| AVS 66th International Symposium & Exhibition | |
| 2D Materials | Thursday Sessions |
| Session 2D+AS+BI+HC+MN+NS+PS+SS+TL-ThA |
| Session: | Surface Chemistry, Functionalization, Bio, Energy and Sensor Applications |
| Presenter: | Vladimir Korolkov, Oxford Instruments-Asylum Research |
| Authors: | V.V. Korolkov, Oxford Instruments-Asylum Research S.C. Chulkov, University of Lincoln, UK M. Watkins, University of Lincoln, UK P.H. Beton, The University of Nottingham, UK |
| Correspondent: | Click to Email |
Although achieving molecular resolution is now almost a routine across various SPM imaging modes, resolving the actual molecular structure at the atomic level has only been accomplished with NC-AFM in UHV often at low temperatures and with a functionalized probe. Of course, the ultimate goal in SPM is to resolve the chemical structure of a molecule identifying each atom.
In this work we are presenting an approach to achieve intra-molecular resolution on adsorbed molecules in the ambient at room temperatures with a standard AFM cantilever with unmodified tip. We have discovered that using a combination of higher eigenmodes and low oscillation amplitudes (~3-5Å) of a standard Si-cantilever routinely provides ultra-high resolution on adsorbed molecules on surfaces1,2 and bulk polymers3.
With this approach we have been able to observe both intra-molecular features and inter-molecular contrast in thin films of coronene and melem molecules on the surface of hexagonal boron nitride (hBN). In case of coronene, all six benzene rings have been resolved as well as underlying atomic lattice of hBN. Unlike coronene, melem forms molecular assemblies with square symmetry stabilized with in-plane strong hydrogen bonds between amino groups. We have observed a strong inter-molecular contrast where the hydrogen bonds are expected to be. Similar to coronene, the observed intra-molecular contrast was associated with three triazine rings. We have used Probe particle model4 to simulate our experimental AFM images and found very good agreement between them. In fact, PPM allowed us a correct interpretation of melem square phase assembly.
Both systems were studied at room and elevated temperatures where we observed phase transitions leading to thermodynamically stable systems. The experimental results are in excellent agreement with density functional theory calculations.
We believe the proposed approach, yet still in its infancy, could potentially provide a pathway to unambiguous identification of molecules on surfaces in the ambient on standard AFM systems.
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1Korolkov et al., Nat. Chem., 2017
2Korolkov et al., Nat. Comm., 2017
3Korolkov et al., Nat. Comm., 2019
4Hapala et al., Phys. Rev. B 90, 085421