Electronic Properties of Electroactive Ferrocenyl-Functionalized MoS2

The attachment of redox-active molecules to transition metal dichalcogenides, such as MoS₂, constitutes a promising approach for designing electrochemically switchable devices through the control of the material’s charge/spin transport properties by the redox state of the grafted molecule and thus the applied electrical potential. In this work, defective plasma-treated MoS₂ is functionalized by a ferrocene derivative and thoroughly investigated by various characterization techniques, such as Raman, photoluminescence, and X-ray photoelectron spectroscopies; atomic force microscopy (AFM); and electrochemistry. Furthermore, in-plane and out-of-plane conductive AFM measurements (I–V and first derivative ∂I/∂V–V curves) are measured to investigate the effect of the chemical functionalization of MoS₂ on the electron transport properties. While the conduction and valence bands are determined at +0.7 and −1.2 eV with respect to the electrode’s Fermi energy for pristine MoS₂, additional states in an energy range of ≈0.45 eV below the MoS₂ conduction band are measured after plasma treatment, attributed to S-vacancies. For ferrocene-functionalized MoS₂, the S-vacancy states are no longer observed, resulting from the defect healing. However, two bumps at lower voltages in the ∂I/∂V–V indicate a contribution to electron transport through ferrocene’s highest occupied molecular orbital, which is located in the MoS₂ band gap at ≈0.4/0.6 eV below the Fermi energy. These results are in good agreement with theoretical density functional theory calculations and UV photoelectron spectroscopy measurements.

Trung Nghia Nguyên Lê, Kirill Kondratenko, Imane Arbouch, Alain Moréac, Jean-Christophe Le Breton, Colin van Dyck, Jérôme Cornil, Dominique Vuillaume, and Bruno Fabre*, J. Phys. Chem. C 2024, 128, 18, 7706–7722