Room Temperature H₂S Gas Sensor Using One-Step CVD Grown MoS₂ and 2H - MoS₂/1T@ 2H - MoS₂ Heterostructure

MoS₂; a 2D TMDC (Transition Metal Dichalcogenides) has attracted immense attention in energy storage devices, optoelectronic devices, optical switching devices, and gas sensors due to its unique physical and chemical properties. MoS₂thin films and nanostructures can be synthesized by different physical and chemical growth mechanisms. CVD is one of the most effective methods to achieve large-area growth of atomically thin horizontal and vertical 2D TMDCs for device applications. The vertically aligned MoS₂ nanostructures are reported to have maximum edge sites, reactive dangling bonds, and high adsorption-desorption capacity, making them an attractive candidate for gas sensing. In CVD the growth conditions such as the temperature of the heating zone, growth duration, the pressure inside the tube, and the carrier gas flow rate can be tuned to change the alignment and number of layers of MoS₂ thin films. In this work growth parameters such as temperature, Mo:S ratio, sulfur-source to substrate position, and growth time have been optimized for synthesizing few-layered vertically aligned MoS₂ thin films through a one-step CVD process. The formation of MoS₂ thin film was confirmed by the presence of and peaks in the Raman spectra. The presence of an intense (002) peak in the XRD pattern further indicates the formation of c- axis oriented MoS₂ thin film. FESEM and TEM images show an obvious evolution from horizontal to vertical morphology of MoS₂ nanoflakes with the variation in growth condition. The vertical morphology, provides a high rate of adsorption and desorption processes and outstanding gas sensing properties due to the presence of dangling bonds and higher aspect ratio. Herein, few-layered vertically aligned MoS₂ nanoflakes were obtained directly on Si/SiO₂ substrate supported with interdigital Au electrodes and were used for gas sensing measurement. The fabricated MoS₂ sensor shows response towards H₂S at room temperature. However, sensors fabricated from 2D TMDCs suffered sluggish response and recovery time. Therefore to prevent homogeneous restacking and to enlarge the active surface area 2D/2D heterostructure was developed by decorating MoS₂thin films on Si/SiO₂substrate with the hydrothermally synthesized 1T/2H MoS₂ nanostructures_.These 2D / 2D heterostructure-based gas sensors showed enhanced response and sensitivity towards H₂S sensing at room temperature and the architecture can be considered for developing efficient gas sensors.