Ultralow effective work function surfaces using diamondoid monolayers

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Abstract

Electron emission is critical for a host of modern fabrication and analysis applications including mass spectrometry, electron imaging and nanopatterning. Here, we report that monolayers of diamondoids effectively confer dramatically enhanced field emission properties to metal surfaces. We attribute the improved emission to a significant reduction of the work function rather than a geometric enhancement. This effect depends on the particular diamondoid isomer, with [121]tetramantane-2-thiol reducing gold's work function from 5.1 eV to 1.60 ± 0.3 eV, corresponding to an increase in current by a factor of over 13,000. This reduction in work function is the largest reported for any organic species and also the largest for any air-stable compound1,2,3. This effect was not observed for sp3-hybridized alkanes, nor for smaller diamondoid molecules. The magnitude of the enhancement, molecule specificity and elimination of gold metal rearrangement precludes geometric factors as the dominant contribution. Instead, we attribute this effect to the stable radical cation of diamondoids. Our computed enhancement due to a positively charged radical cation was in agreement with the measured work functions to within ±0.3 eV, suggesting a new paradigm for low-work-function coatings based on the design of nanoparticles with stable radical cations.

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Figure 1: Field emission apparatus.
Figure 2: Diamondoid field emission.
Figure 3: Summary of the work functions obtained using the various experimental and computational techniques used in the present work.
Figure 4: Diamondoid radical cation mechanism.
Figure 5: Calculated field emission with radical cations.

References

  1. 1

    Alloway, D. M. et al. Tuning the effective work function of gold and silver using ω-functionalized alkanethiols: varying surface composition through dilution and choice of terminal groups. J. Phys. Chem. C 113, 20328–20334 (2009).

  2. 2

    Alloway, D. M. et al. Interface dipoles arising from self-assembled monolayers on gold: UV–photoemission studies of alkanethiols and partially fluorinated alkanethiols. J. Phys. Chem. B 107, 11690–11699 (2003).

  3. 3

    Bröker, B. et al. Gold work function reduction by 2.2eV with an air-stable molecular donor layer. Appl. Phys. Lett. 93, 243303 (2008).

  4. 4

    Robertson, J. Mechanisms of electron field emission from diamond, diamond-like carbon, and nanostructured carbon. J. Vac. Sci. Technol. B 17, 659–665 (1999).

  5. 5

    Silva, S. R. P., Carey, J. D., Guo, X., Tsang, W. M. & Poa, C. H. P. Electron field emission from carbon-based materials. Proc. ICMAT 03 482, 79–85 (2005).

  6. 6

    Zhu, W., Kochanski, G. P. & Jin, S. Low-field electron emission from undoped nanostructured diamond. Science 282, 1471–1473 (1998).

  7. 7

    Koeck, F. A. M., Garguilo, J. M. & Nemanich, R. J. On the thermionic emission from nitrogen-doped diamond films with respect to energy conversion. Diamond Relat. Mater. 13, 2052–2055 (2004).

  8. 8

    Koeck, F. A. M. & Nemanich, R. J. Emission characterization from nitrogen-doped diamond with respect to energy conversion. Diamond Relat. Mater. 15, 217–220 (2006).

  9. 9

    Robertson, J. Diamond-like amorphous carbon. Mater. Sci. Eng. R Rep. 37, 129–281 (2002).

  10. 10

    Dahl, J. E., Liu, S. G. & Carlson, R. M. Isolation and structure of higher diamondoids, nanometer-sized diamond molecules. Science 299, 96–99 (2003).

  11. 11

    Schwertfeger, H., Fokin, A. A. & Schreiner, P. R. Diamonds are a chemist's best friend: diamondoid chemistry beyond adamantane. Angew. Chem. Int. Ed. 47, 1022–1036 (2008).

  12. 12

    Clay, W. A., Dahl, J. E. P., Carlson, R. M. K., Melosh, N. A. & Shen, Z.-X. Physical properties of materials derived from diamondoid molecules. Rep. Prog. Phys. 78, 016501 (2015).

  13. 13

    Clay, W. A. et al. Diamondoids as low-κ dielectric materials. Appl. Phys. Lett. 93, 172901 (2008).

  14. 14

    Willey, T. M. et al. Near-edge X-ray absorption fine structure spectroscopy of diamondoid thiol monolayers on gold. J. Am. Chem. Soc. 130, 10536–10544 (2008).

  15. 15

    Willey, T. M. et al. Determining orientational structure of diamondoid thiols attached to silver using near-edge X-ray absorption fine structure spectroscopy. J. Electron Spectrosc. Rel. Phenom. 172, 69–77 (2009).

  16. 16

    Schreiner, P. R. et al. Functionalized nanodiamonds: triamantane and [121]tetramantane. J. Org. Chem. 71, 6709–6720 (2006).

  17. 17

    Schwertfeger, H. et al. Diamondoid phosphines—selective phosphorylation of nanodiamonds[1]. Adv. Synth. Catal. 352, 609–615 (2010).

  18. 18

    Tkachenko, B. A. et al. Functionalized nanodiamonds part 3: thiolation of tertiary/bridgehead alcohols. Org. Lett. 8, 1767–1770 (2006).

  19. 19

    Clay, W. A. et al. Origin of the monochromatic photoemission peak in diamondoid monolayers. Nano Lett. 9, 57–61 (2009).

  20. 20

    Yang, W. L. et al. Monochromatic electron photoemission from diamondoid monolayers. Science 316, 1460–1462 (2007).

  21. 21

    Fokin, A. A. et al. Stable alkanes containing very long carbon–carbon bonds. J. Am. Chem. Soc. 134, 13641–13650 (2012).

  22. 22

    Schreiner, P. R. et al. Overcoming lability of extremely long alkane carbon–carbon bonds through dispersion forces. Nature 477, 308–311 (2011).

  23. 23

    Willey, T. M. et al. Molecular limits to the quantum confinement model in diamond clusters. Phys. Rev. Lett. 95, 113401 (2005).

  24. 24

    LaRue, J. L. et al. The work function of submonolayer cesium-covered gold: a photoelectron spectroscopy study. J. Chem. Phys. 129, 024709 (2008).

  25. 25

    Forbes, R. G. Simple good approximations for the special elliptic functions in standard Fowler–Nordheim tunneling theory for a Schottky–Nordheim barrier. Appl. Phys. Lett. 89, 113122 (2006).

  26. 26

    Fokin, A. A., Tkachenko, B. A., Gunchenko, P. A., Gusev, D. V. & Schreiner, P. R. Functionalized nanodiamonds part I.: an experimental assessment of diamantane and computational predictions for higher diamondoids. Chem. Eur. J. 11, 7091–7101 (2005).

  27. 27

    Guerrero, A. et al. Single-electron self-exchange between cage hydrocarbons and their radical cations in the gas phase. ChemPhysChem 11, 713–721 (2010).

  28. 28

    Lenzke, K. et al. Experimental determination of the ionization potentials of the first five members of the nanodiamond series. J. Chem. Phys. 127, 084320 (2007).

  29. 29

    Pirali, O., Alvaro Galué, H., Dahl, J. E., Carlson, R. M. K. & Oomens, J. Infrared spectra and structures of diamantyl and triamantyl carbocations. Int. J. Mass Spectrom. 297, 55–62 (2010).

  30. 30

    Steglich, M., Huisken, F., Dahl, J. E., Carlson, R. M. K. & Henning, Th. Electronic spectroscopy of FUV-irradiated diamondoids: a combined experimental and theoretical study. Astrophys. J. 729, 91 (2011).

  31. 31

    Chou, S. H., Voss, J., Vojvodic, A., Howe, R. T. & Abild-Pedersen, F. DFT study of atomically-modified alkali-earth metal oxide films on tungsten. J. Phys. Chem. C 118, 11303–11309 (2014).

  32. 32

    Simmons, J. G. Generalized formula for the electric tunnel effect between similar electrodes separated by a thin insulating film. J. Appl. Phys. 34, 1793–1803 (1963).

  33. 33

    Lu, X., Grobis, M., Khoo, K. H., Louie, S. G. & Crommie, M. F. Charge transfer and screening in individual C60 molecules on metal substrates: a scanning tunneling spectroscopy and theoretical study. Phys. Rev. B 70, 115418 (2004).

  34. 34

    Li, F. H. et al. Covalent attachment of diamondoid phosphonic acid dichlorides to tungsten oxide surfaces. Langmuir 29, 9790–9797 (2013).

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Acknowledgements

This work was supported by the Department of Energy Office of Basic Energy Sciences, Materials Sciences and Engineering Division (contract no. DE-AC02-76SF00515). The authors thank F. Wang and T. Carver for metal sputtering, S. Sun for assistance with UPS measurements and T. Deveraux and A. Sorini for discussions about the DFT model.

Author information

K.T.N., C.G., Z.S. and N.A.M. conceived and designed the electron emission experiments. J.E.D. and R.M.K.C. isolated and purified the unfunctionalized diamondoids. B.A.T., A.A.F. and P.R.S. designed and performed the thiol functionalization. K.T.N., C.G., J.D.F. and W.C. developed the attachment and monolayer UPS characterization. K.T.N., C.G. and N.A.M. performed the computations and analysed the emissions data. K.T.N., J.D.F. and N.A.M. performed the DFT calculations, and the paper was primarily written by K.T.N., C.G. and N.A.M., with edits by all authors.

Correspondence to Nicholas A. Melosh.

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Narasimha, K., Ge, C., Fabbri, J. et al. Ultralow effective work function surfaces using diamondoid monolayers. Nature Nanotech 11, 267–272 (2016) doi:10.1038/nnano.2015.277

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