Gas Sensor Devices Research Articles

Studies of NO2 Gas-Sensing Characteristics of a Novel Room-Temperature Surface-Photovoltage Gas Sensor Device.

In this work the characteristics of a novel type of room temperature NO2 gas sensor device based on the surface photovoltage effect are described. It was shown that for our SPV gas sensor device, using porous sputtered ZnO nanostructured thin films as the active gas sensing electrode material, the basic gas sensor characteristics in a toxic NO2 gas atmosphere are strongly dependent on the target NO2 gas flow rate. Moreover, it was also confirmed that our SPV gas sensor device is able to detect the lowest NO2 relative concentration at the level of 125 ppb, with respect to the commonly assumed signal-to-noise (S/N) ratio, as for the commercial devices.

Gas Sensitivity of In0.3Ga0.7As Surface QDs Coupled to Multilayer Buried QDs

A detailed analysis of the electrical response of In0.3Ga0.7As surface quantum dots (SQDs) coupled to 5-layer buried quantum dots (BQDs) is carried out as a function of ethanol and acetone concentration while temperature-dependent photoluminescence (PL) spectra are also analyzed. The coupling structure is grown by solid source molecular beam epitaxy. Carrier transport from BQDs to SQDs is confirmed by the temperature-dependent PL spectra. The importance of the surface states for the sensing application is once more highlighted. The results show that not only the exposure to the target gas but also the illumination affect the electrical response of the coupling sample strongly. In the ethanol atmosphere and under the illumination, the sheet resistance of the coupling structure decays by 50% while it remains nearly constant for the reference structure with only the 5-layer BQDs but not the SQDs. The strong dependence of the electrical response on the gas concentration makes SQDs very suitable for the development of integrated micrometer-sized gas sensor devices.

A Micromachined Metal Oxide Composite Dual Gas Sensor System for Principal Component Analysis-Based Multi-Monitoring of Noxious Gas Mixtures.

Microelectronic gas-sensor devices were developed for the detection of carbon monoxide (CO), nitrogen dioxides (NO2), ammonia (NH3) and formaldehyde (HCHO), and their gas-sensing characteristics in six different binary gas systems were examined using pattern-recognition methods. Four nanosized gas-sensing materials for these target gases, i.e., Pd-SnO2 for CO, In2O3 for NOX, Ru-WO3 for NH3, and SnO2-ZnO for HCHO, were synthesized using a sol-gel method, and sensor devices were fabricated using a microsensor platform. Principal component analysis of the experimental data from the microelectromechanical systems gas-sensor arrays under exposure to single gases and their mixtures indicated that identification of each individual gas in the mixture was successful. Additionally, the gas-sensing behavior toward the mixed gas indicated that the traditional adsorption and desorption mechanism of the n-type metal oxide semiconductor (MOS) governs the sensing mechanism of the mixed gas systems.

Ultra thin NiO nanosheets for high performance hydrogen gas sensor device

Unstacked two dimensional (2-D) NiO nanosheets are synthesized via easy surfactant-free hydrothermal chemical route. NiO sensor is investigated for high performance and selective hydrogen (H2) gas sensing properties. Structural analysis is carried out using XRD pattern. The morphology of NiO is confirmed by using FESEM and TEM micrographs. Atomic state and elemental composition are analyzed by recording XPS and EDS spectra respectively. NiO sensor exhibited a high gas response of 191% for 150 ppm H2 concentration at 250 °C operating temperature with response time 150 s. The lowest H2 detection is observed at the concentration of 10 ppm having the gas response of 22%. The H2 response of NiO sensor was tested at different operating temperatures as well as gas concentrations. The dynamic gas response and sensor stability were recorded and analyzed. The sensing mechanism of NiO sensor was discussed.

CdSe Reinforced Polyaniline Nanocomposites as Superior Material for Future Applications as Gas Sensor and Diodes

In the present research CdSe quantum dots were reinforced into as-polymerized polyaniline (PANI) to yield polymer nanocomposites. The lattice constants of CdSe and CdSe in the nanocomposites were calculated to be 6.24 Å and 5.44 Å, respectively for cubic phase. The surface morphology of pure PANI showed agglomeration of spherical particles. The EDAX spectrum confirmed the presence of compositional elements of PANI and CdSe in the nanocomposite. Ohmic behavior of composite evidenced the possibility of its use in P-N junction diodes. The morphological observations revealed that DC conductivity of PANI/CdSe nanocomposites was higher than that of the PANI. The value of short circuit current also increased from 0.3 [A (cm)−2] to 150 [A (cm)−2]. The observed findings revealed that the present material has potential to fabricate protective devices, P-N junction diodes, electronic devices, and gas sensor devices.

Adsorption of gas molecules on a C3N monolayer and the implications for NO2 sensors

Recent reports have raised exciting prospects for the use of C3N monolayers exhibiting excellent adsorptive properties in nanodevice applications. In this study, we carried out first-principle calculations to investigate the adsorption of NO2, NO, CO, HCN, NH3, CO2, H2, N2, CH4, H2O, O2, and N2O gas molecules on a C3N monolayer as well as its potential applications in gas sensor devices. Our results reveal that the chemisorption of NO2 can significantly influence the electronic properties of the C3N monolayer (e.g., changing semiconducting behavior to conducting behavior). In contrast, physisorption of the other gas molecules had little effect on the electronic properties of the C3N monolayer. These results suggest that the C3N monolayer is much more sensitive and selective to NO2 than to the other gases. The recovery time of NO2 at T = 300 K is only 0.62 s. Moreover, the optical properties of the C3N monolayer can be modified as a result of the adsorption of different molecules, especially the NO2 molecule. Thus, the C3N monolayer is a promising and desirable candidate for use as a suitable material in gas sensors for NO2 detection.

Excellent ambipolar gas sensing response of Eu[Pc(OC4H9)8]2/acidified multiwalled carbon nanotubes hybrid at room temperature

A new hybrid material has been developed by mixing a sandwich-type double-decker, Eu[Pc(OC4H9)8]2 = 2,3,9,10,16,17,23,24-octabutoxyphthalocyaninate] with acidified multiwalled carbon nanotubes (aMWCNTs) through non-covalent interactions. The UV-vis spectrum, X-ray diffraction and scanning electron microscope have been employed to reveal the [Formula: see text]-aggregate mode and optimized morphology of Eu[Pc(OC4H9)8]2 molecules in the Eu[Pc(OC4H9)8]2/aMWCNTs hybrid material. The gas-sensing devices based on this hybrid material are fabricated by a simple solvent-processing quasi-Langmuir–Shäfer (QLS) progress. The [Formula: see text]-type and [Formula: see text]-type response is shown by the Eu[Pc(OC4H9)8]2/aMWCNTs hybrid film at room temperature. The detection limit of the hybrid for ammonia and nitrogen dioxide gas is 0.5 ppm and 0.3 ppm, respectively.

Ultra-sensitive NO2 gas sensors based on single-wall carbon nanotube field effect transistors: Monitoring from ppm to ppb level

Owing to their sensitive chemical-to-electrical transducer capabilities and compatibility with device miniaturization and low operation temperature, single-walled carbon nanotube field-effect transistor (SWCNT-FET) represents an attractive platform to provide solutions in the gas sensing field. In this work, SWCNT-FETs were fabricated and their performances for detecting low NO2 concentrations were evaluated. Outstanding devices response was obtained, which was shown to follow a 2 power law dependence between the response and the NO2 concentration in the range of 100 ppb up to 10 ppm. Such ultra-high response is attributed to an enhancement of the Schottky barrier modulation triggered by the specific device configuration. The device configuration is based on individual semiconducting SWCNTs directly connecting the interdigitated Source-Drain electrodes. To the best of our knowledge, the results reported here correspond to the most sensitive device among the devices based on non-functionalized carbon materials and operational at low temperatures. Furthermore, the obtained results are supported by a deep SWCNT characterization, and the changes in Schottky barrier's height induced by the presence of gas molecules are estimated and discussed. Overall, the present reported results provide useful information for establishing a robust process for the fabrication of the next generation of CNT based gas-sensing devices.

Investigation of Gas-Sensitive Properties of Thin-Film Thermovoltaic Sensor Elements Based on Zinc Oxide

Systematic research on a new type of gas sensor devices based on the thermovoltaic effect in zinc oxide, inhomogeneously doped with impurities of variable valence, is presented in the article. The ZnO–ZnO–Me two-layer sandwich structure, in which the thermovoltaic effect is observed, is synthesized using sol–gel technology from sols by dissolving the inorganic zinc salt in alcohol and adding a surfactant, followed by the mixing and maturation of the sol. The lower layer of the nanostructure is formed from pure zinc oxide by immersing the substrate at ⅔ length in sol and drying. The upper layer of zinc oxide doped with copper or iron is formed by two or three immersions of the other end of the substrate by ⅔ length, followed by drying and annealing. It has been established that, based on the developed sensor device, it is possible to obtain an increased response to gas-analyzers (ethanol being an example).

Synthesis of Nanoporous TiO2 with the Use of Diluted Hydrogen Peroxide Solution and Its Application in Gas Sensing

The chemical routes of metal oxidation in presence of hydrogen peroxide solutions are tailor-made for the synthesis of biocompatible metal oxide surfaces with clean intermediate and end products, such as oxides, hydroxides, hydrogen and water. The hydrolysis of titanium in hydrogen peroxide solutions is particularly interesting for medical applications, forming micro- and nanoscale titania surfaces. In this paper, the content of the hydrolysis solution is revised, allowing the fabrication of gas sensor devices based on nanoporous titania. Nanopore and microcrack formations were discussed in detail by monitoring the structural changes on the thin film surface with field-emission scanning electron microscopy (FE-SEM). A stable rutile crystalline phase was detected by glancing incidence X-ray diffraction (GI-XRD) measurement after repetitive hydrothermal processes. Electrical conductance measurements were carried out at high temperatures (400–600 °C) under humid airflow (40% RH@20 °C) with the injection of various concentrations of a wide set of test compounds (C2H3N, CO, H2, NO2, C2H6O), to observe the sensing capabilities of the material. Furthermore, the humidity effects on the sensing properties toward H2, CO, and C2H6O have been discussed.

Highly sensitive and selective detection of dimethylamine through Nb-doping of TiO2 nanotubes for potential use in seafood quality control

Dimethylamine is an important indicator to check the degradation and control the quality of seafood. In this work, we present a novel, simple, fast and inexpensive method to detect dimethylamine in the range of 5–50 ppm that might be potentially useful to control the seafood quality in the future. The developed gas sensor is based on niobium-doped titanium dioxide nanotubes. The tubular structures were successfully synthesized using anodic oxidation method. The sensing properties of the obtained materials were studied towards dimethylamine gas for the first time. Dimethylamine behaves like an electron donor and induces an increase in conductivity of the n-type titanium dioxide. The presence of niobium in the titanium dioxide structure plays a crucial role to improve the functional properties of the material. Niobium acts as a donor promoting the process of gas adsorption on the structure. The response of Nb doped-material towards 10 ppm of dimethylamine is higher more than an order of magnitude compared to the pristine titanium dioxide nanotubes, leading to an essential improvement in their gas sensing performance. The obtained results enable the development of a dimethylamine gas sensor device based on titanium dioxide for the real-time monitoring and freshness detection of seafood products.

Performance analysis of gas sensing device and corresponding IoT framework in mines

Gas sensor devices usage have found prominence in fields like artificial olfactory systems and is often used to keep in check pollution and other toxic gas hazards. Graphene mono-layered sensing material along with Gold nano-particles have been previously used to formulate a sensor device. In recent times, internet of things (IoT) capable gas sensing device is a subject of great interest. Previously, it has been implemented through various wired and wireless communications like Zigbee Protocol, IBM Bluemix and sensor nodes but they have their own limitations. In this work nano gas sensor device used for detecting perilous and toxic gas has been fabricated and enhanced to increase its selectivity and sensitivity. Fabrication of Au based TiO2, CuO, ZnO, and WO3 resistive type gas sensor array has been done using sol gel method and analyzed to ensure better conduction. Application of the proposed sensing device can prevent accident in mines by precise and prompt checking of hazardous gases present inside. An IoT frame work has been proposed in this study where Node MCU (ESP8266) is used as a WiFi module along with Message Queuing Telemetry Transport protocol, which resulted in better speed and efficiency. Increased sensitivity and selectivity of the sensor nodes with better efficiency and speed of communication ensures a productive mine hazard management.

Intact Crystalline Semiconducting Graphene Nanoribbons from Unzipping Nitrogen-Doped Carbon Nanotubes.

Unzipping carbon nanotubes (CNTs) may offer a valuable route to synthesize graphene nanoribbon (GNR) structures with semiconducting properties. Unfortunately, currently available unzipping methods commonly rely on a random harsh chemical reaction and thereby cause significant degradation of the crystalline structure and electrical properties of GNRs. Herein, crystalline semiconducting GNRs are achieved by a synergistic, judiciously designed two-step unzipping method for N-doped CNTs (NCNTs). NCNTs are effectively unzipped by damage-minimized, dopant-specific electrochemical unzipping and subsequent sonochemical treatment into long ribbon-like nanostructures with crystalline basal planes. Owing to the nanoscale dimension originating from the dense nucleation of the unzipping reaction at highly NCNTs, the resultant GNRs demonstrate semiconducting properties, which can be exploited for chemiresistor-type gas-sensing devices and many other applications.

Superior Hydrogen Sensing Property of Porous NiO/SnO2 Nanofibers Synthesized via Carbonization.

In this paper, the porous NiO/SnO2 nanofibers were synthesized via the electrospinning method along with the carbonization process. The characterization results show that the pristine SnO2-based nanofibers can form porous structure with different grain size by carbonization. The hydrogen gas-sensing investigations indicate that the NiO/SnO2 sensor exhibits more prominent sensing properties than those of pure SnO2 sensor devices. Such enhanced performance is mainly attributed to the porous nanostructure, which can provide large active adsorption sites for surface reaction. Moreover, the existence of p-n heterojunctions between NiO and SnO2 also plays a key role in enhancing gas-sensing performances. Finally, the H2 sensing mechanism based on the NiO/SnO2 nanocomposite was proposed for developing high-performance gas sensor devices.

A First-Principles Study of the SF6Decomposed Products Adsorbed Over Defective WS2Monolayer as Promising Gas Sensing Device

In this paper, the adsorption of four types of SF6 decomposed products over the perfect and defective (containing one S or W vacancy) WS2 monolayer was theoretically investigated using the density functional theory (DFT). By calculating the adsorption energy, electron transfer, and comparing the band structure and the density of states (DOSs) before and after gas adsorption, the physical and chemical interactions can be evaluated. The results show that the adsorptions of the gas molecule over the perfect WS2 monolayer are mainly physisorption with the low possibility of new bond formation. In the presence of the S vacancy, the SO2 adsorption can repair the S vacancy with an energy barrier of 1.28 eV and the adsorption leads to a significant increase of the band gap and high possibility of new bond formation. The introduction of the W vacancy could not increase the adsorption energy for all gas molecules. However, it enhances the electron transfer between the SO2/H2S and the WS2 monolayer. The larger electron transfer may lead to the higher response of strong n-type or p-type WS2 monolayers toward the detected gas molecules. This paper may provide a prospective insight into the future application of the defective WS2 monolayer as gas sensing device.

Fabrication, Characterization, and Gas Sensing Performance of Pd, RGO, and MnO2 Nanoflowers-Based Ternary Junction Device

Pd, reduced graphene oxide (RGO), and MnO2 nanoflowers-based ternary hybrid junction was fabricated, characterized, and its gas sensing potentiality was established and reported in this paper. Four different types of devices, viz., pristine MnO2 nanoflowers (Device I), Pd/MnO2 nanoflowers (Device II), RGO/MnO2 nanoflowers (Device III), and Pd/RGO/MnO2 nanoflowers (Device IV) were fabricated to study the influence of each of the elements and to account for its contribution towards improving the gas sensor device performance towards alcohol vapors as the test species. After detailed structural characterizations, field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy, alcohol vapor sensing performance was studied using methanol, ethanol, and 2-propanol in the temperature range of room temperature (~27 °C) to 150 °C targeting the concentration range of 5–100 ppm. Ternary structure (Device IV) was found to offer remarkably superior performance in terms of response magnitude (RM) (~92.52% at 100 ppm), response time (~11 s), and recovery time (~16 s) compared to its binary (For Pd/MnO2: (~86.86%, ~36 s, ~43 s and for RGO/MnO2: ~80.85%, ~21 s, ~27 s) or pristine counterparts (~27.22%, ~59 s, ~67 s). The plausible cause of such remarkable improvement was attributed to the synergistic contribution of both RGO and Pd. While Pd as a catalyst helped in easy dissociation of target species ensuring the improved performance at low temperature, RGO enhanced the vapor adsorption rate due to of its additional adsorption sites and fast response/recovery kinetics due to high carrier mobility.

3D Hollow Quasi-Graphite Capsules/Polyaniline Hybrid with a High Performance for Room-Temperature Ammonia Gas Sensors.

Designing sensing materials with novel morphologies and compositions is eminently challenging to achieve high-performance gas sensor devices. Herein, an in situ oxidative polymerization approach is developed to construct three-dimensional (3D) hollow quasi-graphite capsules/polyaniline (GCs/PANI) hierarchical hybrids by decorating protonated PANI on the surface of GCs; as a result, an immensely active and sensitive material was developed for sensing ammonia gas at room temperature. Moreover, the GCs possessed a capsule-like hollow/open structure with partially graphitized walls, and PANI nanospheres were uniformly decorated on the GC surfaces. Furthermore, the inflexible and rigid 3D ordered chemistry of these materials provides the resulting hybrids with a large interfacial surface area, which not only allows for rapid adsorption and charge transfer but also provides the necessary structural stability. The 3D hollow GCs/PANI hybrids exhibit excellent performance; the GCs/PANI-3 hybrid is highly sensitive (with a response value of 1.30) toward 10 ppm NH3 gas and has short response and recovery times of 34 and 42 s, respectively. The GCs/PANI-3 hybrid also demonstrates a good selectivity, repeatability, and long-term stability, which are attributed to the substantial synergistic effect of the GCs and PANI. The design of such a unique 3D ordered framework provides a promising pathway to achieve room-temperature gas sensors for commercial applications.

First Principles Investigation of NH3 and NO2 Adsorption on Transition Metal-Doped Single-Walled Carbon Nanotubes

Density functional theory calculations were carried out to investigate the binding ability of transition metals (TM = Cr, Mo, W, Mn, Tc, and Re) on (5,5) armchair single-walled carbon nanotubes (SWCNTs) and their adsorption ability with ammonia (NH3) and nitrogen dioxide (NO2). The geometric, electronic, and energetic properties of pristine SWCNT doping with TM and their NH3 and NO2 adsorptions were calculated to explore their potentials as gas adsorptions and sensors. The binding abilities of TMs to the SWCNT are found to be in the order: Cr > Mo > Tc > Re > W > Mn. According to the results, compared to the pristine SWCNT, TM atom doping can significantly increase gas adsorption ability in which W-SWCNT has the strongest interaction, and the ability to absorb NO2 is higher than NH3. The density of states and orbital distributions display that the band gaps and electron delocalizations of TM-SWCNTs are significantly changed upon gas adsorption. These observations suggest that the TM-doped SWCNTs can be introduced as promising candidates in gas adsorptions and sensor devices for storage and detecting NH3 and NO2 molecules.

Electrochemical detection of NOx gas based on disposable paper-based analytical device using a copper nanoparticles-modified screen-printed graphene electrode

A disposable gas-sensing paper-based device (gPAD) was fabricated in origami design which integrates the gas adsorbent and the electrochemical detection zone in a single device. The gPAD for the determination of NOx gas uses a screen-printed graphene electrode modified with copper nanoparticles (CuNP/SPGE) to achieve high sensitivity and selectivity. The gPAD detects both, NO and NO2 (as NOx) with same current responses. The measurement could be performed directly through differential pulse voltammetry (DPV) with a detection limit as low as 0.23 vppm and 0.03 vppm with exposure times of 25 min and 1 h, respectively. The reproducibility in terms of relative standard deviation was less than 5.1% (n = 7 devices) at 25, 75 and 125 vppm NO2 and the life-time of this device was more than 30 days. The gPAD was applied to detect NOx in air and exhaust gases from cars. In comparison with spectrophotometry, there are no significant differences between both methods using a paired t-test of the results on a 95% confidence level. The designed gPAD can provide a new template model for other gas sensors with features of disposability and portability for fieldwork analysis at low cost.

Gas adsorption induces the electronic and magnetic properties of metal modified divacancy graphene

In this study, based on density functional theory calculations, we investigated the stable configurations, electronic structures, and magnetic properties of metal and non-metal atom-modified graphene substrates. The single-atom metal embedded divacancy (555–777) graphene (555-777-graphene-M, M = Fe, Ni and Pd) exhibited high stability, and the 555-777-graphene-Fe system had a larger magnetic moment than the Ni-doped system. The adsorption of NO on 555-777-graphene-Fe (or -Ni) was more stable than that of the HCN, NH3 and SO2 molecules. Among the other substrates, the NO adsorbed on 555-777-graphene-Fe system had the largest magnetic moment (3.0 μB). The metal atoms anchored on 3Si doped 555–777 graphene (3Si-graphene-M) had larger adsorption energies than the corresponding cohesive energy values for the bulk metal. The gas molecules adsorbed on 3Si-graphene-M sheets were more stable than those on 555-777-graphene-M. NO can be detected easily as a specific gas molecule because it has the largest adsorption energy. The NH3 or NO adsorbed on different 3Si-graphene-M substrates could lose or gain less transferred electrons and they exhibited moderate stability, thereby indicating that they are more sensitive than other gases and can be detected easily. Moreover, the electronic structures and magnetic properties of 3NM-graphene-M sheets were regulated by selecting different gas molecules, thereby facilitating the design of novel graphene-based spintronic or gas sensor devices.