High-sensitivity Gas Research Articles

A portable low-power integrated current and temperature laser controller for high-sensitivity gas sensor applications.

A low-noise, low power, high modulation-bandwidth design integrated laser current and temperature driver with excellent long-term stability is described. The current driver circuit is based on the Hall-Libbrecht design. A high sensitivity and a stable driver current were obtained using a differential amplifier and an integral amplifier. The set-point voltage for the current driver came from an ultra-compact, ultra-low temperature coefficient voltage reference chip or the digital to analog convertor output of a microcontroller or a modulation signal. An integral temperature chip, referred to as ADN8834, was used to drive the thermoelectric cooler controller of the distributed feedback (DFB) laser. The internal amplifier acquired the feedback current of the temperature sensor. The proportional-integral-derivative parameters such as proportion, integration, and derivative were set by external resistors. The short- and long-term stability and linearity of the developed laser driver were tested using a DFB laser with a central wavelength of 6991 cm-1. The laser driver was validated for high-sensitivity gas sensing of CO2 and C2H2 via a laser absorption spectroscopy experiment. The limits of detection were less than 11.5 ppm and 0.124 ppm for CO2 and C2H2, respectively. Direct absorption measurements and the 1-f and 2-f demodulation signals confirmed the capabilities of the proposed laser driver system in high-sensitivity gas sensing applications. The driver unit can readily be accommodated into many portable laser sensing devices for industrial applications.

Evaluation of various solid wastes produced after the Great East Japan Earthquake

In order to know the risk of fire of disaster waste, radioactive waste and recycled materials, thermal analysis and gas emission test were conducted. Huge amount of disaster waste and radioactive waste were produced after the Great East Japan Earthquake (March 2011). During recovery work, we experienced many fires and accidents due to spontaneous ignitions from massive disaster and radioactive wastes. Some of wastes should be recycled for biofuel and constructive materials. To know the risk of ignitions and fires, we conducted risk evaluation for these materials using high sensitive calorimeters and gas emission. The investigation process and results are shown. Microorganism in the wastes caused faint heat generation which might be a trigger of fires. However disaster wastes are much safer than most solid biofuel, because disaster wastes contained large amount of incombustible materials.

Real-time monitoring of skin ethanol gas by a high-sensitivity gas phase biosensor (bio-sniffer) for the non-invasive evaluation of volatile blood compounds

In this study, a highly sensitive and selective biochemical gas sensor (bio-sniffer) and real-time monitoring system with skin gas cell was constructed for the determination of ethanol gas concentration on human skin. This bio-sniffer measured the concentration of ethanol according to the change in fluorescence intensity of nicotinamide adenine dinucleotide (NADH), which is produced in an enzymatic reaction by alcohol dehydrogenase (ADH). The NADH detection system used an ultraviolet light emitting diode (UV–LED) as the excitation light, and a highly sensitive photomultiplier tube as a fluorescence intensity detector. The calibration range of the ethanol bio-sniffer was validated from 25 ppb to 128 ppm. To measure the concentration of ethanol within skin gas, subjects ingested an alcohol beverage, and the sensor output was monitored. We chose the central part of the palm, a back of the hand, and a wrist as targets. The real-time concentration of skin ethanol gas at each target was measured after drinking. The maximum output values were reached at approximately 70 min after drinking and then gradually decreased. We showed that ethanol release kinetics were different depending on the part of the hand measured with the developed monitoring system. Accordingly, this highly sensitive and selective bio-sniffer with a skin gas cell could be used to measure ethanol on the skin surface and could be applied for breath and skin gas research, as well as investigation of volatile blood compounds used as biomarkers for clinical diagnosis.

Fabrication of three-dimensional zinc oxide nanoflowers for high-sensitivity fiber-optic ammonia gas sensors

ZnO is identified as one of the promising coating materials in optical fiber for ammonia gas sensors. In this work, three-dimensional ZnO nanoflowers are fabricated via a facile hydrothermal method and used as sensitive coating materials for optical fiber ammonia gas sensors. Results show that the sensor with ZnO nanoflowers exhibits a high sensitivity of 5.75 pm/(μg·L-1) for ammonia concentration ranging from 0 to 5460 μg·L-1, which is more than 2.6 times higher than that of the sensor with a coating of ZnO microspheres [2.2 pm/(μg·L-1)].

Electrospinning of Ultrafine Conducting Polymer Composite Nanofibers with Diameter Less than 70 nm as High Sensitive Gas Sensor.

Polyvinyl alcohol/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PVA/PEDOT:PSS) composite ultrafine fibers were successfully fabricated by high pressure airflow assisted electrospinning. The electrical properties of PVA/PEDOT:PSS nanofibers with different diameters were characterized. The average diameter of the nanofibers can be down to 68 nm. Due to its large specific surface area, ammonia sensing of the ultrafine nanofibers is more sensitive than the traditional electrospun fibers (average fiber diameter of 263 nm). The ammonia sensing properties of the samples were tested by impedance analysis. The results show that ultrafine PVA/PEDOT:PSS nanofibers are more suitable for detecting low concentrations of ammonia with higher sensitivity.

Highly-sensitive gas sensor based on two-dimensional material field effect transistor

Atomically thin two-dimensional (2D) materials are ideal gas sensing materials for achieving an ultra-low detection limit, due to the high surface-to-volume ratio, low electronic noise and sensitively tunable Fermi level. However, the sensitivity of 2D materials to their surrounding environment may also severely degrade the long-term stability of sensing devices, since most of them use the same 2D material flake as both the sensing and conduction material. In this work, we report a gas sensor based on a 2D material field effect transistor (FET) which uses few-layer black phosphorus (BP), boron nitride (BN) and molybdenum disulfide (MoS2) as the top-gate, dielectric layer and conduction channel, respectively. In this device configuration, the top-gate of BP with a superior gas adsorption capability serves as the sensing material, while the conduction channel of MoS2 is isolated from ambient environment by the coverage of the BN dielectric layer. The separation of the sensing and conduction materials not only improves the long-term stability of the device, but also enables us to use different materials for gas adsorption and conduction purposes to achieve optimum sensing performances. In addition, the adsorption kinetics of the gas molecules on the sensing channel can be sensitively detected by the current/resistance variation of the conduction channel, since the adsorbed gas molecules can effectively tune the Fermi level of sensing and conduction materials (BP and MoS2, respectively) through band alignment. We experimentally demonstrated that the proposed 2D material FET not only achieved a detection limit of 3.3 ppb to NO2, but was also capable to differentiate oxidizing and reducing gases.

A High-Sensitivity Hydrogen Gas Sensor Based on Carbon Nanotubes Fabricated on Glass Substrate

A hydrogen (H2) gas sensor had been fabricated using a carbon nanotube (CNT) which was produced via a conventional microwave oven. It was deposited onto a glass substrate between two Palladium (Pd) electrodes using the dielectrophoretic deposition method. The hydrogen sensing capability of the multiwall carbon nanotube (MWCNT) gas sensor was determined at different operating temperatures and gas concentrations, ranging from 20 ppm to 1000 ppm. The results indicate that the gas sensor exhibits high sensitivity, up to 240% upon exposure to 1000 ppm of H2 at room temperature (RT). Additionally, at room temperature, the sensor shows an excellent sensitivity of 31% when exposed to a very low H2 gas concentration of 20 ppm. The fabricated MWCNT sensors displayed excellent reproducible and reversible responses towards hydrogen at room temperature. Furthermore, MWCNTs were fabricated onto a glass substrate for the detection of H2 gas without the supplementary assistance of metal decoration, vacuum system, or additional film coatings. The high response, low cost, fast recovery, and low power consumption of the fabricated MWCNTs gas sensor validates its superior potential for H2 gas sensing ability at low temperatures.

A High Sensitivity and Compact Real Time Gas Concentration Sensor for Semiconductor and Electronic Device Manufacturing Process

We have been studying in-line gas concentration sensor units for various metal-organic(MO) gases used in electronic device manufacturing process. MO gases are low vapor pressure and are generally supplied by bubbling. At the time of bubbling supply, concentration control is performed by internal pressure control and feedback control by in-line gas concentration sensor units for concentration correction due to lowering of the liquid level inside the MO tank. We have evaluated a high sensitivity in-line gas concentration sensor that adopts ultraviolet absorption method and charge amplifier detection circuit and demonstrated that it is a unit with high response speed of 400 msec or less and high detection sensitivity. In this report, we confirmed that it is possible to measure the concentration of Zr, Hf type MO gas used for semiconductor gate insulating film.

Sensing characteristics of clad-modified (Ho-doped Bi2O3 nanoparticles) fibre optic gas sensor

Abstract Sensing characteristics of Ho (1, 3 and 5% mol) – doped Bi 2 O 3 clad-modified fibre optic gas sensor are studied for ammonia, ethanol, methanol and acetone gases at ambient temperature. Bi 2 O 3 doped with all concentrations of Ho shows good gas response to acetone, whereas, 1% and 3% mol of Ho show to methanol. Ammonia and ethanol show very poor gas response for all the doping concentrations. The highest gas sensitivity and gas selectivity property are shown with 3% mol of Ho with acetone. Time response characteristics of the sensor are also reported.

Ultra-Low-Power Smart Electronic Nose System Based on Three-Dimensional Tin Oxide Nanotube Arrays.

In this work, we present a high-performance smart electronic nose (E-nose) system consisting of a multiplexed tin oxide (SnO2) nanotube sensor array, read-out circuit, wireless data transmission unit, mobile phone receiver, and data processing application (App). Using the designed nanotube sensor device structure in conjunction with multiple electrode materials, high-sensitivity gas detection and discrimination have been achieved at room temperature, enabling a 1000 times reduction of the sensor's power consumption as compared to a conventional device using thin film SnO2. The experimental results demonstrate that the developed E-nose can identify indoor target gases using a simple vector-matching gas recognition algorithm. In addition, the fabricated E-nose has achieved state-of-the-art sensitivity for H2 and benzene detection at room temperature with metal oxide sensors. Such a smart E-nose system can address the imperative needs for distributed environmental monitoring in smart homes, smart buildings, and smart cities.

A High Sensitivity and Compact Real Time Gas Concentration Sensor for Semiconductor and Electronic Device Manufacturing Process

Various metal-organic(MO) gases are used in manufacturing processes of electronic device such as semiconductors, power devices, LEDs and displays. These MO gas are generally supplied with bubbling, and the in-line concentration sensor is used to control their concentration [1]. However, due to diversification of semiconductor processes, adaptation to various MO gas, high sensitivity and high speed sampling are required [2]. Various MO gases have the light absorption in the ultraviolet light wavelength region of 400 nm or less, and we developed a concentration sensor by measuring ultraviolet absorbance. Fig. 1 shows the developed concentration sensor unit. A small gas cell with a good sealing performance against reactive gases was prepared, and a detection circuit section was fabricated by adopting a charge amplifier method to obtain high sensitivity, instead of the commonly-used transimpedance amplifier method. So far, we demonstrated that highly sensitivity to commonly used MO gases such as Bis(cyclopentadienyl)magnesium[Cp2Mg] with the response speed of 400 msec or less could be realized using the developed sensor [3]. In this abstract, we report on the possibility of measuring the concentration of Zr and Hf MO gases that are commonly used in semiconductor High-k process. The measurement was carried out by heating the gas cell with an optical path length of 50 mm at 50 ° C. In the measurement, the LED with a wavelength λ of 360 nm and the LED with λ of 255 nm were switched and irradiated alternatively. The output voltage difference of the two wavelength LEDs according to concentration was taken into the PC with 16bit output and data processing was performed. The sampling period was 400 msec. For Zr MO gas, Tetrakis(ethylmethylamino)zirconium[TEMAZ] and Tris(dimethylamino)cyclopentadienylzirconium[ZAC] were evaluated and for the Hf MO gas, and Tetrakis (ethylmethylamino)hafnium[TEMAH] was evaluated for the Hf MO gas. Fig.2 shows the evaluation results for TEMAZ. Fig. 2 (a) shows the output of the concentration sensor unit when 41.5ppm-TEMAZ and 100%-Ar are switched at intervals of about 5 min by the valve operation. Good repeatability for the output signals were obtained for each gases in each periods. Fig. 2 (b) shows a calibration curve for TEMAZ, where the output signal as a function of the TEMAZ concentration is shown. The calibration curve was superior in linearity. Also, because the charge amplifier method was adopted, we confirmed that very small minimum detection sensitivity of 95 ppb could be achieved by taking into account of 5 σ of circuit noise. Similarly, we found that the minimum detection sensitivities of ZAC and TEMAH were 141 ppb and 80 ppb, respectively. The results demonstrated that the developed concentration sensor is very useful for realizing the precise measurement of various MO gases in semiconductor manufacturing. [1] T. W. Woods et al., ECS Transactions, 3 (7) 215-217, 2006. [2] V. Miikkulainen et al., J. Appl. Phys. 113, 021301 (2013) [3] H. Ishii et al., IEEE Sensors 2016 (IEEE), 877-879, 2016. Figure 1

High-sensitive transmission type of gas sensor based on guided-mode resonance in coupled gratings

A new type of high-sensitive transmission gas sensor based on the coupled gratings (CGs) and the corresponding Fabry–Pérot-like (FP-like) model for evaluating the resonance peaks are presented. The estimated locations of the FP-like resonance obtained by this theoretical model are well agreed with those of the exact results. It is shown that a narrow FP-like channel with high transmissivity occurs in the opaque background of the CGs, and its location is shifted linearly with the variation of the refractive index (RI) of the gaseous analyte. The transmission peak of the sideband can be selected as a reference, and it remains nearly fixed as the RI of the analyte is varied. Good sensing properties of the CGs sensor can be maintained, regardless of whether the two grating membranes are laterally aligned or not. The sensitivity of the CGs sensor is immune to the variation of the RI of the substrate. By selecting the higher order FP-like mode (m = 4), sensitivity as high as 748 nm/RIU with the figure of merit of 374 can be achieved.

Analysis of pyrethroid pesticides in Chinese vegetables and fruits by GC–MS/MS

A rapid and economical method using modified QuEChERS sample pretreatment coupled with high-sensitivity gas chromatography/triple quadrupole mass spectrometry was established to simultaneously determine ten pyrethroid pesticides in fruits and vegetables. All pesticides were detected within 20 min of one injection. Concurrent backflushing provided column protection, greatly facilitating instrument maintenance. For quantitation, matrix-matched calibration was used to compensate for signal-enhancement effects and to ensure the precision of the method. The limit of detection (LOD) was in the range of 0.3–4.9 μg/kg. The recovery rate was from 78.8 to 118.6%, with relative standard deviation (RSD) below 14.8%. The developed method is suitable for rapid and sensitive multi-residue analysis of pyrethroid pesticides in fruits and vegetables. It is good for users in professional institutions that implement safety controls for testing hundreds of agricultural product samples everyday.

The radiation gas detectors with novel nanoporous converter for medical imaging applications

For many reason it is tried to improve the quantum efficiency (QE) of position sensitive gas detectors. For energetic X-rays, the imaging systems usually consist of a bulk converter and gas amplification region. But the bulk converters have their own limitation. For X-rays, the converter thickness should be increased to achieve a greater detection efficiency, however in this case, the chance of escaping the photoelectrons is reduced. To overcome this limitation, a new type of converter, called a nanoporous converter such as Anodizing Aluminum Oxide (AAO) membrane with higher surface to volume ratio is proposed. According to simulation results with GATE code, for this nanoporous converter with the 1 mm thickness and inter pore distance of 627 nm, for 20–100 keV X-ray energies with a reasonable gas pressure and different pore diameters, the QE can be one order of magnitude greater than the bulk ones, which is a new approach for proposing high QE position sensitive gas detectors for medical imaging application and also high energy physics.

In-fiber integrated gas pressure sensor based on a hollow optical fiber with two cores

We demonstrate an in-fiber integrated highly-sensitive gas pressure sensor based on a special designed hollow eccentric twin-core optical fiber (HTCF). In this design, the core in the hole and the core in the annular cladding of the HTCF are separately used as sensing arm and reference arm. Then, in-fiber gas pressure detection can be first realized in the long hole of the HTCF. The experimental results show that the sensor exhibits a gas pressure sensitivity of 0.42 nm/bar, with low temperature sensitivity of −51 pm/℃, and a maximum bending sensitivity of 98 pm/μm. Comparing with traditional optical fiber gas pressure sensors, this device first realizes in-fiber gas pressure detecting through the special designed optical fiber with a compact size which can be easily connected and integrated in practical applications.

Design and experimental verification of a photoacoustic flow sensor using computational fluid dynamics.

A photoacoustic (PA) sensor for fast and real-time gas sensing is demonstrated. The PA sensor is a stand-alone system controlled by a field-programmable gate array. The PA cell has been designed for flow noise immunity using computational fluid dynamics (CFD) analysis. The aim of the CFD analysis was to investigate and minimize the influence of the gas distribution and flow noise on the PA signal. PA measurements were conducted at different flow rates by exciting molecular C-H stretch vibrational bands of hexane (C6H14) and decane (C10H22) molecules in clean air at 2950 cm-1 (3.38μm) with a custom-made mid-infrared interband cascade laser. We observe a (1σ, standard deviation) sensitivity of 0.4±0.1 ppb (nmol/mol) for hexane in clean air at flow rates up to 1.7L/min, corresponding to a normalized noise equivalent absorption coefficient of 2.5×10-9 W cm-1 Hz-1/2, demonstrating high sensitivity and fast real-time gas analysis. An Allan deviation analysis for decane shows that the detection limit at optimum integration time is 0.25ppbV (nmol/mol).

A facile route to batch synthesis CuO hollow microspheres with excellent gas sensing properties

CuO hollow microspheres had been batch synthesized by a facile route of precipitating and annealing at 270 °C, which was derived from CuSO4·5H2O, Na2CO3 and CTAB. The morphology and structure of synthesized CuO powder were characterized by XRD, SEM, UV–Vis and BET. The formation mechanism of CuO hollow microspheres had been proposed based on the characterized structure and morphology. Firstly, the tiny Cu2(OH)2CO3 crystal strips are formed from CuSO4 and Na2CO3 aqueous solutions. Secondly, the tiny Cu2(OH)2CO3 crystal strips are assembled perpendicularly to the spherical CTA+ micelles surface due to the template of CTAB. Finally, the CuO hollow microspheres have been obtained due to the decomposition of Cu2(OH)2CO3 and burning of CTAB after annealing at 270 °C. High gas sensitivity to ethanol was achieved for the CuO hollow microspheres. The response of CuO hollow microspheres sensor is 5.6 to ethanol with the concentration of 400 ppm at 250 °C, and the responses/recover time is 17.0/11.9 s. Therefore, it indicates that the facile and batch route is a promising method to synthesize CuO hollow microspheres with excellent gas sensing properties.

High Sensitive Formaldehyde Gas Sensing Devices Based on Nickel Oxide Nanowires and Nanodisks

High Sensitive Formaldehyde Gas Sensing Devices Based on Nickel Oxide Nanowires and Nanodisks

A first-principles study of gas molecule adsorption on borophene

Borophene, a new two-dimensional material, was recently synthesized. The unique anisotropic structure and excellent properties of borophene have attracted considerable research interest. This paper presents a first-principles study of the adsorption of gas molecules (CO, CO2, NH3, NO, NO2 and CH4) on borophene. The adsorption configurations, adsorption energies and electronic properties of the gas molecules absorpted on borophene are determined, and the mechanisms of the interactions between the gas molecules and borophene are evaluated. We find that CO, CO2, NH3, NO and NO2 are chemisorbed on borophene, while CH4 is physisorbed on borophene. Furthermore, our calculation also indicate that CO and CO2 are chemisorbed on borophene with moderate adsorption energy and NO, NO2 and NH3 are chemisorbed on borophene via strong covalent bonds. Moreover, CO is found as an electron donor, while CO2 an electron acceptor. The chemisorption of CO and CO2 on borophene increases the electrical conductivity, so It seems that borophene has the potential to be used in high-sensitivity CO and CO2 gas sensors.

Enhanced gas sensing performance of graphene/ZnS-CdS hetero-nanowires gas sensor synthesized by Langmuir-Blodgett self-assembly method

Graphene is a promising material in the field of solid-state gas sensors due to the unique two-dimensional structure. Here, we have shown by fabricating graphene/ZnS-CdS heteronanowire structure, the gas sensor sensitivity has a two-fold increase to 20% under 15 ppm gaseous concentration compared to a 10% response in pristine graphene. Spectroscopy and microscopy analysis indicate that the semi-conducting ZnS-CdS hetero-nanowires are 2 nm wide and densely packed on top of graphene. By combining UV illumination, the device approaches a fast response/recovery and high gas sensitivity, thus has a potential to be used in a detection of wide range of gases.