Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Tracking the ultrafast motion of a single molecule by femtosecond orbital imaging

Nature volume 539, pages 263–267 (2016)Cite this article

Subjects

Abstract

Watching a single molecule move on its intrinsic timescale has been one of the central goals of modern nanoscience, and calls for measurements that combine ultrafast temporal resolution1,2,3,4,5,6,7,8 with atomic spatial resolution9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30. Steady-state experiments access the requisite spatial scales, as illustrated by direct imaging of individual molecular orbitals using scanning tunnelling microscopy9,10,11 or the acquisition of tip-enhanced Raman and luminescence spectra with sub-molecular resolution26,27,28. But tracking the intrinsic dynamics of a single molecule directly in the time domain faces the challenge that interactions with the molecule must be confined to a femtosecond time window. For individual nanoparticles, such ultrafast temporal confinement has been demonstrated18 by combining scanning tunnelling microscopy with so-called lightwave electronics1,2,3,4,5,6,7,8, which uses the oscillating carrier wave of tailored light pulses to directly manipulate electronic motion on timescales faster even than a single cycle of light. Here we build on ultrafast terahertz scanning tunnelling microscopy to access a state-selective tunnelling regime, where the peak of a terahertz electric-field waveform transiently opens an otherwise forbidden tunnelling channel through a single molecular state. It thereby removes a single electron from an individual pentacene molecule’s highest occupied molecular orbital within a time window shorter than one oscillation cycle of the terahertz wave. We exploit this effect to record approximately 100-femtosecond snapshot images of the orbital structure with sub-ångström spatial resolution, and to reveal, through pump/probe measurements, coherent molecular vibrations at terahertz frequencies directly in the time domain. We anticipate that the combination of lightwave electronics1,2,3,4,5,6,7,8 and the atomic resolution of our approach will open the door to visualizing ultrafast photochemistry and the operation of molecular electronics on the single-orbital scale.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Rent or buy this article

Prices vary by article type

from$1.95

to$39.95

Learn more

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Ultrafast THz-induced tunnelling of a single electron out of a single molecule.
Figure 2: Ultrafast THz-STM imaging of a pentacene molecular orbital.
Figure 3: Ultrafast dynamics of a single molecule.
Figure 4: Influence of substrate surface and molecular species on ultrafast single-molecule dynamics.

References

  1. Itatani, J. et al. Tomographic imaging of molecular orbitals. Nature 432, 867–871 (2004)

    Article  CAS  ADS  Google Scholar 

  2. Goulielmakis, E. et al. Attosecond control and measurement: lightwave electronics. Science 317, 769–775 (2007)

    Article  CAS  ADS  Google Scholar 

  3. Neppl, S. et al. Direct observation of electron propagation and dielectric screening on the atomic length scale. Nature 517, 342–346 (2015)

    Article  CAS  ADS  Google Scholar 

  4. Hohenleutner, M. et al. Real-time observation of interfering crystal electrons in high-harmonic generation. Nature 523, 572–575 (2015)

    Article  CAS  ADS  Google Scholar 

  5. Feist, A. et al. Quantum coherent optical phase modulation in an ultrafast transmission electron microscope. Nature 521, 200–203 (2015)

    Article  CAS  ADS  Google Scholar 

  6. Krüger, M., Schenk, M. & Hommelhoff, P. Attosecond control of electrons emitted from a nanoscale metal tip. Nature 475, 78–81 (2011)

    Article  Google Scholar 

  7. Wimmer, L. et al. Terahertz control of nanotip photoemission. Nature Phys. 10, 432–436 (2014)

    Article  CAS  ADS  Google Scholar 

  8. Iwaszczuk, K., Zalkovskij, M., Strikwerda, A. C. & Jepsen, P. U. Nitrogen plasma formation through terahertz-induced ultrafast electron field emission. Optica 2, 116–123 (2015)

    Article  CAS  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

  10. Stroscio, J. A. & Celotta, R. J. Controlling the dynamics of a single atom in lateral atom manipulation. Science 306, 242–247 (2004)

    Article  CAS  ADS  Google Scholar 

  11. Stipe, B. C., Rezaei, M. A. & Ho, W. Single-molecule vibrational spectroscopy and microscopy. Science 280, 1732–1735 (1998)

    Article  CAS  ADS  Google Scholar 

  12. Hamers, R. J. & Cahill, D. G. Ultrafast time resolution in scanned probe microscopies. Appl. Phys. Lett. 57, 2031 (1990)

    Article  CAS  ADS  Google Scholar 

  13. Nunes, G., Jr & Freeman, M. R. Picosecond resolution in scanning tunneling microscopy. Science 262, 1029–1032 (1993)

    Article  CAS  ADS  Google Scholar 

  14. Kemiktarak, U., Ndukum, T., Schwab, K. C. & Ekinci, K. L. Radio-frequency scanning tunnelling microscopy. Nature 450, 85–88 (2007)

    Article  CAS  ADS  Google Scholar 

  15. Terada, Y., Yoshida, S., Takeuchi, O. & Shigekawa, H. Real-space imaging of transient carrier dynamics by nanoscale pump-probe microscopy. Nature Photon. 4, 869–874 (2010)

    Article  CAS  ADS  Google Scholar 

  16. Loth, S., Etzkorn, M., Lutz, C., Eigler, D. M. & Heinrich, A. J. Measurement of fast electron spin relaxation times with atomic resolution. Science. 329, 1628–1630 (2010)

    Article  CAS  ADS  Google Scholar 

  17. Wu, S. W. & Ho, W. Two-photon-induced hot-electron transfer to a single molecule in a scanning tunneling microscope. Phys. Rev. B 82, 085444 (2010)

    Article  ADS  Google Scholar 

  18. Cocker, T. L. et al. An ultrafast terahertz scanning tunnelling microscope. Nature Photon. 7, 620–625 (2013)

    Article  CAS  ADS  Google Scholar 

  19. Yoshida, S. et al. Probing ultrafast spin dynamics with optical pump-probe scanning tunnelling microscopy. Nature Nanotech. 9, 588–593 (2014)

    Article  CAS  ADS  Google Scholar 

  20. Merino, P., Große, C., Rosławska, A., Kuhnke, K. & Kern, K. Exciton dynamics of C60-based single-photon emitters explored by Hanbury Brown-Twiss scanning tunnelling microscopy. Nature Commun. 6, 8461 (2015)

    Article  CAS  ADS  Google Scholar 

  21. Wagner, M. et al. Ultrafast and nanoscale plasmonic phenomena in exfoliated graphene revealed by infrared pump-probe nanoscopy. Nano Lett. 14, 894–900 (2014)

    Article  CAS  ADS  Google Scholar 

  22. Eisele, M. et al. Ultrafast multi-terahertz nano-spectroscopy with sub-cycle temporal resolution. Nature Photon. 8, 841–845 (2014)

    Article  CAS  ADS  Google Scholar 

  23. Gao, M. et al. Mapping molecular motions leading to charge delocalization with ultrabright electrons. Nature 496, 343–346 (2013)

    Article  CAS  ADS  Google Scholar 

  24. Zewail, A. H. Four-dimensional electron microscopy. Science 328, 187–193 (2010)

    Article  CAS  ADS  Google Scholar 

  25. Jahng, J. et al. Ultrafast pump-probe force microscopy with nanoscale resolution. Appl. Phys. Lett. 106, 083113 (2015)

    Article  ADS  Google Scholar 

  26. Zhang, R. et al. Chemical mapping of a single molecule by plasmon-enhanced Raman scattering. Nature 498, 82–86 (2013)

    Article  CAS  ADS  Google Scholar 

  27. Lee, J. et al. Vibronic motion with joint angstrom–femtosecond resolution observed through Fano progressions recorded within one molecule. ACS Nano 8, 54–63 (2014)

    Article  CAS  Google Scholar 

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

    Article  CAS  ADS  Google Scholar 

  29. Park, H. et al. Nanomechanical oscillations in a single-C60 transistor. Nature 407, 57–60 (2000)

    Article  CAS  ADS  Google Scholar 

  30. Yoshida, K., Shibata, K. & Hirakawa, K. Terahertz field enhancement and photon-assisted tunneling in single-molecule transistors. Phys. Rev. Lett. 115, 138302 (2015)

    Article  ADS  Google Scholar 

  31. Meyer, G. A simple low-temperature ultrahigh-vacuum scanning tunneling microscope capable of atomic manipulation. Rev. Sci. Instrum. 67, 2960–2965 (1996)

    Article  CAS  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

  33. Chen, C. J. Introduction to Scanning Tunneling Microscopy (Oxford Univ. Press, 1993)

  34. Ahlrichs, R., Bär, M., Häser, M., Horn, M. & Kölmel, C. Electronic structure calculations on workstation computers: the program system TURBOMOLE. Chem. Phys. Lett. 162, 165–169 (1989)

    Article  CAS  ADS  Google Scholar 

  35. Witte, G. & Wöll, C. External vibrations of hydrocarbons on Cu(100). J. Chem. Phys. 103, 5860–5863 (1995)

    Article  CAS  ADS  Google Scholar 

  36. Witte, G. et al. Damping of molecular motion on a solid substrate: evidence for electron-hole pair creation. Phys. Rev. Lett. 80, 121–124 (1998)

    Article  CAS  ADS  Google Scholar 

Download references

Acknowledgements

We thank A. Pöllmann, F. Albrecht, R. Kronfeldner, M. Eisele and M. Furthmeier for assistance, and F. Evers, F. A. Hegmann, V. Jelic, P. C. M. Planken, M. Grifoni and K. Richter for discussions. We acknowledge financial support from the Volkswagen Foundation (Lichtenberg program), the European Research Council through grant number 305003 (QUANTUMsubCYCLE), and the Deutsche Forschungsgemeinschaft (DFG) through GRK 1570 and research grants HU1598/3 and CO1492/1. T.L.C. thanks the A. v. Humboldt Foundation.

Author information

Author notes

  1. Tyler L. Cocker and Dominik Peller: These authors contributed equally to this work.

Authors and Affiliations

  1. Department of Physics, University of Regensburg, Regensburg, 93040, Germany

    Tyler L. Cocker, Dominik Peller, Ping Yu, Jascha Repp & Rupert Huber

Authors
  1. Tyler L. Cocker
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Dominik Peller
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Ping Yu
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Jascha Repp
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Rupert Huber
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

T.L.C., D.P., P.Y., J.R. and R.H. conceived, set up and carried out the experiments. T.L.C., D.P., J.R. and R.H. analysed the data and wrote the manuscript.

Corresponding authors

Correspondence to Jascha Repp or Rupert Huber.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Additional information

Reviewer Information

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

Extended data figures and tables

Extended Data Figure 1 Spatial resolution of THz-STM imaging.

a, b, Line-scan cuts (a) through a constant-height, zero-bias THz-STM image (b), where the THz-induced current ITHz is shown in units of rectified electrons per THz pulse. The pixel size in the image is 0.25 Å × 0.25 Å and the white scale bar is 1 Å long. The image contains edges where the signal rises from the background level to a maximum within 0.75 Å. The signal rise from 10% to 90% in these cases occurs over approximately 0.6 Å, which provides an upper bound for the spatial resolution of the image. This estimate agrees with simulations of the spatial distribution of the rectified current (Fig. 2d, i). There, we calculate the square of the matrix element between the pentacene HOMO and the tip wavefunction (Bardeen model). The tip wavefunction, which ultimately determines the attainable spatial resolution, is modelled as an s-wave (as in the Tersoff–Hamann approach) and the spatial decay of this wavefunction is used as a fitting parameter, as is the tip height. The best agreement between the experimental and simulated images is found for s-waves with decay lengths of ≤ 0.5 Å, consistent with our spatial resolution estimate of 0.6 Å based on the line scans in a.

Extended Data Figure 2 Ultrafast THz-STM imaging of the lowest unoccupied orbital of pentacene.

a, When Au(110) is replaced with Cu(100) as the substrate, the HOMO and LUMO levels realign with respect to the Fermi level of the substrate in such a way that the LUMO can be probed by THz-induced currents. This situation is depicted schematically here, in analogy to Fig. 1b. Left, steady-state differential conductance measured on a pentacene molecule adsorbed on NaCl/Cu(100). Right, THz electric-field waveform measured by electro-optic sampling. Although the THz waveform is the same as that in Fig. 1b, it now induces sequential tunnelling into the pentacene LUMO at the most intense positive half-cycle, while the negative half-cycle is too weak to allow for HOMO tunnelling. b, Steady-state constant-current STM image of three pentacene molecules side-by-side at VDC = 100 mV and I = 1.4 pA. Greyscale range = 2.4 Å. c, Constant-height THz-STM image of the same sample area as in b, with VDC = 0 mV and the maximum positive THz voltage set to  ≈ +1.3 V. The spatial distribution of the THz-induced current closely resembles the LUMO density for each molecule, indicating state-selective THz-induced LUMO tunnelling. The onset field for this process agrees with the modified alignment of the orbitals. Specifically, the peak THz voltage in the positive direction that is predicted based on the field enhancement determined from HOMO tunnelling is consistent with the new LUMO transport level voltage observed in the steady-state dI/dV curve here. This agreement lends further support to the proposed mechanism for THz-STM in this regime.

Extended Data Figure 3 Modelling ultrafast terahertz-induced tunnelling out of a pentacene HOMO.

a, Terahertz voltage waveforms used in the simulations. We approximate the time trace of the THz voltage with the THz electric-field waveform measured in the far field by electro-optic sampling. In all plots, the pink curve corresponds to a waveform with a peak of −2.05 V and the navy-blue curve corresponds to a waveform with a peak of −2.22 V. The scaling factor and resulting peak voltages are determined by fitting the shape of the experimental autocorrelation (Fig. 3a) as follows. We simulate the autocorrelation by taking the sum of two THz pulses and calculating the total rectified current from the resulting transient as a function of the delay time between the pulses. b, The dI/dV characteristic needed for the simulation is obtained by modelling the HOMO and LUMO molecular-resonance peaks in the experimental dI/dV curve (Fig. 2b, centre) with two Gaussians. This dI/dV curve is then scaled up to account for the significantly lower tip height for THz-STM imaging. Note that the scaling factor does not affect the shape of the autocorrelation. Blue line, centre of HOMO Gaussian, −1.93 V (0.62 V full width at half-maximum, FWHM). Red line, centre of LUMO Gaussian, 2.06 V (0.58 V FWHM). c, Resulting current response induced by the THz voltage waveform in a when applied to a junction with a dI/dV relation defined by b. The asymmetry of the THz voltage pulse leads to a much larger current response in the negative bias direction than in the positive bias direction. Inset, induced current response during the negative crest of the THz voltage waveform. Pink curve, 120-fs FWHM; navy-blue curve, 140-fs FWHM. d, Total number of electrons that have tunnelled across the junction, calculated from the integral of c. Negative numbers refer to the negative bias direction, that is, electron tunnelling from the HOMO to the tip. Inset, rise of the rectified electron signal during the negative crest of the THz voltage waveform. The rise time from 10% to 90% of the maximum signal is 115 fs for the pink curve and 130 fs for the navy-blue curve. The simulated autocorrelation for the −2.22 V peak (navy-blue curve) provides the best fit to the shape of the measured autocorrelation. The dI/dV curve is scaled such that the autocorrelation peak at −2.22 V matches the measured peak of approximately −0.75 electrons per THz pulse. The peak voltage of the THz pulses used in the imaging configuration is then determined by finding the THz peak for which the simulations yield this number of rectified electrons per THz pulse. For example, in Fig. 2e the maximum observed signal is approximately −0.58 electrons per THz pulse, and the best agreement is found for −2.05 V (pink curve). We note that the simulations are based on the assumption that the THz pulse modulates the bias of the junction quasi-instantaneously. In our simulations we disregard any blocking of tunnelling or other effects resulting from the finite time until an electron from the substrate refills the molecular state. This blocking is expected to become important if the THz current reaches or even exceeds one electron per pulse.

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Cocker, T., Peller, D., Yu, P. et al. Tracking the ultrafast motion of a single molecule by femtosecond orbital imaging. Nature 539, 263–267 (2016). https://doi.org/10.1038/nature19816

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nature19816

This article is cited by

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing