Abstract
In the past few years, the effect of strain on the optical and electronic properties of MoS2 layers has attracted particular attention as it can improve the performance of optoelectronic and spintronic devices. Although several approaches have been explored, strain is typically externally applied on the two-dimensional material. In this work, we describe the preparation of a reversible ‘self-strainable’ system in which the strain is generated at the molecular level by one component of a MoS2-based composite material. Spin-crossover nanoparticles were covalently grafted onto functionalized layers of semiconducting MoS2 to form a hybrid heterostructure. Their ability to switch between two spin states on applying an external stimulus (light irradiation or temperature change) serves to generate strain over the MoS2 layer. A volume change accompanies this spin crossover, and the created strain induces a substantial and reversible change of the electrical and optical properties of the heterostructure.
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Data availability
The data that support the findings of this study are available within the paper and its Supplementary Information files and from the corresponding authors upon request. Source data are provided with this paper.
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Acknowledgements
We acknowledge the financial support from the EU (ERC-Advanced Grant 78822-MOL-2D and FET-OPEN COSMICS 766726), the Spanish MICINN (PID2020-117152RB-I00, PID2020-117264GB-I00, Excellence Unit María de Maeztu CEX2019-000919-M, RTI2018-098568-A-I00 to S.T. and EQC2018-004888-P, co-financed by FEDER) and the Generalitat Valenciana (Prometeo Program of Excellence: PROMETEO/2017/066, PO FEDER Program IDIFEDER/2018/061 and IDIFEDER/2020/063 and the GentT Program CIDEGENT/2018/005 to J.C.-F. and SEJI/2020/036 to M.G.-M.). M.M.-G. thanks the Spanish MECD for the award of a FPU Grant. The Spanish MICINN is also acknowledged for a predoctoral fellowship (to R.T.-C.), two Juan de la Cierva Incorporación postdoctoral Grants (IJCI-2016-27441 to S.C.-S. and IJCI-2017-33538 to M.G.) and two Ramón y Cajal Contracts (RYC-2016-19817 to S.T. and RYC2019-027902-I to M.G.-M.). M.G.-M. thanks ‘la Caixa’ Foundation for support (LCF/BQ/PI19/11690022). The authors are grateful to J. M. Herrera from the Department of Inorganic Chemistry (Universidad de Granada) for his helpful discussion on the core–shell SCO nanoparticles.
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R.T.-C. and M.M.-G. contributed equally to this work. R.T.-C. was responsible for the design, synthesis and characterization of the new heterostructure and was involved in all the experimental measurements, the discussion and the preparation of the manuscript. M.M.-G. was in charge of the preparation of the exfoliated material and helped with all the characterization steps of the new system. M.G. was in charge of all the transport characterizations, in which G.E.-A., J.D. and S.T. were involved. S.C.-S. helped with the discussion and theoretical interpretation of the observed properties. M.G.-M. contributed to the SCO-NPs preparation and the discussion and interpretation of the results. J.C.-F. was involved in the PL experiments and their interpretation. A.F.-A. designed the work and was involved in the development and coordination of all the experimental parts, discussion of the results and preparation of the manuscript. E.C. supervised all the work and the preparation of the manuscript. All the authors revised and contributed to the presented manuscript.
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Extended data
Extended Data Fig. 1 Magnetic characterization of the composites.
a,b, Thermal variation of the χMT product for the SCO/MoS2-1 (a) and SCO/MoS2-2a (b). In both cases, the χMT value increases at the transition temperature from LS to HS, ulteriorly recovering its initial value with the reverse transition supporting the integrity of the SCO-NPs in the composites. χM, molar magnetic susceptibility.
Extended Data Fig. 2 Temperature-dependent photoluminescence of the composites.
a-d, Evolution of the PL emission maximum with the temperature of SCO/MoS2-1 (left panels) and SCO/MoS2-2a (right panels) during the heating (a,b) and the cooling (c,d) processes. The excitation power was fixed at 0.08 mW/µm2 to avoid thermal interferences. At any temperature between spin transition temperatures (380-340 K), the A peak position depends on the SCO-NPs spin state for both samples (that is, on the heating or cooling process), shifting to lower values in the HS (cooling process). This effect is observed to be more substantial for SCO/MoS2-1.
Extended Data Fig. 3 SCO/MoS2-2 optical response.
a, PL spectra of SCO/MoS2-2a at LS (red line, heating), and HS states (blue line, cooling), taken at 373 K and 0.08 mW. Clearly the HS state displays an A peak located at lower energy due to the strain applied by the SCO-NPs with increased volume after spin transition. b, PL shift as a function of the temperature (red dots, heating and blue dots, cooling). The position of the A peak of the MoS2 reflects the hysteretical behaviour of the SCO-NPs spin transition. Error bars represent the standard deviation calculated from at least three different areas measured at each temperature.
Extended Data Fig. 4 Temperature-dependent Raman spectra of the SCO-NPs.
a,b, Raman spectra of the SCO-NPs at different temperatures during the heating (a) and cooling (b) processes. The Raman spectra change depending on the SCO-NPs spin state.
Extended Data Fig. 5 Temperature-dependent photoluminescence of the CE-MoS2(2H).
a,b, Evolution of the PL emission maximum with the temperature of phase converted CE-MoS2(2H) during the heating (a) and the cooling (b) processes. c, PL maximum shifts as a function of temperature (red dots, heating and blue dots, cooling).The position of the PL maximum exhibits a linear displacement with the temperature. Processed error bars represent standard deviation calculated from at least three different areas measured at each temperature. Excitation power at 0.08 mW/µm2.
Extended Data Fig. 6 Raman spectra of the SCO-NPs upon light irradiation.
SCO-NPs Raman spectra at different conditions. a, Temperature: 363 K and laser intensity 0.08 mW (inside SCO-NPs hysteresis between spin transition temperatures), during the heating (LS, purple) and the cooling (HS, yellow) processes. b, At room temperature with two different laser intensities: 0.08 mW (purple) and 0.8 mW (yellow), exhibiting the typical spectrum of the LS and HS states, respectively.
Supplementary information
Supplementary Information
Supplementary Figs. 1–15, Discussion and Tables 1–7.
Supplementary Video 1
Volume modulation as a function of the temperature of the spin-crossover core-shell nanoparticles (core: [Fe(Htrz)2(trz)](BF4); shell: SiO2).
Supplementary Data
Source measured data for histograms.
Source data
Source Data Fig. 5b
Source measured data for statistical analysis.
Source Data Extended Data Fig. 3b
Source measured data for statistical analysis.
Source Data Extended Data Fig. 5c
Source measured data for statistical analysis.
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Torres-Cavanillas, R., Morant-Giner, M., Escorcia-Ariza, G. et al. Spin-crossover nanoparticles anchored on MoS2 layers for heterostructures with tunable strain driven by thermal or light-induced spin switching. Nat. Chem. 13, 1101–1109 (2021). https://doi.org/10.1038/s41557-021-00795-y
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DOI: https://doi.org/10.1038/s41557-021-00795-y
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