Along with the progress of nanoscience and nanotechnology, nanomaterials with attractive structural and functional properties have gained more attention than ever before, especially in the field of electronic sensors. In recent years, the gas sensing devices have made great achievement and also created wide application prospects, which leads to a new wave of research for designing advanced sensing materials. There is no doubt that the characteristics are highly governed by the sensitive layers. For this reason, important advances for the outstanding, novel sensing materials with different dimensional structures including 0D, 1D, 2D, and 3D are reported and summarized systematically. The sensing materials cover noble metals, metal oxide semiconductors, carbon nanomaterials, metal dichalcogenides, g-C3 N4 , MXenes, and complex composites. Discussion is also extended to the relation between sensing performances and their structure, electronic properties, and surface chemistry. In addition, some gas sensing related applications are also highlighted, including environment monitoring, breath analysis, food quality and safety, and flexible wearable electronics, from current situation and the facing challenges to the future research perspectives.

Recent Progress of Nanostructured Sensing Materials from 0D to 3D: Overview of Structure–Property-Application Relationship for Gas Sensors

In this work, 2D/2D ZnO/g-C3N4 heterojunction composite was synthesized through an ultrasonic mixing and subsequent calcination process. The gas-sensing performance to NO2 was investigated at room temperature activated by visible/ultra-violet LED light sources. Noticeably, when ZnO/g-C3N4 composite is illuminated by 460 nm light, it exhibits the highest response of 44.8 to 7 ppm NO2, and the response and recovery time is 142 and 190 s, respectively. Furthermore, it possesses excellent repeatability and selectivity to NO2, and the limit of detection is 38 ppb. In addition, the effect of humidity on the sensing performance under visible light was also investigated. The excellent gas-sensing performance is attributed to the absorbance of g-C3N4 in the visible light region and the charge separation at the interface between ZnO and g-C3N4.

Visible light activated excellent NO2 sensing based on 2D/2D ZnO/g-C3N4 heterojunction composites

We report a highly sensitive and selective ammonia (NH3) gas sensor made from liquid exfoliated MoSe2 nanosheets. The powder obtained after exfoliation was used to make a two-terminal sensor on a q...

MoSe2 Crystalline Nanosheets for Room-Temperature Ammonia Sensing

Emerging van der Waals junctions based on TMDs materials for advanced gas sensors

In recent years, the utilization of gas sensors has increased tremendously in daily life and industry. Importantly, appropriate material selection should be made for gas sensors in order to achieve outstanding gas sensing performance, such as high sensitivity, good selectivity, a fast response/recovery time, and long-term stability. Numerous studies have shown that neither pure metal oxide semiconductor nor individual 2D nanomaterial (graphene, transition metal dichalcogenides, metal–organic frameworks, metal oxide nanosheets, MXenes, and phosphorene) based gas sensors are capable of showing excellent gas-sensing performance towards gas molecules. However, synergistic combinations of metal oxides and 2D nanomaterials have demonstrated enhanced gas-sensing performance in many studies. This review aims at providing a comprehensive summary of the current advancements in 2D/metal-oxide based heterostructures as gas sensors. Additionally, the underlying sensing mechanisms of various kinds of gas sensors are systematically described, and the device architectures and their corresponding sensing performances are summarized. Finally, the challenges and future prospects of 2D/metal-oxide nanocomposite-based gas sensors for sensing applications have been outlined.

Gas sensing performance of 2D nanomaterials/metal oxide nanocomposites: a review

Detection and quantification of hydrogen sulfide (H2S) gas is important as it influences directly human health, our environment, and operations of several industries including food and beverages, oil, construction, and medicine. It also acts as biomarker in diagnosis of halitosis at early stage. We report herein liquid exfoliated MoSe2 nanoflakes based stable chemiresistive H2S gas sensor which operate at moderate temperature of 200℃. The response of p-type MoSe2 gas sensor device (when operated in ambient environment) was found to be varying between 15.87%–53.04% when the concentration of H2S was varied between 50 ppb – 5.45 ppm. The response of the device decreases when the measurements were done in synthetic air environment and it varies between 7.13%–19.87% for the concentration range of 500 ppb - 5.45 ppm. The response (%), recovery rate (%), hysteresis, experimental lowest detection limit etc. of the device suggest that the device performs better when operated in ambient than in synthetic air which suggest its real time device application. The response time and recovery time of the sensor are 15 s and 43 s respectively for 100 ppb of H2S. The sensor performance was found to be highly repeatable with sensitivity of 5.57%/ppm of H2S. The theoretical limit of detection and limit of quantization of the device were found to be 6.73 ppb and 22.44 ppb respectively. Based on chemical analysis, a plausible mechanism based on charge transfer phenomenon has been proposed for this sensor.

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MoSe2 nanoflakes based chemiresistive sensors for ppb-level hydrogen sulfide gas detection

A chemiresistive, 1T-TiS2 nanosheet (TNS) based gas sensor has been developed, and its ultrahigh sensitivity toward hydrogen sulfide (H2S) and oxygen (O2) gas at room temperature has been experimen...

1T-Phase Titanium Disulfide Nanosheets for Sensing H2S and O2

The sensing behavior of as-fabricated and annealed WS2 nanosheets towards ammonia (NH3) gas has been demonstrated in this study. The nanosheets were synthesized using liquid-phase exfoliation technique and the effect of the sonication time on gas sensing capability was assessed. It was observed that sonication time affects the ammonia sensing performance and samples sonicated for durations between 3–6 hours show good sensing performance, with the ones sonicated for 5 hours reporting optimal performance. The sensing response towards ammonia was demonstrated in the concentration range of 300 ppb (3.8%) to 3 ppm (79.10%) at an optimized sensing temperature of 250° C. These nanosheets were further annealed for two hours in nitrogen ambient and this significantly enhanced the response by an order of magnitude for the highest ammonia concentration of 3 ppm, i.e. from 79.1% to 1805%. The response and recovery time of the device after annealing were found to be improved in the concentration range of 0.4 ppm - 2 ppm of ammonia. Though the linearity of the device response in high concentration regime is affected by the annealing process, it enables the sensor to push the lowest limit of detection down to 50 ppb. The as-prepared nanosheets were characterized using different material characterization tools and the results are reported here. A plausible mechanism has also been proposed for this sensor based on the detailed chemical composition analysis.

Tungsten Disulphide Nanosheets for High-Performance Chemiresistive Ammonia Gas Sensor

Direct growth of transition metal dichalcogenides over large areas within the back-end-of-line (BEOL) thermal budget limit of silicon integrated circuits is a significant challenge for 3D heterogeneous integration. In this work, we report on the growth of MoS2 films (~1–10 nm) on SiO2, amorphous-Al2O3, c-plane sapphire, and glass substrates achieved at low temperatures (350–550 °C) by chemical vapor deposition in a manufacturing-compatible 300 mm atomic layer deposition reactor. We investigate the MoS2 films as a potential material solution for BEOL logic, memory and sensing applications. Hall-effect/4-point measurements indicate that the ~10 nm MoS2 films exhibit very low carrier concentrations (1014–1015 cm-3), high resistivity, and Hall mobility values of ~0.5–17 cm2 V-1 s-1, affirmed by transistor and resistor test device results. MoS2 grain boundaries and stoichiometric defects resulting from the low thermal budget growth, while detrimental to lateral transport, can be leveraged for the integration of memory and sensing functions. Vertical transport memristor structures (Au/MoS2/Au) incorporating ~3 nm thick MoS2 films grown at 550 °C (~0.75 hours) show memristive switching and a stable memory window of 105 with a retention time > 104 seconds, between the high-low resistive states. The switching set and reset voltages in these memristors demonstrate a significant reduction compared to memristors fabricated from pristine, single-crystalline MoS2 at higher temperatures, thereby reducing the energy needed for operation. Furthermore, interdigitated electrode-based gas sensors fabricated on ~5 nm thick 550 °C-grown (~1.25 hours) MoS2 films show excellent selectivity and sub-ppm sensitivity to NO2 gas, with a notable self-recovery at room temperature. The demonstration of large-area MoS2 direct growth at and below the BEOL thermal budget, alongside memristive and gas sensing functionality, advances a key enabling technology objective in emerging materials and devices for heterogeneous integration.

https://iopscience.iop.org/article/10.1088/2053-1583/abc460/pdf

Large-area growth of MoS2 at temperatures compatible with integrating back-end-of-line functionality

A 2D/0D heteronanostructure (HNS) employing WSe2 as 2D nanosheets and Fe3O4 as 0D nanoparticles has been facilely synthesized at room temperature using a simple wet chemical route. The process invo...

Neha Sakhuja

Papers

MoSe2 nanoflakes based chemiresistive sensors for ppb-level hydrogen sulfide gas detection

1T-Phase Titanium Disulfide Nanosheets for Sensing H2S and O2

Tungsten Disulphide Nanosheets for High-Performance Chemiresistive Ammonia Gas Sensor

Large-area growth of MoS2 at temperatures compatible with integrating back-end-of-line functionality

Fe3O4 Nanoparticle-Decorated WSe2 Nanosheets for Selective Chemiresistive Detection of Gaseous Ammonia at Room Temperature