Bimodal atomic force microscopy driving the higher eigenmode in frequency-modulation mode: Implementation, advantages, disadvantages and comparison to the open-loop case

Daniel Ebeling,Santiago D Solares

doi:10.3762/bjnano.4.20

Daniel Ebeling, Santiago D Solares

Open Access

https://doi.org/10.3762/bjnano.4.20

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Abstract

We present an overview of the bimodal amplitude–frequency-modulation (AM-FM) imaging mode of atomic force microscopy (AFM), whereby the fundamental eigenmode is driven by using the amplitude-modulation technique (AM-AFM) while a higher eigenmode is driven by using either the constant-excitation or the constant-amplitude variant of the frequency-modulation (FM-AFM) technique. We also offer a comparison to the original bimodal AFM method, in which the higher eigenmode is driven with constant frequency and constant excitation amplitude. General as well as particular characteristics of the different driving schemes are highlighted from theoretical and experimental points of view, revealing the advantages and disadvantages of each. This study provides information and guidelines that can be useful in selecting the most appropriate operation mode to characterize different samples in the most efficient and reliable way.

Highlights

Atomic force microscopy (AFM) emerged in the mid-1980s as a powerful tool for measuring topography and forces on microand nanoscale surfaces [1]
Comparisons of the AM-OL and AM-FM techniques are difficult because the two methods do not carry out identical tasks and because there are a number of tradeoffs involved, which may or may not be advantageous depending on the particular application and level of skill of the user
The first question that emerges when discussing AM-FM concerns the reasoning behind the use of FM-AFM, which has in the past been mostly reserved for vacuum operation, with a few exceptions in liquid imaging [16,17] and spectroscopy experiments in air as well as in liquid [18,19,20,21]