Gas Sensitivity Response Research Articles

MoO3/SnO2Nanocomposite-Based Gas Sensor for Rapid Detection of Ammonia

Ammonia is harmful to human health, however, the detection limit of the sensor based on traditional semiconductor gas sensors is high and the speed is slow. Constructing heterostructure is an effective method to improve the performance of sensors. In this article, 1-D MoO3 nanorods and SnO2 nanoparticles are successfully combined to obtain MoO3/SnO2 nanocomposite. The 1-D structure can increase the speed of electron transport, while the nanoparticles on the surface increase the specific surface area, more importantly, the structure maximizes the interface area between the two materials which can transfer electronic more efficiently. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and Barrett–Joyner–Halenda (BJH) are used to analyze the microstructure and elemental composition of MoO3/SnO2. The diameter of MoO3/SnO2 nanocomposite is approximately 200 nm and the distribution is uniform. The response of MoO3/SnO2 nanocomposite to 100-ppm NH3 is 12.7 at 280 °C, and the response/recovery time is 13/2 s. The detection limit for NH3 can reach 10 ppb (response 1.3), which enables rapid detection of NH3 at low concentration. Electron transport requires more energy to overcome the contact barrier between pure SnO2 nanoparticles, which can also lead to electron emission and noise increase. However, the sensitive electrons of MoO3/SnO2 nanocomposite can transmit electrons along the 1-D rod-like structure of MoO3, which undoubtedly accelerates the efficiency of electron transmission. Moreover, n-n heterojunction formed between MoO3 and SnO2 to bend the SnO2 band and show better sensitivity to NH3. Therefore, MoO3/SnO2 nanocomposite shows a low detection limit and a rapid response/recovery speed. Nevertheless, the nanoparticles on the surface of MoO3/SnO2 nanocomposite begin to agglomerate with the increase of SnO2 content, which leads to the decrease of gas-sensitive response. The formation process of MoO3/SnO2 composites is also discussed in this article. The excellent gas sensing results show that MoO3/SnO2 composites are a promising gas sensing material.

Gas-sensing features of nanostructured tellurium thin films.

Nanocrystalline and amorphous nanostructured tellurium (Te) thin films were grown and their gas-sensing properties were investigated at different operating temperatures with respect to scanning electron microscopy and X-ray diffraction analyses. It was shown that both types of films interacted with nitrogen dioxide, which resulted in a decrease of electrical conductivity. The gas sensitivity, as well as the response and recovery times, differed between these two nanostructured films. It is worth mentioning that these properties also depend on the operating temperature and the applied gas concentration on the films. An increase in the operating temperature decreased not only the response and recovery times but also the gas sensitivity of the nanocrystalline films. This shortcoming could be solved by using the amorphous nanostructured Te films which, even at 22 °C, exhibited higher gas sensitivity and shorter response and recovery times by more than one order of magnitude in comparison to the nanocrystalline Te films. These results were interpreted in terms of an increase in disorder (amorphization), leading to an increase in the surface chemical activity of chalcogenides, as well as an increase in the active surface area due to substrate porosity.

Gas sensing nature and characterization of Zr doped TiO2 films prepared by automated nebulizer spray pyrolysis technique

This paper investigates the Zr doped TiO2 films deposited by automated nebulizer spray pyrolysis (ANSP) technique at 500 ºC as coating temperature. The manipulation of Ti/Zr ratio on XRD study shows the stabilized anatase tetragonal crystal structure in all deposited films, and the XPS study shows C 1s, Ti 2p, Zr 3d and O 1s are spin orbits of the relative elements. The surface morphological study of FESEM shows the compact granular spherical structure for all the Zr doped TiO2 films. The optical study reveals the blue-shift of band gap energy Eg = 3.20 eV to 3.64 eV with respect to dopant (Zr). Gas sensitivity response of all films exhibits the better response to NH3 reducing gas among the other gas (C2H6O, C3H6O, CH4O, C3H8O) with a function of constant temperature (ºC) and gas concentration (ppm).

Study on the gas sensitivity of vanadium-doped molybdenum disulfide to mustard gas

As a graphene-like material, molybdenum disulfide has similar properties to graphene, but due to its excellent properties such as adjustable band gap, molybdenum disulfide has a broader application in many aspects (such as gas sensors). With the deepening of research, molybdenum disulfide cannot fully meet the needs of researchers due to defects and other reasons. Therefore, researches on doping and compounding of molybdenum disulfide have gradually attracted attention. At present, most of the research on gas sensitivity has focused on harmful gases (such as nitrogen dioxide, ammonia and carbon monoxide, etc.). There are few studies on the erosive chemical toxic mustard gas. In this paper, vanadium-doped molybdenum disulfide were prepared based on chemical vapor deposition, and the gas-sensitive response of vanadium-doped molybdenum disulfide to mustard gas was studied.

Fast response of CO2 room temperature gas sensor based on Mixed-Valence Phases in Molybdenum and Tungsten Oxide nanostructured thin films

Molybdenum - tungsten oxide (Mo1-xWxO3, x = 1, 0.8, and 0.6) nanostructured thin films-based room temperture (RT) gas sensors are prepared by means of reactive RF magnetron co-sputtering at 400 °C. The structural, morphology, topography, optical, and electrical characterizations of the prepared sensors are carried out by XRD Rietveld structure refinement analyses, SEM, AFM, UV-VIS spectrophotometer, and source meter. By controlling the deposition temperture of 400 °C, a co-existing phase of MoO3 and MoO2 in WO3 matrix is presented with high oxygen vacancies concentration as calculated from the XRD Rietveld Refinement analyses. By increasing the Mo content, the calculated oxygen vacancies concentration increases by factor of 1.36. The optical characterization of Mo0.2W0.8O3 thin film shows a high transparent of 99.6% at 500 nm. The prepared thin films have successfully tested to detect carbon dioxide (CO2) at RT (20 °C) with high selectivity and repeatability. The Mo0.4W0.6O3 sensor film shows an electrical Schottky contact with fast response and recovery times towards CO2 under UV light activation. Mo0.4W0.6O3 thin film under dark and UV conditions were able to detect low CO2 concentration of 2 and 0.5 sccm CO2 at RT, respectively. Under UV illumination, Mo0.4W0.6O3 film shows a fast response and recovery time of 6.53 and 8.05 s at 0.5 sccm with sensitivity of 29.19%. Under UV photonic activation, higher electron concentration is presented in the oxide surface, which leads to high probability for reaction with CO2 molecules, and consequently enhanced the chemisorption of CO2. The enhanced CO2 gas sensitivity and fast response may refer to the high oxygen vacancies concentration and the active role of the grain boundaries in MoO2, MoO3 and WO3 mixed-valence nanostructured under UV activation.

A DFT study of dissolved gas (C2H2, H2, CH4) detection in oil on CuO-modified BNNT

In this work, CuO modified BNNT surface was investigated by DFT calculation. We suppose that BNNT is a potential gas sensitive material. The modified model is present, and the combination between CuO and BNNT proved to be stable by DFT. Besides, CuO-modified BNNT shows high reactivity and sensitivity toward dissolved gas in oil. After the adsorption of dissolved gas in oil, and the adsorption capacity occurred in the following order: C2H2 > H2 > CH4. CuO-BNNT has a chemical adsorption effect on C2H2 only. Meanwhile, band gap of the system increased by 72.0% after the adsorption of C2H2, which leading to a significant decrease in conductivity. Importantly, the recovery time at room temperature (298 K) is significantly shorter than other recently proposed materials. The CuO-BNNT system shows excellent gas-sensitive response to C2H2, but low sensitivity to CH4 and H2. This allows detection of C2H2 in certain gas environments without interference.

Self-Assembled Monolayer of Metal Oxide Nanosheet and Structure and Gas-Sensing Property Relationship.

Semiconducting 2D metal oxides have attracted great research interests for gas-sensing applications because of their considerable specific surface area and highly homogeneous surface. Developing a method for fabricating thin films of 2D metal oxides is crucial for minimizing the negative effects on sensing performance caused by slow diffusion. In this work, a simple, versatile, and highly reproducible self-assembly method is developed for fabricating monolayer film sensors made from metal oxide nanosheets with much superior sensing performance compared with their thick film counterparts. To prepare the monolayer film sensors, a monolayer film of metal oxide nanosheets, self-assembled at the air-water interface, is transferred onto a sensor substrate. The CuO monolayer sensors prepared with this self-assembly method show much improved gas sensitivity (sensor signal: 350% vs 100% at 5 ppm of H2S) and faster response and recovery rate (τres: 20 s vs 110 s; τrec: 120 s vs 320 s) than the thick film sensors prepared from the same sensing material. The enhanced sensing performance demonstrated by the monolayer film of CuO nanosheets is explained quantitively with a modified coupled reaction-diffusion model. Similar enhancement on gas-sensing performance is also observed for the ZnO-nanosheet-based monolayer sensors prepared by the same self-assembly method.

Ab Initio Study of SOF2 and SO2F2 Adsorption on Co-MoS2.

The detection of partial discharge by analyzing the decomposition components of SF6 gas in gas-insulated switchgears plays an important role in the diagnosis and assessment of the operational state of power equipment. Recently, the application of transition metal-modified MoS2 monolayer dioxide in gas detection has received wide attention. In this paper, first-principle density functional theory calculations were adopted to study the gas-sensitive response of Co-MoS2 monolayer to SOF2 and SO2F2. It is found that the conductivity of the Co-MoS2 monolayer has been effectively enhanced after Co atom doping on the MoS2 monolayer. After gas adsorption, electrons transfer from the Co-MoS2 monolayer to the gas molecules, resulting in significant reduction of conductivity of the adsorption system. The calculation results reveal that the Co-MoS2 monolayer is sensitive and selective to SOF2 and SO2F2 gases. This study provides the theoretical possibility of using Co-MoS2 as a gas sensor for SOF2 and SO2F2 gas detection.

НЕЛИНЕЙНЫЕ ЭФФЕКТЫ СОВМЕСТНОГО ВОЗДЕЙСТВИЯ ОКСИДОВ р- И d-ЭЛЕМЕНТОВ ПРИ СОЗДАНИИ ТОНКИХ ПЛЕНОК НА ПОВЕРХНОСТИ GaAs И InP ОБЗОР

Рассмотрен процесс термооксидирования арсенида галлия и фосфида индия под воздействием бинарных оксидных композиций (хемостимулятор+хемостимулятор и хемостимулятор+инертный компонент). Установлены и интерпретированы нелинейные эффекты зависимости толщины оксидной пленки на поверхности GaAs и InP от состава композиции оксидов-хемостиуляторов. Доказана возможность получения аддитивной во всем интервале составов зависимости толщины оксидной пленки на поверхности GaAs от состава при использовании композиций оксид-хемостимулятор+инертный компонент. Установлена пространственная локализация связывающих взаимодействий между оксидами-хемостимуляторами, которые приводят к наблюдаемым нелинейным эффектам. Синтезированные таким способом тонкие пленки на поверхности GaAs и InP обладают улучшенными электрофизическими свойствами и проявляют газочувствительный отклик в атмосфере газов-восстановителей.
 
 Результаты исследований получены на оборудовании Центра коллективного пользования Воронежского государственного университета. URL:http://ckp.vsu.ru
 Работа выполнена при поддержке гранта РФФИ № №18-03-00354_а

Novel Co3O4 nanocrystalline chain material as a high performance gas sensor at room temperature

In this study, a chain structure consisting of single crystal Co3O4 nanoparticles were synthesized by a one-step thermal treatment method. The microstructure and morphology of the samples were characterized by XRD, FT-IR, TEM, XPS and EIS. It is found that Co3O4 materials display chain structure and feature 70 nm particles in the diameter size. Interestingly, the chain structure feature of our Co3O4 materials improves electrode conductivity and carrier transportation with respect to polycrystal Co3O4. When calcined at 550 °C (Co3O4-550), the resulting sample displays good gas sensing performance for NOx at room temperature. Its measured gas sensitive response is 52.1% for 100 ppm NOx, and detection limit is lower than 100 ppb. The outstanding NOx gas sensing performance of the Co3O4-550 may be attributed to its unique chain structure. Tightly stucking particles and lower potential barrier are very beneficial to improve electrical properties of Co3O4-550, which is helpful to enhance its gas sensing performance.

CO sensing properties and mechanism of Pd doped SnO2 thick-films

Abstract Pd doped SnO2 nano-particles were synthesized using co-precipitation method. The resistances of the samples first decrease and then increase, which maybe influenced by the Pd doping and temperature effect. The CO response of SnO2 was improved by doping with Pd. At low temperature range, the response decreases with increasing of operating temperature, which was caused by the physical adsorption. At higher operating temperature (160–400 °C), the response of Pd doped SnO2 for CO increases at first, undergoes a maximum at 260 °C, and finally drops. The 1.5 wt.% PdO doping SnO2 was verified to be significantly sensitive. The largest gas sensitive response of 6.59 was found at 260 °C in 400 ppm CO atmosphere. For 200 ppm CO, the response and recovery time were about 43 s and 10 s, respectively. The possible CO sensing mechanisms for Pd doped SnO2 sensors were investigated with first principles calculations. The calculation results showed that CO molecule can grab O from the pre-adsorbed oxygen on Pd4 cluster or the PdO cluster on the SnO2 (110) surface forming CO2. These processes may play important role in CO sensing for Pd doped SnO2. The calculated result is a good explanation of the experimental observation.

Scalable gas sensors fabrication to integrate metal oxide nanoparticles with well-defined shape and size

In this contribution, we propose and demonstrate a scalable and reproducible process to fabricate nano-sized functional particles and integrate them in microelectromechanical systems. We use a wet-chemistry approach for nanoparticle synthesis in combination with inkjet printing as a production process for metal oxide based gas sensors. This method enables control over size and shape of the nanoparticles as well as an ordered and reproducible deposition of a monolayer of particles onto arbitrary microstructures. Here we present results obtained using copper oxide nanoparticles as well as their synthesis and material characterization. A total of 14 layers has been produced and the baseline resistivity as well as the gas sensitive response towards oxygen, humidity and nitrogen dioxide of each layer has been determined.

Temperature & light modulation to enhance the selectivity of Pt-modified zinc oxide gas sensor

Metal oxide (MOX) has been used as resistive gas sensors for a long time. The gas sensitive response under constant temperature measurement is a broad-spectrum response, resulting in poor selectivity. To solve this problem and enhance the selectivity of a single sensing film, gas sensor based on Pt-modified zinc oxide was prepared by homogeneous precipitation and screen printing method. Afterwards, the temperature & light modulation method is first proposed herein. This method allows us to obtain different Resistance-Temperature (R-T) curves and characteristic parameters, photoresponse and photorelaxation. Combined with pattern recognition method, five tested gases, including ethanol, methanol, acetone, formic acid and ethyl ether, can be successfully classified. Compared with temperature modulation, which is usually used as a method to enhance selectivity, temperature & light modulation method can increase the classification rate from 95.55% to 100% for sensing these five tested gases. The results indicate that the temperature & light modulation method is an effective method for improving the selectivity of the gas sensor.

KOH post-etching-induced rough silicon nanowire array for H2 gas sensing application

The limited surface area and compacted configuration of silicon nanowires (SiNWs), which are made by one-step metal-assisted chemical etching (MACE) go against target gas diffusion and adsorbtion for gas sensing application. To harvest suitable gas sensitivity and fast response–recovery characteristics, an aligned, rough SiNW array with loose configuration and high surface area was fabricated by a two-step etching process. The MACE technique was first employed to fabricate a smooth SiNW array, and then a KOH post-etching method was developed to roughen the NW surface further. The influence of the KOH post-etching time on the array density and surface roughness of the SiNWs was investigated, and the H2-sensing properties of the sensor based on the as-fabricated rough SiNW array were evaluated systematically at room temperature. It was revealed that the post-etching of KOH roughens the NW surface effectively, and also decreases the wire diameter and array density considerably. The resulting configuration of the SiNW array with high active surface and loose geometry is favorable for gas sensing. Consequently, the rough SiNW array-based sensor exhibited a linear response to H2 with a wide range of concentrations (50–10 000 ppm) at room temperature. Good stability and selectivity, satisfying response–recovery characteristics were also achieved. However, over-etching of SiNWs by KOH solution results in a considerable decrease in surface roughness and then in the H2-sensing response of the NWs.

SINGLE ANODE TRIPLE GEM TISSUE EQUIVALENT PROPORTIONAL COUNTER AS THE BASIS FOR A PERSONAL NEUTRON DOSIMETER.

This paper reports on a tissue-equivalent proportional counter (TEPC) based on a triple gas electron multiplier structure, with a single pad readout, as a basis for a personal neutron dosimeter. Its dosimetric response was studied using the 252Cf neutron source at the Health Physics Generator Facility of the Canadian Nuclear Laboratories. Measured lineal energy spectra were found to be in agreement with numerical simulations performed with Monte Carlo N-Particle eXtended (MCNPX). Both simulations and measurements showed that the mean pathlength of secondary charged particles in the TEPC gas was best represented by the thickness of the drift region of the device. It was determined that the Cauchy Theorem, used to calculate the mean chord length in spherical and cylindrical TEPCs, overestimated the simulated mean chord length by nearly a factor of two. Important operational characteristics of the device were investigated, including gas gain, sensitivity and dosimetric response, as functions of tissue-equivalent gas pressure. This work demonstrates that the proposed design can serve as the basis for a personal neutron dosimeter device, which would satisfy the angular dosimetric response criteria of the personal dosimeter standard IEC61526.

Fast identification of CO by using single Pt-modified WO3 sensing film based on optical modulation

CO sensor based on metal oxide has been developed for a long time. Although the gas sensitive response of sensor is greatly improved already, the poor selectivity and interference immunity limit the application. To achieve the purpose of fast identification of CO by a single sensing film, the optical modulation method is first proposed and applied herein. This method allows us to be capable of obtaining the characteristic parameters, the photoresponse and the photogenerated carrier lifetime, based on the optical modulation spectra. According to the characteristic parameters, CO can be successfully distinguished from the other gases, including H2, ethyl alcohol and acetic acid. The results show that the optical modulation provides an effective method for fast and accurately identifying gas species and opens up a way to investigate the selectivity of the MOX sensors.

Ozone flexible sensors fabricated by photolithography and laser ablation processes based on ZnO nanoparticles

Ozone gas sensors on flexible substrate with Ti/Pt interdigitated electrodes have been fabricated by standard photolithography and femtosecond laser ablation processes under the same conditions. ZnO nanoparticles deposited by drop coating method have been used as sensitive thin film material with 280nm thickness due to their excellent characteristics on gas detection. The physical properties obtained by both processes have been studied and their critical effects on the gas sensitive response are discussed. It was found that although both samples present small dimensional variations, the samples fabricated by laser ablation shows a bigger sensitive response to ozone at 200°C. However, both samples have been used as ozone gas sensor and present excellent sensing characteristics, giving good stability, fast response/recovery and excellent range of detection from 5ppb to 300ppb.

Preparation of Cu<sub>2</sub>O (Cu)/MWCNTs Composite Particles and Their Gas Sensor Properties

Multiwall carbon nanotubes (MWCNTs) were embedded in cuprous oxide and copper to give ternary (Cu2O (Cu))/MWCNTs composites, Cu (CH3COO) 2•H2O and the treated MWCNTs were used as source precursor for producing composite particles by polyol method. Ethylene glycol (EG) was used as solvent and reducing agent. The products were characterized through scanning electron microscope (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The results have shown that the MWCNTs are embedded into the cuprous oxide and copper spheres homogeneously. At room temperature, the composite materials to the NOx have excellent gas sensitive response contrast to NH3, CO, H2. The concentration of NOx is 700 ppm, the maximum value of Cu2O/MWCNTs vs. the NOx gas sensor response sensitivity is 20.3 %, and gas sensor response has certain selectivity.

Time influence factor of vanadium oxide nanotube on Si substrate and initial gas sensing test

Vanadium oxide nanotubes are prepared on a Si substrate with hydrothermal method in this experiment with dodecylamine serving as template. X-ray diffraction, Raman spectroscopy and scanning electron microscope (SEM) are employed to characterize the structural and electronic properties of these nanotubes. The results show that the growth of VOX nanotubes and their gas sensing properties are affected by the hydrothermal reaction time rather than mixing time. With longer reaction time, the VOX nanotubes display better properties with smoother walls, stronger gas sensitivity and faster response time (15 s), than with shorter reaction time. SEM results reveal that VOX nanotubes have inner diameters between 25-35 nm and outer diameters between 65-100 nm. The sample inner diameters vary between 25 and 35 nm. The outer diameters are also quite similar in all tubes and lie between 65 and 100 nm.

Synthesis of ultra-thin polypyrrole nanosheets for chemical sensor applications

Ultra-thin polypyrrole nanosheets (UPNSs) are fabricated by organic crystal surface-induced polymerization (OCSP) of pyrrole in an aqueous suspension containing hydrated crystals of sodium decylsulfonate (C 10SO 3Na) below the Krafft temperature using FeCl 3 as an oxidant. The hydrated C 10SO 3Na crystals are used as templates through electrostatic binding of the cationic polypyrrole (PPy) chains oxidized by Fe(III) ions on the anionic C 10SO 3Na crystal surface. The resulting UPNSs have a single layer thickness of ∼21 nm, widths between 2 and 6 μm, and lengths greater than 10 μm. The UPNSs are composed of a single continuous PPy domain. Moreover, the UPNSs exhibit higher conductivity (30.6 Scm −1) and longer conjugation lengths than the PPy nanoparticles (2.4 Scm −1) prepared using emulsion polymerization. We systematically investigate the UPNSs as gas sensors for detecting and quantifying toxic gases such as HCl and NH 3. The UPNSs exhibit much higher gas sensitivity and faster response times compared with the PPy nanoparticles.