H2 Gas Sensor Research Articles

Tailoring the H2 gas detection range of the AlGaN/GaN high electron mobility transistor by tuning the Pt gate thickness

H2 gas sensors for different applications require various detection ranges, such as 1–100 ppm for exhale breath test and 0–40000 ppm for H2 energy vehicles. Coarse-tuning of the detection range could be realized by the selection of the type of H2 sensors. The fine-tuning of the detection range within one type of H2 sensor, however, is little concerned and reported. Herein, we propose to achieve the fine-tuning of the H2 gas detection range of the AlGaN/GaN HEMT devices by adjusting the Pt gate thickness. Devices with various Pt gate thicknesses of 2, 20, 60, and 100 nm were fabricated and investigated. Results show that the HEMT devices have excellent pinch-off characteristic with an on-to-off ratio of ∼four orders of magnitude. For the 100 nm thick device exposed to 500 ppm H2, ultrafast response time of 1.5 s is observed together with high response. With the decrease of gate thickness, both the response and the response time gradually increase, 1850% and 6 s for the 2 nm thick device. Moreover, both the low limit of detection (LOD) and the saturation cencentration decrease from 1.6 to 0.14 ppm and from 30,000 to 5000 ppm, respectively, with the gate thickness reduced from 100 to 2 nm, revealing that fine-tuning of the detection range could be achieved by adjusting the gate thickness. Finally, the response activation energy is also studied, 15.9, 19.7, and 42.8 kJ/mol for 2, 60, and 100 nm thick devices, respectively.

(Sensor Division Outstanding Achievement Award Address) Development of Gas Sensors for Safety and Health by Employing Various Sensor Technology

In our laboratory, numeral efforts have been directed to improving sensing properties of various kinds of gas sensors, which are based on the different sensing principles, capable of using for our safety and health. The following four topics will be delivered in my presentation. Meso- and Marco-Porous Structural Controlled Metal Oxides for Semiconductor Gas Sensors1) To improve the sensing performance of semiconductor metal oxide gas sensors, strict design and control of meso- and macro-porous structure of sensor materials are of primary importance, i.e. controlling of diffusivity of target gases in the sensing layer toward the position of sensor electrodes, which is the most sensitive region of the sensors, in addition to controlling of catalytic activities of sensor materials. We have used various kinds of surfactants and polymethylmethacrylate microspheres with different sizes to control meso- and macro-porous structure of metal oxides, respectively (see Fig. 1). Examples for the improvement of H2 and NO2 sensing properties by porous structural control will be reported. TiO2-Based Diode-Type H2 Gas Sensors Operable both in Air and in N2 2) For future popularization of hydrogen-powered vehicles, household fuel-cell cogeneration systems and etc., development of more sensitive and selective H2 sensors than commercial ones is of primally importance. We have so far demonstrated that diode-type gas sensors using noble-metal (N) sensing electrodes and an anodized titania film show a quite large H2 response even under oxygen-free atmosphere as well as relatively excellent H2 selectivity to other inflammable gases, in comparison with other gas sensors. The mechanism for enhancing the H2-sensing properties by the surface modification of the Pt-sensing electrode with Au (see Fig. 2) will be mainly reported. Solid Electrolyte CO Gas Sensors Operable at Temperatures less than Room Temperature3) Detection of CO is of primary importance from the view point of safety in many industrial processes as well as our daily life. We have found that the sintered disk-type NASICON(Na3Zr2Si2PO12)-based solid electrolyte gas sensors equipped with a metal oxide (MO)-added Pt sensing electrode and a pristine Pt or another metal oxide-added Pt reference electrode on the same side of the disk can detect CO at temperatures less than room temperature (see Fig. 3). The outstanding CO sensing characteristics of this type of CO sensors will be reported. Adsorption/Combustion-Type Micro VOC Sensors4) We have reported that adsorption/combustion-type micro gas sensors, which were fabricated by utilizing the microelectromechanical system (MEMS) technology and an oxide-film fabrication technique by drop coating employing an air-pulse fluid dispenser, are quite promising as gas-sensing devices for detecting a low concentration of various volatile organic compounds (VOCs) in comparison with other types of gas sensors (see Fig. 4). The potential of this type of sensors, in detecting selectively a low concentration of VOCs, which are possible biomakers for diagnosis of specific diseases and health checking, will be reported.References Ueda, I. Boehme, T. Hyodo, Y. Shimizu, U. Weimar, N. Barsan, Enhanced NO2-sensing properties of Au-loaded porous In2O3 gas sensors at low operating temperatures, Chemosensors, 8, 72 (2020).Shimizu, T. Hyodo, Sensing properties of diode-type gas sensors, Advances in Science and Technology, 99, 61-65 (2017).Ueda, H. Takeda, K. Kamada, T. Hyodo, Y. Shimizu, Enhanced CO response of NASICON-based gas sensors using oxide-added Pt sensing electrode at low temperature operation, Electrochemistry, 85(4), 174-178 (2017).Hyodo, Y. Shimizu, Adsorption/combustion-type micro gas sensors: Typical VOC-sensing properties and material-design approach for highly sensitive and selective VOC detection, Analytical Sciences, 36(4), 401-411 (2020). Figure 1

Role of Nanodiamond Grains in the Exfoliation of WS2 Nanosheets and Their Enhanced Hydrogen-Sensing Properties.

Herein, for the first time, a combination of detonation nanodiamond (DND)-tungsten disulfide (WS2) was devised and studied for its selective H2-sensing properties at room temperature. DND-WS2 samples were prepared by a sonication-assisted (van der Waals interaction) liquid-phase exfoliation process in low-boiling solvents with DND as a surfactant. The samples were further hydrothermally treated in an autoclave under high pressure and temperature. The as-prepared samples were separated as two parts named DND-WS2 BH (before hydrothermal) and DND-WS2 AH (after hydrothermal). The exfoliated bilayer to few-layer DND-doped WS2 nanosheets were confirmed by ultraviolet-visible spectra, atomic force microscopy, and transmission electron microscopy studies. It was observed that the DND powder not only acted as a surfactant but also doped and expanded on WS2 nanosheets. The difference between samples BH and AH treatment was further investigated using Raman spectroscopy. The WS2 and DND-WS2 samples on SiO2/Si were fabricated using a sputtered Pd/Ag interdigitated electrode and utilized for H2 gas-sensing measurements. Surprisingly, the DND-WS2 exhibits an ultrahigh sensor response of 72.8% to H2 at 500 ppm when compared to only 9.9% for WS2 alone. Also, the DND-WS2 shows a fast response/recovery time, high selectivity, and stability toward H2 gas. It can be attributed to the correlation of the intergrain phase of DND nanoparticles and WS2 nanosheets, which contributes to the easy transportation of charge carriers when exposed to the air and H2 gas atmosphere. Moreover, it is believed that DND-induced WS2 exfoliation might inspire future synthesis of transition metal dichalcogenides induced by DND in green solvents.

Capacitive sensor based on GaN honeycomb nanonetwork for ultrafast and low temperature hydrogen gas detection

Passive devices are highly desired for the detection of H2 gas due to its high safeness and low energy consumption. In this study, GaN with honeycomb nanonetwork structure (GaN-HN) epitaxially grown on Si wafer by molecular beam epitaxy technique was utilized for the fabrication of capacitive H2 gas sensors, on which 10 nm thick Pd layer was deposited as the sensing electrode. XRD, SEM, and AFM results show that the cubic phase Pd is uniformly coated on the surface of GaN-HN and maintains an interesting structure of honeycomb nanonetwork. It is found that the response time decreases gradually with the increase of the operating temperature and it reaches a steady value ∼3 s at temperatures higher than 50 °C. Ultrafast response time of 1.3 s towards 1000 ppm H2 was observed for the Pd-GaN/Si capacitive sensor operated at the temperature of 70 °C. The low limit of detection (LOD) is also evaluated by experiment and IUPAC definition, 500 ppb and 440 ppb, respectively. Moreover, the capacitive sensor exhibits ignorable response to CH4, NO2 and common VOCs gases. The long-term stability and humidity effect on H2 gas detection were also studied. Schottky junction capacitance of Pd/GaN might be dominated by the hydrogen dipole layer. The proposed Pd-GaN/Si capacitive sensor investigated here exhibits ultrafast response speed, low operating temperature, high selectivity and stability, making it attractive for applications in timely H2 leakage detection.

Sensitive H2 gas sensors based on SnO2 nanowires

Sensitive H2 gas sensors are highly desirable for the prediction and early-warning of H2 leakage. Low-dimensional nanostructures of metal oxide semiconductor emerge as promising materials candidates, but it remains a challenge to preserve the nanostructures in the real sensors. In this work, we demonstrated highly sensitive H2 gas sensors based on porous network of SnO2 nanowires that exhibited ultrasmall diameter ∼ 2 nm. Colloidal SnO2 nanowires synthesized via a solvothermal process were drop-coated onto the commercial alumina substrates, followed by in-situ annealing treatment at 350 °C to remove the surface ligands. The sensors exhibited sensitive response with linear dependence on the H2 gas concentration ranging from 2 ppm to 100 ppm when operated at 250°C. Typically, the sensor had a response of 13 toward 40 ppm of H2, with the response and recovery time being 15 s and 31 s, respectively. To further improve the sensor performance, Palladium doped SnO2 nanowires were thoroughly investigated. It’s shown that, the operating temperature of the sensor decreased from 250 °C to 150 °C after Pd doping, and the response and recovery time decreased to 6 s/3 s. The superb sensitivity was attributed to the enhanced gas reception, electron transport as well as utility factor owing to the network nanostructure of ultrathin SnO2 nanowires and catalytic activity of Pd, according to theoretical calculation and adsorption kinetics studies. Combined with the excellent solution processability, the colloidal SnO2 nanowires are potentially attractive for next-generation gas sensors with lower power consumption and integration with silicon-based substrates.

Location-specific fabrication of suspended nanowires using electrospun fibers on designed microstructure

While there have been remarkable improvements in the fabrication of suspended nanowires, placing a single nanowire at the desired location remains to be a challenging task. In this study, a simple method is proposed to fabricate suspended nanowires at desired locations using an electrospinning process and a designed microstructure. Using electrospun polymer fibers on the designed microstructure as a sacrificial template, various materials are deposited on it, and the electrospun fibers are selectively removed, leaving only nanowires of the deposited material. After the polymer fibers are removed, the remaining metal fibers agglomerate into a single nanowire. Throughout this process, including the removal of the polymer fibers, the samples are not exposed to high temperatures or chemicals, thereby allowing the formation of nanowires without oxidation or contamination. The diameter of the nanowire can be controlled in the electrospinning process, and a suspended Pd nanowire with a minimum diameter of 100 nm is fabricated. Additionally, a suspended single Pd nanowire-based H2 gas sensor fabricated using the proposed process exhibits a highly sensitive response to H2 gas.

Calibration Curve Building and Sensing Characteristics of Low Power Consumption H2 Gas Sensor

Detection and alarm of leakage of hydrogen (H2) gas is an extremely important issue needed to be addressed. In this study, we fabricated and calibation portable devices based on the H2 sensor using SnO2 thin film with Pd nanoscale catalytic as a sensing layer. For practical application of the sensor, we designed and realized PCB circuit boards, microprocessors, data processing, output signals, data storage, power sources and source code. This sensor based portable devices were able to monitor to as low as 25 ppm H2 gas. Power consumption and selectivity of the sensor were also investigated. This study will open another simple and low-cost approach to monitor toxic and flammable gases for environmental monitoring.

A Flexible Indium Oxide Sensor With Anti-Humidity Property for Room Temperature Detection of Hydrogen Sulfide

In this work, flexible hydrogen sulfide (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S) sensors were prepared from nanocomposite mixtures of indium oxide (In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ), graphite flakes (Gt) and polystyrene (PS). Where In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> was chosen as the sensing material. Gt flakes were added to adjust the sensor resistance in the range of 300-400 k Ω. Also, PS were added as a modifier to maintain the sensors integrity, adhesiveness and flexibility properties. A nanocomposite mixture of In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> :10%Gt:17%PS emerged as a promising nanocomposite candidate to develop high performance sensors to detect H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S gas. The flexible sensors were fabricated on top of flexible carbon electrodes that were screen-printed on polyethylene terephthalate (PET) substrate. Herein, we propose a sensitive H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas sensor to detect 100 ppb at room temperature while being resistant to humidity changes. These improvements have been attributed to additional benefits for the Gt flakes and the PS modifier. Both additives contributed to enhance the surface-to-volume ratio for the sensing thin film leading to a superior sensing performance for the In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> based sensor. Furthermore, they improved the hydrophobic property for the sensors to develop their resistance to humidity changes. The sensing mechanism for sensors depends mainly on the sulfuration and/or partial sulfuration of In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> by H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S gas to form In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , which is conductive and responsible to decrease the sensor resistance.

Precise tailoring of multiple nanostructures based on atomic layer assembly via versatile soft-templates

Nanodevices have higher requirements for nanofabrication in tuning the size, shape and spatial arrangement of nanostructures and their assemblies in nanoscale, however, which are often beyond the reach of conventional lithography or self-assembly techniques. In view of the above, we develop atomic layer assembled nanofabrication based on soft-templates to break through the limitations of traditional rigid-templates, having very well scalability and powerful fabrication capability for multiple solid or hollow nanostructures. Versatile soft-templates can be freely patterned at the nanoscale by mature lithographic processes, along which a precisely controlled atomic layer deposition can assemble high-aspect-ratio nanostructures with a flexible tailoring of the size, shape and spatial array, and then a dry etching process removes soft scaffolds and leaves freestanding nanostructures over large-area, rigid or soft substrates. To highlight the potentials of this fabrication strategy, the high-performance optical metasurface and ultra-sensitive H2 gas sensor are demonstrated. This approach endows the conventional lithography and assembly techniques with new powerful functionalities and more scalability in nanofabrication, providing a simply promising route to generating complex multiple nanostructures, towards a broad application in modern nanodevices.

Facile synthesis of mesoporous CdS/PbS/SnO2 composites for high-selectivity H2 gas sensor

• The gas-sensing materials of mesoporous CdS/PbS/SnO 2 were synthesized by an ultra-low-cost and ecofriendly strategy. • The mesoporous CdS/PbS/SnO 2 materials exhibited high specific surface areas, and prominent thermal stability. • The CdS/PbS/SnO 2 gas sensor maintained a swift response/recovery time, reliable reversibility, long-term stability, and high selectivity. • The underlying sensing mechanism of the CdS/PbS/SnO 2 gas sensor towards H 2 gas was illustrated in detail. In this work, novel mesoporous heterostructures composed of CdS, PbS and SnO 2 (CdS/PbS/SnO 2 ) were synthesized via a green and facile treatment. Interestingly, when the CdS/PbS/SnO 2 composites were assembled into sensing layer for the fabrication of H 2 gas sensor for the first time, the sensor based on CdS/PbS/SnO 2 exhibited more prominent gas-sensing properties than those of the CdS/SnO 2 and PbS/SnO 2 sensors. The CdS/PbS/SnO 2 sensor showed a fast response/recovery time of 10.6/36.9 s towards 100 ppm H 2 gas at 200℃, with an ultralow limit of detection of 50 ppb (17.3 %), and the sensor had a largely enhanced response of 1125.2 %, which was approximately 16.8 and 7.4 times higher than those of the CdS/SnO 2 (66.8 %) and PbS/SnO 2 (151.4 %) sensors. In addition, the CdS/PbS/SnO 2 sensor had an outstanding selectivity towards H 2 gas against other gases, reliable reversibility and long-term stability for 40 days. Such enhanced properties was mainly attributed to the large surface-to-volume ratio, which can provide abundant active sites to gas adsorbtion and diffusion in surface redox reaction. Moreover, more numerous heterojunctions of the CdS/PbS/SnO 2 composites may serve as highly conductive channels to accelerate carrier transfer, thus further leading to an improved performance of the sensors. Credibly, our present work will foresee a great potential application for ppb-level H 2 gas monitoring in an extreme environment.

Using Palladium Nanocubes on ZnO Nanostructures in Hydrogen Gas Sensor for Fast Response and Recovery Time.

We developed a novel sensor structure by synthesizing Pd nanocubes (NCs) decorated on ZnO nanostructures (NSs) applied to resistive-type H₂ gas sensor with micro-length in sensing channel. The ZnO NSs were selectively grown between micro-size finger-like interdigital electrodes through microelectromechanical technology. The novel H₂ sensor structure with the sensing channel was reduced to micro-size by this proposed method to obtain a sensor with fast response/recovery time. The as-prepared structure exhibited robust sensing performance with a response of 11% at optimal temperature of 150 °C, good linearity, and fast response/recovery time within 10 s. The speed of chemisorption through the diffusion pathway in Pd NCs combined with micro-length in sensing channel in sensor showed fast response and recovery times of 9 and 15 s, respectively, toward 10,000 ppm (1%) H₂ at 150 °C. The result showed approximate linearity response in H₂ concentration range of 5÷10,000 ppm and a large operating temperature range from room temperature to 200 °C.

Facile Synthesis of Pd-CuO Nanoplates with Enhanced SO2 and H2 Gas-Sensing Characteristics

Facile Synthesis of Pd-CuO Nanoplates with Enhanced SO2 and H2 Gas-Sensing Characteristics

An amperometric H2 gas sensor based on ionic liquid for hydrogen fuel cell ships

Hydrogen fuel cell ship is an important way to realize green shipping, and the safety of hydrogen fuel ship is primary issue that shall be concerned. H2 gas sensors can provide online monitoring of H2 concentration and it is an effective mean to insure safety of hydrogen fuel. In this study, an amperometric electrochemical H2 gas sensor based on room-temperature ionic liquid was developed, which was expected to be applicable to monitoring of H2 concentration in the hydrogen fuel cell ship. A threeelectrode H2 gas sensor was fabricated by using room-temperature ionic liquid N, N, N-trimethyl-Nbutanesulfonic acid ammonium hydrogen sulfate ([TMBSA][HSO4]) as electrolyte and using platinum black as catalyst. The H2 gas sensor not only had the advantages of the conventional aqueous electrolyte sensor, such as high sensitivity, fast response, and the linear relationship between the response current and the concentration of H2, but also overcame the problem that the conventional electrochemical gas sensor cannot be applied to high humidity environment. After storage in high-humidity environment (98% RH) for three weeks, the sensor had stable performances, with current signal drift less than 2.25%. The sensor has a good potential application prospect in ships with high temperature and humidity environment.

Advanced development of metal oxide nanomaterials for H2gas sensing applications

The scheme of the structure of this review includes an introduction from the metal oxide nanomaterials’ synthesis to application in H2gas sensors—a vision from the past to the future.

Low-Temperature Hydrogen Sensor: Enhanced Performance Enabled through Photoactive Pd-Decorated TiO2 Colloidal Crystals.

The high demand for H2 gas sensors is not just limited to industrial process control and leak detection applications but also extends to the food and medical industry to determine the presence of various types of bacteria or underlying medical conditions. For instance, sensing of H2 at low concentrations (<10 ppm) is essential for developing breath analyzers for the noninvasive diagnosis of some gastrointestinal diseases. However, there are major challenges to overcome in order to achieve high sensitivity and hence low limit of detection (LoD) toward H2. In this study, it is demonstrated that light-assisted amperometric gas sensors employing sensitive layers based on Pd-decorated TiO2 long-range ordered crystals can achieve excellent H2 sensing performance. This unique combination of materials and novel layered structure enables the detection of H2 gas down to 50 ppm with highly promising LoD capabilities. The sensor response profiles revealed that the sensor's signal-to-noise ratio was higher in the presence of light when operated with a 9 V bias (relative to other conditions used), producing a LoD of only 3.5 ppm at an operating temperature of 33 °C. The high performance of the sensor makes it attractive for applications that require low-level (ppm as opposed to conventional % levels) H2 gas detection. Most importantly, the developed sensor exhibited high selectivity (>93%) toward H2 over other gas species such as CO2, C4H8O, C3H6O, CH3CHO, and NO, which are commonly found to coexist in the environment.

Hydrogen Sensing of Graphene-based Chemoresistive Gas Sensor Enabled by Surface Decoration

Hydrogen (H2) is considered as a new clean energy resource for replacing petroleum because it produces only H2O after the combustion process. However, owing to its explosive nature, it is extremely important to detect H2 gas in the ambient atmosphere. This has triggered the development of H2 gas sensors. 2-dimensional (2D) graphene has emerged as one of the most promising candidates for chemical sensors in various industries. In particular, graphene exhibits outstanding potential in chemoresistive gas sensors for the detection of diverse harmful gases and the control of indoor air quality. Graphene-based chemoresistive gas sensors have attracted tremendous attention owing to their promising properties such as room temperature operation, effective gas adsorption, and high flexibility and transparency. Pristine graphene exhibits good sensitivity to NO2 gas at room temperature and relatively low sensitivity to H2 gas. Thus, research to control the selectivity of graphene gas sensors and improve the sensitivity to H2 gas has been performed. Noble metal decoration and metal oxide decoration on the surface of graphene are the most favored approaches for effectively controlling the selectivity of graphene gas sensors. Herein, we introduce several strategies that enhance the sensitivity of graphene gas sensors to H2 gas.

Effect of Noble Metals on Hydrogen Sensing Properties of Metal Oxide-based Gas Sensors

As a green and abundant source of energy, H2 has attracted the attention of researchers for use in different applications. Nevertheless, it is highly flammable, and because of its significantly small size, extreme attention is needed to detect its leakage. In this review, we discuss different effects of noble metals on the H2 gas response and performance of metal oxide-based gas sensors. In this regard, we discuss the effects of noble metals, in combination with metal oxides, on H2 gas detection. The catalytic activity towards H2 gas and the formation of heterojunctions with metal oxides are the main contributions of noble metals to the sensing improvement of H2 gas sensors. Furthermore, in the special case of Pd and somewhat Pt, the formation of PdHx and PtHx also affects the H2 sensing performance. This review paper provides useful information for researchers working in the field of H2 gas detection.

Hydrogen Gas Sensor: Significant Role of p-n Heterojunction Based Nanostructures

In the present study we report the design & synthesis of a novel p-n type semiconducting Pd incorporated ZnO: SnO (ZSP) nanocomposite as Hydrogen (H2) gas sensor, which demonstrates an efficient conductivity and superior stability through nanostructured engineering. The structural characteristics were investigated by X-ray diffraction (XRD), Particle Size Analyzer (PSA), X-ray Photoelectron Spectroscopy (XPS) and morphology by High Resolution Transmission electron microscopy (HRTEM). Gas sensing characteristics of ZnO: SnO nanocomposite towards 500 ppm hydrogen gas exhibited Sensitivity of S = 0.6 whereas ZnO: SnO: Pd nanocomposite exhibited higher Sensitivity of S = 0.91 at a lower operating temperature of 150 °C. The achieved features make the sample ZSP a potential candidate for development of highly Sensitive and Selective H2 gas sensor.

Synthesis of ZnO:B thin films Dropped on Porous Silicon for H2 Gas Sensing

Porous Silicon PS has been prepared so as to use it a substrate to dropped ZnO:B thin films with different boron concentrations additions (2- 8) % dropped at 450°C through used the chemical spray pyrolysis (CSP) technique in approximately 150nm thicknesses. Crystallite and Grain size decreases with adding more of boron as a doping for zinc oxide films which dropped on the negative type (n-type) and positive type (p-type) of PS. Surface morphology study for the obtained the ZnO:B thin films and for the n-PS and p-PS was studied by TEM, SEM and AFM. Sensing properties of ZnO:B thin films for H2 gas showed that the increases of boron leads to increases of the thin films sensitivity, measured sensitivity of the n-PS substrate was more than p-PS.

Ultrafast H2 gas nanosensor for ppb-level H2 gas detection based on GaN honeycomb nanonetwork

Material architecture design plays a crucial role in developing gas sensors. GaN has been proposed as a promising material for H2 gas sensor. However, it is subject to long response time and large low limit of detection (LOD).via spherical metal pattern technology, honeycomb can be created in GaN nanostructure but has yet to be explored. Herein, the GaN honeycomb nanonetwork was utilized to fabricate a field effect transistor (FET) type hydrogen (H2) gas nanosensor and its H2 gas sensing performances were systematically investigated. Through the combination of the novel honeycomb nanonetwork with the field effect modulation, we demonstrate high performance H2 gas sensor with wide detection concentration range, fast response, and small LOD. It is worth noting that the response time for H2 gas is very fast, as short as ≤3 s. Most importantly, the LOD for this FET type sensor is as small as ∼ 34 ppb. Density functional theory (DFT) calculation was utilized to study the H2 gas sensing mechanism. Significant reduction of Schottky barrier and improvement of the tunneling probability of the Pt-GaN metal-semiconductor interface were observed. Finally, a model is proposed to explain the H2 gas sensing mechanism.