Single-Electron Alternate-Charging Scanning Tunneling Microscopy on Insulating Surfaces
Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
Final Report Abstract
Understanding the electronic structure of matter at the atomic scale is one of the central goals of nanoscience. In particular, many chemical processes are governed by the exchange of electrons between atoms and molecules, a mechanism known as electron transfer. Probing such phenomena requires the capability to study atoms and molecules at their own length scales, while at the same time, being able to control their charge states. While scanning tunneling microscopy (STM) allows imaging electronic states with angstrom resolution, the requirement of a conductive substrate hinders the investigation of completely electronically isolated adsorbate structures in given charge states. The project aimed to extend scanning tunneling microscopy (STM) to insulating substrates using charge detection by means of atomic force microscopy (AFM). Combining elements of STM and AFM, we successfully developed a novel imaging method, referred to as single-electron alternatecharging scanning tunneling microscopy (AC-STM) during a first funding period of the project. This method allows for electron tunneling without a net DC current flow. In the remainder of the first funding period, we applied the AC-STM imaging method in two more works, shedding light onto the non-equilibrium polarization in switching properties of molecules on insulating surfaces. In the second funding period several milestones were achieved: first, singlet and triplet excitons were successfully formed and detected within single molecules using voltage pulse patterns. Notably, triplet lifetimes of pentacene molecules on insulating surfaces were directly measured, revealing strong quenching by nearby oxygen molecules. Additionally, in the framework of the project single-molecule electron-spin resonance (ESR)-AFM was developed. ESR-AFM spectroscopy has sub-nanoelectronvolt energy resolution and allowed resolving individual isotopologues. Further, coherent control of electron spins over tens of microseconds was achieved, while providing atomic-scale spatial resolution. Finally, the project successfully expanded AC-STM to its full spectroscopic capabilities, mapping out electronic transitions. This method provides insight into energies of excited states and possible cycles of transitions in different kinds of experiments. For example, it aids in the interpretation of complex luminescence data. The work also opens avenues for controlling single-molecule chemical reactions and advancing its understanding.
Publications
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Accessing a Charged Intermediate State Involved in the Excitation of Single Molecules. Physical Review Letters, 123(1).
Patera, Laerte L.; Queck, Fabian; Scheuerer, Philipp; Moll, Nikolaj & Repp, Jascha
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Charge-Induced Structural Changes in a Single Molecule Investigated by Atomic Force Microscopy. Physical Review Letters, 123(6).
Scheuerer, Philipp; Patera, Laerte L.; Simbürger, Felix; Queck, Fabian; Swart, Ingmar; Schuler, Bruno; Gross, Leo; Moll, Nikolaj & Repp, Jascha
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Mapping orbital changes upon electron transfer with tunnelling microscopy on insulators. Nature, 566(7743), 245-248.
Patera, Laerte L.; Queck, Fabian; Scheuerer, Philipp & Repp, Jascha
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Imaging Charge Localization in a Conjugated Oligophenylene. Physical Review Letters, 125(17).
Patera, Laerte L.; Queck, Fabian & Repp, Jascha
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Atomically resolved single-molecule triplet quenching. Science, 373(6553), 452-456.
Peng, Jinbo; Sokolov, Sophia; Hernangómez-Pérez, Daniel; Evers, Ferdinand; Gross, Leo; Lupton, John M. & Repp, Jascha
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Single-molecule electron spin resonance by means of atomic force microscopy. Nature 624, 64 (2023)
L. Sellies, R. Spachtholz, S. Bleher, J. Eckrich, P. Scheuerer & J. Repp
