as a fast, open-loop alternative to Kelvin Probe Force Microscopy for imaging surface photo-voltage with high sensitivity.

Contribution

It develops a novel intermodulation-based method for surface potential imaging, validated through simulations, experiments, and application to organic photovoltaic materials.

Findings

High signal-to-noise ratio measurement of intermodulation products

Quantitative reconstruction of contact potential difference

Successful imaging of surface photo-voltage on organic material

Abstract

We demonstrate an alternative to Kelvin Probe Force Microscopy for imaging surface potential. The open-loop, single-pass technique applies a low-frequency AC voltage to the atomic force microscopy tip while driving the cantilever near its resonance frequency. Frequency mixing due to the nonlinear capacitance gives intermodulation products of the two drive frequencies near the cantilever resonance, where they are measured with high signal to noise ratio. Analysis of this intermodulation response allows for quantitative reconstruction of the contact potential difference. We derive the theory of the method, validate it with numerical simulation and a control experiment, and we demonstrate its utility for fast imaging of the surface photo-voltage on an organic photo-voltaic material.