Molybdenum disulfide (MoS₂) and nanocrystalline diamond (NCD) have attracted considerable attention due to their unique electronic structure and extraordinary physical and chemical properties in many applications, including sensor devices in gas sensing applications. Combining MoS₂ and H-terminated NCD (H-NCD) in a heterostructure design can improve the sensing performance due to their mutual advantages. In this study, the synthesis of MoS₂ and H-NCD thin films using appropriate physical/chemical deposition methods and their analysis in terms of gas sensing properties in their individual and combined forms are demonstrated. The sensitivity and time domain characteristics of the sensors were investigated for three gases: oxidizing NO₂, reducing NH₃, and neutral synthetic air. It was observed that the MoS₂/H-NCD heterostructure-based gas sensor exhibits improved sensitivity to oxidizing NO₂ (0.157%·ppm^-1) and reducing NH₃ (0.188%·ppm^-1) gases compared to pure active materials (pure MoS₂ achieves responses of 0.018%·ppm^-1 for NO₂ and -0.0072%·ppm^-1 for NH₃, respectively, and almost no response for pure H-NCD at room temperature). Different gas interaction model pathways were developed to describe the current flow mechanism through the sensing area with/without the heterostructure. The gas interaction model independently considers the influence of each material (chemisorption for MoS₂ and surface doping mechanism for H-NCD) as well as the current flow mechanism through the formed P-N heterojunction.

Tibor Izsák

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