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. 2023 Jul 19;15(28):34206-34214.
doi: 10.1021/acsami.3c04438. Epub 2023 Jul 2.

Improved Gas Sensing Capabilities of MoS2/Diamond Heterostructures at Room Temperature

Michal Kočí  1   2 , Tibor Izsák  3 , Gabriel Vanko  3 , Michaela Sojková  3 , Jana Hrdá  3 , Ondrej Szabó  1 , Miroslav Husák  2 , Karol Végsö  4   5 , Marian Varga  1   3 , Alexander Kromka  1
Affiliations

Improved Gas Sensing Capabilities of MoS2/Diamond Heterostructures at Room Temperature

Michal Kočí et al. ACS Appl Mater Interfaces. .

Abstract

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.

Keywords: H-terminated diamond; MoS2; MoS2/H-NCD heterostructure; P−N junction; gas interaction model; gas sensors; room temperature; sensitivity.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Schematic top (a) and cross-sectional views of MoS2/H-NCD/SiO2/Si (b), cross-sectional view of H-NCD/SiO2/Si (c) sensors, and schematic illustration of the combination of both materials in a heterostructure (d). In the case of the MoS2/SiO2/Si sensor, the MoS2 layer was prepared directly on the SiO2/Si substrate, and no diamond deposition was performed (not illustrated in this figure).
Figure 2
Figure 2
(a) Top-view SEM images of samples MoS2/SiO2/Si, H-NCD/SiO2/Si, and MoS2/H-NCD/SiO2/Si and (b) corresponding Raman spectra of samples taken at a 442 nm excitation wavelength; (c) GIWAXS reciprocal space maps of the MoS2/SiO2/Si and MoS2/H-NCD/SiO2/Si samples.
Figure 3
Figure 3
Time response of the sensor with MoS2/SiO2/Si (a), MoS2/H-NCD/SiO2/Si after fabrication (b), and MoS2/H-NCD/SiO2/Si after 10 months (c) to three gases (ammonia, nitrogen dioxide, and 90% humidity).
Figure 4
Figure 4
Relative resistance change of sensors with MoS2/H-NCD/SiO2/Si, MoS2/SiO2/Si, MoS2/Si, and H-NCD/SiO2/Si to six different concentrations of ammonia (a) and nitrogen dioxide (b).
Figure 5
Figure 5
Schematic illustration of the gas sensing mechanism between a layer of MoS2 nanoflakes and (a) oxidizing and (b) reducing gases.
Figure 6
Figure 6
Schematic illustration of the gas sensing mechanism and charge transport for two parallel connected layers represented by MoS2 nanoflakes and H-NCD exposed to the (a) oxidizing and (b) reducing gas.
Figure 7
Figure 7
Schematic illustration of two ways (I and II) for the current flow between IDT electrodes, I—horizontal flow through H-NCD and II—combined horizontal/vertical flow, i.e., horizontal through H-NCD and MoS2 and vertical through the MoS2/H-NCD heterostructure.
Figure 8
Figure 8
Qualitative illustration of the relative responses of MoS2, H-NCD, and MoS2/H-NCD sensor devices to different concentrations of oxidizing and reducing gases based on gas interaction models.
See this image and copyright information in PMC

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