This work presents a facile approach for fabricating hybrid heterostructures of tungsten disulfide (WS2), synthesized via atmospheric pressure chemical vapor deposition (APCVD) and commercial graphene. A simple airbrushing technique, with nitrogen (N2) as the carrier gas, was employed to fabricate the sensors. The morphological and structural characterizations of the hybrid material revealed a sheet-like synthesis of edge-enriched 2D WS2 decorated with multilayer graphene nanomaterial. The gas-sensing properties of the pristine and hybrid materials were evaluated for nitrogen dioxide (NO2) at various operating temperatures. The hybrid sensor with a WS2 to graphene ratio of 3:1 demonstrated exceptional sensitivity to ultralow NO2 concentrations (10 ppb) at a remarkably low operating temperature of 100 °C, outperforming both the graphene and WS2 counterparts. Additionally, the sensor's responses to CO, H2, C6H6, and NH3 were examined to assess its selectivity. The sensor was tested under different relative humidity conditions (RH at 25 °C; 25%, 50%, and 75%). The sensor response nearly doubled at RH = 50%, highlighting its potential for practical applications in selective NO2 detection. The sensor responses eventually reached saturation at 75% RH. In addition, the manuscript provides a detailed discussion of the NO2 gas sensing mechanism.

Nanostructured transition metal dichalcogenides have garnered significant research interest for physical and chemical sensing applications due to their unique crystal structure and large effective surface area. However, the high-yield synthesis of these materials on different substrates and in nanostructured films remains a challenge that hinders their real-world applications. In this work, we demonstrate the synthesis of two-dimensional (2D) tungsten disulfide (WS2) sheets on a hundred-milligram scale by sulfurization of tungsten trioxide (WO3) powder in an atmospheric pressure chemical vapor deposition reactor. The as-synthesized WS2 powders can be formulated into inks and deposited on a broad range of substrates using techniques like screen or inkjet printing, spin-coating, drop-casting, or airbrushing. Structural, morphological, and chemical composition analysis confirm the successful synthesis of edge-enriched WS2 sheets. The sensing performance of the WS2 films prepared with the synthesized 2D material was evaluated for ammonia (NH3) detection at different operating temperatures. The results reveal exceptional gas sensing responses, with the sensors showing a 100% response toward 5 ppm of NH3 at 150 degrees C. The sensor detection limit was experimentally verified to be below 1 ppm of NH3 at 150 degrees C. Selectivity tests demonstrated the high selectivity of the edge-enriched WS2 films toward NH3 in the presence of interfering gases like CO, benzene, H-2, and NO2. Furthermore, the sensors displayed remarkable stability against high levels of humidity, with only a slight decrease in response from 100% in dry air to 93% in humid environments. Density functional theory and Bayesian optimization simulations were performed, and the theoretical results agree with the experimental findings, revealing that the interaction between gas molecules and WS2 is primarily based on physisorption.

We report for the first time the successful synthesis of ZnO/WS2 hybrid material using a combination of aerosol-assisted chemical vapor deposition (AA-CVD) and atmospheric pressure CVD techniques. The morphology and the composition of the grown films were investigated and the results confirm the co-existence of both materials. Moreover, gas-sensing results against 500 ppb of NO2 revealed the influence of WS2 material on the ZnO gas-sensing performance. The operating temperature shifted towards lower values, from 300 °C to 150 °C. Furthermore, at room temperature, the ZnO/WS2 sensor was able to detect NO2 at ppb level.

The search for a highly selective ethanol sensor is still an open challenge. Metal oxides still face selectivity issues when it comes to gas sensing especially in case of ethanol. Keeping this in sight, in this work we explore the sensing properties of WO3 nanowires grown via the aerosol assisted chemical vapour deposition and decorated with CeO2 nanoparticles by drop casting. The nanocomposites were characterized by X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray, photoluminescence, Raman and X-ray photoelectron spectroscopies. Upon exposure to different gas analytes, the electrical characterization showed that sensors responded well to ethanol both under dry and humid conditions (RH= 50%, 25 degrees C), though the response towards ethanol decreased in humid atmospheres. The long-term stability was studied, and a gas sensing mechanism is introduced and discussed.

Ambient pressure X-ray photoelectron spectroscopy (APXPS) is combined with simultaneous electrical measurements and supported by density functional theory calculations to investigate the sensing mechanism of tungsten disulfide (WS2)-based gas sensors in an operando dynamic experiment. This approach allows for the direct correlation between changes in the surface potential and the resistivity of the WS2 sensing active layer under realistic operating conditions. Focusing on the toxic gases NO2 and NH3, we concurrently demonstrate the distinct chemical interactions between oxidizing or reducing agents and the WS2 active layer and their effect on the sensor response. The experimental setup mimics standard electrical measurements on chemiresistors, exposing the sample to dry air and introducing the target gas analyte at different concentrations. This methodology applied to NH3 concentrations of 100, 230, and 760 and 14 ppm of NO2 establishes a benchmark for future APXPS studies on sensing devices, providing fast acquisition times and a 1:1 correlation between electrical response and spectroscopy data in operando conditions. Our findings contribute to a deeper understanding of the sensing mechanism in 2D transition metal dichalcogenides, paving the way for optimizing chemiresistor sensors for various industrial applications and wireless platforms with low energy consumption.

In this work, efficient hydrogen gas sensors based on multilayered p-type bare MoS2 and Pd-decorated MoS2 were fabricated. MoS2 was deposited onto alumina transducers using an airbrushing technique to be used as a sensing material. Aerosol-assisted chemical vapor deposition (AACVD) was used to decorate layered MoS2 with Pd nanoparticles at 250 °C. The bare and Pd-decorated MoS2 was characterized using field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), and Raman spectroscopy. The characterization results reveal the multilayered crystalline structure of MoS2 with successful Pd decoration. The size of the Pd nanoparticles ranges from 15 nm to 23 nm. Gas sensing studies reveal that a maximum response of 55% is achieved for Pd-decorated MoS2 operated at 150 °C to 100 ppm of H2, which is clearly below the explosive limit (4%) in air. The higher sensitivity due to Pd nanoparticle decoration was owed to a spillover effect. This study reveals that the sensitivity of the sensors is highly dependent on the amount of Pd decoration. Moreover, sensor responses increase slightly when exposed to 50% relative humidity (RH at 25 °C).

Nanostructured tungsten disulfide (WS2) is one of the most promising candidates for being used as active nanomaterial in chemiresistive gas sensors, as it responds to hydrogen gas at room temperature. This study analyzes the hydrogen sensing mechanism of a nanostructured WS2 layer using near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) and density functional theory (DFT). The W 4f and S 2p NAP-XPS spectra suggest that hydrogen makes physisorption on the WS2 active surface at room temperature and chemisorption on tungsten atoms at temperatures above 150 °C. DFT calculations show that a hydrogen molecule physically adsorbs on the defect-free WS2 monolayer, while it splits and makes chemical bonds with the nearest tungsten atoms on the sulfur point defect. The hydrogen adsorption on the sulfur defect causes a large charge transfer from the WS2 monolayer to the adsorbed hydrogen. In addition, it decreases the intensity of the in-gap state, which is generated by the sulfur point defect. Furthermore, the calculations explain the increase in the resistance of the gas sensor when hydrogen interacts with the WS2 active layer.

In this work, we demonstrate the feasibility and suitability of a hybrid tungsten disulfide (WS 2 ) nanosheet loaded platinum oxide (PtO) nanomaterial, for the detection of dimethyl methylphosphonate (DMMP), a simulant of sarin nerve agent. To the best of our knowledge, there have been no reports on the direct use of a such hybrid material for the detection of nerve agents. The fabricated sensors showed excellent, reliable, sensitive and fast responses at a moderate operating temperature (100 °C). The response towards 2.5 ppm of DMMP was 59 %. The detection limit was experimentally verified and it was below 250 ppb. By comparing the obtained results with those in the literature, we found that PtO/WS 2 showed enhanced gas-sensing performance towards DMMP.

In this work, we report synthesis of tungsten disulfide (WS2) platelets from sulfurization of commercial tungsten trioxide powder $(\text{WO}_{3})$ using hydrogen free atmospheric pressure chemical vapor deposition (APCVD) technique. This methodology has the potential to be scaled up to industrial scale owing to its high yield, reproducibility, low cost, and ease of operation. Composition and morphological investigations revealed the total conversion of the metal oxide powder to metal dichalcogenide nanosheets. Gas sensing results showed the potential of the obtained material in detecting NO 2 at room temperature. The responses were remarkable, stable and reproducible towards 100 ppb of nitrogen dioxide (NO 2 ).

In this work we report a new methodology for the direct growth, onto the sensor transducer, of multilayer transition metal dichalcogenides material (TMDs) such as tungsten diselenide (WSe2) and tungsten disulfide (WS2), via the combination of aerosol assisted chemical vapor deposition (AA-CVD) and atmospheric pressure CVD technique (APCVD). This combination led to uniform films with high yield and coverage, making it possible to overcome the shortcomings of many TMDs synthesis techniques. The morphology and the compositions of the films were investigated. The results revealed the formation of three dimensional (3D) assemblies of WSe2 nanosheets and WS2 nanotriangles. The fabricated sensors showed remarkable gas sensing performances towards 800 ppb of NO 2 at low operating temperature. Thanks to the vertical growth that enhanced the gas sensing performances by increasing the number of exposed edge as well as the number of defects.

The successful controlled growth of edge enriched 3D assemblies of MoS 2 nanosheets for the fabrication of dually selective NH 3 and NO 2 gas sensors using a single step atmospheric pressure CVD method.

In this work tungsten disulphide nanostructures loaded with platinum-oxide (PtO), or palladium-oxide (PdO) were grown directly onto alumina substrates. This was achieved using a combination of aerosol-assisted chemical vapour deposition (AA-CVD) method with atmospheric pressure CVD technique. At first, tungsten oxide nano wires loaded with either PtO or PdO nanoparticles were successfully co-deposited via AA-CVD followed by sulfurization at 900 degrees C in the next step. The morphological, structural, and chemical characteristics were investigated using FESEM, TEM, XRD, XPS and Raman spectroscopy. The results confirm the presence of PdO and PtO in the WS2 host matrix. Gas sensing attributes of loaded and pristine WS2 sensors were investigated, at room temperature, towards different analytes (NO2, NH3, H-2 etc.). Both pristine and metal-oxide loaded WS2 gas sensors show remarkable responses at room temperature towards NO2 detection. Further, the loaded sensors demonstrated stable, reproducible, ultrasensitive, and enhanced gas sensing response, with a detection limit below 25 ppb. Additionally, the effect of ambient humidity on the sensing response of both loaded and pristine sensors was investigated for NO2 gas. The response of PtO loaded sensor considerably decreased in humid environments, while the response for pristine and PdO loaded sensors increased. However, slightly heating (at 100 degrees C) the sensors, suppresses the influence of humidity. Finally, the long-term stability of different sensors is investigated, and the results demonstrate high stability with repeatable results after 6 weeks of gas sensing tests. This work exploits an attractive pathway to add functionality in the transition metal dichalcogenide host matrix.

Herein, we present, for the first time, a chemoresistive-type gas sensor composed of two-dimensional WSe2, fabricated by a simple selenization of tungsten trioxide (WO3) nanowires at atmospheric pressure. The morphological, structural, and chemical composition investigation shows the growth of vertically oriented three-dimensional (3D) assemblies of edge-enriched WSe2 nanoplatelets arrayed in a nanoflower shape. The gas sensing properties of flowered nanoplatelets (2H-WSe2) are investigated thoroughly toward specific gases (NH3 and NO2) at different operating temperatures. The integration of 3D WSe2 with unique structural arrangements resulted in exceptional gas sensing characteristics with dual selectivity toward NH3 and NO2 gases. Selectivity can be tuned by selecting its operating temperature (150 °C for NH3 and 100 °C for NO2). For instance, the sensor has shown stable and reproducible responses (24.5%) toward 40 ppm NH3 vapor detection with an experimental LoD < 2 ppm at moderate temperatures. The gas detecting capabilities for CO, H2, C6H6, and NO2 were also investigated to better comprehend the selectivity of the nanoflower sensor. Sensors showed repeatable responses with high sensitivity to NO2 molecules at a substantially lower operating temperature (100 °C) (even at room temperature) and LoD < 0.1 ppm. However, the gas sensing properties reveal high selectivity toward NH3 gas at moderate operating temperatures. Moreover, the sensor demonstrated high resilience against ambient humidity (Rh = 50%), demonstrating its remarkable stability toward NH3 gas detection. Considering the detection of NO2 in a humid ambient atmosphere, there was a modest increase in the sensor response (5.5%). Furthermore, four-month long-term stability assessments were also taken toward NH3 gas detection, and sensors showed excellent response stability. Therefore, this study highlights the practical application of the 2H variant of WSe2 nanoflower gas sensors for NH3 vapor detection.

Herein, we demonstrate gas sensing characteristics of metal-decorated WS2 towards ammonia (NH3) gas detection at moderate temperature. Chemiresistive sensors are fabricated using a combination of chemical vapor deposition method with sputter deposition technique. WO3 nanowires grown via aerosol assisted chemical vapor deposition technique are sulfurized to form tungsten disulfide nanoflowers. The as grown nanoflowers are then decorated with metal nanoparticles of gold, silver and palladium using the sputtering technique at different deposition time and temperatures. The morphological and structural characteristics were studied using FE-SEM and Raman spectroscopy. The performance of the three fabricated sensors is compared towards NH3 gas detection at room and elevated temperatures. Results show that the synthesized material (WS2/Pd, WS2/Au, WS2/Ag) behaves as a p-type semiconductor towards NH3 gas. Also, the results of NH3 gas sensing characteristics demonstrated the promising effects of palladium decoration for the enhanced response in low-power consumption. Moreover, the room-temperature operation of the three sensors is discussed. Hence, this study demonstrates the realization of a high-performance NH3 gas sensor using a facile route along with low power consumption.

In this paper, we report the fabrication and characterization of a portable transdermal alcohol sensing device via a human finger, using tin dioxide (SnO2) chemoresistive gas sensors. Compared to conventional detectors, this non-invasive technique allowed us the continuous monitoring of alcohol with low cost and simple fabrication process. The sensing layers used in this work were fabricated by using the reactive radio frequency (RF) magnetron sputtering technique. Their structure and morphology were investigated by means of X-ray spectroscopy (XRD) and scanning electron microscopy (SEM), respectively. The results indicated that the annealing time has an important impact on the sensor sensitivity. Before performing the transdermal measurements, the sensors were exposed to a wide range of ethanol concentrations and the results displayed good responses with high sensitivity, stability, and a rapid detection time. Moreover, against high relative humidity (50% and 70%), the sensors remained resistant by showing a slight change in their gas sensing performances. A volunteer (an adult researcher from our volunteer group) drank 50 mL of tequila in order to realize the transdermal alcohol monitoring. Fifteen minutes later, the volunteer's skin started to evacuate alcohol and the sensor resistance began to decline. Simultaneously, breath alcohol measurements were attained using a DRAGER 6820 certified breathalyzer. The results demonstrated a clear correlation between the alcohol concentration in the blood, breath, and via perspiration, which validated the embedded transdermal alcohol device reported in this work.

Herein, we report for the first time on the fabrication of a hybrid material consisting of Cu 2 O nanoparticles-decorated multilayered tungsten disulfide nanostructures and demonstrate their remarkable gas sensing characteristics towards hydrogen sulfide gas. In the first step, a continuous film of WS2 was deposited directly on commercial alumina substrate by adopting a facile route combining aerosol-assisted chemical vapor deposition with H 2 free atmospheric pressure CVD technique. For functionalization an additional step of synthesis was added where copper oxide nanoparticles were grown and deposited directly over as-grown tungsten disulfide at low temperature (i.e., 150 °C) using a simple and cost-effective technique. The morphological, structural and chemical characteristics were investigated using FESEM, TEM, and EDX spectroscopy. The gas-sensing studies performed shows that this hybrid nanomaterial has excellent sensitivity towards hydrogen sulfide (11-times increase in response compared to that of pristine WS 2 sensor) at moderate temperature (150 °C). Additionally, functionalization of pristine WS 2 sensor with Cu 2 O nanoparticles further enhances the gas sensing performance towards the targeted gas even at room temperature (13-times increase in response compared with that of pristine WS 2 sensor). Moreover, results obtained from humidity cross-sensitivity of Cu 2 O-WS 2 sensor indicates superior gas sensing response (with a negligible decrease in response) as compared to pristine WS 2 sensor, when ambient humidity is increased to 50%, which is rarely found in metal oxide-based sensors. This study could add a significant research value in the gas sensor domain.

This file contains the raw data used in the paper entitled CVD growth of self-assembled 2D and 1D WS2 nanomaterials for the ultrasensitive detection of NO2 published in Sensors and Actuators: B. Chemical 326 (2021) 128813 DOI: 10.1016/j.snb.2020.128813

In this paper, we demonstrate a facile route to synthesize a continuous film of WS2 deposited by a combination of aerosol-assisted chemical vapor deposition (AACVD) with H-2 free atmospheric pressure CVD technique. This synthesis strategy allows us a direct integration of the sensing material onto the sensor transducer with high growth yield and uniform coverage. SEM and Raman spectroscopy were used to investigate the morphology and composition of the grown material. The performance of WS2 sensor in the detection of H2S has been studied and results show that the synthesized material behaves as a p-type semiconductor with high sensitivity towards H2S at sub-ppm level.