Hot-electron emission processes in waveguide-integrated graphene

Article metrics


Photoemission plays a central role in a wide range of fields, from electronic structure measurements to free-electron laser sources. In metallic emitters, single-photon1, multiphoton2,3,4,5 or strong-field emission6,7,8,9,10 processes are the primary photoemission mechanisms. Here, using a sub-work-function 3.06 eV continuous-wave laser, photoemission from waveguide-integrated monolayer graphene is observed to occur at peak power densities >5 orders of magnitude lower than reported multiphoton and strong-field emission6,11,12. The behaviour is explained by the emission of hot electrons in graphene. In monolayer graphene, the need for photoelectrons to be transported to an emitting surface is eliminated, dramatically enhancing the probability of emission before thermalization. These results indicate that integrated-photonics-driven hot-electron emission provides a rich new area of exploration for both electron emission and integrated photonics.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: Device schematics and emission processes.
Fig. 2: Waveguide-integrated graphene device.
Fig. 3: Electron emission characterization.
Fig. 4: Hot-electron scattering, electron emission and optical absorption simulation.
Fig. 5: Comparison with literature.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

Code availability

The ensemble Monte Carlo Boltzmann Transport Equation Solver source codes are available from the corresponding author upon reasonable request.


  1. 1.

    Spicer, W. E. Photoemissive, photoconductive, and optical absorption studies of alkali-antimony compounds. Phys. Rev. 112, 114–122 (1958).

  2. 2.

    Ropers, C., Solli, D., Schulz, C., Lienau, C. & Elsaesser, T. Localized multiphoton emission of femtosecond electron pulses from metal nanotips. Phys. Rev. Lett. 98, 043907 (2007).

  3. 3.

    Weber, T. et al. Correlated electron emission in multiphoton double ionization. Nature 405, 658–661 (2000).

  4. 4.

    Bechtel, J., Smith, W. L. & Bloembergen, N. Two-photon photoemission from metals induced by picosecond laser pulses. Phys. Rev. B 15, 4557–4563 (1977).

  5. 5.

    Logothetis, E. & Hartman, P. Laser-induced electron emission from solids: many-photon photoelectric effects and thermionic emission. Phys. Rev. 187, 460–474 (1969).

  6. 6.

    Bormann, R., Gulde, M., Weismann, A., Yalunin, S. & Ropers, C. Tip-enhanced strong-field photoemission. Phys. Rev. Lett. 105, 147601 (2010).

  7. 7.

    Piglosiewicz, B. et al. Carrier-envelope phase effects on the strong-field photoemission of electrons from metallic nanostructures. Nat. Photon. 8, 37–42 (2014).

  8. 8.

    Dombi, P. et al. Ultrafast strong-field photoemission from plasmonic nanoparticles. Nano Lett. 13, 674–678 (2013).

  9. 9.

    Schenk, M., Krüger, M. & Hommelhoff, P. Strong-field above-threshold photoemission from sharp metal tips. Phys. Rev. Lett. 105, 257601 (2010).

  10. 10.

    Putnam, W. P., Hobbs, R. G., Keathley, P. D., Berggren, K. K. & Kärtner, F. X. Optical-field-controlled photoemission from plasmonic nanoparticles. Nat. Phys. 13, 335–339 (2017).

  11. 11.

    Barwick, B. et al. Laser-induced ultrafast electron emission from a field emission tip. New J. Phys. 9, 142 (2007).

  12. 12.

    Yang, D.-S., Mohammed, O. F. & Zewail, A. H. Scanning ultrafast electron microscopy. Proc. Natl Acad. Sci. USA 107, 14993–14998 (2010).

  13. 13.

    Ma, Q. et al. Tuning ultrafast electron thermalization pathways in a van der Waals heterostructure. Nat. Phys. 12, 455–459 (2016).

  14. 14.

    Breusing, M. et al. Ultrafast nonequilibrium carrier dynamics in a single graphene layer. Phys. Rev. B 83, 153410 (2011).

  15. 15.

    Betz, A. et al. Supercollision cooling in undoped graphene. Nat. Phys. 9, 109–112 (2013).

  16. 16.

    Graham, M. W., Shi, S.-F., Ralph, D. C., Park, J. & McEuen, P. L. Photocurrent measurements of supercollision cooling in graphene. Nat. Phys. 9, 103–108 (2013).

  17. 17.

    Falkovsky, L. A. Optical properties of graphene. J. Phys. Conf. Ser. 129, 012004 (2008).

  18. 18.

    Falkovsky, L. & Pershoguba, S. Optical far-infrared properties of a graphene monolayer and multilayer. Phys. Rev. B 76, 153410 (2007).

  19. 19.

    Ferrari, A. C. et al. Raman spectrum of graphene and graphene layers. Phys. Rev. Lett. 97, 187401 (2006).

  20. 20.

    Lumerical (2012).

  21. 21.

    de Vega, S. & de Abajo, F. J. G. Plasmon generation through electron tunneling in twisted double-layer graphene and metal-insulator-graphene systems. Phys. Rev. B 99, 115438 (2019).

Download references


This work was supported by AFOSR grant no. FA9550-16-1-0306 and the Molecular Foundry at Lawrence Berkeley National Laboratory, a user facility supported by the Office of Science, Office of Basic Energy Sciences of the US Department of Energy (DOE) under contract no. DEAC02-05CH11231. R.A acknowledges a USC Provost Graduate Fellowship.

Author information

F.R. and R.K. designed the experiments. F.R. carried out the sample fabrication and measurements. Q.L. carried out graphene growth. R.A. and R.K carried out the electronic simulations. F.R. carried out the optical simulations. All authors contributed to analysing the data. F.R., R.A., H.U.C. and R.K. wrote the paper while all authors provided feedback.

Correspondence to Rehan Kapadia.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary details, Figs. 1–11 and refs. 1–17.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark