Growth of 2-D MoS₂ thin film by facile electrochemical deposition

Among all transition metal dichalcogenides (TMDs), MoS₂ shows very unique conducting and optoelectronic properties, which makes it the most suitable material for fabricating real-time sensors and atomically thin transistors. By chemical modifications, the MoS₂ can be made more useful in the field of various gas sensors, biosensors, and optoelectronic devices. In this study we present a novel facile method to grow 2-D MoS₂ thin films by electrochemical deposition technique. We have successfully grown MoS₂ thin films on ITO substrates through functionalization of MoS₂ nano-flakes in the presence of monochloroacetic acid (MCA). The functionalization of trigonal prismatic MoS2 flakes with carboxyl group was achieved through sonication of MoS₂ solution in DI water in the presence of MCA and KOH. Due to weak van der Walls force between the sulphur-sulphur layers of MoS₂ flake, ultrasonic vibrations can easily intercalate the MoS₂ flakes, creating sulphur vacancies at the two outer side surfaces and further saturated by Cl atoms of the MCA, forming MoS₂-COOH composites. The as grown composites were then driven through linear sweep voltammetry on an ITO glass plate to form MoS₂ thin film by controlling the sweeping cycles. The growth of the thin film was confirmed by the cyclic voltammetric current responses, which show the corresponding change in oxidation peak currents after the deposition of MoS₂ thin film on the ITO substrates. It was further observed that the charge transfer decreases with the increase in thickness of the thin film as expected from the thick MoS₂ semiconductor. These 2-D MoS₂ can be of immense use in designing new type of real-time semiconducting biosensors, gas and electrochemical sensors, and atomically thin 2-D transistors.