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Thiol-free self-assembled oligoethylene glycols enable robust air-stable molecular electronics

Nature Materials volume 19, pages 330–337 (2020)Cite this article

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Abstract

Self-assembled monolayers (SAMs) are widely used to engineer the surface properties of metals. The relatively simple and versatile chemistry of metal–thiolate bonds makes thiolate SAMs the preferred option in a range of applications, yet fragility and a tendency to oxidize in air limit their long-term use. Here, we report the formation of thiol-free self-assembled mono- and bilayers of glycol ethers, which bind to the surface of coinage metals through the spontaneous chemisorption of glycol ether-functionalized fullerenes. As-prepared assemblies are bilayers presenting fullerene cages at both the substrate and ambient interface. Subsequent exposure to functionalized glycol ethers displaces the topmost layer of glycol ether-functionalized fullerenes, and the resulting assemblies expose functional groups to the ambient interface. These layers exhibit the key properties of thiolate SAMs, yet they are stable to ambient conditions for several weeks, as shown by the performance of tunnelling junctions formed from SAMs of alkyl-functionalized glycol ethers. Glycol ether-functionalized spiropyrans incorporated into mixed monolayers lead to reversible, light-driven conductance switching. Self-assemblies of glycol ethers are drop-in replacements for thiolate SAMs that retain all of their useful properties while avoiding the drawbacks of metal–thiolate bonds.

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Fig. 1: Characterization of the SAMs and SABs of PTEG-1.
Fig. 2: Schematic of the exchange process in which SABs of PTEG-1 are converted to GESAMs of alkylGEs.
Fig. 3: Characterization of the charge transport properties of SABs of alkylGEs on PTEG-1.
Fig. 4: Characterization of SABs of SP-GE on PTEG-1 during switching.
Fig. 5: The stability of tunnelling junctions comprising SABs of alkylGEs on PTEG-1 over 35 days.

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Data availability

The raw data used to prepare the STM, AFM, ellipsometry, water contact angle, EGaIn and XPS data in Figs. 1–5 and in the Supplementary Information are hosted at the University of Groningen according to the research data management plans described at https://www.rug.nl/research/zernike/rdmp. All raw and processed data are available for download from https://hdl.handle.net/10411/I3J7II.

Code availability

All of the raw data acquired using EGaIn and CP-AFM were processed using Scientific Python. The source code is publicly available at https://github.com/rchiechi/GaussFit and is retained internally in accordance with the aforementioned data retention policies.

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Acknowledgements

R.C.C. and X.Q. acknowledge financial support from the Zernike Institute of Advanced Materials. R.C.C., V.I., S.R. and J.C.H. acknowledge support from the FOM Focus Group Next-Gen PV.

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  1. Li Qiu

    Present address: School of Materials Science and Engineering, Yunnan Key Laboratory for Micro/Nano Materials & Technology, Yunnan University, Kunming, China

Authors and Affiliations

  1. Stratingh Institute for Chemistry, University of Groningen, Groningen, the Netherlands

    Xinkai Qiu, Viktor Ivasyshyn, Li Qiu, Sylvia Rousseva, Jan C. Hummelen & Ryan C. Chiechi

  2. Zernike Institute for Advanced Materials, University of Groningen, Groningen, the Netherlands

    Xinkai Qiu, Viktor Ivasyshyn, Li Qiu, Mihaela Enache, Jingjin Dong, Sylvia Rousseva, Giuseppe Portale, Meike Stöhr, Jan C. Hummelen & Ryan C. Chiechi

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Contributions

X.Q. and R.C.C. conceived the idea. X.Q. designed the experiments, synthesized the alkylGEs, prepared all samples and junctions, performed the characterizations using EGaIn, AFM, XPS, ellipsometry and water contact angle, and analysed the data. V.I. synthesized SP-GE. L.Q. and J.C.H. synthesized PTEG-1. M.E. and M.S. performed STM measurements and analysed the data. S.R. synthesized the alkylC60s. J.D. and G.P. performed grazing-incidence wide-angle X-ray scattering and X-ray reflectivity measurements and analysed the data. X.Q. wrote the paper with R.C.C. All of the authors edited the manuscript before submission.

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Correspondence to Ryan C. Chiechi.

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Supplementary Information

Supplementary Figs. 1–34, Supplementary discussions in sections 3, 4.3, 5.1, 5.3, 5.5, 6, 8, 9 and 10 and Tables 1–11.

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Statistical source data of Fig. 1e,f.

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Qiu, X., Ivasyshyn, V., Qiu, L. et al. Thiol-free self-assembled oligoethylene glycols enable robust air-stable molecular electronics. Nat. Mater. 19, 330–337 (2020). https://doi.org/10.1038/s41563-019-0587-x

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