Gas Detection Mechanism Research Articles

Dependence of n-Type Metal-Oxide Gas Sensor Response on the Pressure of Oxygen and Reducing Gases.

The adsorption of oxygen and its reaction with target gases are the basis of the gas detection mechanism by using metal oxides. Here, we present a theoretical analysis of the sensor response, within the ionosorption model, for an n-type polycrystalline semiconductor. Our goal of our work is to reveal the mechanisms of gas sensing from a fundamental point of view. We revisit the existing models in which the sensor response presents a power-law behavior with a reducing gas partial pressure. Then, we show, based on the Wolkenstein theory of chemisorption, that the sensor response depends not only on the reducing gas partial pressure but also on the oxygen partial pressure. We also find that the obtained sensor response does not explicitly depend on the grain size, and if it does, it is exclusively through the rate constants related to the involved reactions.

Combustion synthesis of spinel structured NiCo2O4 nanostructures: An efficient material for gas sensing and supercapacitor electrode applications

Nanostructured spinel NiCo2O4 powder has been effectively synthesized using the solution combustion technique. The synthesized material was annealed at 500 °C and further utilised for gas sensing and energy storage applications. The thermal, structural, optical, electrical, magnetic and morphological properties of synthesized material were investigated in detail. The annealed synthesized NiCo2O4 powder was tested for the electrochemical studies with galvanostatic charge-discharge (GCD), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and cyclic stabilitytests for the supercapacitor electrode applications. The specific capacitance (CS), energy density (E) and power density (P) of the synthesized materials were estimated from the GCD plot and it was 730 F/g, 16.22 WhKg−1 and 398.71 Wkg-1 respectively at the current densities 2 A/g. The fabricated electrode from NiCo2O4 powder had an initial retention of capacitance value is 92.23 % after 5000 cycles. The synthesized material was further tested with different gases detection at various temperatures. The fabricated NiCo2O4 sensor was used for the estimation of gas sensing properties of acetone, carbon dioxide, ammonia and ethanol gases at various working temperatures. The gas-detection measurements illustrate that the NiCo2O4 material reacts differently to various gases at different temperatures and observes maximum sensitivity, superior selectivity, quick response and recovery ability for the ammonia gas as compared with other test gases. The feasible NH3 gas detection mechanism is pictorially presented in this manuscript. The present works conclude that nanostructured spinel NiCo2O4 is the promising material in the high performance electrode material for supercapacitor applications and ammonia gas sensing application.

Aggregation‐Induced Emission Luminogens for Gas Sensors

AbstractLuminescent chromophores armed with aggregation‐induced emission (AIE) characteristics can switch their fluorescence sensing by manipulating the aggregation and disaggregation states, leading to high sensitivity and high signal‐to‐noise ratio sensors. Accordingly, aggregation‐induced emission luminogens (AIEgens) have been widely applied to various biosensing, one of which is the gas sensors. Due to the weak signal, easy diffusion, difficult capture, and instability of gas molecules, electrochemical or infrared tests are generally used for detection. However, electrochemical tests have high power consumption, and the environment easily disturbs infrared tests. Fortunately, photochemical sensors utilizing AIE properties can effectively overcome these deficiencies. AIEgens usually exhibit large Stokes shift, good photostability, and low random blinking, suggesting excellent sensing reproducibility and many achievements have been obtained in AIEgens‐based gas sensors. This review summarizes the gas detection mechanism of AIEgens, and enumerate the reported gas sensors based on AIEgens. Then a perspective on the field and challenges facing it are elaborated so that researchers can better understand the development status of this field and develop more AIE‐type spectroscopic probes with gas‐responsive functions. It is expected to greatly enrich the types of gas sensors and promote the development of the application of AIE properties.

Numerical investigation of a Ge1-xSnx-on-AlN waveguide and its sensing mechanism for the detection of trace gases in the mid-infrared regime

This work reports the integration of a Ge1−xSn x -on-AlN optical waveguide (WG) on SiO2 substrate to facilitate mid-infrared (MIR) trace gas detection. Here, the proposed structure makes use of Ge1−xSn x in the core of the WG and the AlN cladding; this enables the effective guidance and confinement of a broad spectrum of MIR light waves within the GeSn WG. The gas detection mechanism of the device is based on the evanescent wave field component of a guided mode to examine particular molecular absorption/trace gas characteristics of the upper cladding environment. The designed WGs exhibit high power confinement (∼90%) and low propagation loss of 0.61–1.18 dB/cm at λ=4.3−4.74µm with x=6% in the Ge1−xSn x core. We also discuss the capability of the proposed WG to detect trace gases such as CO, CO2, and N2O. The results show that the minimum detectable concentrations (Cmin) of these gases are ∼0.42, 0.12, and 0.16 ppm, respectively, for x=6%. These encouraging results enable a new sensor platform for GeSn-based MIR trace/atmospheric gas detection.

Nonanal Gas Sensors Using Porous Glass as a Reaction Field for Ammonia-Catalyzed Aldol Condensation.

Transmittance in porous-glass gas sensors, which use aldol condensation of vanillin and nonanal as the detection mechanism for nonanal, decreases because of the production of carbonates by the sodium hydroxide catalyst. In this study, the reasons for the decrease in transmittance and the measures to overcome this issue were investigated. Alkali-resistant porous glass with nanoscale porosity and light transparency was employed as a reaction field in a nonanal gas sensor using ammonia-catalyzed aldol condensation. In this sensor, the gas detection mechanism involves measuring the changes in light absorption of vanillin arising from aldol condensation with nonanal. Furthermore, the problem of carbonate precipitation was solved with the use of ammonia as the catalyst, which effectively resolves the issue of reduced transmittance that occurs when a strong base, such as sodium hydroxide, is used as a catalyst. Additionally, the alkali-resistant glass exhibited solid acidity because of the incorporated SiO2 and ZrO2 additives, which supported approximately 50 times more ammonia on the glass surface for a longer duration than a conventional sensor. Moreover, the detection limit obtained from multiple measurements was approximately 0.66 ppm. In summary, the developed sensor exhibits a high sensitivity to minute changes in the absorbance spectrum because of the reduction in the baseline noise of the matrix transmittance.

The effects of gas exposure on the graphene/AlGaN/GaN heterostructure under UV irradiation

This work demonstrates a graphene/AlGaN/GaN sensing device with two-dimensional electron gas (2DEG) toward nitrogen dioxide (NO2), tetrahydrofuran, and acetone detection under UV light irradiation. We propose combining measurements of the DC characteristics with a fluctuation-enhanced sensing method to provide insight into the gas detection mechanisms in the synergistic structure of highly stable GaN and gas-sensitive graphene. Both DC and low-frequency noise studies reveal the impact of UV irradiation (275 nm) on the GaN-based field-effect transistor (FET). Gas detection improves under UV light with higher differentiability between selected concentrations of inorganic (NO2) gas and the possibility of discrimination between weakly adsorbing organic species (tetrahydrofuran and acetone). Time-domain experiments confirm the stability and reversibility of sensor (short-time and long-time) responses and reduced time drift after employing UV light. Features observed in the 1/f noise spectra may indicate the high impact of the irradiation on the trapping states in the GaN-based heterostructure, which further modulates the fluctuations of the channel carriers in our device. Our findings broaden the view on AlGaN/GaN heterostructures modulated with a graphene gate for gas sensing purposes, including strongly binding inorganic gas and weakly adsorbing organic species.

Comment on "Understanding the Increasing Trend of Sensor Signal with Decreasing Oxygen Partial Pressure by a Sensing-Reaction Model Based on O2-Species".

In the original paper, Zhao and co-workers describe a sensing model to explain the response to a reducing gas as a function of the oxygen partial pressure. In this Comment we specifically analyze the basic gas detection mechanisms proposed in such a work and expressed through surface reactions (eqs 1-5). The consequence of these presented mechanisms lead to inconsistencies that are also regularly found in the literature.

Design and performance analyses of graphene-nano plasmonic devices for wireless gas sensor applications

Graphene gained more attention in industrial applications owing to its unique characteristics. A simple and inexpensive photodeposition technique was used to fabricate the nanoparticles. Herein, ZnO, Au/ZnO, and the neat rGOx@Au/ZnO heterostructure plasmonic nanocomposites were applied to detect the sensitivity of CO2, LPG, and O2 gases using a sensing device with a rapid response at ambient temperature. The gas detection mechanism explains the synergistic influence between the localized plasmonic phenomena of AuNPs and the π-π interaction among rGOx/ZnO. Compared to pure ZnO and AuNPs/ZnO nanocomposite, the sensing response of rGOx@Au/ZnO (x = 10 wt %) exposed to CO2 gas is optimized, achieving a response of 625.63% over a 16-s reaction time at room temperature. The heterostructure's morphological, crystal structure, and electronic properties were determined using different techniques. The devices were exposed to various gases such as CO2, O2, and liquified petroleum gas (LPG) to test the selectivity of the composite sensor, and the sensor response for these gases was measured and significant. A wireless gas detector can be built using an Arduino module. The circuit is created by connecting a gas sensor to an Arduino rGOx@Au/ZnO (x = 10 wt %) weight board, which determines the gas content in the air and whether it exceeds the allowable value. At the level programmed in the Arduino kit, Global System Mobile (GSM) sends an SMS to the cell phone number that was also investigated.

Organic Vapor Sensing Mechanisms by Large-Area Graphene Back-Gated Field-Effect Transistors under UV Irradiation.

The gas sensing properties of graphene back-gated field-effect transistor (GFET) sensors toward acetonitrile, tetrahydrofuran, and chloroform vapors were investigated with the focus on unfolding possible gas detection mechanisms. The FET configuration of the sensor device enabled gate voltage tuning for enhanced measurements of changes in DC electrical characteristics. Electrical measurements were combined with a fluctuation-enhanced sensing methodology and intermittent UV irradiation. Distinctly different features in 1/f noise spectra for the organic gases measured under UV irradiation and in the dark were observed. The most intense response observed for tetrahydrofuran prompted the decomposition of the DC characteristic, revealing the photoconductive and photogating effect occurring in the graphene channel with the dominance of the latter. Our observations shed light on understanding surface processes at the interface between graphene and volatile organic compounds for graphene-based sensors in ambient conditions that yield enhanced sensitivity and selectivity.

Pivotal role of nucleation layers in the hydrothermally-assisted growth of ZnO and its H2 gas sensing performance

Although hydrogen is a non-poisonous gas that can dissipate quickly once is released, it causes suffocation at high concentrations and is very risky on some occasions if not suitably handled. In this study, an effective approach was suggested for developing and tuning hydrogen gas sensors, where the crucial effect of nucleation layers and chemical stabilizing agents on the morphology of hydrothermally-assisted growth and its gas sensing performance was demonstrated. For this purpose, ZnO seed layers were separately synthesized by different solution-based chemical processes based on the successive ionic layer adsorption and reaction, spin, and dip coating techniques followed by a hydrothermal treatment under the same conditions. X-ray diffraction measurements revealed that all the synthesized samples have a similar pure hexagonal wurtzite structure with a big difference in the degree of textural orientation along the c-axis of ZnO. Optical transmittances, forbidden bandgap energies, and Urbach energies of the produced samples were influenced to a great extent by the coating techniques and the chemical solutions used. Aside from that, the morphology of the synthesized samples and their overall thicknesses together with the available oxygen vacancies detected by X-ray photoelectron spectroscopy changed considerably. The change in structure and morphology have influenced the wettability of the synthesized samples. They have also greatly influenced the gas sensing performance of the sensors in terms of optimal working temperature, sensitivity, and response/recovery periods. The hydrogen gas detection mechanism of the fabricated sensors and the logic behind the change that occurred in gas sensing performance based on morphology are discussed.

Formaldehyde gas sensing using metal oxide semiconductor: a brief review

PurposeThis review aims to give an overview about zinc oxide (ZnO) based gas sensors and the role of doping in enhancing the gas sensing properties. Gas sensors based on ZnO thin film are preferred for sensing applications because of their modifiable surface morphology, very large surface-to-volume ratio and superior stability due to better crystallinity. The gas detection mechanism involves surface reaction, in which the adsorption of gas molecules on the ZnO thin film affects its conductivity and reduces its electrical properties. One way to enhance the gas sensing properties is by doping ZnO with other elements. A few of the common and previously used dopants include tin (Sn), nickel (Ni) and gallium (Ga).Design/methodology/approachIn this brief review, previous works on doped-ZnO formaldehyde sensing devices are presented and discussed.FindingsMost devices provided good sensing performance with low detection limits. The reported operating temperatures were within the range of 200̊C –400̊C. The performance of the gas sensors can be improved by modifying their nanostructures and/or adding dopants.Originality/valueAs of yet, a specific review on formaldehyde gas sensors based on ZnO metal semiconductors has not been done.

Nanosilicon-Based Composites for (Bio)sensing Applications: Current Status, Advantages, and Perspectives.

This review highlights the application of different types of nanosilicon (nano-Si) materials and nano-Si-based composites for (bio)sensing applications. Different detection approaches and (bio)functionalization protocols were found for certain types of transducers suitable for the detection of biological compounds and gas molecules. The importance of the immobilization process that is responsible for biosensor performance (biomolecule adsorption, surface properties, surface functionalization, etc.) along with the interaction mechanism between biomolecules and nano-Si are disclosed. Current trends in the fabrication of nano-Si-based composites, basic gas detection mechanisms, and the advantages of nano-Si/metal nanoparticles for surface enhanced Raman spectroscopy (SERS)-based detection are proposed.

Electro-Plasmonic Gas Sensing Based on Reduced Graphene Oxide/Ag Nanoparticle Heterostructure

Graphene has been entitled as a promising candidate for gas sensing applications, however suffers from low selectivity, as a limit for commercialization. We propose a gas sensor based on reduced graphene oxide (rGO)/Ag nanoparticles (Ag NPs), which can overcome this limitation by benefiting from both localized surface plasmon resonance of Ag NPs, and chemisorption capability of gas molecules on rGO sheets. These simultaneous gas detection mechanisms help to reveal both physical and chemical aspects of gas molecules. We show that gas-induced plasmonic shift is enhanced in rGO/Ag NPs (Δλ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LSPR</sub> ≈ 5 nm), comparing with Ag NPs (Δλ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LSPR</sub> ≈ 1.4 nm) versus 250 ppm of nitrogen concentration. Furthermore, electrical measurements prove that gas-induced variation in the conductivity response is higher in rGO/Ag NPs (ΔG/G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ≈ 3.6%), in comparison with Ag NPs (ΔG/G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ≈ 1.5%). Finally, we have utilized electro-plasmonic measurement in the proposed structure, leading to about 47% enhancement in the measured sensitivity, when λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">incident</sub> = 440 nm is illuminated during nitrogen exposure. The proposed structure allows both electrical sensing and electro-plasmonic sensing by means of a simple measurement configuration, revealing both chemisorption and physisorption finger prints of the test gas.

Simulations of Propane and Butane Gas Sensor Based on Pristine Armchair Graphene Nanoribbon

Over the last decade graphene and its derivatives have gained a remarkable place in research field. As silicon technology is approaching to its geometrical limits so there is a need of alternate that can replace it. Graphene has emerged as a potential candidate for future nano-electronics applications due to its exceptional and extraordinary chemical, optical, electrical and mechanical properties. Graphene based sensors have gained significance for a wide range of sensing applications like detection of biomolecules, chemicals and gas molecules. It can be easily used to make electrical contacts and manipulate them according to the requirements as compared to the other nanomaterials. The intention of the work presented in this article is to contribute in this field by simulating a novel and cheap graphene nanoribbon sensor for the household gas leakage detection. QuantumWise Atomistix (ATK) software is used for the simulations of propane and butane gas sensor. Projected device density of the states (PDDOS) and the transmission spectrum of the device in the proximity of gas molecules are calculated and discussed. The change in the electric current through the device in the presence of the gas molecules is used as a gas detection mechanism for the simulated sensor.

Different Interaction Mechanisms of Evaporated Porphyrin Films Exposed to NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;

In this work, metal free and zinc tetraphenylporphyrin films were employed as nitrogen dioxide (NO2) gas sensors. The films were vacuum evaporated and the sensor response was evaluated as changes in the optical absorption spectra, hydrophobic properties and conductivity at different gas concentrations. From UV-Vis results, important changes in the absorption peaks were observed after gas exposure. The morphology of the films before and after gas interaction was obtained by using scanning electron and atomic force microscopy. The films morphology showed a degradation after gas adsorption for the metal free system but gas entrapment for the zinc porphyrin film. In order to elucidate the gas adsorption phenomena, density functional theory calculations were also performed. Here, it was observed that the porphyrin chemical structure not only affects the gas coordination sites which affect the porphyrin electronic distribution and packing arrangement, but also, determines the gas detection mechanism for sensing applications.

Analytical assessment of carbon allotropes for gas sensor applications

Feasibility of a gas sensor with NH3 as a prototype using carbon allotropes (graphene and CNT) is demonstrated, with graphene displaying superior sensitivity and conductance. Such devices are expected to be considerably smaller and faster than the ones used in the present technology. Salient features of current–voltage characteristics of charge transfer as NH3 reacts with carbon atoms and transfer charge is demonstrated. A mathematical model is proposed for change in conductance of the CNT/graphene channel resulting from the chemical reaction between the gas and channel surface molecules. An analytical understanding of the FET-based gas detection mechanism and the corresponding current–voltage (I–V) characteristics is acquired. The CNT model shows a satisfactory agreement with the experimental data on nanotube-based NH3 gas detection. The results of the graphene-based gas sensor model are compared to those from the CNT model. It is shown that for similar ambient conditions, the graphene gas sensor exhibits superior conduction as compared to its CNT counterpart due to higher exposed surface of graphene.

Structural, morphological, gas sensing and photocatalytic characterization of MoO3 and WO3 thin films prepared by the thermal vacuum evaporation technique

Thin films of molybdenum trioxide and tungsten trioxide were deposited on glass substrates using a simplified thermal evaporation under vacuum method monitored by heat treatment in flowing oxygen at 500°C for 1h. The structural and morphological properties of the films were investigated using X-ray diffraction, Raman spectroscopy, atomic force microscopy and scanning electron microscopy. The X-ray diffraction analysis shows that the films of MoO3 and WO3 were well crystallized in orthorhombic and monoclinic phase respectively with the crystallites preferentially oriented toward (200) direction parallel a-axis for both samples. In literature, we have shown in previous papers that structural and surface morphology of metal thin films play an important role in the gas detection mechanism. In this article, we have studied the response evolution of MoO3 and WO3 thin films sensors ethanol versus time, working temperature and the concentration of the ethanol. It was found that these films had high sensitivity to ethanol, which made them as a good candidate for the ethanol sensor. Finally, the photocatalytic activity of the samples was evaluated with respect to the degradation reaction of a wastewater containing methylene blue (MB) under UV–visible light irradiation. The molybdenum trioxide exhibits a higher degradation rate than the tungsten trioxide thin films under similar experimental conditions.

Impedance spectroscopy and sensors under ethanol vapors application of sprayed vanadium-doped ZnO compounds

Thin films of vanadium-doped zinc oxide with different vanadium-doping levels (0, 1, 2 and 3at%) were deposited on glass substrates by employing an inexpensive, simplified spray technique using at relatively low substrate temperature (460°C). The effect of V doping on the structural, morphological and optical properties of the films was investigated by Mhamdi et al. (2013). The X-ray diffraction analysis shows that the films were well crystallized in würtzite phase with the crystallites preferentially oriented toward (002) direction parallel c-axis. As also that the average particle size along the surface of the films decreases with increasing of concentration of vanadium. In this work we study the AC and DC conductivity and gas sensor application on ZnO:V thin films. The dielectric properties of ZnO:V thin films were studied by means of complex impedance spectroscopy and frequency dependence of conductivity measured from the impedance data at a range of frequency intervals between 10Hz and 13MHz with a temperature between 355 and 445°C. The frequency dependence of the dielectric constant ɛ′, dielectric loss ɛ″, loss tangent (tanδ) and AC electrical conductivity (σAC) of the layers was subsequently investigated. In literature, we have shown in previous papers that structural and surface morphology of ZnO thin films, prepared by spray, plays an important role in the gas detection mechanism. In this article, we have studied the response evolution of ZnO:V sensors ethanol versus time and working temperature, relative doping and the concentration of the ethanol vapor.

An analytical approach to evaluate the performance of graphene and carbon nanotubes for NH3 gas sensor applications.

Carbon, in its variety of allotropes, especially graphene and carbon nanotubes (CNTs), holds great potential for applications in variety of sensors because of dangling π-bonds that can react with chemical elements. In spite of their excellent features, carbon nanotubes (CNTs) and graphene have not been fully exploited in the development of the nanoelectronic industry mainly because of poor understanding of the band structure of these allotropes. A mathematical model is proposed with a clear purpose to acquire an analytical understanding of the field-effect-transistor (FET) based gas detection mechanism. The conductance change in the CNT/graphene channel resulting from the chemical reaction between the gas and channel surface molecules is emphasized. NH3 has been used as the prototype gas to be detected by the nanosensor and the corresponding current–voltage (I–V) characteristics of the FET-based sensor are studied. A graphene-based gas sensor model is also developed. The results from graphene and CNT models are compared with the experimental data. A satisfactory agreement, within the uncertainties of the experiments, is obtained. Graphene-based gas sensor exhibits higher conductivity compared to that of CNT-based counterpart for similar ambient conditions.

Field Emission Model of CNT Based Ionization Gas Sensor

A new model to study the gas detection mechanism of carbon nanotube (CNT) based ionization gas sensor has been developed. The model incorporates the effect of electron field emission due to the presence of CNT. The model is then embedded in the standard Particle-In-Cell / Monte-Carlo-Collision (PIC-MCC) codes. This enhanced PIC-MCC codes serve as a tool to optimize CNT based ionization gas sensor. The functionality of the new model is validated by running simulations of DC discharges in argon and comparing the results with published experimental and simulated works. From the simulation, one order of magnitude decrease in the breakdown voltages and three orders of magnitude faster response time was observed.