Highly Selective and Low-Power Carbon Monoxide Gas Sensor Based on the Chain Reaction of Oxygen and Carbon Monoxide to WO3

Enhancing sensitivity, selectivity, and intelligence of gas detection based on field-effect transistors: Principle, process, and materials

A sensor, serving as a transducer, produces a quantifiable output in response to a predetermined input stimulus, which may be of a chemical or physical nature. The field of gas detection has experienced a substantial surge in research activity, attributable to the diverse functionalities and enhanced accessibility of advanced active materials. In this work, recent advances in gas sensors, specifically those utilizing Field Effect Transistors (FETs), are summarized, including device configurations, response characteristics, sensor materials, and application domains. In pursuing high-performance artificial olfactory systems, the evolution of FET gas sensors necessitates their synchronization with material advancements. These materials should have large surface areas to enhance gas adsorption, efficient conversion of gas input to detectable signals, and strong mechanical qualities. The exploration of gas-sensitive materials has covered diverse categories, such as organic semiconductor polymers, conductive organic compounds and polymers, metal oxides, metal-organic frameworks, and low-dimensional materials. The application of gas sensing technology holds significant promise in domains such as industrial safety, environmental monitoring, and medical diagnostics. This comprehensive review thoroughly examines recent progress, identifies prevailing technical challenges, and outlines prospects for gas detection technology utilizing field effect transistors. The primary aim is to provide a valuable reference for driving the development of the next generation of gas-sensitive monitoring and detection systems characterized by improved sensitivity, selectivity, and intelligence.

Mesoporous Boron Subphosphide: Intrinsic Electron Deficiency Enabling Selective Low-ppm of Chemiresistive CO Detection in Harsh Environments

Carbon monoxide (CO) is infamous for its hazardous effects, mainly because it displaces oxygen in the bloodstream. Its danger is amplified by its odorless and colorless nature, making it difficult to detect. Exposure to even low concentrations of CO (≤50 ppm) is considered harmful to human health. Common sources of CO, such as fossil fuel-powered vehicles and machinery, primarily operate under harsh high-temperature conditions. Currently, available low-ppm of CO sensors struggle in these environments typical of CO emitters, highlighting the urgent need for advanced sensors capable of reliable operation in such conditions. In this study, nanocrystalline mesoporous icosahedral boron subphosphide is synthesized via a solid-state technique and evaluated for its CO sensing capabilities. The material exhibits selective detection of low ppm of CO at temperatures exceeding 500 °C, demonstrating a significant sensing response of ∼4 toward 50 ppm of CO at 600 °C. Electronic and structural analyses attribute boron subphosphide's chemiresistive behavior to its electron-deficient nature, which is crucial for effective CO interaction. Additionally, the sensitivity of boron subphosphide to CO can be modulated under external magnetic fields, underscoring its potential for adaptable sensing applications. This work introduces boron subphosphide as a promising candidate for CO sensing in harsh conditions and provides fundamental insights into its sensing mechanism driven by intrinsic electron deficiency. The findings offer a pathway for the development of advanced sensors capable of reliably detecting low concentrations of CO in harsh environments where precise monitoring is critical to public health and safety.

Machine learning-motivated trace triethylamine identification by bismuth vanadate/tungsten oxide heterostructures

Triethylamine, an extensively used material in industrial organic synthesis, is hazardous to the human respiratory and nervous systems, but its accurate detection and prediction has been a long-standing challenge. Herein, a machine learning-motivated chemiresistive sensor that can predict ppm-level triethylamine is designed. The zero-dimensional (0D) bismuth vanadate (BiVO4) nanoparticles were anchored on the surface of three-dimensional (3D) tungsten oxide (WO3) architectures to form hierarchical BiVO4/WO3 heterostructures, which demonstrates remarkable triethylamine-sensing performance such as high response of 21 (4 times higher than pristine WO3) at optimal temperature of 190 °C, low detection limit of 57 ppb, long-term stability, reproducibility and good anti-interference property. Furthermore, an intelligent framework with good visibility was developed to identify ppm-level triethylamine and predict its definite concentration. Using feature parameters extracted from the sensor responses, the machine learning-based classifier provides a decision boundary with 92.3 % accuracy, and the prediction of unknown gas concentration was successfully achieved by linear regression model after training a series of as-known concentrations. This work not only provides a fundamental understanding of BiVO4-based heterostructures in gas sensors but also offers an intelligent strategy to identify and predict trace triethylamine under an interfering atmosphere.

Selective sensing of NH3 and NO2 on WSe2 monolayers based on defect concentration regulation

Defect engineering is an important method to control material properties. In this paper, large-scale sampling density functional theory (DFT) was used to investigate the adsorption and sensing behavior of NH3 and NO2 on a WSe2 monolayer, with a focus on the effect of selenium vacancy concentration. The results demonstrate that selectivity is inhibited on a perfect monolayer due to the similar adsorption energy of the two gases, NH3 and NO2, while selectivity can be obtained for both of them under different selenium vacancy concentrations (NH3 about 2-5.6%, NO2 about >8.3%). It is believed that the good match between the unique surface structure of the double-color (double-charged) wave wheel disk-like structure of the WSe2 monolayer and the molecular structure of both of the two representative molecules, NH3 and NO2, contributes dominantly to the unusual performance. The results demonstrate that one kind of material-WSe2 monolayer-can perform selective sensing of both NH3 and NO2, respectively, using only defect adjustment. It is particularly important to acquire the selectivity to NH3 in the mixture of NO2 and NH3. It also provides opportunities for understanding materials and patterned catalyst design.

Oxygen Vacancy Enabled Electronic Structure Engineering of Pt-WO3 Nanosheets toward Highly Efficient BTEX Sensing

A Pt nanoparticle-immobilized WO3 material is a promising candidate for catalytic reactions, and the surface and electronic structure can strongly affect the performance. However, the effect of the intrinsic oxygen vacancy of WO3 on the d-band structure of Pt and the synergistic effect of Pt and the WO3 matrix on reaction performance are still ambiguous, which greatly hinders the design of advanced materials. Herein, Pt-decorated WO3 nanosheets with different electronic metal-support interactions are successfully prepared by finely tuning the oxygen vacancy structure of WO3 nanosheets. Notably, Pt-modified WO3 nanosheets annealed at 400 °C exhibit excellent benzene series (BTEX) sensing performance (S = 377.33, 365.21, 348.45, and 319.23 for 50 ppm ethylbenzene, benzene, toluene, and xylene, respectively, at 140 °C), fast response and recovery dynamics (10/7 s), excellent reliability (σ = 0.14), and sensing stability (φ = 0.08%). Detailed structural characterization and DFT results reveal that interfacial Ptδ+-Ov-W5+ sites are recognized as the active sites, and the oxygen vacancies of the WO3 matrix can significantly affect the d-band structure of Pt nanoparticles. Notably, Pt/WO3-400 with improved surface oxygen mobility and medium electronic metal-support interaction facilitates the activation and desorption of BTEX, which contributes to the highly efficient BTEX sensing performance. Our work provides a new insight for the design of high-performance surface reaction materials for advanced applications.

Fast-Response and Low-Power Self-Heating Gas Sensor Using Metal/Metal Oxide/Metal (MMOM) Structured Nanowires

With the escalating global awareness of air quality management, the need for continuous and reliable monitoring of toxic gases by using low-power operating systems has become increasingly important. One of which, semiconductor metal oxide gas sensors have received great attention due to their high/fast response and simple working mechanism. More specifically, self-heating metal oxide gas sensors, wherein direct thermal activation in the sensing material, have been sought for their low power-consuming characteristics. However, previous works have neglected to address the temperature distribution within the sensing material, resulting in inefficient gas response and prolonged response/recovery times, particularly due to the low-temperature regions. Here, we present a unique metal/metal oxide/metal (MMOM) nanowire architecture that conductively confines heat to the sensing material, achieving high uniformity in the temperature distribution. The proposed structure enables uniform thermal activation within the sensing material, allowing the sensor to efficiently react with the toxic gas. As a result, the proposed MMOM gas sensor showed significantly enhanced gas response (from 6.7 to 20.1% at 30 ppm), response time (from 195 to 17 s at 30 ppm), and limit of detection (∼1 ppm) when compared to those of conventional single-material structures upon exposure to carbon monoxide. Furthermore, the proposed work demonstrated low power consumption (2.36 mW) and high thermal durability (1500 on/off cycles), demonstrating its potential for practical applications in reliable and low-power operating gas sensor systems. These results propose a new paradigm for power-efficient and robust self-heating metal oxide gas sensors with potential implications for other fields requiring thermal engineering.

Bismuth ferrite based acetone gas sensor: evaluation of graphene oxide loading

We report a BiFeO3/graphene oxide (BFO/GO) perovskite, synthesized using a CTAB-functionalized glycine combustion route, as a potential material for acetone gas sensing applications. The physicochemical properties of the developed perovskite were analysed using XRD, FE-SEM, TEM, HRTEM, EDAX and XPS. The gas sensing performance was analysed for various test gases, including ethanol, acetone, propanol, ammonia, nitric acid, hydrogen sulphide and trimethylamine at a concentration of 500 ppm. Among the test gases, the developed BFO showed the best selectivity towards acetone, with a response of 61% at an operating temperature of 250 °C. All the GO-loaded BFO samples showed an improved gas sensing performance compared with pristine BFO in terms of sensitivity, the response/recovery times, the transient response curves and the stability. The 1 wt% GO-loaded BiFeO3 sensor showed the highest sensitivity of 89% towards acetone (500 ppm) at an operating temperature of 250 °C. These results show that the developed perovskites have significant potential for use in acetone gas sensing applications.

Ultrathin Serpentine Insulation Layer Architecture for Ultralow Power Gas Sensor

Toxic gases have surreptitiously influenced the health and environment of contemporary society with their odorless/colorless characteristics. As a result, a pressing need for reliable and portable gas-sensing devices has continuously increased. However, with their negligence to efficiently microstructure their bulky supportive layer on which the sensing and heating materials are located, previous semiconductor metal-oxide gas sensors have been unable to fully enhance their power efficiency, a critical factor in power-stringent portable devices. Herein, an ultrathin insulation layer with a unique serpentine architecture is proposed for the development of a power-efficient gas sensor, consuming only 2.3 mW with an operating temperature of 300 °C (≈6% of the leading commercial product). Utilizing a mechanically robust serpentine design, this work presents a fully suspended standalone device with a supportive layer thickness of only ≈50 nm. The developed gas sensor shows excellent mechanical durability, operating over 10 000 on/off cycles and ≈2 years of life expectancy under continuous operation. The gas sensor detected carbon monoxide concentrations from 30 to 1 ppm with an average response time of ≈15 s and distinguishable sensitivity to 1 ppm (ΔR/R0 = 5%). The mass-producible fabrication and heating efficiency presented here provide an exemplary platform for diverse power-efficient-related devices.

Reconfigurable Manipulation of Oxygen Content on Metal Oxide Surfaces and Applications to Gas Sensing

Oxygen vacancies and adsorbed oxygen species on metal oxide surfaces play important roles in various fields. However, existing methods for manipulating surface oxygen require severe settings and are ineffective for repetitive manipulation. We present a method to manipulate the amount of surface oxygen by modifying the oxygen adsorption energy by electrically controlling the electron concentration of the metal oxide. The surface oxygen control ability of the method is verified using first-principles calculations based on density functional theory (DFT), X-ray photoelectron spectroscopy (XPS), and electrical resistance analysis. The presented method is implemented by fabricating oxide thin film transistors with embedded microheaters. The method can reconfigure the oxygen vacancies on the In2O3, SnO2, and IGZO surfaces so that specific chemisorption dominates. The method can selectively increase oxidizing (e.g., NO and NO) and reducing gas (e.g., H2S, NH3, and CO) reactions by electrically controlling the metal oxide surface to be oxygen vacancy-rich or adsorbed oxygen species-rich. The proposed method is applied to gas sensors and overcomes their existing limitations. The method makes the sensor insensitive to one gas (e.g., H2S) in mixed-gas environments (e.g., NO2+H2S) and provides a linear response (R2 = 0.998) to the target gas (e.g., NO2) concentration within 3 s. We believe that the proposed method is applicable to applications utilizing metal oxide surfaces.

Transducer-Aware Hydroxy-Rich-Surface Indium Oxide Gas Sensor for Low-Power and High-Sensitivity NO2 Gas Sensing

Low-power metal oxide (MOX)-based gas sensors are widely applied in edge devices. To reduce power consumption, nanostructured MOX-based sensors that detect gas at low temperatures have been reported. However, the fabrication process of these sensors is difficult for mass production, and these sensors are lack uniformity and reliability. On the other hand, MOX film-based gas sensors have been commercialized but operate at high temperatures and exhibit low sensitivity. Herein, commercially advantageous highly sensitive, film-based indium oxide sensors operating at low temperatures are reported. Ar and O₂ gases are simultaneously injected during the sputtering process to form a hydroxy-rich-surface In₂O₃ film. Conventional indium oxide (In₂O₃) films (A0) and hydroxy-rich indium oxide films (A1) are compared using several analytical techniques. A1 exhibits a work function of 4.92 eV, larger than that of A0 (4.42 eV). A1 exhibits a Debye length 3.7 times longer than that of A0. A1 is advantageous for gas sensing when using field effect transistors (FETs) and resistors as transducers. Because of the hydroxy groups present on the surface of A1, A1 can react with NO₂ gas at a lower temperature (∼100 °C) than A0 (180 °C). Operando diffuse reflectance infrared Fourier transform spectrometry (DRIFTS) shows that NO₂ gas is adsorbed to A1 as nitrite (NO₂^-) at 100 °C and nitrite and nitrate (NO₃^-) at 200 °C. After NO₂ is adsorbed as nitrate, the sensitivity of the A1 sensor decreases and its low-temperature operability is compromised. On the other hand, when NO₂ is adsorbed only as nitrite, the performance of the sensor is maintained. The reliable hydroxy-rich FET-type gas sensor shows the best performance compared to that of the existing film-based NO₂ gas sensors, with a 2460% response to 500 ppb NO₂ gas at a power consumption of 1.03 mW.