Gas-sensing Characteristics Research Articles

Methods and Tools for Evaluating the Characteristics of MIS-Capacitor Gas Sensors

Methods and Tools for Evaluating the Characteristics of MIS-Capacitor Gas Sensors

P-Doped h-BN Monolayer: A High-Sensitivity SF6 Decomposition Gases Sensor

SF6 decomposition gas monitoring is of great significance to gas-insulated switchgear (GIS) fault detection and early warning and even the safe and stable operation of the power system. As a gas sensing material, the h-BN monolayer shows good application potential in sensing technology. Therefore, this study calculated and analyzed the gas-sensing response characteristics of P-BN monolayers to SF6 decomposition gases (SO2F2 and SOF2) based on the first-principles density functional theory, such as total density of state and sensitivity. In order to prove the selectivity of the P-BN monolayer for SO2 F2 and SOF2 gas molecules, the gas-sensitive adsorption parameters of the P-BN monolayer for H2O and CO2 gas molecules were calculated. The results show that the adsorption of SO2 F2 and SOF2 gas molecules on the P-BN monolayer is relatively strong, which is in the critical state of physical adsorption and chemical adsorption. The adsorption of H2 O and CO2 molecules is relatively weak. P-BN monolayer showed good selectivity and high sensitivity for SO2 F2 and SOF2 gas molecules. This study provides a theoretical basis for the application of P-BN monolayer in the field of SF6 decomposition gas monitoring and provides a novel way and idea for the development of other gas sensors.

Spray-Deposited Rare Earth Metal Ion (Sm3+, Ce3+, Pr3+, La3+)-Doped CdO Thin Films for Enhanced Formaldehyde Gas Sensing Characteristics.

This study shows the electrical conductivity-dependent gas sensing characteristics of spray-deposited rare earth (RE) metal ion (Sm3+, Ce3+, Pr3+, La3+)-doped cadmium oxide (CdO) thin films on soda-lime microscope glass substrates at 300 °C. We examined the deposited films’ structural, surface microstructural, DC electrical, and gas sensing features. The X-ray diffraction study indicates that all samples were polycrystalline, with the favored growth direction shifting from the (111) plane to the (200) plane. The highest root-mean-square values were obtained for the Pr-doped CdO thin film (5.86 nm). The surface microstructure of CdO thin films was significantly influenced by the RE metal ion dopant, with typical grain size values ranging from 64 nm to 134 nm depending on the dopant. The carrier concentration and resistivity of CdO films vary based on the RE metal ions used as dopants. Low resistivity (3.01 × 10–4 Ω.cm) was achieved for the CdO thin film doped with La. High gas sensitivity (71.42%) was achieved for CdO thin films doped with La. The donor dopant regulated the electrical conductivity and gas sensing capabilities of CdO thin films.

Selective acetone gas sensing of Cu2(OH)3F/CuO enhanced by hydroxy bonds and fluorine substitution

Acetone gas in human breath could be examined in terms of biomarker applications for diagnosis of diabetes and detection of body fat decomposition. In this work, Cu2(OH)3F is hydrothermally synthesized and then pre-annealed in the interest of low ppm acetone gas-sensing. Cu2(OH)3F/CuO hierarchical structures were built after pre-annealing, and 250°C-annealed samples show the highest response of 23.6 toward 10 ppm acetone gas and 2.1 toward 400 ppb at operating temperature 200 ℃. Upon characterization for Cu2(OH)3F/CuO material properties, 250 ℃-annealed nanobranches show fluent hydroxy bonds, fluorine ion substitutions, and wide bandgap which could enhance the gas-sensing characteristics. The pre-annealing of Cu2(OH)3F between 200 ℃ and 350 ℃ was thoroughly characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR), elemental analysis (EA) and thermal gravitational analysis (TGA) to analyze mechanism of the acetone gas-sensing behaviors.

Surface-modified Ti-MOF/TiO2 membrane and its gas-sensing characteristics

A titanium metal–organic framework/titanium dioxide (Ti-MOF/TiO2) composed membrane was fabricated by light inductive growth of Ti-MOF ([Ti2-(TpA)2-NDI] n ; TpA = terephthalic acid, NDI = 1,8,4,5-naphthalene-tetracarboxdiimide) on a titanium dioxide film composite optical waveguide (COWG) substrate. The Ti-MOF/TiO2 membrane conforms to a mesoporous structure with a 24 nm pore size and a 108 nm thickness through continuous growth for 40 min under 340 nm ultraviolet light illumination. Under ambient conditions, in terms of COWG sensors, Ti-MOF/TiO2 exhibited the greatest response to ethylenediamine (EDA), followed by nitrogen dioxide (NO2), methylamine and trimethylamine, when exposed to 15 types of benzenes, amines and acidic gases. To improve response selectivity, the Ti-MOF/TiO2 film was modified with 1,3,3-trimethylindolinonaphthospirooxazine (SP), forming an SP@Ti-MOF/TiO2 COWG. This modified COWG showed improved selectivity response by showing robust response to EDA and a negligible response to others. When an EDA gas molecule was adsorbed on the surface of the membrane, charge transfer between them preferentially occurred, leading to a change in the optical parameter. The surface-modified SP@Ti-MOF/TiO2 COWG showed a fast (3 s) and reversible response with a wide detection range (0.1–1000 parts per billion) to EDA gas without the interference of benzene, toluene, xylene, styrene and chlorobenzene; acidic gases; and other amines.

Gas sensing performance of carbon monoxide sensor based on rod-shaped tin diselenide/MOFs derived zinc oxide polyhedron at room temperature

This paper introduces a high-efficiency CO gas sensor based on ZnO/SnSe2 composite film. The rod-shaped SnSe2 and polyhedral ZnO composite nanostructures were prepared by template sacrificial method and solvothermal method. The developed composite material was characterized by scanning X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and I-V testing methods, and its microstructure and composition were explored. Through comparative experiments, it was found that the response of ZnO/SnSe2 was the highest when the loading rate of SnSe2 is 25%, which was superior to pure ZnO and SnSe2 sensors. The ZnO/SnSe2 composite sensor showed excellent selectivity and good dynamic characteristics to CO at room temperature (RT). To further improve the performance of the prepared CO sensor, we studied the effect of ultraviolet (UV) light on the sensor, and the research concluded that UV light can improve the gas-sensing characteristics of the sensors. The possible CO sensing mechanism is related to the heterostructure between n-type SnSe2 and n-type ZnO nanomaterials and the photoelectrons excited by UV light.

Metal Oxide Semiconductor Sensors for Triethylamine Detection: Sensing Performance and Improvements

Triethylamine (TEA) is an organic compound that is commonly used in industries, but its volatile, inflammable, corrosive, and toxic nature leads to explosions and tissue damage. A sensitive, accurate, and in situ monitoring of TEA is of great significance to production safety and human health. Metal oxide semiconductors (MOSs) are widely used as gas sensors for volatile organic compounds due to their high bandgap and unique microstructure. This review aims to provide insights into the further development of MOSs by generalizing existing MOSs for TEA detection and measures to improve their sensing performance. This review starts by proposing the basic gas-sensing characteristics of the sensor and two typical TEA sensing mechanisms. Then, recent developments to improve the sensing performance of TEA sensors are summarized from different aspects, such as the optimization of material morphology, the incorporation of other materials (metal elements, conducting polymers, etc.), the development of new materials (graphene, TMDs, etc.), the application of advanced fabrication devices, and the introduction of external stimulation. Finally, this review concludes with prospects for using the aforementioned methods in the fabrication of high-performance TEA gas sensors, as well as highlighting the significance and research challenges in this emerging field.

Recent Progress in Gas Sensor Based on Nanomaterials.

Nanomaterials-based gas sensors have great potential for substance detection. This paper first outlines the research of gas sensors composed of various dimensional nanomaterials. Secondly, nanomaterials may become the development direction of a new generation of gas sensors due to their high sensing efficiency, good detection capability and high sensitivity. Through their excellent characteristics, gas sensors also show high responsiveness and sensing ability, which also plays an increasingly important role in the field of electronic skin. We also reviewed the physical sensors formed from nanomaterials in terms of the methods used, the characteristics of each type of sensor, and the advantages and contributions of each study. According to the different kinds of signals they sense, we especially reviewed research on gas sensors composed of different nanomaterials. We also reviewed the different mechanisms, research processes, and advantages of the different ways of constituting gas sensors after sensing signals. According to the techniques used in each study, we reviewed the differences and advantages between traditional and modern methods in detail. We compared and analyzed the main characteristics of gas sensors with various dimensions of nanomaterials. Finally, we summarized and proposed the development direction of gas sensors based on various dimensions of nanomaterials.

NO2 sensing with CdS nanowires at room temperature under green light illumination

Detection of ppb-level NO2 gas under atmosphere is urgent to meet the requirements of the rapidly developing internet of things. Compared with traditional sensing methods, light illumination has been considered as a key approach for excellent gas sensor performance under moderate conditions. Herein, we developed a green-light-assisted gas sensor based on cadmium sulfide nanowires (CdS NWs) that has good NO2 sensing capability at ambient temperature. The response values of NO2 are 236% and 11% to 10 ppm and 12.5 ppb, respectively. Furthermore, the CdS NWs sensor has a high selectivity for NO2 over a variety of interference gases, as well as good stability. The cleaning light activation and the sulfur vacancy-trapped charge behavior of CdS NWs are observed, which suggest a light-assisted sensing mechanism. These results suggest that light-induced charge separation behavior might significantly improve gas-sensing characteristics.

Analysis of the Response Characteristics of Toluene Gas Sensors with a ZnO Nanorod Structure by a Heat Treatment Process.

The sensing characteristics of toluene gas are monitored by fabricating ZnO nanorod structures. ZnO nanostructured sensor materials are produced on a Zn film via an ultrasonic process in a 0.01 M aqueous solution of C6H12N4 and Zn(NO3)2∙6H2O. The response of the sensors subjected to heat treatment in oxygen and nitrogen atmospheres is improved by 20% and 10%, respectively. The improvement is considered to be correlated with the increase in grain size. The relationship between the heat treatment and sensing characteristics is evaluated.

Fabrication of a Flexible, Wireless Micro-Heater on Elastomer for Wearable Gas Sensor Applications.

Thin-film microdevices can be applied to various wearable devices due to their high flexibility compared to conventional bulk-type electronic devices. Among the various microdevice types, many IoT-based sensor devices have been developed recently. In the case of such sensor elements, it is important to control the surrounding environment to optimize the sensing characteristics. Among these environmental factors, temperature often has a great influence. There are cases where temperature significantly affects the sensor characteristics, as is the case for gas sensors. For this purpose, the development of thin-film-type micro-heaters is important. For this study, a wirelessly driven thin-film micro-heater was fabricated on the flexible and stretchable elastomer, a polydimethylsiloxane (PDMS); the antenna was optimized; and the heater was driven at the temperature up to 102 degrees Celsius. The effect of its use on gas-sensing characteristics was compared through the application of the proposed micro-heater to a gas sensor. The heated SnO2 nanowire gas sensor improved the performance of detecting carbon monoxide (CO) by more than 20%, and the recovery time was reduced to less than half. It is expected that thin-film-type micro-heaters that can be operated wirelessly are suitable for application in various wearable devices, including those for smart sensors and health monitoring.

The Structure, Magnetic, and Gas Sensing Characteristics of W-Substituted Co-Ferrite Nanoparticles

Ferrites have been broadly investigated as gas sensors. The present article reports on the synthesis of Co-ferrite doped with W ions and their gas sensing abilities. A series of single phase CoFe2O4 powder with different W-doping (0.0 ≤ x ≤ 0.15) was synthesized using sol-gel synthesis. A variation in the saturation magnetization (Ms) and the lattice dimension with W(VI) substitution was associated with a change in the distribution of Fe(III) ions between tetrahedral and octahedral sites. Introducing W(VI) ions into the spinel lattice induced the rearrangement of Fe(III) ions. The total Ms increased with W-doping up to x = 0.05 (Ms = 50.1 Am2/kg) and it dramatically decreased to 34.6 Am2/kg with x = 0.15 of doping. However, the lattice parameter increased with increasing doping levels. Different W-doped CoFe2O4 were examined for a gas sensing response in the temperature range of 200–450 °C. Comparing the sensor responses to various reducing gases, the material’s response was shown to be sensitive and selective for acetone. The addition of W (0.15%) had a significant impact on the response and on the operating temperature of the sensor material, indicating that it might be used as an acetone sensor.

Chemoresistive Sensor Readout Circuit Design for Detecting Gases with Slow Response Time Characteristics.

Based on an analysis of the signal characteristics of gas sensors, this work presents a chemoresistive sensor readout circuit design for detecting gases with slow response time characteristics. The proposed readout circuit directly generates a reference voltage corresponding to the initial value of the gas sensor and extracts only the amount of gas concentration change in the sensor. Because the proposed readout circuit can adaptively regenerate the suitable reference voltage under various changing ambient conditions, it can alleviate the variation in output values at the same gas concentration caused by non-uniformities among gas sensors. Furthermore, this readout circuit effectively eliminates the initial value shifts due to the poor reproducibility of the gas sensor itself without requiring complex digital signal calibrations. This work focuses on a commercially viable readout circuit structure that can effectively obtain slow response gas information without requiring a large capacitor. The proposed readout circuit operation was verified by simulations using spectre in cadence simulation software. It was then implemented on a printed circuit board with discrete components to confirm the effectiveness with existing gas sensor systems and its commercial viability.

Response characteristics of CO2 gas sensors using KSmSi2O6 as electrolyte and Li2CO3/K2CO3 as sensing electrode

Response characteristics of CO2 gas sensors using KSmSi2O6 as electrolyte and Li2CO3/K2CO3 as sensing electrode

Improvement of No2 Gas Sensing Characteristics of Graphene-Sno2 Hybrid Nanocomposites by Proton Irradiation: Experimental and Dft Studies

Improvement of No2 Gas Sensing Characteristics of Graphene-Sno2 Hybrid Nanocomposites by Proton Irradiation: Experimental and Dft Studies

Growth mechanism and gas-sensing characteristics of organic-additive-free zinc oxide of various shapes

Zinc oxide is widely used in gas sensors, solar cells, and photocatalysts because of its wide bandgap and exciton binding energy of 60 meV in various metal oxides. To use ZnO as a gas sensor, it is necessary to synthesize it with surface defects and a large specific surface area. In this study, hydrothermal synthesis without surfactants was employed to obtain organic-additive-free ZnO. For morphology control, we varied the ratio of the hydroxide ion concentration to the zinc ion concentration. To confirm the growth mechanism of ZnO, we performed X-ray diffraction, scanning electron microscopy, and transmission electron microscopy analyses. Raman spectroscopy and photoluminescence measurements were performed to analyze the surface properties. The Brunauer–Emmett–Teller method and probe stations were used to measure the specific surface area and sensitivity of the gas sensor, respectively. The results confirmed that flower-shaped ZnO is the most suitable gas-sensing material.

State-of-the-Art Research on Chemiresistive Gas Sensors in Korea: Emphasis on the Achievements of the Research Labs of Professors Hyoun Woo Kim and Sang Sub Kim.

This review presents the results of cutting-edge research on chemiresistive gas sensors in Korea with a focus on the research activities of the laboratories of Professors Sang Sub Kim and Hyoun Woo Kim. The advances in the synthesis techniques and various strategies to enhance the gas-sensing performances of metal-oxide-, sulfide-, and polymer-based nanomaterials are described. In particular, the gas-sensing characteristics of different types of sensors reported in recent years, including core–shell, self-heated, irradiated, flexible, Si-based, glass, and metal–organic framework sensors, have been reviewed. The most crucial achievements include the optimization of shell thickness in core–shell gas sensors, decrease in applied voltage in self-heated gas sensors to less than 5 V, optimization of irradiation dose to achieve the highest response to gases, and the design of selective and highly flexible gas sensors-based WS2 nanosheets. The underlying sensing mechanisms are discussed in detail. In summary, this review provides an overview of the chemiresistive gas-sensing research activities led by the corresponding authors of this manuscript.

Polymer-Templated Durable and Hydrophobic Nanostructures for Hydrogen Gas Sensing Applications.

A simple and hands-on one-step process has been implemented to fabricate polymer-templated hydrophobic nanostructures as hydrogen gas sensing platforms. Topographic measurements have confirmed irregular hills and dips of various dimensions that are responsible for creating air bubble pockets that satisfy the Cassie–Baxter state of hydrophobicity. High-resolution field-emission scanning electron microscopy (FESEM) has revealed double-layer structures consisting of fine microscopic flower-like structures of nanoscale petals on the top of base nanostructures. Wetting contact angle (WCA) measurements further revealed the contact angle to be ~142.0° ± 10.0°. Such hydrophobic nanostructures were expected to provide a platform for gas-sensing materials of a higher surface area. From this direction, a very thin layer of palladium, ca. 100 nm of thickness, was sputtered. Thereafter, further topographic and WCA measurements were carried out. FESEM micrographs revealed that microscopic flower-like structures of nanoscale petals remained intact. A sessile drop test reconfirmed a WCA of as high as ~130.0° ± 10.0°. Due to the inherent features of hydrophobic nanostructures, a wider surface area was expected that can be useful for higher target gas adsorption sites. In this context, a customized sensing facility was set up, and H2 gas sensing performance was carried out. The surface nanostructures were found to be very stable and durable over the course of a year and beyond. A polymer-based hydrophobic gas-sensing platform as investigated in this study will play a dual role in hydrophobicity as well as superior gas-sensing characteristics.

Preparation of YVO4 octahedral nanomaterials and gas-sensing characteristics to triethylamine

Pure YVO4 octahedral nanomaterials were obtained by hydrothermal method and acidification treatment. Through the characterization, the XRD results showed that the prepared sample was high purity YVO4 with a tetragonal structure. Moreover, the prepared YVO4 was octahedral nanomaterials with rough surfaces, which was observed by SEM and TEM. XPS analysis showed that the prepared YVO4 material had surface adsorption oxygen. In addition, the novel gas sensor based on n-type polycrystalline YVO4 octahedral nanomaterials with rough surfaces had a low operating temperature of 200 ℃ for triethylamine, as well as appropriate selectivity and response/recovery time, good stability and repeatability. Therefore, octahedral YVO4 may be a promising gas sensitive material.

Selective CO gas sensing by Au-decorated WS2-SnO2 core-shell nanosheets on flexible substrates in self-heating mode

The effect of shell thickness and noble metal decoration on the gas-sensing characteristics of two-dimensional (2D) materials has not been reported yet. Herein, we synthesized 2D pristine and Au-decorated WS2-SnO2 core-shell nanosheets (Au NSs). SnO2 shells with various thicknesses (up to 60 nm) were deposited on the WS2 NSs. Subsequently, Au was deposited on the synthesized WS2-SnO2 core-shell NSs (WS2-SnO2 NSs) under UV irradiation. Flexible polyamide substrates were used to fabricate gas sensors, which operated in self-heating mode upon applying different voltages for CO detection. Bare and Au-decorated gas sensors with shell thicknesses of 15 and 30 nm revealed the highest CO sensing performance at a low voltage of 3.4 V. The flexibility of the gas sensors was demonstrated by the negligible degradation of the sensing performance after 10,000 bending cycles. We also evaluated the sensing characteristics under humid conditions. The developed gas sensors with very low applied voltage and high performance for CO gas sensing are very promising for commercial applications.