Quantitative atomic force microscopy, regardless of operation mode

Since the invention of the atomic force microscope (AFM), various mode-specific methods for analysis of AFM data have emerged. However, a recent article by Hagen Söngen, Ralf Bechstein and Angelika Kühnle sets out a unique approach for quantitative analysis of AFM data, which works for all operation modes. The researchers from the Johannes Gutenberg University Mainz take us through their Open Access Journal of Physics: Condensed Matter paper below:

In our paper, we derive the three AFM equations, which allow us to quantitatively analyze AFM data obtained in any mode. Our analysis reveals that any dynamic AFM experiment allows us to obtain three (and only three) pieces of information about the tip-sample force: the averaged even force, the averaged tip-sample force gradient and the averaged tip-sample damping constant.

In 1986, the atomic force microscope was invented, and shortly afterwards, several different operation modes were developed. These modes include, for example, the static AFM mode and the dynamic AFM modes amplitude modulation, phase modulation and frequency modulation. The great variety of AFM operation modes has led to the development of various methods for the quantitative analysis of AFM data. However, these methods have been developed in view of specific modes only, often relying on mode-specific assumptions. This may lead to the conclusion that different modes require different methods for data analysis. In our article, we demonstrate that the contrary is the case: the three AFM equations we present allow to quantitatively analyze AFM data obtained in any mode.

We employ only one approximation for deriving the three AFM equations: the harmonic approximation. This facilitates a comparison of data acquired in different modes. Moreover, no mode-specific analysis is necessary. Even at poor feedback-loop performance (for example in the frequency-modulation mode), the three AFM equations remain valid.

Find the full, free-to-read paper HERE

This paper forms part of the new Special issue on Advanced Applications of Non-Contact Atomic Force Spectroscopy.

Find out more about the Special issue HERE

About the Authors

Hagen Söngen is just about to finish his PhD at the Johannes Gutenberg University Mainz in Germany. His scientific work focuses on an atomistic understanding of mineral—water interfaces.

Ralf Bechstein is senior researcher in the group of Angelika Kühnle. He studied Physics in Jena, obtained his PhD with Angelika Kühnle and was a postdoc with Flemming Besenbacher at Aarhus University.  His scientific interest covers interfacial properties and processes.

Angelika Kühnle is professor at the Institute of Physical Chemistry at the Johannes Gutenberg University Mainz, Germany. Her works focuses on the behavior of molecules at interfaces, where she is particularly interested in their self-assembly. In her group, she applies AFM under ultra-high vacuum conditions and in liquid environments – using both the amplitude modulation and the frequency modulation mode.

This work is licensed under a Creative Commons Attribution 3.0 Unported License.

Cover image from J. Phys.: Condens. Matter 29 274001 © IOP Publishing

Categories: Journal of Physics: Condensed Matter, JPhys+

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