Harry Mönig1,2*, Saeed Amirjalayer1,2, Alexander Timmer1,2, Zhixin Hu3, Lacheng Liu1,2, 4 Oscar Díaz Arado1,2, Marvin Cnudde1,2, Cristian Alejandro Strassert1,2, Wei Ji4, Michael 5 Rohlfing5, and Harald Fuchs1,2
1Physikalisches Institut, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany.
2Center for Nanotechnology, Heisenbergstraße 11, 48149 Münster, Germany. 3Center for Joint Quantum Studies and Department of Physics, Tianjin University, Tianjin 300350, China.
4Department of Physics and Beijing Key Laboratory of Optoelectronic Functional Materials & Micro-Nano Devices, Renmin University of China, Beijing 100872, China.
5Institut für Festkörpertheorie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany.
DOI:10.1038/s41565-018-0104-4 Publication Date: 10.1038/s41565-018-0104-4
Atomic force microscopy (AFM) is an impressive tool to directly resolve the bonding structure of organic compounds1-5. The methodology usually involves the chemical passivation of the probe-tip termination by attaching single molecules or atoms (e.g. CO or Xe)1,6-9. However, these probe particles are only weakly connected to the metallic apex, which results in a considerable dynamic deflection. This probe particle deflection leads to pronounced image distortions, a systematic overestimation of bond lengths, and in some cases even to spurious bond-like contrast features inhibiting a reliable data interpretation8-11. Recently, an alternative approach of tip passivation has been employed by slightly indenting a tip into oxidized copper substrates where subsequent contrast analysis allows for the verification of an oxygen-terminated Cu tip (CuOx tip)13-15. Here we show that due to the covalently bound configuration of the terminal oxygen atom, this tip shows high structural stability, allowing not only a quantitatively determination of individual bond lengths and accessing bond order effects, but also leading to reliable intermolecular bond characterization. In particular, by removing 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 allows characterising the strength and configuration of individual hydrogen bonds within a molecular assembly.