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To achieve good living standards, it is critical to make high-performance toxic gas sensing devices for public safety, environmental pollutant control, industrial operations, and other applications. For this purpose, we demonstrate CuO anchored SnO 2 nanostructures for H 2 S gas sensors. The selectivity was improved by anchoring with CuO for a total 60 s duration at four equal consecutive cycles to achieve good selectivity towards H 2 S molecules. The pristine CuO shows instability and metallic behaviour when it is exposed to H 2 S for a longer time. Furthermore, the proposed gas sensor shows good selectivity toward H 2 S as compared to other gases H 2 , NO 2 , CO 2 , and NH 3. The sensing response was measured at around 69 % at the optimal operating temperature of 150 °C. It is observed that CuS formation has better selectivity as compared to pristine SnO 2 and a slight improvement in sensitivity is observed. As a result, a promising strategy for designing and producing good-performance H 2 S gas sensors would be to CuO anchor on SnO 2 nanostructures. The proposed sensors may be integrated with IoT platforms and used for the detection of H 2 S in the sewer line and leak detection in the petroleum industry. [Display omitted] • SnO 2 thin film was anchored with CuO at different time duration using RF sputtering for H 2 S gas sensing. • The sensor exhibits higher sensing response of 69 % at 150 ºC for 100 ppm of H 2 S with a LoD of 1 ppm. • Comparative analysis was performed for H 2 S gas detection for both SnO 2 and CuO/SnO 2 based sensors. • Excellent selectivity and slight improved sensitivity was observed with CuO/SnO 2 based gas sensor. [ABSTRACT FROM AUTHOR]

The hole accumulation layer (HAL) configuration of p-type oxides (including Co 3 O 4) in ambient air causes intrinsically low gas response and hinders their promising applications in exhaled gas analysis. Herein, Sn and Ni co-doping has been proposed to trigger the response of chemiresistive Co 3 O 4 sensor toward acetone (biomarker of diabetes). Via incorporating 1 at% Sn and 0.5 at% Ni doping (Co 2.95 Sn 0.03 Ni 0.02 O 4), the response to 100 ppm acetone has been boosted ∼2 orders (from 1.24 to 125.6) at 70 °C, the limit of detection (LoD) has been reduced ∼4 times (from 47.9 to 12.4 ppb), the optimal operation temperature has been decreased from 130 °C to ∼70 °C. Various characterizations suggest that co-doping induced abundant surface asymmetric oxygen vacancy defects (Co-□-Ni, Sn-□-Ni), which facilitate the catalytic oxidation of acetone molecules at relatively low operation temperature. In addition to excellent reproducibility and long-term stability, Co 2.95 Sn 0.03 Ni 0.02 O 4 sensor could also operate under highly humid air background and reliably detect acetone concentration in exhaled breath at 150 °C, opening the opportunity for the practical application of p-type oxide sensors for diabetes diagnosis. [Display omitted] • Sn, Ni co-doped Co3O4 dramatically improves the response to acetone. • Sn, Ni co-doped Co3O4 drastically reduces optimal operation temperature (70 °C). • Humidity influence of Co2.95Sn0.03Ni0.02O4 could be suppressed at 150 °C. • Application of Co2.95Sn0.03Ni0.02O4 sensor for non-invasive diabetes monitoring. [ABSTRACT FROM AUTHOR]

The Internet of Things (IoT) has a crucial role in advancing various fields such as Industry 4.0, Big Data, and Machine-to-Machine technologies. All systems continuously gather information on various parameters such as temperature, speed, pressure, health data, environmental conditions, and consumption. Considering this, we've developed a novel fabrication method for H 2 S gas sensor prototypes. These sensors are based on noble metal-functionalized on metal oxide semiconductor (MOS) chemiresistors. The fabrication process involved growing CuCrO 2 sensing thin film on SiO 2 /Si substrates using the RF sputtering method. Subsequently, Pd nanoparticles, known for their excellent gas-sensing catalyst properties, were functionalized onto the CuCrO 2 films using DC sputtering with varying sputtering times of 3, 6, 9, and 12 s. Nanorice morphology boosts gas absorption, capturing more target molecules. A 9 s Pd sputtering time greatly improved H 2 S sensing over other gases. CuCrO 2 film with Pd showed the highest 72.3% response to 50 ppm H 2 S, detecting down to 0.5 ppm. These results were achieved at the optimal working temperature of 150 °C. After optimizing parameters, we transferred the technology to develop a sensor module for the prototype with IoT integration. The prototype sensor connects to NODEMCU-ESP8266 Wi-Fi, which links to a smartphone through a mobile hotspot. [Display omitted] • Fabrication of Pd anchored CuCrO 2 nano rice morphology for highly toxic H 2 S gas sensors. • Pd NPs increase surface-to-volume ratio and improved the sensing performance due to spillover effect. • The measured sensing response was 72.3% at 150 °C for 50 ppm of H 2 S around with a lower detection limit of.5 ppm. • In Pd/CuCrO 2 better selectivity as compared to pristine CuCrO 2 and drastic improvement in sensitivity is observed. • Optimized sensor is interface with IoT platform for the real-life application. [ABSTRACT FROM AUTHOR]

Novel metal functionalization of the semiconductor metal oxide surface is an effective approach to address the poor selectivity with increased sensing performance. Functionalization enhances sensitivity through chemical and electronic sensitization, while metal nanoparticles catalyze target gas molecule adsorption. Taking this approach into consideration, we demonstrated Silver (Ag) nanoparticles functionalized α-Fe 2 O 3 nanostructured thin film gas sensor for sensing of NO 2 molecules. The RF-sputtered α-Fe 2 O 3 nanostructured thin film were deposited at 600 °C followed by materials characterizations. Furthermore, we functionalized the α-Fe 2 O 3 sensor with various quantity of Ag NPs using sputtering techniques and observed the effect on sensing performance. The α-Fe 2 O 3 sensor with 10 s Ag functionalization shows the highest relative response among all samples of ∼71.02% for 100 ppm NO 2 concentration at 150 °C. Further, the selectivity was dramatically improved upon the functionalization with Ag due to its catalytic properties in comparison with the pristine sensor. The Ag functionalization results in an improved surface-to-volume ratio and more reaction and adsorption sites for gas molecules. As a result, Ag functionalization seems to be a potential strategy to increase the sensing response of an α-Fe 2 O 3 sensor for selective sensing of NO 2. [Display omitted] • Fabrication of Ag anchored α-Fe 2 O 3 nanostructures for NO 2 gas sensors. • Further α-Fe 2 O 3 thin film was anchored with Ag for 5, 10 and 15 s using DC sputtering. • Ag NPs increase surface-to-volume ratio and adsorption sites for gas molecules. • The measured sensing response was 71.02% at 150 °C for 100 ppm of NO 2 around with a lower detection limit of 1 ppm. • In Ag/α-Fe 2 O 3 better selectivity as compared to pristine α-Fe 2 O 3 and drastic improvement in sensitivity is observed. [ABSTRACT FROM AUTHOR]

We demonstrate RF sputtered Ni-doped ZnO nanostructures for detection of extremely low concentration (1 ppm) of hydrogen gas at moderate operating temperature of 75 °C. Structural, morphological, electrical and hydrogen sensing behavior of the Ni-doped ZnO nanostructures strongly depends on doping concentration. Ni doping exceptionally enhances the sensing response and reduces the operating temperature of the sensor as compared to undoped ZnO. The major role of the Ni-doping is to create more active sites for chemisorbed oxygen on the surface of sensor and, correspondingly, to improve the sensing response. The 4 at% of Ni-doped ZnO exhibits the highest response (∼69%) for 1% H 2 at 150 °C, which are ∼1.5 times higher than for the undoped ZnO. This is ascribed to lowest activation energy ∼6.47 KJ/mol. Diminishing of the relative response was observed in 6% Ni- doped ZnO due to separation of NiO phase. [ABSTRACT FROM AUTHOR]

In this study, we have reported the fabrication of p-NiO/n-SnO 2 heterojunction based formaldehyde (HCHO) sensor by decorating the surface of pre-deposited SnO 2 thin film with laser ablated NiO nanoparticles (NPs). In atmospheric air, NiO NPs were produced by a moving laser beam on the surface of pure (99.99%) Ni pellet to decorate sputtered deposited SnO 2 thin film directly to form NiO/SnO 2 p-n heterojunction. After fabrication, gas sensing properties of NiO/SnO 2 sensor were investigated systemically towards HCHO and it exhibited higher response (R a /R g) of about 31.04 towards 50 ppm HCHO at 210 °C with good selectivity compared with pristine SnO 2 sensor. Moreover, adsorption (K a) and desorption rate constant (K d), response time (τ res), recovery time (τ rec) and surface coverage (θ) of NiO/SnO 2 sensor were extracted from experimental data using Langmuir gas adsorption-desorption model via curve fitting method and the models demonstrated the irreversible type of gas sensing behaviour towards HCHO. The experimental results revealed that the laser ablation method has a great potential to use as alternative chemical free surface decoration route to fabricate metal oxide heterojunction based sensors for the detection of formaldehyde or other toxic gases. [Display omitted] • The NiO nanoparticles were synthesized in air by laser ablation technique. • The p-NiO/n-SnO 2 heterojunction has been formed by direct deposition of NiO nanoparticles on SnO 2 thin-film. • The NiO/SnO 2 sensor shows fast and high response to formaldehyde at 210 °C with good selectivity. • Langmuir adsorption-desorption model and curve fitting were used to extract gas sensing parameters. [ABSTRACT FROM AUTHOR]

Though temperature modulation has demonstrated its capability in addressing selectivity issue of metal oxide semiconductor (MOS) gas sensors, integration of (micro)heater not only drastically adds power consumption and device manufacture complexity, but also hinders the use of flexible polymer substrate/platform. Exploring an approach enabling outstanding selectivity at room temperature (RT) is highly required, but it remains a big challenge. Herein, UV light modulation (ULM) with a rectangular UV wave has been proposed to regulate the transient response signals of sensor arrays, composed of ZnO/(Sr 0.6 Bi 0.305) 2 Bi 2 O 7 (ZnO/SBO), ZnO and In 2 O 3. Upon pulsed UV excitation, chemisorption (or redox reaction) of injected target vapors (on MOS surface) could be activated at RT. Arising from the specific gas/MOS binding configurations for different gases and MOSs, quite different recovery kinetics under UV illumination (associated with deactivation of chemisorbed target molecules) were found, which endow nonselective MOS sensors with superior selectivity. Multilayer perceptron (MLP) indicates a 99% recognition accuracy ratio of eleven kinds of tested gases, including four kinds of benzene molecules. Our work demonstrates that transient response signals during ULM contain rich features of adsorbed gas molecules, which offers an opportunity for the facile design of advanced smart gas molecule recognition chips on both rigid and flexible platforms. • Novel UV-light-modulation (ULM) strategy is proposed for gas molecule recognition. • ULM outshines continuous UV irradiation in enriching features of gas molecules. • Achieving good selectivity by nonselective sensors operated at room temperature. • Structurally similar VOCs molecules could be accurately discriminated. [ABSTRACT FROM AUTHOR]

Heterojunction based metal oxide semiconductors have a great potential to detect toxic gases and volatile organic compounds. Here, we report a synthesis technique to obtain ZnO nanoparticles (NPs) via laser ablation method in ambient atmosphere using a nanosecond pulse laser. The laser ablated ZnO NPs were used for the decoration of sputtered deposited SnO 2 thin film to realize n-type ZnO/n-type SnO 2 heterojunction based formaldehyde (HCHO) gas sensor. Fabricated ZnO/SnO 2 sensor shows 3 times higher response (response = 20) to 50 ppm HCHO, faster response-recovery dynamics (τ res = 4 s and τ rec = 30 s) and better selectivity compared to pristine SnO 2 sensor at lower operating temperature (250 °C). The ZnO/SnO 2 heterojunction based sensor also can detect < 0.25 ppm HCHO, which allows for lower detectable limit of sub-ppm HCHO. Therefore, the ZnO/SnO 2 sensor shows enhanced sensing performance due to oxygen vacancies and n-n heterojunction structures provides more effective electrons for oxygen adsorption which speeds up the electronic transport at the interface of two materials. Synthesis of metal oxide composite NPs using pulse laser ablation method could be a promising alternative rapid route for the fabrication of highly sensitive gas sensors to detect most common indoor air pollutant. • Fabrication of highly selective and ultrasensitive n-SnO 2 /n-ZnO heterojunction-based formaldehyde gas sensor. • ZnO nanoparticles were synthesized using rapid and cost-effective laser ablation techniques in air. • The sensor exhibits high gas sensing response at 200 °C with ultra-low detection limit of 0.25 ppm. • SnO 2 /ZnO sensor shows better sensitivity and selectivity of as compared to pristine SnO 2. [ABSTRACT FROM AUTHOR]

Two dimensional chalcogenides and metal sulfide materials with their sensitive surfaces are promising and potential postulant for the purpose of chemical gas sensing as a consequence of extraordinary vast surface area to volume ratio and significant band gap. We demonstrate a highly selective and sensitive NO 2 gas sensor using vertically aligned 2D SnS 2 flakes, grown by a chemical vapor deposition method in controlled gas flow. The vertically aligned SnS 2 flakes were confirmed by scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. The sensing behaviour of the vertical aligned structures was analyzed for various concentrations of NO 2 at different temperatures. The sensor exhibits high gas sensing response (ΔR/R%) of ~164 at 120 °C with 50 ppm of NO 2 gas, which is the highest response among the SnS 2 based reports. The device shows excellent sensing response at room temperature but poor recovery. The selectivity of the sensor was performed under different gas environments and found highly selective towards NO 2 gas, and the results are supported by electronic structure calculations. Based on experimental results and electronic structure calculations, a gas sensing mechanism is proposed. The result indicates that fabricated sensor can be used in air purification industries and in air monitoring. • Vertically aligned 2D SnS 2 flakes were grown by CVD in controlled gas flow. • Highly selective and sensitive NO 2 gas sensor was fabricated using vertically aligned 2D SnS 2 flakes. • The sensor exhibits high gas sensing response (ΔR/R%) of ~164 at 120 °C with 50 ppm of NO 2 gas. • The selectivity of the sensor is supported by electronic structure calculations. • The sensing mechanism responsible for the dramatically increased sensitivity was also discovered. [ABSTRACT FROM AUTHOR]

Two dimensional chalcogenides and metal sulfide materials with their sensitive surfaces are promising and potential postulant for the purpose of chemical gas sensing as a consequence of extraordinary vast surface area to volume ratio and significant band gap. We demonstrate a highly selective and sensitive NO 2 gas sensor using vertically aligned 2D SnS 2 flakes, grown by a chemical vapor deposition method in controlled gas flow. The vertically aligned SnS 2 flakes were confirmed by scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. The sensing behaviour of the vertical aligned structures was analyzed for various concentrations of NO 2 at different temperatures. The sensor exhibits high gas sensing response (ΔR/R%) of ~164 at 120 °C with 50 ppm of NO 2 gas, which is the highest response among the SnS 2 based reports. The device shows excellent sensing response at room temperature but poor recovery. The selectivity of the sensor was performed under different gas environments and found highly selective towards NO 2 gas, and the results are supported by electronic structure calculations. Based on experimental results and electronic structure calculations, a gas sensing mechanism is proposed. The result indicates that fabricated sensor can be used in air purification industries and in air monitoring. • Vertically aligned 2D SnS 2 flakes were grown by CVD in controlled gas flow. • Highly selective and sensitive NO 2 gas sensor was fabricated using vertically aligned 2D SnS 2 flakes. • The sensor exhibits high gas sensing response (ΔR/R%) of ~164 at 120 °C with 50 ppm of NO 2 gas. • The selectivity of the sensor is supported by electronic structure calculations. • The sensing mechanism responsible for the dramatically increased sensitivity was also discovered. [ABSTRACT FROM AUTHOR]

• A MoS 2 functionalized Au gated AlGaN/ GaN HEMT sensor has been developed for the detection of toxic Hg2+ ions. • The synthesis of MoS 2 was performed by hydrothermal approach. • The characterization suggests the vertically aligned, flower like MoS 2 formation. • The sensor exhibits a rapid response of 1.8 s at 1 ppt, high sensitivity of 0.64 μA/ppb and high selectivity for Hg2+ ions. A sensor for highly sensitive, selective, and rapid determination of the trace amount of toxic Hg2+ ions is developed for the first-time using molybdenum disulfide (MoS 2) functionalized AlGaN/GaN high electron mobility transistor (HEMT). The vertically aligned, flower-like MoS 2 structures are synthesized through a simple hydrothermal route and applied on the gate region of AlGaN/GaN HEMT. The scanning electron microscopy, Raman spectroscopy, and X-ray diffraction are performed for structural characterization of MoS 2. Further, the sensing of Hg2+ ions is performed by electrical characterizations of MoS 2 functionalized AlGaN/GaN HEMT. The sensor showed an excellent sensitivity of 0.64 μA/ppb and detection limit of 0.01152 ppb with the rapid response time of 1.8 s. The sensor exhibits the linear range of detection from 0.1 ppb to 100 ppb and highly selective behavior towards Hg2+ ions. The results demonstrated that the MoS 2 possess excellent Hg2+ ions capture property, that could be attributed to the complexation of Hg2+ ions with sulfur and the electrostatic interaction between MoS 2 and Hg2+ ions alters the drain to source current (I DS) of the HEMT at a constant drain to source voltage (V DS). Therefore, the MoS 2 based AlGaN/ GaN HEMT devices have a huge potential for next-generation ion sensing applications. [ABSTRACT FROM AUTHOR]

• Pt Sensitizers are functionalized on W 18 O 49 porous spheres via atomic layer deposition. • The sensor based on W 18 O 49 /Pt shows high sensitivity and selectivity to acetone at 180 °C, • A very low limit of detection of 52 ppb is obtained for acetone detection. Metal oxide semiconductors (MOS) are important candidates as the sensing layer for chemical gas sensors to detect volatile organic compounds (VOCs). However, the low surface activity limits the use of MOS in future high performance gas sensors. The design of susceptive nanostructures with prominent surface modification can be an effective strategy to achieve high sensitivity and high selectivity. Herein, Pt nanoparticles with a fine size of below 1 nm serving as the sensitizers are functionalized on porous W 18 O 49 nanospheres via atomic layer deposition and investigated for acetone detection. The W 18 O 49 /Pt spheres combine the advantages of fast gas diffusion enabled by the porous shells and catalytic properties of Pt nanocatalysts. Gas sensing tests reveal that W 18 O 49 /Pt has a very high response to 20 ppm acetone (R a /R g = 85), which is ∼40 times higher than that of pure W 18 O 49 (R a /R g = 2.1) at a low operating temperature of 180 °C. Meanwhile, W 18 O 49 /Pt shows fast response-recovery speed and good stability as well as excellent selectivity to acetone against other interfering gases. In addition, an ultrahigh sensitivity of 1.01 ppm−1 and a very low limit of detection of 52 ppb is obtained. The superior gas sensing performances of the W 18 O 49 /Pt materials indicates a strong potential for detection of biomarkers for exhaled breath diagnosis, and also paves the way to manipulate other metal oxide semiconductor-based sensors with high performances. [ABSTRACT FROM AUTHOR]

• Different concentration of carbon nanofibers were loaded on Au pattern interdigitated electrodes over ZnO nanostructures. • Pure CNF, pure ZnO nanostructures, and CNF/ZnO samples were utilized to measure the sensing response for hydrogen gas. • Highest relative response towards hydrogen gas was found in 0.2 wt% CNF/ZnO nanostructures. • Enhanced sensing response can be seen due to formation of p-n heterojunctions between CNF and ZnO. The present report investigates hydrogen gas sensing properties on PAN/(PAN-b-PMMA) derived electrospun nanoporous carbon nanofibers loaded on ZnO nanostructures. Polymer blend of PAN and PAN-b-PMMA is used to obtain the high surface area porous CNF which improve further sensing performance. Moreover, a facile technique such as drop cast method is used to load the CNF (0.1–0.5 wt%) on Au pattern interdigitated electrodes over ZnO nanostructures. Loading of CNF was optimized to ensure proper connection between the electrodes over ZnO surface, which was measured using I–V characteristics. Initially, current decreased for less amount of CNF (0.1–0.2 wt%), which later increased for high concentration of CNF (0.3–0.5 wt%). It was further observed that 0.2 wt% CNF/ZnO nanostructures based sensor exhibited maximum sensing response (73.54%) as compared to CNF (3.29%) and ZnO (44.51%) for 100 ppm hydrogen at 150 °C. This enhanced sensing response may be attributed to diffusion of hydrogen molecules through the nanoporous CNF, thus enabling the formation of p - n heterojunction at the interface of CNF and ZnO. The presence of oxygen functional groups on CNF surface also contributes to the enhancement of the sensing performance. [ABSTRACT FROM AUTHOR]