Progressive NO2 Sensors with Rapid Alarm and Persistent Memory-Type Responses for Wide-Range Sensing Using Antimony Triselenide Nanoflakes

Antimony triselenide (Sb₂Se₃) nanoflake-based nitrogen dioxide (NO₂) sensors exhibit a progressive bifunctional gas-sensing performance, with a rapid alarm for hazardous highly concentrated gases, and an advanced memory-type function for low-concentration (<1 ppm) monitoring repeated under potentially fatal exposure. Rectangular and cuboid shaped Sb₂Se₃ nanoflakes, comprising van der Waals planes with large surface areas and covalent bond planes with small areas, can rapidly detect a wide range of NO₂ gas concentrations from 0.1 to 100 ppm. These Sb₂Se₃ nanoflakes are found to be suitable for physisorption-based gas sensing owing to their anisotropic quasi-2D crystal structure with extremely enlarged van der Waals planes, where they are humidity-insensitive and consequently exhibit an extremely stable baseline current. The Sb₂Se₃ nanoflake sensor exhibits a room-temperature/low-voltage operation, which is noticeable owing to its low energy consumption and rapid response even under a NO₂ gas flow of only 1 ppm. As a result, the Sb₂Se₃ nanoflake sensor is suitable for the development of a rapid alarm system. Furthermore, the persistent gas-sensing conductivity of the sensor with a slow decaying current can enable the development of a progressive memory-type sensor that retains the previous signal under irregular gas injection at low concentrations.     

Internally Referenced Remote Sensors for HF and Cl2 Using Reactive Porous Silicon Photonic Crystals

Remote detection of reactive analytes using optical films constructed from electrochemically prepared porous Si‐based photonic crystals is demonstrated. Porous Si samples are prepared to contain either surface oxide or surface Si‐H species, and analyte detection is based on irreversible reactions with HF_(aq) or Cl_2(g) analytes, respectively. HF dissolves silicon oxide from the porous matrix, causing an irreversible blue‐shift in the resonance peak of the photonic crystal. Cl₂ reacts with the native Si‐H species present on the surface of as‐etched porous Si to generate reactive silicon halides that evaporate from the surface and/or react with air to convert to silicon oxide. Either Cl₂‐related process reduces the net refractive index of the material that is detected as a blue shift in the spectrum. With sufficient analyte concentrations or exposure times, the spectral blue shifts are visible to the unaided eye. A portion of the porous nanostructure is filled with inert polystyrene, which acts as an internal spectral reference. The polymer fiducial protects that portion of the sensor from attack by the corrosive analytes. Reflectance spectra from both the polymer‐filled and the unfilled, reactive porous layers are acquired simultaneously. The fiducial marker also allows elimination of artifacts associated with shifts of the resonance peak upon changing the angle of incidence of the optical probe. Theoretical angle‐resolved spectra (transfer matrix method) show a good match with the experimental data. High‐temperature air or room‐temperature ozone oxidation reactions are used to prepare the HF‐reactive surface, and it is found that the ozone oxidation reaction produces a greater sensitivity to HF (LLOD of 0.1% HF in water).     

Room-Temperature Hydrogen Sensor with High Sensitivity and Selectivity using Chemically Immobilized Monolayer Single-Walled Carbon Nanotubes

Although semiconducting single-walled carbon nanotubes (sc-SWNTs) exhibit excellent sensing properties for various gases, commercialization is hampered by several obstacles. Among these, the difficulty in reproducibly fabricating sc-SWNT films with uniform density and thickness is the main one. Here, a facile fabrication method for sc-SWNT-based hydrogen (H₂) sensors with excellent reproducibility, high sensitivity, and selectivity against CO, CO₂, and CH₄ is reported. Uniform-density and monolayer sc-SWNT films are fabricated using chemical immobilized through the click reaction between azide-functionalized polymer-wrapped sc-SWNTs and immobilized alkyne polymer on a substrate before decorating with Pd nanoparticles (0.5–3.0 nm). The optimized sc-SWNT sensor has a high room-temperature response of 285 with the response and recovery times of 10 and 3 s, respectively, under 1% H₂ gas in air. In particular, this sensor demonstrates highly selective H₂ detection at room temperature (25 °C), compared to other gases and humidity. Therefore, the chemical immobilization of the monolayer SWNT films with reproducible and uniform density has the potential for large-scale fabrication of robust room-temperature H₂ sensors.     

用于臭氧技术产品中的传感器

简述了传感器在臭氧技术产品中的应用。对臭氧技术产品中使用最多的温度传感器、光传感器和红外遥控技术的工作原理进行了详述。进一步对应用于臭氧技术产品中的传感器进行了分类,并对压力式温度传感器、热敏传感器、双金属热保护器、热聚合开关、光敏二极管和红外遥控技术的工作原理、使用场所进行了逐一介绍。设计了几个使用这些传感器来对臭氧产品进行控制的控制电路。     

Excitation of luminescence in porous silicon with adsorbed ozone molecules

A new effect of the excitation of luminescence in porous silicon during adsorption of ozone from the gaseous phase was investigated. The signals of ozone-induced luminescence and photoluminescence decay with time of ozone exposure in a strictly correlated way; simultaneously, an oxide-phase growth is observed in porous silicon. A linear relationship was found between the luminescence intensity and the amount of oxide phase formed in the presence of ozone. Correlated shifts in the spectra of ozone-induced luminescence and photoluminescence are observed if the porosity of silicon varies. A mechanism for this effect is proposed. According to this mechanism, in the case of the dissociative adsorption of ozone, the exothermic reaction of oxidation of backbonds of a silicon atom takes place on the surface of nanocrystallites. Energy released is spent for the excitation of electron spectrum of silicon crystallites. The radiative relaxation in the case of ozone excitation proceeds similarly to that of the photon excitation of luminescence in porous silicon.     

Highly concentrated ozone gas supplied at an atmospheric pressure condition as a new oxidizing reagent for the formation of SiO2 thin film on Si

We have investigated the characteristics of silicon oxidation by concentrated ozone gas through the comparison of the oxidation by oxygen molecules. A sophisticated high-concentration ozone generator, which exploits the ozone/oxygen gas separation technique with silica gel, has been developed for the study. The generator can continuously supply ozone-oxygen mixtures with ozone concentrations up to 30 at.% at one atmospheric pressure. Ozone gas with a concentration of 25 at.% from the generator formed SiO₂ films as thick as 2 nm and 6 nm on Si for a 30 min. exposure at 200°C and 600°C, respectively. On the other hand, oxygen gas by itself could form SiO₂ films with only 1 nm and 3 nm thickness, respectively, at the same conditions. Moreover, in the oxide film formation at 600°C, the oxide film growth by ozone was proceeded with an oxidation time in excess of 240 min., while it saturated within very short time in the oxidation by oxygen. These phenomena verify the strong oxidation power of ozone. In addition, we confirmed that the growth rate of the silicon oxide with ozone dramatically changed when the substrate temperature was over 500°C, and this suggested the change of oxidation mechanism at this point. However, such a characteristic was not found in oxidation with oxygen.     

Porous Silicon‐Based Optical Microsensors for Volatile Organic Analytes: Effect of Surface Chemistry on Stability and Specificity

Sensing of the volatile organic compounds (VOCs) isopropyl alcohol (IPA) and heptane in air using sub‐millimeter porous silicon‐based sensor elements is demonstrated in the concentration range 50–800 ppm. The sensor elements are prepared as one‐dimensional photonic crystals (rugate filters) by programmed electrochemical etch of p⁺⁺ silicon, and analyte sensing is achieved by measurement of the wavelength shift of the photonic resonance. The sensors are studied as a function of surface chemistry: ozone oxidation, thermal oxidation, hydrosilylation (1‐dodecene), electrochemical methylation, reaction with dicholorodimethylsilane and thermal carbonization with acetylene. The thermally oxidized and the dichlorodimethylsilane‐modified materials show the greatest stability under atmospheric conditions. Optical microsensors are prepared by attachment of the porous Si layer to the distal end of optical fibers. The acetylated porous Si microsensor displays a greater response to heptane than to IPA, whereas the other chemical modifications display a greater response to IPA than to heptane. The thermal oxide sensor displays a strong response to water vapor, while the acetylated material shows a relatively weak response. The results suggest that a combination of optical fiber sensors with different surface chemistries can be used to classify VOC analytes. Application of the miniature sensors to the detection of VOC breakthrough in a full‐scale activated carbon respirator cartridge simulator is demonstrated.     

Suspended SnS2 Layers by Light Assistance for Ultrasensitive Ammonia Detection at Room Temperature

2D materials are extensively studied as candidates for chemical sensors due to their large surface‐to‐volume‐ratio and the low working temperature. However, the performance of 2D material‐based sensors is limited when detecting ammonia, due to the weak binding between ammonia molecules and channel materials. Previous reports show sensitivity in the ppb range upon NO₂ exposure, and in ppm levels of ammonia under the same conditions. Compared with the traditional SnS₂ sensors, the demonstrated suspended devices with light excitation exhibit a higher sensitivity, a faster response, and recovery rate. At room temperature, the devices show obvious response to NH₃ vapor at a concentration as low as 20 ppb. High selectivity to ammonia over many other chemical gases is observed. Such arresting features originate from the suspended structure enhancing reaction area and the light excitation inducing increased charge density that facilitates the ammonia detection. The enhanced sensing performance demonstrates the superiority of the suspended structure with light assistance, and this method can be applied to other 2D material‐based sensors on optimizing their performance.     

室温工作双敏感膜HSGFET型O3传感器的研究

本文研究室温下工作,具有双敏感膜,检测ppb范围内O₃浓度的复合悬浮栅FET(Hybrid Suspended Gate Field Effect Transistor即HSGFET)型臭氧传感器.文中给出了四种固态HSGFET型臭氧传感器的实验结果,发现具有 结构的传感器对O₃有很好的响应特性;实验结果与由开尔芬(Kelvin)探针得到的结果进行了比较.     

Ozone oxidation methods for aluminum oxide formation: Application to low-voltage organic transistors

Four atmospheric pressure ozone oxidation methods were used to produce ultra-thin layers of aluminum oxide for organic thin-film transistors. They are UV/ozone oxidation in ambient (UV-AA) and dry (UV-DA) air, UV/ozone oxidation combined with high-voltage discharge-generated ozone in dry air (UV+O₃-DA), and discharge-generated ozone in dry air (O₃-DA). The lack of the high-energy UV photons during the O₃-DA oxidation led to low relative permittivity and high leakage current density of the AlO_x layer that rendered this method unsuitable for transistor dielectrics. Although this oxidation method led to the incorporation of oxygen into the film, the FTIR confirmed an increased concentration of the subsurface oxygen while the XPS showed the highest portion of the unoxidized Al among all four methods. The remaining three oxidation methods produced AlO_x films with thicknesses in excess of 7 nm (2-h oxidation time), relative permittivity between 6.61 and 7.25, and leakage current density of (1–7) × 10⁻⁷ A/cm² at 2 MV/cm, and were successfully implemented into organic thin-film transistors based on pentacene and DNTT. The presence of –OH groups in all oxides is below the detection limit, while some carbon impurities appear to be incorporated.     

A miniature hybrid reflection type optical sensor for measurementof hemoglobin content and oxygen saturation of whole blood

A reflection-type hybrid optical sensor was designed for continuous measurement of both hemoglobin content ([Hb]) and oxygen saturation (OS) of whole blood. The sensor was based on a theoretical model using the photon diffusion theory. The prototype sensor consists of a light emitting diode (LED) and photodiode chips mounted on a single substrate and cased in a TO-5 can with its surface covered with clear epoxy resin. The effect of hematocrit variation was eliminated. It was test in goat, calf, and human whole blood over hematocrit range of 20-45%. The modified ratio method reduced the effect of hematocrit variation of hemoglobin OS measurement with improvement in standard deviation of errors from about 7.0 to 2.0%. The standard errors in the estimation of hemoglobin content ranged from 1.5 to 0.5 gm%. The oxygen contents of whole blood derived from the prototype sensor correlated well (r=0.997) with those analyzed using a hemoximeter. The prototype sensors have been used for continuous measurement of oxygen delivery to, and oxygen consumption by, peripheral tissues in artificial heart animals for a duration of 40 days, demonstrating satisfactory performance     

A Plant-inspired Light Transducer for High-performance Near-infrared Light Mediated Gas Sensing

Constructing near-infrared light (NIR) light-enhanced room temperature gas sensors is becoming more promising for practical application. In this study, learning from the structure and photosynthetic process of chlorophyll thylakoid membranes in plants, the first “Thylakoid membrane” structural formaldehyde (HCHO) sensor is constructed by matching the upconversion emission of the lanthanide-doped upconversion nanoparticles (UCNPs) and the UV–vis adsorption of the as-prepared nanocomposites. The NIR-mediated sensor exhibits excellent performances, including ultra-high response (R_a / R_g = 2.22, 1 ppm), low practical limit of detection (50 ppb), reliable repeatability, high selectivity, and broadband spectral response. The practicality of the NIR-mediated gas sensor is confirmed through the remote and external stimulation test. A study of sensing mechanism demonstrates that it is the UCNPs-based light transducer produces more light-induced oxygen species for gas response in the process of non-radiative/radiative energy transfer, playing a key role in significantly improving the sensing properties of the sensor. The universality of NIR-mediated gas sensors based on UCNPs is verified using ZnO, In₂O_3, and SnO₂ systems. This work paves a way for fabricating high-performance NIR-mediated gas sensors and will expand the application fields of NIR light.     

All-silicon avalanche photodiode sensitive at 1.3 μm withpicosecond time resolution

The first experimental demonstration that an all-silicon photodiode can be used to measure the pulse shape of laser diodes emitting at 1.3 μm is reported. In order to allow for light absorption at these wavelengths, the bandgap narrowing phenomenon in heavily doped silicon is exploited. The device operates as a single photon detector in a time-correlated photon counting setup. The quantum efficiency of the detector (though only 10^-7), together with the very low noise (≈100 dark pulses per second) enable easy measurements on standard diode lasers. The use of standard silicon processing and the room-temperature operation are definite advantages of the device     

High Performance Three‐Dimensional Chemical Sensor Platform Using Reduced Graphene Oxide Formed on High Aspect‐Ratio Micro‐Pillars

The sensing performance of chemical sensors can be achieved not only by modification or hybridization of sensing materials but also through new design in device geometry. The performance of a chemical sensing device can be enhenced from a simple three‐dimensional (3D) chemiresistor‐based gas sensor platform with an increased surface area by forming networked, self‐assembled reduced graphene oxide (R‐GO) nanosheets on 3D SU8 micro‐pillar arrays. The 3D R‐GO sensor is highly responsive to low concentration of ammonia (NH₃) and nitrogen dioxide (NO₂) diluted in dry air at room temperature. Compared to the two‐dimensional planar R‐GO sensor structure, as the result of the increase in sensing area and interaction cross‐section of R‐GO on the same device area, the 3D R‐GO gas sensors show improved sensing performance with faster response (about 2%/s exposure), higher sensitivity, and even a possibly lower limit of detection towards NH₃ at room temperature.     

A theoretical analysis of the coupling of light to surface-plasmonoscillations at the edge of a slab waveguide

A theoretical method that accounts for diffraction and backcoupling of surface plasmon (SP) oscillations excited at the metallized edge of a planar waveguide is described in this paper. The model explains previously reported experimental studies related to the development of SP-based optical-fiber sensors. The method is based on a Fourier transform approach and predicts the appearance of a spatial SP resonance within the light diffracted from the waveguide edge. The approach also allows one to obtain the spectral dependence of light guided back from the remote waveguide edge and can be used to determine design parameters for optimum sensor operation     

Seeing Hydrogen in Colors: Low‐Cost and Highly Sensitive Eye Readable Hydrogen Detectors

There is a great interest in the development of reliable and low‐cost hydrogen sensors for applications in the hydrogen economy, industrial processes, space application, detection of environmental pollution, and biomedical applications. Here, a new type of optical detector that indicates the presence of hydrogen in concentration range 5 ppm to 0.1 vol% H₂ merely by a reversible and tunable color change is reported. The device takes advantage of the reversible change in optical properties of a Pd‐capped Y thin film upon exposure to H₂, while the color is tuned using the interference of light reflected between the Y and Pd layers. In this way, an eye‐readable optical sensor that circumvents the need for electronics and external digital readouts is created. Using surface modifications, the performance of the H₂ detector in humid and oxygen rich environment is greatly improved. Therefore, the device has the potential to be used for chemical and also biochemical/biomedical H₂ sensing applications such as breathe hydrogen tests.     

UV light activated gas sensor for NO2 detection

In the present study, UV light activated gas sensor was investigated for Al/Al₂O₃/p-Si and Al/TiO₂/Al₂O₃/p-Si samplesby atomic layer deposition method (ALD). Generally, in order to obtain the sensing performance, traditional metal oxide semiconductor gas sensors are operated at 100–400 °C. However, this temperature range limits their applications to flammable gases, and causes high power consumption. It is important to note that sensing performance experiments should have been performed at room temperature. With the support of UV light, gas sensors do not need to be heated and they can work at room temperature easily. For this purpose, electrical measurements have been performed on sensing performance with and without UV irradiation for dedection of NO₂ gas. With the help of UV irradition, we obtained good sensitivity at the room temperature for Al/TiO₂/Al₂O₃/p-Sistructure but under the same conditions no result was obtained for Al/Al₂O₃/p-Si structure. Without UV irradiation, there was no sensitivity for both.We observed that increasing of sensitivities at the room temperature show a direct effect of the light on the adsorbed oxygen ions. According to the relation of photocatalytic reaction and photoactivated gas sensing process, we concluded that TiO₂ might be an acceptable sensor for detection of nitrogen dioxide (NO₂) at room temperature under UV illumination.     

Materials issues for InGaN-based lasers

InGaN multi-quantum-well-structure (MQW) laser diodes (LDs) with Al_0.14Ga_0.86N/GaN modulation doped strained-layer superlattice (MD-SLS) cladding layers grown on an epitaxially laterally overgrown GaN (ELOG) substrate were demonstrated to have a lifetime of more than 1800 h under the condition of room-temperature continuous-wave operation. On the other hand, the LDs grown directly on the sapphire substrate had a lifetime of shorter than 900 h. With the operating current increasing to above the threshold, a self-pulsation was observed to have a high frequency of 3 GHz and a photon lifetime of 0.7 ps. The use of the MD-SLS was effective for reducing the operating voltage of the LDs. The ELOG substrate was used to reduce the number of threading dislocations in the InGaN MQW structure.     

Semiconductor‐Type MEMS Gas Sensor for Real‐Time Environmental Monitoring Applications

Low power consuming and highly responsive semiconductor‐type microelectromechanical systems (MEMS) gas sensors are fabricated for real‐time environmental monitoring applications. This subsystem is developed using a gas sensor module, a Bluetooth module, and a personal digital assistant (PDA) phone. The gas sensor module consists of a NO₂ or CO gas sensor and signal processing chips. The MEMS gas sensor is composed of a microheater, a sensing electrode, and sensing material. Metal oxide nanopowder is drop‐coated onto a substrate using a microheater and integrated into the gas sensor module. The change in resistance of the metal oxide nanopowder from exposure to oxidizing or deoxidizing gases is utilized as the principle mechanism of this gas sensor operation. The variation detected in the gas sensor module is transferred to the PDA phone by way of the Bluetooth module.     

Improved sensing characteristics of MISiC Schottky-diode hydrogen sensor by using HfO2 as gate insulator

Hafnium dioxide deposited by RF sputtering is used as the gate insulator of metal–insulator–silicon–carbide (MISiC) Schottky-diode hydrogen sensors. Sensors with different gate insulator thicknesses are fabricated for investigation. Their hydrogen-sensing properties are compared with each other by taking measurements at various temperatures and hydrogen concentrations using a computer-controlled measurement system. Experimental results show that for the same insulator thickness, the HfO₂ sensor is more sensitive than its SiO₂ counterpart. This should be mainly attributed to the larger barrier-height at the Pt/HfO₂ interface which can reduce the current of the sensor before hydrogen exposure. Moreover, the sensitivity initially increases with the thickness of the HfO₂ film because a thicker oxide layer can provide a larger barrier-height reduction upon hydrogen exposure. However, further increasing the thickness of the HfO₂ dielectric beyond about 3.3 nm reduces the sensitivity, possibly due to more trapped charges in thicker high-k dielectric which can screen the effect of the polarized hydrogen layer.