Mapping orbital changes upon electron transfer with tunnelling microscopy on insulators

Abstract

Electron transfer plays a crucial part in many chemical reactions1,2, including photosynthesis, combustion and corrosion. But even though redox-state transitions change the electronic structure of the molecules involved, mapping these changes at the single-molecule level is challenging. Scanning tunnelling microscopy provides insights into the orbital structure3 of single molecules and their interactions4,5, but requires the use of a conductive substrate that keeps molecules in a given charge state and thereby suppresses redox-state transitions. Atomic force microscopy can be used on insulating substrates to obtain structural6 and electrostatic7,8 information but does not generally access electronic states. Here we show that when synchronizing voltage pulses that steer electron tunnelling between a conductive atomic force microscope tip and a substrate with the oscillation of the tip, we can perform tunnelling experiments on non-conductive substrates and thereby map the orbital structure of isolated molecules as a function of their redox state. This allows us to resolve previously inaccessible electronic transitions in space and energy and to visualize the effects of electron transfer and polaron formation on individual molecular orbitals. We anticipate that our approach will prove useful for the investigation of complex redox reactions and charging-related phenomena with sub-ångström resolution.

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Fig. 1: Working principle of single-electron AC-STM.
Fig. 2: Imaging of electronic transitions of pentacene.
Fig. 3: Jahn-Teller effect in CuPc.
Fig. 4: Electronic transition imaging of BDHN-TTF.

Data availability

The data that support the findings of this study are available from the corresponding author on reasonable request.

References

  1. 1.

    Marcus, R. A. Electron transfer reactions in chemistry: theory and experiment (Nobel lecture). Angew. Chem. Int. Ed. 32, 1111–1121 (1993).

    Article  Google Scholar 

  2. 2.

    Bauer, A., Westkämper, F., Grimme, S. & Bach, T. Catalytic enantioselective reactions driven by photoinduced electron transfer. Nature 436, 1139–1140 (2005).

    ADS  CAS  Article  Google Scholar 

  3. 3.

    Repp, J., Meyer, G., Stojković, S. M., Gourdon, A. & Joachim, C. Molecules on insulating films: scanning-tunneling microscopy imaging of individual molecular orbitals. Phys. Rev. Lett. 94, 026803 (2005).

    ADS  Article  Google Scholar 

  4. 4.

    Imada, H. et al. Real-space investigation of energy transfer in heterogeneous molecular dimers. Nature 538, 364–367 (2016).

    ADS  CAS  Article  Google Scholar 

  5. 5.

    Zhang, Y. et al. Visualizing coherent intermolecular dipole-dipole coupling in real space. Nature 531, 623–627 (2016).

    ADS  CAS  Article  Google Scholar 

  6. 6.

    Gross, L., Mohn, F., Moll, N., Liljeroth, P. & Meyer, G. The chemical structure of a molecule resolved by atomic force microscopy. Science 325, 1110–1114 (2009).

    ADS  CAS  Article  Google Scholar 

  7. 7.

    Gross, L. et al. Measuring the charge state of an adatom with noncontact atomic force microscopy. Science 324, 1428–1431 (2009).

    ADS  CAS  Article  Google Scholar 

  8. 8.

    Steurer, W., Fatayer, S., Gross, L. & Meyer, G. Probe-based measurement of lateral single-electron transfer between individual molecules. Nat. Commun. 6, 8353 (2015).

    ADS  CAS  Article  Google Scholar 

  9. 9.

    Giessibl, F. J. Atomic resolution on Si(111)-(7×7) by noncontact atomic force microscopy with a force sensor based on a quartz tuning fork. Appl. Phys. Lett. 76, 1470–1472 (2000).

    ADS  CAS  Article  Google Scholar 

  10. 10.

    Johnson, J. P., Zheng, N. & Williams, C. C. Atomic scale imaging and spectroscopy of individual electron trap states using force detected dynamic tunnelling. Nanotechnology 20, 055701 (2009).

    ADS  CAS  Article  Google Scholar 

  11. 11.

    Wang, R. & Williams, C. C. Dynamic tunneling force microscopy for characterizing electronic trap states in non-conductive surfaces. Rev. Sci. Instrum. 86, 093708 (2015).

    ADS  CAS  Article  Google Scholar 

  12. 12.

    Lotze, C., Corso, M., Franke, K. J., von Oppen, F. & Pascual, J. I. Driving a macroscopic oscillator with the stochastic motion of a hydrogen molecule. Science 338, 779–782 (2012).

    ADS  CAS  Article  Google Scholar 

  13. 13.

    Cockins, L. et al. Energy levels of few-electron quantum dots imaged and characterized by atomic force microscopy. Proc. Natl Acad. Sci. USA 107, 9496–9501 (2010).

    ADS  CAS  Article  Google Scholar 

  14. 14.

    Steurer, W., Gross, L. & Meyer, G. Local thickness determination of thin insulator films via localized states. Appl. Phys. Lett. 104, 231606 (2014).

    ADS  Article  Google Scholar 

  15. 15.

    Fatayer, S. et al. Reorganization energy upon charging a single molecule on an insulator measured by atomic force microscopy. Nat. Nanotechnol. 13, 376–380 (2018).

    ADS  CAS  Article  Google Scholar 

  16. 16.

    Neese, F. The ORCA program system. WIRES Comput. Mol. Sci. 2, 73–78 (2012).

    CAS  Article  Google Scholar 

  17. 17.

    Szabo, A. & Ostlund, N. S. Modern Quantum Chemistry: Introduction to Advanced Electronic Structure Theory (Courier Corporation, North Chelmsford, 2012).

    Google Scholar 

  18. 18.

    Repp, J., Meyer, G., Olsson, F. E. & Persson, M. Controlling the charge state of individual gold adatoms. Science 305, 493–495 (2004).

    ADS  CAS  Article  Google Scholar 

  19. 19.

    Schulz, F. et al. Many-body transitions in a single molecule visualized by scanning tunnelling microscopy. Nat. Phys. 11, 229–234 (2015).

    CAS  Article  Google Scholar 

  20. 20.

    Wachowiak, A. et al. Visualization of the molecular Jahn-Teller effect in an insulating K4C60 monolayer. Science 310, 468–470 (2005).

    ADS  CAS  Article  Google Scholar 

  21. 21.

    Uhlmann, C., Swart, I. & Repp, J. Controlling the orbital sequence in individual Cu-phthalocyanine molecules. Nano Lett. 13, 777–780 (2013).

    ADS  CAS  Article  Google Scholar 

  22. 22.

    Setvin, M. et al. Direct view at excess electrons in TiO2 rutile and anatase. Phys. Rev. Lett. 113, 086402 (2014).

    ADS  Article  Google Scholar 

  23. 23.

    Esch, F. et al. Electron localization determines defect formation on ceria substrates. Science 309, 752–755 (2005).

    ADS  CAS  Article  Google Scholar 

  24. 24.

    Stähler, J., Deinert, J. C., Wegkamp, D., Hagen, S. & Wolf, M. Real-time measurement of the vertical binding energy during the birth of a solvated electron. J. Am. Chem. Soc. 137, 3520–3524 (2015).

    Article  Google Scholar 

  25. 25.

    Li, B. et al. Ultrafast interfacial proton-coupled electron transfer. Science 311, 1436–1440 (2006).

    ADS  CAS  Article  Google Scholar 

  26. 26.

    Miller, A. D. et al. Electron solvation in two dimensions. Science 297, 1163–1166 (2002).

    ADS  CAS  Article  Google Scholar 

  27. 27.

    O’Driscoll, L. J. et al. Electrochemical control of the single molecule conductance of a conjugated bis(pyrrolo)tetrathiafulvalene based molecular switch. Chem. Sci. 8, 6123–6130 (2017).

    Article  Google Scholar 

  28. 28.

    Holstein, T. Studies of polaron motion: part II. The ‘small’ polaron. Ann. Phys. 8, 343–389 (1959).

    ADS  CAS  Article  Google Scholar 

  29. 29.

    Toroz, D., Rontani, M. & Corni, S. Proposed alteration of images of molecular orbitals obtained using a scanning tunneling microscope as a probe of electron correlation. Phys. Rev. Lett. 110, 018305 (2013).

    ADS  Article  Google Scholar 

  30. 30.

    Wang, R., King, S. W. & Williams, C. C. Atomic scale trap state characterization by dynamic tunneling force microscopy. Appl. Phys. Lett. 105, 052903 (2014).

    ADS  Article  Google Scholar 

  31. 31.

    Payne, A., Ambal, K., Boehme, C. & Williams, C. C. Atomic-resolution single-spin magnetic resonance detection concept based on tunneling force microscopy. Phys. Rev. B 91, 195433 (2015).

    ADS  Article  Google Scholar 

  32. 32.

    Cocker, T. L., Peller, D., Yu, P., Repp, J. & Huber, R. Tracking the ultrafast motion of a single molecule by femtosecond orbital imaging. Nature 539, 263–267 (2016).

    ADS  Article  Google Scholar 

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Acknowledgements

We thank L. Gross, S. Fatayer, F. Giessibl, F. Evers, R. Huber and G. Meyer for discussions. Financial support from the Marie Curie Initial Training Network ‘MOLESCO’ (number 606728) and Deutsche Forschungsgemeinschaft (numbers RE2669/6-1 and GRK 1570) is gratefully acknowledged.

Reviewer information

Nature thanks C. Williams and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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Authors

Contributions

All authors designed and performed the experiments and analysed the data. L.L.P. and J.R. were responsible for DFT calculations and co-wrote the paper. All authors revised the manuscript.

Corresponding authors

Correspondence to Laerte L. Patera or Jascha Repp.

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Extended data figures and tables

Extended Data Fig. 1 Scheme and detailed shape of a.c.

voltage pulses.

Extended Data Fig. 2 Orbital confinement upon electron transfer in pentacene.

a, b, Electronic transitions probed by the same metal tip apex (A = 1 Å): 0→1 (a; Vd.c. = 1.87 V, Va.c. = 1.00 Vpp, Δz = 2 Å); 1→0 (b; Vd.c. = 1.87 V, Va.c. = 1.50 Vpp, Δz = 2 Å). Δz is given with respect to an AFM setpoint of Δf = −3.2 Hz at Vd.c. = 0 V. Scale bar, 5 Å. c, Line profiles taken along the directions indicated in a and b.

Extended Data Fig. 3 Modulus square of calculated orbitals for neutral and negatively charged CuPc.

a, b, Constant-height cuts of the superposition of degenerate LUMOs (a) and of only one of the degeneracy-lifted LUMOs (b). Scale bar, 5 Å.

Extended Data Fig. 4 Dissipation signal as a function of tip–sample distance.

Spectrum acquired above the centre of an isolated pentacene molecule (Vd.c. = 1.76 V, Va.c. = 1.00 V, A = 1 Å, 0→1). Δz is given with respect to an AFM setpoint of Δf = −3.2 Hz at Vd.c. = 0 V. Signal saturation is observed at short tip–sample distances because not more than one electron per set pulse can be transferred.

Extended Data Fig. 5 Imaging of electronic transitions in constant-detuning mode.

a, AFM topography image (Δf = −28.5 Hz, Vd.c. = 1.60 V, Va.c. = 1.00 V, A = 1 Å) of an isolated pentacene molecule on NaCl. b, Simultaneously acquired dissipation channel, corresponding to the 0→1 transition.

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Patera, L.L., Queck, F., Scheuerer, P. et al. Mapping orbital changes upon electron transfer with tunnelling microscopy on insulators. Nature 566, 245–248 (2019). https://doi.org/10.1038/s41586-019-0910-3

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