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Covalently interconnected transition metal dichalcogenide networks via defect engineering for high-performance electronic devices

Abstract

Solution-processed semiconducting transition metal dichalcogenides are at the centre of an ever-increasing research effort in printed (opto)electronics. However, device performance is limited by structural defects resulting from the exfoliation process and poor inter-flake electronic connectivity. Here, we report a new molecular strategy to boost the electrical performance of transition metal dichalcogenide-based devices via the use of dithiolated conjugated molecules, to simultaneously heal sulfur vacancies in solution-processed transition metal disulfides and covalently bridge adjacent flakes, thereby promoting percolation pathways for the charge transport. We achieve a reproducible increase by one order of magnitude in field-effect mobility (µFE), current ratio (ION/IOFF) and switching time (τS) for liquid-gated transistors, reaching 10−2 cm2 V−1 s−1, 104 and 18 ms, respectively. Our functionalization strategy is a universal route to simultaneously enhance the electronic connectivity in transition metal disulfide networks and tailor on demand their physicochemical properties according to the envisioned applications.

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Fig. 1: Functionalization strategy for production of covalently interconnected MS2 networks.
Fig. 2: Characterization of MS2 films and networks.
Fig. 3: Electrical properties of LG-TFTs based on MoS2 films and networks.
Fig. 4: Temperature-dependent electrical characteristics.

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Source data are provided with this paper. The data that support the findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

We acknowledge funding from the European Commission through the Graphene Flagship, the ERC Grants SUPRA2DMAT (GA-833707), FUTURE-PRINT (GA-694101), Hetero2D and GSYNCOR, the EU Grant Neurofibres, the Agence Nationale de la Recherche through the Labex projects CSC (ANR-10-LABX-0026 CSC) and NIE (ANR-11-LABX-0058 NIE) within the Investissement d’Avenir programme (ANR-10-120 IDEX-0002-02), the International Center for Frontier Research in Chemistry (icFRC), EPSRC Grants EP/K01711X/1, EP/K017144/1, EP/N010345/1 and EP/L016057/1, and the Faraday Institution. The HAADF-STEM characterization was carried out at the Advanced Microscopy Laboratory (Dublin), a Science Foundation Ireland (SFI) supported centre.

Author information

Authors and Affiliations

Authors

Contributions

S.I. and P.S. conceived the experiments and designed the study. A.G.K., Z.B., L.L., Y.A.S., A.C.F. and J.N.C. produced the raw materials and characterized them by spectroscopic and electrochemical techniques. S.I. designed and performed the multiscale characterizations on the final functionalized materials. R.F.O. and M.-A.S. designed and performed the charge-carrier transport measurements and studies. D.I. carried out the NMR measurements and analysis. A.R., C.D. and V.N. designed and performed the HAADF-STEM investigations. All authors discussed the results and contributed to the interpretation of data. S.I., R.F.O. and P.S. co-wrote the paper with input from all co-authors.

Corresponding author

Correspondence to Paolo Samorì.

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The authors declare no competing interests.

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Peer review information Nature Nanotechnology thanks Damien Voiry and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Spectroscopic and morphological characterization of solution-processed MS2.

a, UV-Vis spectra (solution). b, Raman spectra (film). c, Statistical AFM analysis performed on 300 individual MS2 flakes and comparison with values estimated via UV-Vis spectroscopy. d, Typical SEM image of drop-cast MoS2 flakes.

Extended Data Fig. 2 HAADF-STEM investigation.

HAADF-STEM images and related histograms of Mo-Mo distance for the a, basal plane of LPE-MoS2, b, edge of LPE-MoS2, c, basal plane of MC-MoS2 and d, basal plane of CVD-MoS2. The histograms show a similar average Mo-Mo distance for the basal plane of all samples, with a significant decrease ~30 pm for the edge of LPE-MoS2, pointing to a higher defect density.

Extended Data Fig. 3 XPS analysis.

a, Sulfur/Metal XPS ratio before and after exposure to BDT molecules for MoS2, WS2 and ReS2. b, Summary of the XPS constraints (spin-orbit splitting and intensity ratio) implemented for the fitting of Mo3d, Re4f, W4f and S2p regions, before and after exposure to BDT molecules.

Extended Data Fig. 4 Ex-situ functionalization with BDT.

a, Schematic illustration for the ex-situ functionalization of MS2 inks with BDT. b, Outcome of stability test for pristine and BDT-functionalized MoS2 ink, along with the related zeta potential values. c, Optical image of a IDE device covered with BDT-functionalized MoS2 ink via ex-situ approach.

Extended Data Fig. 5 NMR investigation.

a, Tested reactions between MoS2 and thiolated molecules under exam (TP and BDT). Related NMR spectra at different time intervals for b, control experiment (BDT without MoS2), c, MoS2 + BDT and d, MoS2 + TP.

Extended Data Fig. 6 Mechanical test.

a, Experimental setup. b, Sketch of the samples subjected to bending deformation. c, Variation of the relative channel resistance ΔR/R0 of bare IDEs, MoS2 films, and MoS2 networks upon 5k and 10k bending cycles, along with related d, optical images of MoS2 films and networks before (left) and after (right) mechanical deformation.

Extended Data Fig. 7 Influence of the linker structure on electrical performance of MoS2 networks.

Transfer curves for MoS2 LG-TFTs a, before and after treatment with BDT linkers and b, before and after treatment with PDT linkers. All curves are recorded at Vds = -100 mV, using EMI-TFSI as electrolyte and a Pt wire as gate electrode. The molecular structures of BDT and PDT are also indicated.

Extended Data Fig. 8 Thermally-activated current response.

Ln I vs. 1000/T for VGback = + 80 V in a, MoS2 films b, TP-functionalized samples and c, MoS2 networks. EA is calculated from the curve slope with errors associated to different applied bias on the IDEs (from 1-2.5 V, that is, E = 4 x 105 – 1 x 106 V/m).

Supplementary information

Supplementary Information

Supplementary Figs. 1–30, discussion and Tables 1–7.

Source data

Source Data Fig. 2

Source data for the XPS (Fig. 2a) and Raman (Fig. 2b) of MoS2 films and networks.

Source Data Fig. 3

Source data for the electrical characterization of MoS2 films and networks reported in Fig. 3b and Fig. 3c.

Source Data Fig. 4

Source data for the temperature-dependent electrical characteristics of MoS2 films and networks reported in Fig. 4.

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Ippolito, S., Kelly, A.G., Furlan de Oliveira, R. et al. Covalently interconnected transition metal dichalcogenide networks via defect engineering for high-performance electronic devices. Nat. Nanotechnol. 16, 592–598 (2021). https://doi.org/10.1038/s41565-021-00857-9

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