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Quantitative assessment of intermolecular interactions by atomic force microscopy imaging using copper oxide tips


Atomic force microscopy is an impressive tool with which to directly resolve the bonding structure of organic compounds1,2,3,4,5. The methodology usually involves chemical passivation of the probe-tip termination by attaching single molecules or atoms such as CO or Xe (refs 1,6,7,8,9). However, these probe particles are only weakly connected to the metallic apex, which results in considerable dynamic deflection. This probe particle deflection leads to pronounced image distortions, systematic overestimation of bond lengths, and in some cases even spurious bond-like contrast features, thus inhibiting reliable data interpretation812. Recently, an alternative approach to tip passivation has been used in which slightly indenting a tip into oxidized copper substrates and subsequent contrast analysis allows for the verification of an oxygen-terminated Cu tip13,14,15. Here we show that, due to the covalently bound configuration of the terminal oxygen atom, this copper oxide tip (CuOx tip) has a high structural stability, allowing not only a quantitative determination of individual bond lengths and access to bond order effects, but also reliable intermolecular bond characterization. In particular, by removing the previous limitations of flexible probe particles, we are able to provide conclusive experimental evidence for an unusual intermolecular N–Au–N three-centre bond. Furthermore, we demonstrate that CuOx tips allow the characterization of the strength and configuration of individual hydrogen bonds within a molecular assembly.

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Fig. 1: Bond length and bond order analysis of C60 by AFM imaging with an ex situ functionalized CuOx tip.
Fig. 2: Imaging a molecule with two protruding S atoms with a CuOx tip.
Fig. 3: CuOx AFM imaging proves a theoretically predicted N–Au–N bond.
Fig. 4: Hydrogen-bonded assembly imaged with a CuOx tip reveals the intermolecular hydrogen bond structure.


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This work was supported by the Deutsche Forschungsgemeinschaft through collaborative research centres TRR 61 and SFB 858, and through projects MO 2345/4-1, AM 460/2-1, and FU 299/19. W.J. thanks the National Science Foundation of China for support through grant no. 11622437. D. Yesilpinar is thanked for technical support.

Author information




H.M. conceived the experiments. H.M., O.D.A., A.T. and L.L. performed the experiments. H.M., S.A. and O.D.A. analysed the data. S.A., Z.H., W.J. and M.R. performed the DFT simulations. M.C. and C.A.S. synthesized the DBTH molecules. S.A. and H.F. contributed significantly to the scientific discussion of the project. All authors discussed the results and commented on the manuscript, which was drafted by H.M.

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Correspondence to Harry Mönig.

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Mönig, H., Amirjalayer, S., Timmer, A. et al. Quantitative assessment of intermolecular interactions by atomic force microscopy imaging using copper oxide tips. Nature Nanotech 13, 371–375 (2018).

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