Optical rectification and field enhancement in a plasmonic nanogap

Abstract

Metal nanostructures act as powerful optical antennas1,2 because collective modes of the electron fluid in the metal are excited when light strikes the surface of the nanostructure. These excitations, known as plasmons, can have evanescent electromagnetic fields that are orders of magnitude larger than the incident electromagnetic field. The largest field enhancements often occur in nanogaps between plasmonically active nanostructures3,4, but it is extremely challenging to measure the fields in such gaps directly. These enhanced fields have applications in surface-enhanced spectroscopies5,6,7, nonlinear optics1,8,9,10 and nanophotonics11,12,13,14,15. Here we show that nonlinear tunnelling conduction between gold electrodes separated by a subnanometre gap leads to optical rectification, producing a d.c. photocurrent when the gap is illuminated. Comparing this photocurrent with low-frequency conduction measurements, we determine the optical frequency voltage across the tunnelling region of the nanogap, and also the enhancement of the electric field in the tunnelling region, as a function of gap size. The measured field enhancements exceed 1,000, consistent with estimates from surface-enhanced Raman measurements16,17,18. Our results highlight the need for more realistic theoretical approaches that are able to model the electromagnetic response of metal nanostructures on scales ranging from the free-space wavelength, λ, down to λ/1,000, and for experiments with new materials, different wavelengths and different incident polarizations.

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Figure 1: Measurement approach and layout.
Figure 2: Demonstration of optical rectification.
Figure 3: Further evidence for optical rectification.
Figure 4: Theoretical basis for validity of rectification.
Figure 5: Field (right axis) at the tunnelling region as a function of gap distance (top axis) for five devices (shown in different colours) measured a number of times at 80 K.

References

  1. 1

    Mühlschlegel, P., Eisler, H., Martin, O., Hecht, B. & Pohl, D. Resonant optical antennas. Science 308, 1607–1609 (2005).

    Article  Google Scholar 

  2. 2

    Schuck, P. J., Fromm, D. P., Sundaramurthy, A., Kino, G. S. & Moerner, W. E. Improving the mismatch between light and nanoscale objects with gold bowtie nanoantennas. Phys. Rev. Lett. 94, 017402 (2005).

    CAS  Article  Google Scholar 

  3. 3

    Jiang, J., Bosnick, K., Maillard, M. & Brus, L. Single molecule Raman spectroscopy at the junctions of large Ag nanocrystals. J. Phys. Chem. B 107, 9964–9972 (2003).

    CAS  Article  Google Scholar 

  4. 4

    Li, K., Stockman, M. I. & Bergman, D. J. Self-similar chain of metal nanospheres as an efficient nanolens. Phys. Rev. Lett. 91, 227402 (2003).

    Article  Google Scholar 

  5. 5

    Otto, A., Mrozek, I., Grabhorn, H. & Akemann, W. Surface enhanced Raman scattering. J. Phys. Condens. Matter 4, 1143–1212 (1992).

    CAS  Article  Google Scholar 

  6. 6

    Hartstein, A., Kirtley, J. R. & Tsang, J. C. Enhancement of the infrared absorption from molecular monolayers with thin metal overlayers. Phys. Rev. Lett. 45, 201–204 (1980).

    CAS  Article  Google Scholar 

  7. 7

    Fort, E. & Gresillon, S. Surface enhanced fluorescence. J. Phys. D. 41, 013001 (2008).

    Article  Google Scholar 

  8. 8

    Danckwerts, M. & Novotny, L. Optical frequency mixing at coupled gold nanoparticles. Phys. Rev. Lett. 98, 026104 (2007).

    Article  Google Scholar 

  9. 9

    Bouhelier, A., Beversluis, M. R. & Novotny, L. Characterization of nanoplasmonic structures by locally excited photoluminescence. Appl. Phys. Lett. 83, 5041–5043 (2003).

    CAS  Article  Google Scholar 

  10. 10

    Ghenuche, P., Cherukulappurath, S., Taminiau, T. H., van Hulst, N. F. & Quidant, R. Spectroscopic mode mapping of resonant plasmon nanoantennas. Phys. Rev. Lett. 101, 116805 (2008).

    Article  Google Scholar 

  11. 11

    Akimov, A. V. et al. Generation of single optical plasmons in metallic nanowires coupled to quantum dots. Nature 450, 402–406 (2007).

    CAS  Article  Google Scholar 

  12. 12

    Dionne, J. A., Diest, K., Sweatlock, L. A. & Atwater, H. A. PlasMOStor: a metal-oxide-Si field effect plasmonic modulator. Nano Lett. 9, 897–902 (2009).

    CAS  Article  Google Scholar 

  13. 13

    Yu, N. et al. Plasmonic quantum cascade laser antenna. Appl. Phys. Lett. 91, 173113 (2007).

    Article  Google Scholar 

  14. 14

    Oulton, R. F. et al. Plasmon lasers at deep subwavelength scale. Nature 461, 629–632 (2009).

    CAS  Article  Google Scholar 

  15. 15

    Noginov, M. A. et al. Demonstration of a spaser-based nanolaser. Nature 460, 1110–1112 (2009).

    CAS  Article  Google Scholar 

  16. 16

    Ward, D. R. et al. Electromigrated nanoscale gaps for surface-enhanced Raman spectroscopy. Nano Lett. 7, 1396–1400 (2007).

    CAS  Article  Google Scholar 

  17. 17

    Ward, D. R. et al. Simultaneous measurements of electronic conduction and Raman response in molecular junctions. Nano Lett. 8, 919–924 (2008).

    CAS  Article  Google Scholar 

  18. 18

    Ward, D. R., Scott, G. D., Keane, Z. K., Halas, N. J. & Natelson, D. Electronic and optical properties of electromigrated molecular junctions. J. Phys. Condens. Matter 20, 374118 (2008).

    CAS  Article  Google Scholar 

  19. 19

    Cutler, P. H. et al. Proposed use of a scanning-tunnelling-microscope tunnel junction for the measurement of a tunnelling time. Phys. Rev. B 35, 7774–7775 (1987).

    CAS  Article  Google Scholar 

  20. 20

    Tu, X. W., Lee, J. H. & Ho, W. Atomic-scale rectification at microwave frequency. J. Chem. Phys. 124, 021105 (2006).

    CAS  Article  Google Scholar 

  21. 21

    Nguyen, H. Q. et al. Mechanisms of current rectification in an STM tunnel junction and the measurement of an operational tunnelling time. IEEE Trans. Elect. Dev. 36, 2671–2678 (1989).

    CAS  Article  Google Scholar 

  22. 22

    Bragas, A. V., Landi, S. M. & Martínez, O. E. Laser field enhancement at the scanning tunnelling microscope junction measured by optical rectification. Appl. Phys. Lett. 72, 2075–2077 (1998).

    CAS  Article  Google Scholar 

  23. 23

    Viljas, J. K. & Cuevas, J. C. Role of electronic structure in photoassisted transport through atomic-sized contacts. Phys. Rev. B 75, 075406 (2007).

    Article  Google Scholar 

  24. 24

    Guhr, D. C. et al. Influence of laser light on electronic transport through atomic-size contacts. Phys. Rev. Lett. 99, 086801 (2007).

    CAS  Article  Google Scholar 

  25. 25

    Ittah, N., Noy, G., Yutsis, I. & Selzer, Y. Measurement of electronic transport through 1G0 gold contacts under laser irradiation. Nano Lett. 9, 1615–1620 (2009).

    CAS  Article  Google Scholar 

  26. 26

    Tien, P. K. & Gordon, J. P. Multiphoton process observed in the interaction of microwave fields with the tunnelling between superconductor films. Phys. Rev. 129, 647–651 (1963).

    Article  Google Scholar 

  27. 27

    Park, H., Lim, A. K. L., Alivisatos, A. P., Park, J. & McEuen, P. L. Fabrication of metallic electrodes with nanometer separation. Appl. Phys. Lett. 75, 301–303 (1999).

    CAS  Article  Google Scholar 

  28. 28

    Pauly, F. et al. Cluster-based density-functional approach to quantum transport through molecular and atomic contacts. New J. Phys. 10, 125019 (2008).

    Article  Google Scholar 

  29. 29

    Zuloaga, J., Prodan, E. & Nordlander, P. Quantum description of the plasmon resonances of a nanoparticle dimer. Nano Lett. 9, 887–891 (2009).

    CAS  Article  Google Scholar 

  30. 30

    Mao, L., Li, Z., Wu, B. & Xu, H. Effects of quantum tunnelling in metal nanogap on surface-enhanced Raman scattering. Appl. Phys. Lett. 94, 243102 (2009).

    Article  Google Scholar 

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Acknowledgements

D.N. and D.R.W. acknowledge support from the Robert A. Welch Foundation (grant C-1636) and the Lockheed Martin Advanced Nanotechnology Center of Excellence at Rice (LANCER). F.H. and J.C.C. acknowledge support from the Deutsche Forschungsgemeinschaft, the Baden-Württemberg Stiftung, the European Union through the Bio-Inspired Approaches for Molecular Electronics network (grant MRTN-CT-2006-035859) and the Spanish Ministry of Science and Innovation (Ministerio de Ciencia e Innovacion) (grant FIS2008-04209). F.P. acknowledges funding from a Young Investigator Group.

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D.R.W. fabricated the devices, performed all measurements and analysed the data. D.N. supervised and provided continuous guidance for the experiments and the analysis. F.P., F.H. and J.C.C. carried out the theoretical modelling and DFT calculations. The bulk of the paper was written by D.R.W. and D.N. All authors discussed the results and contributed to manuscript revision.

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Correspondence to Douglas Natelson.

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The authors declare no competing financial interests.

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Ward, D., Hüser, F., Pauly, F. et al. Optical rectification and field enhancement in a plasmonic nanogap. Nature Nanotech 5, 732–736 (2010). https://doi.org/10.1038/nnano.2010.176

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