Fabrication of diamond nanorods for gas sensing applications

Diamond nanorods were fabricated for a sensing device by utilizing reactive ion etching in CF₄/O₂ radio frequency plasma. The length of the nanorods has been controlled by the ion etching time. The obtained morphologies were investigated by scanning electron microscopy. The gas sensing properties of the H-terminated diamond-based sensor structures are indicating that we have achieved high sensitivity to detect phosgene gas. Also, our sensor exhibited good selectivity between humid air and phosgene gas if the measurement is conducted at elevated temperatures, such as 140 °C. Furthermore, such sensor response rating could reach as high value as 4344 for the phosgene gas, which was evaluated for the sample consisting of the longest nanorods (up to 200 nm).     

A Sensitive “Optical Nose” for Detection of Volatile Organic Molecules Based on Au@MOFs Nanoparticle Arrays through Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) is an effective technique for detecting toxic gas and volatile organic molecules (VOMs); however, recent SERS-based gas sensors have disadvantages and lack an effective approach to capture toxic gas and insufficient reproducibility of SERS substrates. Herein, a facile strategy is developed to integrate metal-organic frameworks with Au nanoparticle (NP) arrays to form Au@ZIF-8 NP arrays, which can be used as an “optical nose” based on SERS to detect toxic VOMs with good reproducibility and sensitivity. Toluene as a target molecule is recognized at ppm levels by the Au@ZIF-8 NP arrays in situ. And the analytical enhancement factor of Au@ZIF-8 NP arrays for toluene is about 1.2 × 10⁵. Importantly, this SERS substrate can also detect the 1-butanol molecule, which provides an idea for designing a universal VOM sensor. In addition, the coating method of the ZIF-8 shell can be extended to synthetize various NPs@ZIF-8 core–shell composites, such as Au nanospheres@ZIF-8, Au@Ag nanorods@ZIF-8, PS microspheres@ZIF-8, and Fe₂O₃ microellipsoids@ZIF-8 composites.     

Sensor based on a Pt/LaF3/SiO2/SiC structure for the detection of chlorofluorocarbons

A metal-insulator-semiconductor structure based on silicon carbide with a subgate layer of LaF₃ solid electrolyte is discussed as a gas sensor. The kinetics of the variation of the flat-band potential of a Pt/LaF₃/SiO₂/SiC structure in interaction with chlorofluorocarbons (Freons) is investigated in the temperature range from 300 to 530 °C. The activation energies of the gas sensitivity are estimated from the temperature dependences of the response rate of the sensor to various Freons. The possibility of detecting all the investigated chlorofluorocarbons at a concentration level of 10 ppm in air is demonstrated. Zh. Tekh. Fiz. 69, 80–85 (November 1999)     

Adsorption behaviour of SO2 and SOF2 gas on Rh-doped BNNT: a DFT study

Abstract

As the insulating medium, SF₆ is widely used in gas insulation equipment. Partial discharge and local overheating can cause the decomposition of SF₆, resulting in a decrease in insulation strength of the equipment. The detection of SF₆ decomposition gas can be used for on-line insulation detection of gas insulation equipment in electric power industry. In order to develop a new sensor gas sensing material for gas detecting. In this work, based on the first-principles density functional calculation (DFT) method of DMol³, the adsorption of SF₆ decomposition gas on (5,0) Z-type Rh-BNNT in different ways was explored. The adsorption energy, adsorption distance, charge transfer as well as density of states were discussed. The results show that the adsorption strength between SO₂ molecule with Rh-BNNT is larger than with SOF₂ molecule, combined with desorption time, theoretically predicts Rh -BNNT have the potential to be a material for SO₂ gas sensors.     

Universal SAW gas sensor

A new principle of designing a SAW gas sensor is described. This sensor, being essentially of sorption type, also offers properties of thermometric SAW sensors. The basic idea here is that heat fluxes propagate between the SAW substrate and the working surface of the temperature-regulating system with some delay. A sensor based on this principle can detect not only the vapors of volatile substances but also gases by their thermal properties, retaining high temperature stability and speed of response unlike conventional SAW thermometric sensors. The design of this sensor built around a LiNbO₃ SAW delay line is described, and experiments on detecting a household propane-butane mixture with this sensor are reported. In particular, the responses of the sensor are measured at different gas-flow rates, two different SAW substrate temperatures, and two propane-butane concentrations. Ways of improving the sensor’s performance are discussed.     

A photonic crystal fiber sensor based on differential optical absorption spectroscopy for mixed gases detection

A photonic crystal fiber sensor based on differential optical absorption spectroscopy for mixed gas detection is presented. In such sensor, hollow core photonic crystal fiber is utilized as gas cell and the feasibility for gas detection is verified by experiment. The components concentration of mixed gas NH₃ and C₂H₂ are measured and the detection sensitivity is 143 ppmv.     

Response of a thermocatalytic sensor with a single-crystal silicon heater

The sensor response of a thermocatalytic gas sensor with a heater made of single-crystal p-type silicon to gases H₂, CO, CH₄, and C₃H₈ is studied. The sensor response to propane, carbon monoxide, and hydrogen has positive and negative components. The positive sensor responses to carbon monoxide and propane exhibit well pronounced maxima at silicon heater currents of 21 and 23 mA, respectively. For hydrogen, the maximum sensor response depends on the gas concentration. This specific feature of the sensor response to hydrogen is explained by the sequential action of the following two processes: absorption of H₂ molecules on the silicon heater surface and the catalytic oxidation of hydrogen on a Pt-Pd catalyst. The sensor response to methane only has a negative component.     

QEPAS for chemical analysis of multi-component gas mixtures

A gas sensor based on quartz-enhanced photoacoustic spectroscopy and using near-infrared, fiber-coupled diode lasers as an excitation source was developed for chemical analysis of gas mixtures containing H₂S, CO₂, and CH₄ at concentrations from 0 to 100%. Analysis of physical phenomena affecting the sensor operation is performed, the sensor performance is evaluated, and simple algorithms are developed to derive concentrations of the gases from detected electrical signals.     

A Significant Fluorescent Aptamer Sensor Based on Carbon Dots and Graphene Oxide for Highly Selective Detection of Progesterone

In this paper, a fluorescent aptamer sensor was constructed based on the carbon dots (CDs) and graphene oxide (GO). This sensor combines the excellent fluorescence performance of CDs with the high specificity of aptamer, which can detect progesterone (P₄) with high sensitivity and selectivity. In the absence of P₄, the CDs-aptamer system and GO form a fluorescence resonance energy transfer process (FRET), which quenches the fluorescence of the CDs. When P₄ is added, the aptamer specifically binds to it, resulting the fluorescence of the CDs is recovered. At optimal conditions, the fluorescence intensity recovered by the CDs has a linear relationship with the concentration of P₄ in the range of 0.1–120 nM and the detection limit is 3.3?×?10^–11 M. Besides, the sensor has satisfactory detection results of P₄ in milk, indicating that constructed method has enormous potential for application in food safety.

     

Optimum sensitivities of D-type optical fiber sensor at a specific incident angle

The optimum incident angle for a 4 mm long and 4 μm core thickness D-type optical fiber sensor in the intensity measurements is near at 89°. The sensitivity is higher than 40 (1/RIU) and its resolution is better than 2.5×10^-5 RIU. This sensor is used to detect the refractive index or gas or liquid concentration in real-time, and it has some merits such as small, simple and inexpensive and provides an in vivo test. PACS 42.81.Pa; 07.07.Df; 73.20.Mf; 42.62.Eh; 07.60.Vg     

Synthesis of multi-walled carbon nanotubes for NH3 gas detection

It has been recently demonstrated that carbon nanotubes (CNTs) represent a new type of chemical sensor capable of detecting a small concentration of molecules such as CO, NO₂, NH₃.In this work, CNTs were synthesized by chemical vapor deposition (CVD) on the SiO₂/Si substrate by decomposition of acetylene (C₂H₂) on sputtered Ni catalyst nanoparticles. Their structural properties are studied by atomic force microscopy, high-resolution scanning electron microscopy (HRSEM) and Raman spectroscopy. The CNTs grown at 700 °C exhibit a low dispersion in size, are about 1 μm long and their average diameter varies in the range 25–60 nm as a function of the deposition time. We have shown that their diameter can be reduced either by annealing in oxygen environment or by growing at lower temperature (less than 600 °C).We developed a test device with interdigital Pt electrodes on an Al₂O₃ substrate in order to evaluate the CNTs-based gas sensor capabilities. We performed room temperature current–voltage measurements for various gas concentrations. The CNT films are found to exhibit a fast response and a high sensitivity to NH₃ gas.     

Arsenic pentafluoride surface adsorption studies on Kagome-phosphorene – a DFT outlook

Arsenic pentafluoride (AsF₅) is a highly toxic gas molecule that finds its application in the manufacturing of electro-conductive polymers. Besides, exposure to AsF₅ molecule may invite several health issues, for instance, central-nervous-system disorders. Thus, the detection of AsF₅ gas is a significant and important concern for public health. For the very first time, we built a novel Kagome phosphorene nanosheet (Kagome-PNS) to study the adsorption behavior of AsF₅ molecule on the Kagome-PNS surface using density-functional theory method. The Kagome-PNS owns semiconductor property with an energy gap value of 1.22 eV. Initially, the geometrical stability of Kagome-PNS was verified with the negative value of cohesive formation energy. The transport properties of Kagome-PNS have also been carried out using current-voltage characteristics. Moreover, AsF₅ gas molecules are physisorbed on Kagome-PNS, the adsorption energy of the preferential complex structures is found to be −0.099 to −0.377 eV. An innovative finding of the present study acclaims that Kagome-PNS can be proficiently used as a chemical sensor to detect AsF₅ gas molecules.     

Resonance detection of dark matter axions using a DC SQUID

A method for detecting dark matter axions in which a dc SQUID serves as a detector is proposed. The SQUID is shown to be able to detect the magnetic field perturbations induced by its interaction with axions. The resonance signal appears as a current step in the SQUID current–voltage characteristic. The voltage of the step corresponds to the axion mass, while its height depends on the axion energy density in near-Earth space. The proposed method is aimed at detecting axions with masses m_a ? 10^–4 eV, which are of interest for both cosmology and particle physics.     

Exhaled gas detection by a novel Rh-doped CNT biosensor for prediagnosis of lung cancer: a DFT study

Lung cancer has received considerable attention in recent years due to its high mortality. The difficulty in awareness of such disease can be attributed to its strong insidiousness during the early stage. Therefore, the prognosis of lung cancer becomes significant so as to nip this disease in the bud. In this paper, the Rh-doped CNT-based biosensors were introduced to realise the diagnosis of lung cancer through detecting the exhaled gas of possible patients. The adsorption property and sensing mechanism of Rh-CNT towards two kinds of mainly typical gases of lung cancer, namely, C₆H₆ and C₆H₇N, were analysed based on density functional theory, aiming at evaluating the potential application of such material to be gas sensors. The results indicated that the Rh-CNT not only has good adsorption towards such two gases but also obvious conductivity increase when interacted with any of them, while presents insensitivity upon the common exhaled gas, CO₂. We suggest the Rh-CNT be prepared as biosensors applied in the field of lung cancer pre-diagnosis that can be used in our daily life without pain and complex clinical examination.     

Preparation and characterisation of ZnFe2O4/ZnO polymer nanocomposite sensors for the detection of alcohol vapours

During the last 10 years, a large interest has developed in the preparation of nanocomposite structures by embedding inorganic nanoparticles into polymeric materials. These materials combine the properties of the inorganic fillers with the processability and flexibility of polymers. The versatility of polymer nanocomposite systems is of special interest to the gas sensor industry where arrays of polymer/carbon black composites have been used to identify gases and odours. These polymer gas sensors provide selectivity based on their chemical structures and operate at room temperature, which provide advantages over thick-film metal oxide gas sensors. ZnFe₂O₄ and ZnO have excellent stability, high sensitivity, low fabrication complexity and moderate operating temperatures, which are ideal properties for a gas sensing material. In this work, the development of a thick-film ZnFe₂O₄/ZnO sensor, which operates at room temperature and a drop-coated conducting polymer composite sensor containing 30 w/w% ZnFe₂O₄/ZnO nanoparticles is discussed. The sensors were tested in a fully automated test rig and showed promising results for the detection of alcohol vapours.     

Two-channel IR gas sensor with two detectors based on LiTaO3 single-crystal wafer

An infrared (IR) single-element detector based on a lithium tantalate (LiTaO₃) single-crystal wafer has been successfully fabricated. The preparation and design of the device are discussed and analyzed in detail. The processing of a thin LiTaO₃ wafer, the characterization of an IR filter window, and the assembly of the wafer and filter are explained. A LiTaO₃ sensor element, a CMOS amplifier, a narrow-band filter (which can be selected to operate within the appropriate spectral region), and the read-out circuits are set into a TO-18 vessel. Each TO-18-type detector offers a single channel (a single detection wavelength). Two TO-18 detectors with different filters, one acting as a detection channel and the other as a reference, a broadband light source, a circuit board and a flake of wire gauze are assembled and integrated into a gilded gas cell for the purpose of detecting ethene gas.     

Grain Size Effects in Sensor Response of Nanostructured SnO2- and In2O3-Based Conductometric Thin Film Gas Sensor

Based on the experimental results, obtained by studying both structural and gas-sensing properties of the SnO₂ and In₂O₃ films deposited by the spray pyrolysis method, we analyzed the influence of crystallite size on the parameters of the SnO₂- and In₂O₃-based thin film solid-state gas sensors. For comparison, the behavior of ceramic-type gas sensors was considered as well. In particular, we examined the correlation between the grain size and parameters of conductometric-type gas sensors such as the magnitude of sensor signal, the rate of sensor response, thermal stability, and the sensitivity of sensor signal to air humidity. Findings confirmed that that grain size is one of the most important parameters of metal oxides, controlling almost all operating characteristics of the solid state gas sensors fabricated using both the ceramic and thin film technologies. However, it was shown that there is no single universal requirement for the grain size, because changes in grain size could either improve, or worsen of operating characteristics of gas sensors. Therefore, the choice of optimal grain size should be based on the detailed consideration of all possible consequences of their influence on the parameters of sensors designed.     

Combustion synthesis of magnesium ferrite as liquid petroleum gas (LPG) sensor: Effect of sintering temperature

We report synthesis of Spinel type magnesium ferrite (MgFe₂O₄) material by a simple, inexpensive combustion method with glycine as a fuel and their application as a gas sensor for reducing gases (LPG, Acetone, Ethanol, Ammonia). The dependence of reducing gas sensing properties on the structural and surface morphological properties has been studied as an effect of sintering temperatures. The structural and surface morphological properties were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The MgFe₂O₄ were highly oriented along (311) with the spinel type crystal structure. The SEM observation reveals that porous morphology decreases due to the grain growth as sintering temperature increases. The mechanism of reducing gas sensing by the MgFe₂O₄ pellets is explained on the basis of adsorbed oxygen on the sensor surface. The selectivity and maximum response of 71% to 2000 ppm of LPG was observed at 698 K with the (MgFe₂O₄) material sintered at 1173 K.     

UV-LED Photo-activated Chemical Gas Sensors: A Review

Metal oxide semiconductor gas sensors operating under UV irradiation have been validated for detection of variety of chemicals in wide ranges of concentrations at room temperature. This article reviews recent advances in UV-activated metal oxide gas sensors in general and outlines the operating principles and sensing performance of UV-LED based sensors in particular. The sensing properties of several metal oxide semiconductors such as ZnO, TiO₂, SnO₂, In₂O₃, and metal oxide composites under UV-LED irradiation are individually presented and their advantages and shortcomings toward various gases are compared. Moreover, it is demonstrated that for the UV-LED based gas sensors, the performance can be improved by optimizing the sensor platform design and UV source parameters such as wavelength and power intensity. Further, it is illustrated that the gas sensing selectivity can be tuned by modifying the semiconductor layer structure or adjusting appropriate wavelength to an optimal value.     

Fiber-Optic Ammonia Sensors Utilizing Rectangular-Cladding Eccentric-Core Fiber

A new fiber-optic ammonia sensor utilizing rectangular-cladding eccentric-core fiber and a sensitive film containing an indicator dye is demonstrated. The sensitive film is a SiO₂-GeO₂ gel film including an indicator dye of bromocresol purple or bromocresol green, which is dip-coated by a sol-gel technique. The attenuation of this sensor changes depending on the concentration of ammonia at the wavelength range of 500–700 nm. This sensor can detect several ppm of gaseous ammonia. Various factors determining the sensitivity to detect the ammonia gas and time response of the sensor are also studied.