Resistive Gas Sensors Research Articles

Алгоритм комп'ютерної обробки кінетичних залежностей відгуку газового сенсора з інтелектуальними компонентами

The purpose of the work is to develop an algorithm using intelligent components that will allow processing of experimental data of response kinetics of resistive gas sensors based on the algorithm of the model of the stretched exponential function of Kohlrausch-Williams-Watts, without operator intervention. The problems of implementing full automation of the information-measuring system for the study of the main characteristics of gas-sensitive sensors - the selection of the most informative time interval - are describe. The algorithm for processing the experimental kinetic dependence of the response of gas sensors based on the model of a stretched exponential function with intelligent components that allow choosing the most informative time interval from the processed kinetic dependences is present.

Ru-Doped MoS2 Monolayer for Exhaled Breath Detection on Early Lung Cancer Diagnosis: A First-Principles Investigation.

Nanosensor-based patient exhaled breath detection is a practical and effective way to detect lung cancer early. In this paper, a Ru-doped MoS2 monolayer (Ru-MoS2) is proposed as a promising novel biosensor based on first-principles theory for the detection of three typical early stage lung cancer exhaled volatile organic compounds, namely, C3H4O, C3H6O, and C5H8. Replacement of a S atom in the MoS2 monolayer with a Ru dopant atom to form a stable Ru-MoS2 monolayer with a binding energy of -4.78 eV is further demonstrated by the thermostability and chemical stability analysis as well as improving the adsorption performance of the system for three VOCs. The adsorption configuration structures, adsorption properties, and electronic behavior of the Ru-MoS2 monolayer are investigated by electron deformation density and density of states analysis to gain a comprehensive understanding of the physicochemical properties as sensing material. The results show that the adsorption energies of the Ru-MoS2 monolayer for C3H4O, C3H6O, and C5H8 are 3.42, -1.53, and -2.80 eV, respectively, all of which are chemisorption with excellent adsorption performance. The sensitivities for the three VOCs could be up to 1.09, 140.50, and 5.90, respectively, and the band structure and work function further elucidate the sensing mechanism of the Ru-MoS2 monolayer as a resistive gas sensor. The type and concentration of these exhaled breaths may reflect changes in the patient's physiological and biochemical status and may serve as a probe for the diagnosis of lung cancer. The results in this work could provide a guidance for researchers to explore the practical applications in the early diagnosis of lung cancer by gas sensors.

Recent developments and challenges in resistance-based hydrogen gas sensors based on metal oxide semiconductors.

In recentyears, the energy crisis has made the world realize the importance and need for green energy. Hydrogen safety has always been a primary issue that needs to be addressed for the application and large-scale commercialization of hydrogen energy, and precise and rapid hydrogen gas sensing technology and equipment are important prerequisites for ensuring hydrogen safety. Based on metal oxide semiconductors (MOS), resistive hydrogen gas sensors (HGS) offer advantages, such as low cost, low power consumption, and high sensitivity. They are also easy to test, integrate, and suitable for detecting low concentrations of hydrogen gas in ambient air. Therefore, they are considered one of the most promising HGS. This article provides a comprehensive review of the surface reaction mechanisms and recent research progress in optimizing the gas sensing performance of MOS-based resistive hydrogen gas sensors (MOS-R-HGS). Particularly, the advancements in metal-assisted or doped MOS, mixed metal oxide (MO)-MOS composites, MOS-carbon composites, and metal-organic framework-derived (MOF)-MOS composites are extensively summarized. Finally, the future research directions and possibilities in this field are discussed.

Molten salt-modified Ti3C2Tx MXene with tunable oxygen-functionalized surfaces for effective detection of NO2 at room temperature

The abundant tunable functional groups and room-temperature sensing properties of MXenes have garnered increasing interest in the field of gas sensing. However, the majority of research has exclusively focused on the combined impact of external substances with MXenes functional groups, with limited exploration into the modulation of MXenes’ intrinsic functional groups. In this work, we successfully produced molten salt-modified Ti3C2Tx MXene (M-Ti3C2Tx) with tunable oxygen-functionalized surfaces using the molten salt immersion method and employed it as a chemical resistive gas sensor to detect NO2 at room temperature (RT). Using diverse analytical techniques, we propose the O−addition effect on the surface titanium atoms and the O−substitution effect on the edge carbon atoms, refining the existence form of –O functional groups as well as realizing the effective regulation of the intrinsic functional groups. With a high response (∼25.87%−100 ppm NO2, whose response value is five times higher than that of pristine Ti3C2Tx), relatively rapid response speed (∼99 s−25 ppm NO2), high sensitivity (∼0.29 ppm−1), low detection limits (theoretical LoD is 3.3 ppm), good selectivity and long-term stability (maintain stable within 28 days) at RT, the sensor based on M-Ti3C2Tx demonstrates excellent NO2 sensing performance. To understand the sensing mechanism, density functional theory (DFT) calculations were conducted to explore adsorption behaviors. Theoretical analysis validates that M-Ti3C2Tx has a stronger adsorption capacity for NO2 (Ead = −1.149 eV) owing to the formation of covalent bond between the –O functional group and the nitrogen atom of NO2. The application of the molten salt can effectively modulate the intrinsic functional groups of MXenes, expanding the scope of MXenes surface modification engineering and creating new opportunities for enhancing the gas sensing capabilities of MXenes.

Electronic structure and composition of tin oxide thin epitaxial and magnetron layers according to synchrotron XANES studies

The materials of the tin-oxygen system and thin-film structures based on them are modern and actual for the creation of a wide range of electronic devices, for example, resistive gas sensors of high sensitivity and short response time with low energy consumption and high manufacturability. An important direction in the study of such materials and structures is the control of properties with variations in technological formation regimes. Information on the composition, local atomic and electronic structure of thin layers of the tin-oxygen system with varying approaches to their production is in demand. The work is devoted to the study of the electronic structure of thin layers of tin oxides obtained by modern methods of molecular beam epitaxy and magnetron sputtering. A study of the local partial density of electronic states in the conduction band by X-ray absorption near edge structure spectroscopy of tin and oxygen has been carried out. The data were obtained using high-intensity synchrotron radiation, which allows varying the monochromatized radiation quantum energy without loss in intensity, that is necessary to obtain high-resolution X-ray spectral data. It is shown that the composition, local atomic surrounding, electronic spectrum and their features depend on the technology of formation and storage conditions of the studied structures. Synchrotron X-ray spectroscopy data show the presence of intermediate oxides of the tin-oxygen system in the studied materials after prolonged storage in laboratory conditions. The data obtained indicate the possibility of controlled variation in the composition, local atomic surrounding and electronic spectrum of thin-film structures of tin oxides of small thickness. The results of the work can be used in the formation and subsequent modification of thin and ultrathin layers of tin oxides by magnetron sputtering and molecular beam epitaxy, as well as in their further application as active layers of microelectronics devices

Optimization of Deposition Parameters of SnO2 Particles on Tubular Alumina Substrate for H2 Gas Sensing

Resistive gas sensors, which are widely used for the detection of various toxic gases and vapors, can be fabricated in planar and tubular configurations by the deposition of a semiconducting sensing layer over an insulating substrate. However, their deposition parameters are not often optimized to obtain the highest sensing results. Here, we have investigated the effect of deposition variables on the H2 gas sensing performance of commercially available SnO2 particles on tubular alumina substrate. Utilizing a tubular alumina substrate equipped with gold electrodes, we varied the number of deposited layers, rotational speed of the substrate, and number of rotations of the substrate on the output of the deposited sensor in terms of response to H2 gas. Additionally, the effect of annealing temperatures (400, 500, 600, and 700 °C for 1 h) was investigated. According to our findings, the optimal conditions for sensor fabrication to achieve the best performance were the application of one layer of the sensing material on the sensor with ten rotations and a rotation speed of 7 rpm. In addition, annealing at a lower temperature (400 °C) resulted in better sensor performance. The optimized sensor displayed a high response of ~12 to 500 ppm at 300 °C. This study demonstrates the importance of optimization of deposition parameters on tubular substrates to achieve the best gas sensing performance, which should be considered when preparing gas sensors.

Optoelectronic Transimpedance Converter Based on MOS Photovaricap for High Resistive Gas Sensors

The gas detectors consist of two parts: metal-oxides gas sensor and transducer. The sensing material is made of a thin semiconductor layer. The transducer is responsible for converting the change in the several physical parameters of the thin sensitive layer into a measurable signal. Due to the high output resistance of high resistive gas sensors and the low input currents of amplifiers, electrometric cascades are employed, followed by the conversion of the gas sensors small direct current into an active current signal using a mechanical modulator (dynamic capacitor) to enhance sensitivity and stability. The aim of this research is to analyze the main characteristics of a novel type of dynamic capacitor that utilizes a surface metal-oxide-semiconductor (MOS) photovaricap (PV) as the regulating element when detecting signals from high resistive gas sensors. For the creation of surface MOS PVs, samples of p-Si with varying resistivity were chosen. A thin layer of SiO2 was deposited on these samples, onto which a translucent metallic electrode was applied. Modulation of the PV capacitance was achieved by illuminating it with a gallium arsenide LED. As a result, the capacitance of the PV is changed, producing a variable voltage across the load resistor, which was then amplified and recorded. It was observed that the settling time of the useful signal is determined by two factors. The first is the RC chain composed of the load resistance of the gas sensor and the input capacitance of the PV, and the second is slow relaxation phenomena in the structure of the MOS PV that lead to the screening of the induced charge. Characteristics of the MOS PV as a dynamic capacitor and the features of the photo capacitance as a semiconductor element, in turn, determine the transimpedance conversion coefficient. The conducted research showed that MOS PVs can be applied to register small DC currents and voltages from high resistive gas sensors. In this case, ordinary narrowband or wideband amplifiers with relatively low input resistance can be used instead of electrometric amplifiers with mechanical dynamic capacitors. The considered circuit has been experimentally tested with commercial resistors.

Flicker Noise in Resistive Gas Sensors-Measurement Setups and Applications for Enhanced Gas Sensing.

We discuss the implementation challenges of gas sensing systems based on low-frequency noise measurements on chemoresistive sensors. Resistance fluctuations in various gas sensing materials, in a frequency range typically up to a few kHz, can enhance gas sensing by considering its intensity and the slope of power spectral density. The issues of low-frequency noise measurements in resistive gas sensors, specifically in two-dimensional materials exhibiting gas-sensing properties, are considered. We present measurement setups and noise-processing methods for gas detection. The chemoresistive sensors show various DC resistances requiring different flicker noise measurement approaches. Separate noise measurement setups are used for resistances up to a few hundred kΩ and for resistances with much higher values. Noise measurements in highly resistive materials (e.g., MoS2, WS2, and ZrS3) are prone to external interferences but can be modulated using temperature or light irradiation for enhanced sensing. Therefore, such materials are of considerable interest for gas sensing.

Investigation of Surface Affinity and Desorption Kinetics of Mixture of Volatile Organic Compounds on CuO-Based Resistive Gas Sensors

Investigation of Surface Affinity and Desorption Kinetics of Mixture of Volatile Organic Compounds on CuO-Based Resistive Gas Sensors

Capacitively coupled contactless conductivity detection (C4D) of ZnO nanostructures gas sensor by adding Au:Pd metal with response to ethanol and acetone vapor

In this work, we present a new gas sensor detection method using the capacitively coupled contactless conductivity detection (C4D) technique. The ZnO nanostructures were prepared by the current heating technique and then added Au: Pd nanoparticles on their surface by a sputtering technique. The gas detector with a C4D system had been fabricated. A data acquisition system was designed to record the signal obtained from the detection electrode. The sensing properties of the sensor with different gas vapor concentrations and operating temperatures have been investigated. Sensitivity was defined as the ratio of signal data in air and vapor gas ambient. The results found that the signal data depend on gas concentration and temperature. However, the results showed lower sensitivity than other techniques, such as the resistive ZnO gas sensor. Finally, the gas sensing mechanism in terms of surface charge density was proposed and used to explain the sensitivity enhancement of C4D ZnO gas sensors.

SnO2 – x Nanocrystal Films with Additives of Heavy Rare-Earth Metals and Sb for Resistive Gas Sensors

SnO2 – x Nanocrystal Films with Additives of Heavy Rare-Earth Metals and Sb for Resistive Gas Sensors

Flexible resistive NO2 gas sensor of SnO2@Ti3C2Tx MXene for room temperature application

SnO2 nanoparticles@Ti3C2Tx MXene have been successfully synthesized by a flexible solvothermal method. The Ti3C2Tx MXene was evenly anchored by the SnO2 nanoparticles (∼5 nm) through the controllable assembly heterojunction. Ti3C2Tx MXene contributed to the improvement of material conductivity compared to SnO2 nanoparticles. The combination of SnO2@Ti3C2Tx exhibits excellent sensitivity and selectivity to NO2 at room temperature (RT). Compared with pure Ti3C2Tx MXene, the sensitivity of TCS1.5 nanocomposite increases more than 20 times to 300 ppm NO2 at RT. In order to explore the sensing mechanism of SnO2@Ti3C2Tx nanocomposite to NO2, nitrogen adsorption-desorption isotherm technology and DFT calculations were performed. They demonstrated that the high specific surface area, well-proportioned heterogeneous structure of SnO2@Ti3C2Tx MXene, and the vital ionic bonds of Sn–N and O–N formed between substrate and NO2 gas had beneficial effect on improving the gas response capability.

Metal Oxide Nanowires Grown by a Vapor-Liquid-Solid Growth Mechanism for Resistive Gas-Sensing Applications: An Overview.

Metal oxide nanowires (NWs) with a high surface area, ease of fabrication, and precise control over diameter and chemical composition are among the best candidates for the realization of resistive gas sensors. Among the different techniques used for the synthesis of materials with NW morphology, approaches based on the vapor-liquid-solid (VLS) mechanism are very popular due to the ease of synthesis, low price of starting materials, and possibility of branching. In this review article, we discuss the gas-sensing features of metal oxide NWs grown by the VLS mechanism, with emphasis on the growth conditions and sensing mechanism. The growth and sensing performance of SnO2, ZnO, In2O3, NiO, CuO, and WO3 materials with NW morphology are discussed. The effects of the catalyst type, growth temperature, and other variables on the morphology and gas-sensing performance of NWs are discussed.

A Fast Interface Circuit for the Measurement of 10 Ω to 1 GΩ Resistance

In this work, an interface circuit applied to resistive gas or chemical sensors is proposed. The interface circuit includes a detection front-end, a single-end to differential circuit, a successive approximation analog-to-digital converter (SAR ADC), and some reference auxiliary circuits. In detection front-end circuits, mirrored currents in a current mirror usually differ by several orders of magnitude. In order to ensure that the current mirror can be copied accurately, this work uses a negative feedback structure consisting of an operational amplifier and an NMOS tube to ensure that the VDS of the current mirroring tube remains consistent. Simulation results show that the replication error of the current mirror is 0.015%. The proposed interface circuit has a detection range of 10 Ω to 1 GΩ with a relative error of 0.55%. The current multiplication or divided technique allows the interface circuit to have a high sampling frequency of up to 10 kHz. The proposed circuit is based on a 180 nm CMOS process with a chip area of 0.308 mm2 (723 μm ∗ 426 μm). The power consumption of the whole interface circuit is 3.66 mW when the power supply voltage is 1.8 V.

Optimization of the Technology of Creating Sensitive Gas Sensors Based on Zinc Oxide

The main achievements in the development of resistive type gas sensors are analyzed, in particular, the creation of nanostructures based on metal oxides, which make it possible to significantly improve the performance characteristics of the sensors. Experimental samples of the gas sensor based on ZnO were obtained by magnetron sputtering on direct current. The effectiveness of the gas sensor system for recognition and analysis of gases and their mixtures has been established. A study of the sensitivity of experimental samples to the influence of the target gas CO was carried out. The target gas concentration varied from 50 to 150 ppm. It was established that the ZnO-based gas sensor exhibits the highest sensitivity at a target gas concentration of 100 ppm. The sensitivity of the gas sensor increases with increasing exposure time to the target gas.

Resistive Gas Sensors Based on Porous Sp-Containing Films Obtained by Dehydrohalogenation of PVDC and PVDC-PVC Copolymer

Resistive sensing responses of the thin films obtained by dehydrohalogenation of polyvinylidene chloride (PVDC) and polyvinylidene chloride–polyvinyl chloride (PVDC-PVC) copolymer were investigated. The structure of the samples was studied by transmission electron microscopy, Fourier-transform infrared spectroscopy and Raman spectroscopy. The analyses demonstrate the formation of a porous structure based on polyyne–polyene chains. The formation of a foam-like oxidized sp-rich structure was observed for the samples obtained via the chemical treatment of the PVDC. However, a loose film with a developed structure and a lower fraction of sp-hybridized carbon was observed for KOH-treated PVDC-PVC. The resistive sensing responses of both of the dehydrohalogenated structures were measured for various concentrations of acetone, acetic acid, ammonia hydroxide, methanol, ethanol, benzene and water. The interplay between the efficiency of the dehydrohalogenation of the films, their structure and sensing selectivity is discussed.

Investigating of transition state on the Pd–Au decorated ZnO nanoparticle layers for gas sensor application

In this work, the mechanism of the transition state of electron transfer reaction on the surface of the ZnO nanoparticles-based gas sensor has been investigated. The deposited ZnO nanoparticles thick films on glass slides had been synthesized by the current heating method and modified its surface by coating novel metals of gold and palladium with a sputtering technique with different sputtering times of 45–180 s. Field emission electron microscopy (FE-SEM), x-ray diffraction spectroscopy (XRD), and energy dispersive spectroscopy (EDS) were used for the characterization of ZnO nanoparticle thick films. After that, the reflectance spectra of films were investigated using Near-IR spectroscopy in the range of 900–2500 nm to study the surface absorption efficiency. The decrease in reflectance spectra was observed for conditions over 90 s of sputtering time. The particle size distribution and zeta potential of ZnO nanoparticles were analyzed using the dynamic light scattering technique for the calculation of particle size and the electrical charge potential. The results showed that the size particle distribution ranged from 155 to 245 nm and the more extensive range of 360–1100 nm. The optimized zeta potential of −14.44 mV was exhibited at the sputtering time of 45 s. Finally, the gas sensing mechanism in terms of surface charge density was proposed and used to explain the sensitivity enhancement of both resistive and capacitive gas sensors.

UV light activated g-C3N4 nanoribbons coated surface acoustic wave sensor for high performance sub-ppb level NO2 detection at room temperature

The demand for efficient gas sensors in detecting low ppb-level NO2 gas is increasing rapidly for the human life and environmental protection. In this regard, surface acoustic wave (SAW) based gas sensor with selectively coated one dimensional (1D) graphitic carbon nitride (g-C3N4/GCN) nanostructure interface layer is a viable strategy for the sub-ppb level NO2 gas detection at room temperature (RT∼30 °C). Here, we explore SAW gas sensor employed with 1D GCN nanoribbons (NRs) for NO2 detection under UV-irradiation at RT. Intriguingly, the GCN NRs SAW sensor achieves an ultrahigh frequency response (Δf∼28.13 kHz), short response/recovery times (131 s/116 s), excellent selectivity to NO2 (10 ppm) gas and also records a lowest detection limit (∼42 ppb) under UV activation at RT. The enhanced sensing performances were attributed to the high mass loading effect induced by the enhanced charge transfer between the 1D GCN NRs surface and NO2 gas molecules, boosted by the photoexcited charge carriers, numerous surface sites, and improved specific surface area of 1D GCN NRs. The proposed GCN NRs SAW sensor demonstrates exceptional repeatability, good long-term stability with a minimal loss in its Δf, and exhibited robust sensitivity towards NO2 (10 ppm) under diverse relative humidity conditions (0–80%) at RT. The peculiar sensing results of GCN NRs SAW sensor was elucidates using energy band theory sensing mechanism assisted with resistive type gas sensor. Overall, this study offers significant insights into the development of cost-effective real-time RT based NO2 sensor, paving the way for practical air quality monitoring.

Gas-Sensing Performance of Gadolinium Ferrates with Rod and Butterfly Morphologies

There is an urgent need to develop a low-cost and high-performance gas sensor for industrial production and daily life. Perovskite-type oxides are appropriate materials for resistive gas sensors. In this paper, two gas-sensing materials of gadolinium orthoferrite (GdFeO3) with rod and butterfly morphologies were obtained by annealing the corresponding precursors at 800 °C in a muffle furnace for 3 h. The precursors of GdFe(CN)6·4H2O with novel morphologies were prepared by a co-precipitation method at room temperature. The materials were evaluated in terms of their structure, morphology, and gas-sensing performance. The gas sensor based on GdFeO3 rods showed a better sensing performance than the sensor based on GdFeO3 butterflies. It exhibited the largest response value of 58.113 to 100 ppm n-propanol at a relatively low operating temperature of 140 °C, and the detection limit was 1 ppm. The results show that the GdFeO3 rods-based sensor performed well in detecting low concentration n-propanol. The satisfactory gas-sensing performance of the GdFeO3 rods-based sensor may be due to the porous structure and the large percentages of defect oxygen and adsorbed oxygen (37.5% and 14.6%) on the surface. This study broadens the application of GdFeO3 in the gas sensor area.

A durable gas sensor based on AgVO3/TiO2 nanoheterostructures to ethanol gas

Semiconductor metal oxides (MOS) have been hot research topics in the field of gas sensors. However, the applicability of MOS-based gas sensors is severely constrained by the low sensitivity, poor selectivity, and high working temperature. One-dimensional AgVO3/TiO2 nanoheterostructures (NHSs) were fabricated using a hydrothermal technique to address above issues. The resulting AgVO3/TiO2 NHSs-based chemo resistive gas sensor shows good selectivity to ethanol (EtOH) gas. Moreover, the AgVO3/TiO2 with a molar ratio of 1:1 (AT) shows the highest sensing performance. The sensitivity of AT to 100 ppm EtOH at 200 ℃ is evaluated as 46.3, which is 22.0 and 1.8 times greater than that of TiO2 and AgVO3, respectively. Especially, AT possesses good sensing performance at room temperature, and its sensitivity to 100 ppm EtOH is 1.2. Simultaneously, it exhibits fast response/recovery times (17/32 s) in EtOH gas detection and excellent stability after 50 continuous cycle tests and 50 days of cycle life testing. The gas sensing mechanism is systematically analyzed from the carrier transfer ability, the synergy of AgVO3 and TiO2, the heterojunction effect, and the morphology promotion. This work reports an excellent EtOH gas sensor based on the constructed AgVO3/TiO2 NHSs, providing an insight into the fabrication of MOS-based nanocomposites for effective EtOH detection.