Atomic-resolution scanning tunneling spectroscopy - from creating artificial molecules to understanding single-molecule fluorescence

Session

Atomic and Molecular Resolution Phenomena via AFM, STM and Scanning Probes

Authors

Daniel Wegner (1)

Affiliations

1. Institute for Molecules and Materials, Radboud University

Keywords

scanning tunneling microscopy, scanning tunneling spectroscopy, STM, STS, artificial lattices, atomic manipulation, single-molecule spectroscopy, single-molecule fluorescence, STM-induced light emission

Abstract text

Nijmegen’s SPM group at Radboud University focuses on pushing the state of the art in cryogenic SPM development, including spin-resolved techniques [1,2]. For instance, this enabled us to discover a novel magnetic state of matter in an element of the periodic table [3,4]. We also employ STM-based manipulation techniques to control matter down to a single atom [5-7].

In the first part of my talk, I will present a novel platform that serves as a solid-state quantum simulator in two dimensions, based solely on positioning individual cesium atoms on the surface of indium antimonide [7]. We can create artificial atoms that possess s- and p-orbitals and serve as building blocks for artificial molecules and lattices. We show evidence for coupling of artificial atoms as well as sp² hybridization in emulated organic structures. This platform can be used to simulate various planar molecular structures as well as to monitor the interplay between atomic structures and the resulting molecular orbital landscape with sub-molecular precision.

In the second part, I will focus on single-molecule fluorescence spectroscopy with submolecular resolution, based on STM-induced light emission experiments [8,9]. In organic light emitting devices, electroluminescence occurs as a consequence of electron and hole transfer into the emitter molecule. The exact excitation and relaxation pathways can be surprisingly complex. I will present new results on the fluorescence of individual ZnPc molecules on NaCl/Ag(111), showing evidence that the molecule can emit light when in its neutral and both charged states (i.e. cationic and anionic), depending on the tip-sample bias polarity [9]. Based on a systematic study that employs all measurement modes of STM, we can propose a unified many-body energy diagram that consistently explains all excitation and relaxation pathways of ZnPc leading to electroluminescence. The results have relevance, beyond STM experiments, for any electroluminescent device.

References

1. H. von Allwörden, A. Eich, E. J. Knol, J. Hermenau, A. Sonntag, J. W. Gerritsen, D. Wegner, and A. A. Khajetoorians, Design and performance of an ultra-high vacuum spin-polarized scanning tunneling microscope operating at 30 mK and in a vector magnetic field, Rev. Sci. Instrum. 89, 033902 (2018).
2. N. Hauptmann, J. W. Gerritsen, D. Wegner, and A. A. Khajetoorians, Sensing Noncollinear Magnetism at the Atomic Scale Combining Magnetic Exchange and Spin-Polarized Imaging, Nano Lett. 17, 5660 (2017).
3. U. Kamber, A. Bergman, A. Eich, D. Iuşan, M. Steinbrecher, N. Hauptmann, L. Nordström, M. I. Katsnelson, D. Wegner, O. Eriksson, A. A. Khajetoorians, Self-induced spin glass state in elemental and crystalline neodymium, Science 368, 966 (2020).
4. B. Verlhac, L. Niggli, A. Bergman, U. Kamber, A. Bagrov, D. Iuşan, L. Nordström, M. I. Katsnelson, D. Wegner, O. Eriksson, A. A. Khajetoorians, Thermally-induced magnetic order from glassiness in elemental neodymium, Nat. Phys. 18, 905 (2022),
5. A. A. Khajetoorians, D. Wegner, A. F. Otte and I. Swart, Creating designer quantum states of matter atom-by-atom, Nat. Rev. Phys. 1, 703 (2019).
6. W. Jolie, T.-C. Hung, L. Niggli, B. Verlhac, N. Hauptmann, D. Wegner, A. A. Khajetoorians, Creating Tunable Quantum Corrals on a Rashba Surface Alloy, ACS Nano 16, 4876 (2022).
7. E. Sierda, X. Huang, D. I. Badrtdinov, B. Kiraly, E. Knol, G. C. Groenenboom, M. I. Katsnelson, M. Rösner, D. Wegner and A. A. Khajetoorians, Emulating molecular orbitals with artificial atoms on a surface, arXiv:2210.06754 (2022).
8. T.-C. Hung, B. Kiraly, J. H. Strik, A. A. Khajetoorians, and D. Wegner, Plasmon-Driven Motion of an Individual Molecule, Nano Lett. 21, 5006 (2021).
9. T.-C. Hung, R. Robles, B. Kiraly, J. H. Strik, B. A. Rutten, A. A. Khajetoorians, N. Lorente and D. Wegner, Bipolar single-molecule electroluminescence and electrofluorochromism, arXiv:2210.11118 (2022).