Abstract
Near-infrared sensitization of monolayer MoS2 is here achieved via the covalent attachment of a novel heteroleptic nickel bis-dithiolene complex into sulfur vacancies in the MoS2 structure. Photocurrent action spectroscopy of the sensitized films reveals a discreet contribution from the sensitizer dye centred around 1300 nm (0.95 eV), well below the bandgap of MoS2 (2.1 eV), corresponding to the excitation of the monoanionic dithiolene complex. A mechanism of conductivity enhancement is proposed based on a photo-induced flattening of the corrugated energy landscape present at sulfur vacancy defect sites within the MoS2 due to a dipole change within the dye molecule upon photoexcitation. This method of sensitization might be readily extended to other functional molecules that can impart a change to the dielectric environment at the MoS2 surface under stimulation, thereby extending the breadth of detector applications for MoS2 and other transition metal dichalcogenides.
Highlights
Near-infrared sensitization of monolayer MoS2 is here achieved via the covalent attachment of a novel heteroleptic nickel bis-dithiolene complex into sulfur vacancies in the MoS2 structure
transition metal dichalcogenides (TMDCs)-field-effect transistor (FET) have been shown to be extremely sensitive to the ambient conditions under which they are measured[12], which can severely affect the electrical properties of devices but, if controlled[10], makes them an excellent platform for sensing applications
By varying the end group of the thiol between electron rich and electron poor groups, it is possible to modify the carrier density in the MoS2, and thereby the threshold voltage (VT) of charge accumulation in the channel, in a controlled and permanent manner. To date, such studies have been limited to passive thiol molecules that are insensitive to external stimuli, the response of the devices is limited to the properties of the TMDC, such as its range of light absorption and non-specific interaction with adsorbates
Summary
Near-infrared sensitization of monolayer MoS2 is here achieved via the covalent attachment of a novel heteroleptic nickel bis-dithiolene complex into sulfur vacancies in the MoS2 structure. Dye-sensitization was achieved in a similar manner to that reported by Sim et al.[13], whereby thermal annealing was used to introduce sulfur vacancies in the MoS2, which was soaked in a solution of 2, followed by copious washing with fresh DCM.
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