Intermolecular contrast in atomic force microscopy images without intermolecular bonds

TL;DR

This study demonstrates that intermolecular features in AFM images can arise from tip flexibility rather than actual bonds, challenging previous interpretations of AFM contrast.

Contribution

The paper provides experimental evidence that AFM intermolecular contrast can occur without intermolecular bonds, emphasizing the role of tip flexibility in image features.

Findings

Intermolecular features appear in AFM images even without bonds.

Tip flexibility can produce contrast similar to bonds.

Intermolecular contrast is not definitive evidence of bonds.

Abstract

Intermolecular features in atomic force microscopy (AFM) images of organic molecules have been ascribed to intermolecular bonds. A recent theoretical study [P. Hapala et al., Phys. Rev. B 90, 085421 (2014)] showed that these features can also be explained by the flexibility of molecule terminated tips. We probe this effect by carrying out AFM experiments on a model system that contains regions where intermolecular bonds should and should not exist between close-by molecules. Intermolecular features are observed in both regions, demonstrating that intermolecular contrast cannot be directly interpreted as intermolecular bonds.