Photothermally Excited Contact Resonance Imaging in Air and Water

TL;DR

This paper introduces a photothermal excitation method for Contact Resonance Force Microscopy, enabling clear resonance imaging in air and liquids, which enhances the technique's applicability to biological and soft samples.

Contribution

The study demonstrates that photothermal actuation produces cleaner resonance spectra in CR-FM, allowing accurate measurements in both air and liquid environments, unlike traditional piezo excitation.

Findings

Clear contact resonance spectra obtained with photothermal excitation

Quantitative modulus measurements agree with expected values

Extended CR-FM applicability to biological and soft samples in liquids

Abstract

Contact Resonance Force Microscopy (CR-FM) is a leading AFM technique for measuring viscoelastic nano-mechanical properties. Conventional piezo-excited CR-FM measurements have been limited to imaging in air, since the "forest of peaks" frequency response associated with acoustic excitation methods effectively masks the true cantilever resonance. Using photothermal actuation results in clean contact resonance spectra, that closely match the ideal frequency response of the cantilever, allowing unambiguous and simple resonance frequency and quality factor measurements in air and liquids alike. This extends the capabilities of CR-FM to biologically relevant and other soft samples in liquid environments. We demonstrate CR-FM in air and water on both stiff silicon/titanium samples and softer polystyrene-polyethylene-polypropylene polymer samples with the quantitative moduli having very good agreement between expected and measured in both environments.