High performance NO2 sensor using MoS2 nanowires network
TL;DR: In this paper, a high-performance NO2 sensor based on a one dimensional MoS2 nanowire (NW) network was synthesized using chemical transport reaction through controlled turbulent vapor flow.
Abstract: We report on a high-performance NO2 sensor based on a one dimensional MoS2 nanowire (NW) network The MoS2 NW network was synthesized using chemical transport reaction through controlled turbulent vapor flow The crystal structure and surface morphology of MoS2 NWs were confirmed by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy Further, the sensing behavior of the nanowires was investigated at different temperatures for various concentrations of NO2 and the sensor exhibited about 2-fold enhanced sensitivity with a low detection limit of 46 ppb for NO2 at 60 °C compared to sensitivity at room temperature Moreover, it showed a fast response (16 s) with complete recovery (172 s) at 60 °C, while sensitivity of the device was decreased at 120 °C The efficient sensing with reliable selectivity toward NO2 of the nanowires is attributed to a combination of abundant active edge sites along with a large surface area and tuning of the potential barrier
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TL;DR: The resulting Au/MoS2/Au optoelectronic gas sensor showed a significant enhancement of the device sensitivity S toward ppb level of NO2 gas exposure reaching S = 4.9%/ppb (4900% /ppm), where S is a slope of dependence of relative change of the sensor resistance on NO2 concentration.
Abstract: Red light illumination with photon energy matching the direct band gap of chemical vapor deposition grown single-layer MoS2 with Au metal electrodes was used to induce a photocurrent which was employed instead of dark current for NO2 gas sensing. The resulting Au/MoS2/Au optoelectronic gas sensor showed a significant enhancement of the device sensitivity S toward ppb level of NO2 gas exposure reaching S = 4.9%/ppb (4900%/ppm), where S is a slope of dependence of relative change of the sensor resistance on NO2 concentration. Further optimization of the MoS2-based optoelectronic gas sensor by using graphene (Gr) with a work function lower than that of Au for the electrical contacts to the MoS2 channel allowed an increase of photocurrent. The limit of detection of NO2 gas at the level of 0.1 ppb was obtained for the MoS2 channel with graphene electrodes coated by Au. This value was calculated using experimentally obtained sensitivity and noise values and exceeds the U.S. Environment Protection Agency requirement for NO2 gas detection at ppb level.
304 citations
TL;DR: In this article, a few-layer MoS2 nanosheet/ZnO nanowire composites serving as the sensing layer were used for detecting trace NO2 gas below the ppm level.
Abstract: Nitrogen dioxide (NO2) is a hazardous gas species that could impose a great threat on environmental protection and human health even at very low doses. Thus, it is of great importance to selectively detect trace NO2 gas below the ppm level. This has been a serious challenge so far, especially in the presence of other interfering gases. Herein, we report ultrasensitive, room-temperature and UV light-assisted NO2 gas sensing based on few-layer MoS2 nanosheet/ZnO nanowire composites serving as the sensing layer. A series of characterization techniques, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), Raman, energy-dispersive X-ray spectroscopy (EDS), UV-Visual and ultraviolet photoelectron spectroscopy (UPS), were employed to explore the componential and structural properties of the obtained sensitive materials. Initially, the as-prepared MoS2/ZnO composites showed a tiny response (40%) and an incomplete recovery to 10 ppm NO2 gas in dark condition. While under UV illumination, the sensing response attained 8.4 and 188, toward 50 ppb and 200 ppb NO2 with a full recovery. Meanwhile, a sensitivity of 0.93 ppb−1, a detection limit of 50 ppq (10−15), and excellent repeatability and selectivity were also achieved. The experimental results were better than most previous work on NO2 detection to the best of our knowledge. Two main aspects are responsible for the outstanding performance. One is that a mass of photo-excited electron–hole pairs participated in the reaction with NO2 molecules under UV illumination. The other lies in numerous p–n MoS2/ZnO nanojunctions, favorable for the extension of the depletion region and the separation of the charge carrier. Additionally, long-term stability, as well as the effect of film thickness and carrier gas species on sensor performance, were simply investigated. We combined p–n nanojunctions with the UV illumination method, providing an alternative strategy to realize room-temperature operation and high sensitivity in the field of gas sensors.
208 citations
TL;DR: The recent first principle studies on the interaction between gas molecules and novel promising materials like arsenene, borophene, blue phosphorene, GeSe monolayer and germanene are reviewed to understand the surface interaction mechanism.
Abstract: Toxic gases, such as NOx, SOx, H2S and other S-containing gases, cause numerous harmful effects on human health even at very low gas concentrations. Reliable detection of various gases in low concentration is mandatory in the fields such as industrial plants, environmental monitoring, air quality assurance, automotive technologies and so on. In this paper, the recent advances in electrochemical sensors for toxic gas detections were reviewed and summarized with a focus on NO2, SO2 and H2S gas sensors. The recent progress of the detection of each of these toxic gases was categorized by the highly explored sensing materials over the past few decades. The important sensing performance parameters like sensitivity/response, response and recovery times at certain gas concentration and operating temperature for different sensor materials and structures have been summarized and tabulated to provide a thorough performance comparison. A novel metric, sensitivity per ppm/response time ratio has been calculated for each sensor in order to compare the overall sensing performance on the same reference. It is found that hybrid materials-based sensors exhibit the highest average ratio for NO2 gas sensing, whereas GaN and metal-oxide based sensors possess the highest ratio for SO2 and H2S gas sensing, respectively. Recently, significant research efforts have been made exploring new sensor materials, such as graphene and its derivatives, transition metal dichalcogenides (TMDs), GaN, metal-metal oxide nanostructures, solid electrolytes and organic materials to detect the above-mentioned toxic gases. In addition, the contemporary progress in SO2 gas sensors based on zeolite and paper and H2S gas sensors based on colorimetric and metal-organic framework (MOF) structures have also been reviewed. Finally, this work reviewed the recent first principle studies on the interaction between gas molecules and novel promising materials like arsenene, borophene, blue phosphorene, GeSe monolayer and germanene. The goal is to understand the surface interaction mechanism.
189 citations
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TL;DR: This review provides an overview of the utilization of photoactivated nanomaterials in gas sensing field and excellent gas sensing performance of emerging two-dimensional materials-based sensors under light illumination is discussed in details with proposed gas sensing mechanism.
Abstract: Room-temperature gas sensors have aroused great attention in current gas sensor technology because of deemed demand of cheap, low power consumption and portable sensors for rapidly growing Internet of things applications. As an important approach, light illumination has been exploited for room-temperature operation with improving gas sensor’s attributes including sensitivity, speed and selectivity. This review provides an overview of the utilization of photoactivated nanomaterials in gas sensing field. First, recent advances in gas sensing of some exciting different nanostructures and hybrids of metal oxide semiconductors under light illumination are highlighted. Later, excellent gas sensing performance of emerging two-dimensional materials-based sensors under light illumination is discussed in details with proposed gas sensing mechanism. Originated impressive features from the interaction of photons with sensing materials are elucidated in the context of modulating sensing characteristics. Finally, the review concludes with key and constructive insights into current and future perspectives in the light-activated nanomaterials for optoelectronic gas sensor applications.
Highlights:
1 Operations of metal oxide semiconductors gas sensors at room temperature under photoactivation are discussed.2 Emerging two-dimensional (2D) materials-based gas sensors under light illumination are summarized.3 The advantages and limitations of metal oxides and 2D-materials-based sensors in gas sensing at room temperature under photoactivation are highlighted.
164 citations
TL;DR: In this paper, a review of the recent and past developments carried out in the field of 2D MoS2 material is presented, where the authors try to cover the recent developments in the literature.
Abstract: The evolutions of nanomaterials have played a significant role in altering the shape and structure of the materials at the nanoscale level to achieve desired applications. Early carbon nanotubes were considered to be an optimistic material for electronics but their incapacity to differentiate semiconducting and metallic phases results into development of Quasi two dimensional (Q2D) materials which include graphene, black phosphorous, 2D ZnO, hexagonal boron nitride, 2D honeycomb silicon, and layered transition metal dichalcogenides (TMDs) like molybdenum disulfide (MoS2) and Tungsten disulfide (WS2). Among them, molybdenum disulfide (MoS2) is considered as convincingly multipurpose material because it exhibits a capacity to show different properties as it changes from bulk to nanoscale. Single layer MoS2 is assuredly capable of post-silicon electronics due to its direct bandgap value i.e. (~1.9 eV). It exhibits a high on/off current ratio (108) at room temperature and mobility of about 200 cm2 (Vs)−1. Also based on structure, MoS2 has two characteristics (i) it possesses a hexagonal arrangement in which S-Mo-S atomic layers are covalently bonded (ii) Van der Waals interaction lies between the adjacent layers of MoS2 that makes it suitable for gas sensing purpose. At 300 K, MoS2 comprises thermal conductivity value 131 Wm−1 k−1. MoS2 consists of different polytypes. The promising properties and characteristics of MoS2 make it suitable for various practical applications. In this review, we try to cover the recent and past developments carried out in the field of 2D MoS2 material.
113 citations
References
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TL;DR: The electronic properties of ultrathin crystals of molybdenum disulfide consisting of N=1,2,…,6 S-Mo-S monolayers have been investigated by optical spectroscopy and the effect of quantum confinement on the material's electronic structure is traced.
Abstract: The electronic properties of ultrathin crystals of molybdenum disulfide consisting of N=1,2,…,6 S-Mo-S monolayers have been investigated by optical spectroscopy Through characterization by absorption, photoluminescence, and photoconductivity spectroscopy, we trace the effect of quantum confinement on the material's electronic structure With decreasing thickness, the indirect band gap, which lies below the direct gap in the bulk material, shifts upwards in energy by more than 06 eV This leads to a crossover to a direct-gap material in the limit of the single monolayer Unlike the bulk material, the MoS₂ monolayer emits light strongly The freestanding monolayer exhibits an increase in luminescence quantum efficiency by more than a factor of 10⁴ compared with the bulk material
12,822 citations
TL;DR: This work exemplifies the evolution of structural parameters in layered materials in changing from the three-dimensional to the two-dimensional regime by characterized by Raman spectroscopy.
Abstract: Molybdenum disulfide (MoS2) of single- and few-layer thickness was exfoliated on SiO2/Si substrate and characterized by Raman spectroscopy. The number of S−Mo−S layers of the samples was independently determined by contact-mode atomic force microscopy. Two Raman modes, E12g and A1g, exhibited sensitive thickness dependence, with the frequency of the former decreasing and that of the latter increasing with thickness. The results provide a convenient and reliable means for determining layer thickness with atomic-level precision. The opposite direction of the frequency shifts, which cannot be explained solely by van der Waals interlayer coupling, is attributed to Coulombic interactions and possible stacking-induced changes of the intralayer bonding. This work exemplifies the evolution of structural parameters in layered materials in changing from the three-dimensional to the two-dimensional regime.
3,969 citations
1,395 citations
TL;DR: The results show that, compared to the single-layer counterpart, transistors of few MoS2 layers exhibit excellent sensitivity, recovery, and ability to be manipulated by gate bias and green light, and ab initio DFT calculations show that the charge transfer is the reason for the decrease in resistance in the presence of applied field.
Abstract: Most of recent research on layered chalcogenides is understandably focused on single atomic layers. However, it is unclear if single-layer units are the most ideal structures for enhanced gas–solid interactions. To probe this issue further, we have prepared large-area MoS2 sheets ranging from single to multiple layers on 300 nm SiO2/Si substrates using the micromechanical exfoliation method. The thickness and layering of the sheets were identified by optical microscope, invoking recently reported specific optical color contrast, and further confirmed by AFM and Raman spectroscopy. The MoS2 transistors with different thicknesses were assessed for gas-sensing performances with exposure to NO2, NH3, and humidity in different conditions such as gate bias and light irradiation. The results show that, compared to the single-layer counterpart, transistors of few MoS2 layers exhibit excellent sensitivity, recovery, and ability to be manipulated by gate bias and green light. Further, our ab initio DFT calculations...
1,126 citations
TL;DR: The gas-phase reaction between MoO3-x and H2S in a reducing atmosphere at elevated temperatures (800� to 950�C) has been used to synthesize large quantities of an almost pure nested inorganic fullerene (IF) phase of MoS2, obtaining a uniform IF phase with a relatively narrow size distribution.
Abstract: The gas-phase reaction between MoO3-x and H(2)S in a reducing atmosphere at elevated temperatures (800 degrees to 950 degrees C) has been used to synthesize large quantities of an almost pure nested inorganic fullerene (IF) phase of MoS(2). A uniform IF phase with a relatively narrow size distribution was obtained. The synthesis of IFs appears to require, in addition to careful control over the growth conditions, a specific turbulent flow regime. The x-ray spectra of the different samples show that, as the average size of the IF decreases, the van der Waals gap along the c axis increases, largely because of the strain involved in folding of the lamella. Large quantities of quite uniform nanotubes were obtained under modified preparation conditions.
1,103 citations