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Anna L. Eichhorn, Christian Dietz

Adv. Mater. Interfaces 2021, 2101288

DOI: https://doi.org/10.1002/admi.202101288 [Article]

Multifrequency atomic force microscopy (AFM) is shown to be an excellent tool for imaging crystal structures at atomic resolution in different spatial directions. However, determining the forces between single atoms remains challenging, particularly in air under ambient conditions. Developed here is a trimodal AFM approach that simultaneously acquires torsional and flexural frequency-shift images and spectroscopic data to transfer these observables into in-plane and out-of-plane forces between single bonds of highly oriented pyrolytic graphite (HOPG) at atomic resolution in air under ambient conditions based on the Fourier method. It is found that the cantilever mean deflection is an excellent indicator to understand that strong attractive interactions between the tip and the surface of HOPG in dynamic AFM imply a local lift of the topmost carbon layer when using higher eigenmodes for the topographical feedback. Cross-talk between torsional and flexural-oscillation modes is shown to be negligible. Interestingly, significant differences are observed in the in-plane forces depending on the orientation of the carbon bonds relative to the direction of torsional oscillation.