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.

The role of van der Waals forces in the performance of molecular diodes

Abstract

One of the main goals of organic and molecular electronics is to relate the performance and electronic function of devices to the chemical structure and intermolecular interactions of the organic component inside them, which can take the form of an organic thin film, a self-assembled monolayer or a single molecule1,2,3,4,5,6,7. This goal is difficult to achieve because organic and molecular electronic devices are complex physical–organic systems that consist of at least two electrodes, an organic component and two (different) organic/inorganic interfaces. Singling out the contribution of each of these components remains challenging. So far, strong ππ interactions have mainly been considered for the rational design and optimization of the performances of organic electronic devices8,9,10, and weaker intermolecular interactions have largely been ignored. Here, we show experimentally that subtle changes in the intermolecular van der Waals interactions in the active component of a molecular diode dramatically impact the performance of the device. In particular, we observe an odd–even effect as the number of alkyl units is varied in a ferrocene–alkanethiolate self-assembled monolayer. As a result of a more favourable van der Waals interaction, junctions made from an odd number of alkyl units have a lower packing energy (by 0.4–0.6 kcal mol–1), rectify currents 10 times more efficiently, give a 10% higher yield in working devices, and can be made two to three times more reproducibly than junctions made from an even number of alkyl units.

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

Access options

Rent or buy this article

Prices vary by article type

from$1.95

to$39.95

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

Figure 1: Schematic illustration of junctions of the type AgTS–SCnFc//Ga2O3/EGaIn and the mechanism of charge transport across them.
Figure 2: Electrical characteristics of the tunnelling junctions of AgTS–SCnFc//Ga2O3/EGaIn with n = 6–15.
Figure 3: Structural characterization of the SAMs by molecular dynamics and NEXAFS.
Figure 4: Packing energies as a function of n derived from electrochemistry and molecular dynamics.

References

  1. Mujica, V., Ratner, M. A. & Nitzan, A. Molecular rectification: why is it so rare? Chem. Phys. 281, 147–150 (2002).

    Article  CAS  Google Scholar 

  2. Lindsay, S. M. & Ratner, M. A. Molecular transport junctions: clearing mists. Adv. Mater. 19, 23–31 (2007).

    Article  CAS  Google Scholar 

  3. Moth-Poulson, K. & Bjornholm, T. Molecular electronics with single molecules in solid-state devices. Nature Nanotech. 4, 551–556 (2009).

    Article  Google Scholar 

  4. Diez-Perez, I. et al. Controlling single-molecule conductance through lateral coupling of π orbitals. Nature Nanotech. 6, 226–231 (2011).

    Article  CAS  Google Scholar 

  5. McCreery, R. L. & Bergren, A. Progress with molecular electronic junctions: meeting experimental challenges in design and fabrication. Adv. Mater. 21, 4303–4322 (2009).

    Article  CAS  Google Scholar 

  6. Choi, S. H., Kim, B. & Frisbie, C. D. Electrical resistance of long conjugated molecular wires. Science 320, 1482–1486 (2008).

    Article  CAS  Google Scholar 

  7. Park, S. et al. Flexible molecular-scale electronic devices. Nature Nanotech. 7, 438–442 (2012).

    Article  CAS  Google Scholar 

  8. Cornil, J., Beljonne, D., Calbert, J-P. & Brédas, J-L. Interchain interactions in organic π-conjugated materials: impact on electronic structure, optical response, and charge transport. Adv. Mater. 13, 1053–1067 (2001).

    Article  CAS  Google Scholar 

  9. Henson, Z. B., Müllen, K. & Bazan, G. C. Design strategies for organic semiconductors beyond the molecular formula. Nature Chem. 4, 699–704 (2012).

    Article  CAS  Google Scholar 

  10. Wu, S. M. et al. Molecular junctions based on aromatic coupling. Nature Nanotech. 3, 569–574 (2008).

    Article  CAS  Google Scholar 

  11. Hoeben, F. J. M., Jonkheijm, P., Meijer, E. W. & Schenning, A. P. H. J. Supramolecular assemblies of π-conjugated systems. Chem. Rev. 105, 1491–1546 (2005).

    Article  CAS  Google Scholar 

  12. Zaworotko, M. J. & Moulton, B. From molecules to crystal engineering: supramolecular isomerism and polymorphism in network solids. Chem. Rev. 101, 1629–1658 (2001).

    Article  Google Scholar 

  13. Krishnamurthy, V. M. et al. Carbonic anhydrase as a model for biophysical and physical–organic studies of proteins and protein–ligand binding. Chem. Rev. 108, 946–1051 (2008).

    Article  CAS  Google Scholar 

  14. Ho, P. K. H. et al. Molecular-scale interface engineering for polymer light-emitting diodes. Nature 404, 481–484 (2000).

    Article  CAS  Google Scholar 

  15. Tao, F. & Bernasek, S. L. Understanding odd–even effects in organic self-assembled monolayers. Chem. Rev. 107, 1408–1453 (2007).

    Article  CAS  Google Scholar 

  16. Thuo, M. N. et al. Odd–even effects in tunneling across self-assembled monolayers. J. Am. Chem. Soc. 133, 2962–2975 (2011).

    Article  CAS  Google Scholar 

  17. Chiechi, R. C., Weiss, E. A. Dickey, M. D. & Whitesides, G. M. Eutectic gallium–indium (EGaIn): a moldable liquid metal for electrical characterization of self-assembled monolayers. Angew. Chem. Int. Ed. 47, 142–146. (2008).

    Article  CAS  Google Scholar 

  18. Reus, W. F., Thuo, M. N., Shapiro, N. D., Nijhuis, C. A. & Whitesides, G. M. The SAM, not the electrodes, dominates charge transport in metal-monolayer// Ga2O3/gallium-indium eutectic junctions. ACS Nano 6, 4806–4822 (2012).

    Article  CAS  Google Scholar 

  19. Fracasso, D., Valkenier, H., Hummelen, J. C., Solomon, G. C. & Chiechi, R. C. Evidence for quantum interference in SAMs of arylethynylene thiolates in tunneling junctions with eutectic Ga-In (EGaIn) top-contacts J. Am. Chem. Soc. 133, 9556–9563 (2011).

    Article  CAS  Google Scholar 

  20. Masillamani, A. M. et al. Multiscale charge injection and transport properties in self-assembled monolayers of biphenyl thiols with varying torsion angles Chem. Eur. J. 18, 10335–10347 (2012).

    Article  CAS  Google Scholar 

  21. Nijhuis, C. A., Reus, W. F., Barber, J., Dickey, M. D. & Whitesides, G. M. Charge transport and rectification in arrays of SAM-based tunneling junctions. Nano Lett. 10, 3611–3619 (2010).

    Article  CAS  Google Scholar 

  22. Reus, W. F. et al. Statistical tools for analyzing measurements of charge transport. J. Phys. Chem. C 116, 6714–6733 (2012).

    Article  CAS  Google Scholar 

  23. Auletta, T., van Veggel, F. C. J. M. & Reinhoudt, D. N. Self-assembled monolayers on gold of ferrocene-terminated thiols and hydroxyalkanethiols. Langmuir 18, 1288–1293 (2002).

    Article  CAS  Google Scholar 

  24. Joachim, C. & Ratner, M. A. Molecular electronics: some views on transport junctions and beyond Proc. Natl Acad. Sci. USA 102, 8801–8808 (2005).

    Article  CAS  Google Scholar 

  25. Ye, S., Sato, Y. & Uosaki, K. Redox-induced orientation change of a self-assembled monolayer of 11-ferrocenyl-1-undecanethiol on a gold electrode studied by in situ FT-IRRAS. Langmuir 13, 3157–3161 (1997).

    Article  CAS  Google Scholar 

  26. Venkataraman, L., Klare, J. E., Nuckolls, C., Hybertson, M. A. & Steigerwald, M. L. Dependence of single-molecule junction conductance on molecular conformation. Nature 442, 904–907 (2006).

    Article  CAS  Google Scholar 

  27. Rühl, E. & Hitchcock, A. P. Carbon K-shell excitation of metallocenes J. Am. Chem. Soc. 111, 5069–5075 (1989).

    Article  Google Scholar 

  28. Creager, S. E. & Rowe, G. K. Competitive self-assembly and electrochemistry of some ferrocenyl-n-alkanethiol derivatives on gold. J. Electroanal. Chem. 370, 203–211 (1994).

    Article  CAS  Google Scholar 

  29. Perl, A. et al. Gradient-driven motion of multivalent ligand molecules along a surface functionalized with multiple receptors. Nature Chem. 3, 317–322 (2011).

    Article  CAS  Google Scholar 

  30. Gannon, G., Greer, J. C., Larsson, J. A. & Thompson, D. Molecular dynamics study of naturally occurring defects in self-assembled monolayer formation. ACS Nano 4, 921–932 (2010).

    Article  CAS  Google Scholar 

Download references

Acknowledgements

The Singapore National Research Foundation (NRF award no. NRF-RF2010-03 to C.A.N.) is acknowledged for supporting this research. D.T. acknowledges financial support from the Science Foundation Ireland (SFI; grant no. 11/SIRG/B2111) and the use of computing resources at Tyndall and the SFI/Higher Education Authority Irish Centre for High-End Computing (ICHEC). The authors thank Su Ying Quek for useful discussions and the technical support from the Singapore Synchrotron Light Source.

Author information

Authors and Affiliations

Authors

Contributions

N.N. synthesized the compounds and characterized the SAMs. L.Y. performed the J(V) measurements. J.L. prepared the template-stripped substrates. Q.D.C. and L.Y. recorded and analysed the NEXAFS spectra. D.T. performed the molecular dynamics simulations. C.A.N. supervised the project. All authors contributed to writing the manuscript.

Corresponding authors

Correspondence to Damien Thompson or Christian A. Nijhuis.

Supplementary information

Supplementary information

Supplementary information (PDF 16846 kb)

Rights and permissions

Reprints and permissions

About this article

Cite this article

Nerngchamnong, N., Yuan, L., Qi, DC. et al. The role of van der Waals forces in the performance of molecular diodes. Nature Nanotech 8, 113–118 (2013). https://doi.org/10.1038/nnano.2012.238

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nnano.2012.238

This article is cited by

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