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Optical properties of hydrothermally synthesised and thermally annealed ZnO/ZnO <sub/>2</sub> composites
摘要： ZnO/ZnO2 composites grown by hydrothermal synthesis at low temperature (180 °C) and thermally annealed at 300 °C were fully analysed by morphological, structural and optical techniques. X-ray diffraction patterns (XRD) and Raman spectroscopy clearly evidences the presence of both crystalline phases in the ZnO/ZnO2 sample. The differential scanning calorimetry analysis and thermogravimetric profiles indicate an exothermic event with a peak temperature ca. 225 °C, which is accompanied by a 8.5 % weight loss, being attributed to the crystallization of ZnO from ZnO2. Upon a thermal annealing treatment at 300 °C in the ZnO2 phase was completely converted into ZnO as measured by XRD and Raman spectroscopy. Photoluminescence investigations reveal that the emission is dominated by a broad band recombination in both samples, which are due to the overlapping of different emitting centres, and that the peak position of the PL emission is dependent on the excitation density. The ZnO/ZnO2 sample exhibits a widening of the bandgap when compared to the one only containing ZnO, likely related with the presence of the additional ZnO2 phase and suggesting a bandgap energy of 3.42 eV for this compound. Surface analysis revealed that sample exhibits a surface area of 90 m2/g, which decreases to 30 m2/g after the thermal annealing and the full conversion into ZnO. This difference in the surface area showed a particular relevance in the stability of the measured optical properties. Particularly, the intensity of the photoluminescence signal was seen to be higher in the ZnO/ZnO2 sample and strongly dependent on the measurement atmosphere, highlighting their potential to be employed in the fabrication of optical-based sensing systems for environmental applications, namely in gas sensors.
关键词： photoluminescence,gas sensors,ZnO/ZnO2 composites,hydrothermal synthesis,optical properties
更新于2025-09-19 17:13:59
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[IEEE 2019 4th International Symposium on Instrumentation Systems, Circuits and Transducers (INSCIT) - Sao Paulo, Brazil (2019.8.26-2019.8.30)] 2019 4th International Symposium on Instrumentation Systems, Circuits and Transducers (INSCIT) - Normalized Spectral Responsivity Measurement of Photodiode by Direct Method Using a Supercontinuum Laser Source
摘要： A Taguchi-based-genetic algorithm (TBGA) is used in an adaptive neuro-fuzzy inference system (ANFIS) to optimize design parameters for surface acoustic wave (SAW) gas sensors. The Taguchi method is used to reduce the number of experiments and collect performance data for an SAW gas sensor. The TBGA has two optimization roles. In the ANFIS, the TBGA selects appropriate membership functions and optimizes both the premise and the consequent parameters by minimizing the performance criterion of the root mean squared error. Another role of the TBGA is optimizing design parameters for an SAW gas sensor. Simulated experimental application of the proposed TBGA-based ANFIS approach showed that, in terms of both resonant frequency shift and precision performance, this systematic design approach obtains far superior results compared with the conventional trial-and-error design methods and other Taguchi-based design methods.
关键词： Adaptive network fuzzy inference system,Taguchi-genetic algorithm,surface acoustic wave (SAW) gas sensors
更新于2025-09-19 17:13:59
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[IEEE 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - Xiamen, China (2019.12.17-2019.12.20)] 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - A Wideband Fabry-Perot Antenna with Low-RCS High-GBP Using Embed-chessboard Polarization Conversion Metasurface
摘要： An improved adaptive neuro-fuzzy inference system (IANFIS) is proposed to build a model to predict the resonant frequency shift performance of surface acoustic wave (SAW) gas sensors. In the proposed IANFIS, by directly minimizing the root-mean-squared-error performance criterion, Taguchi-genetic learning algorithm is used in the ANFIS to find both the optimal premise and consequent parameters and to simultaneously determine the most suitable membership functions. The five design parameters of SAW gas sensors are considered to be the input variables of the IANFIS model. The input variables include the number of electrode finger pairs, the electrode overlap, the separation distance of two interdigital transducers on the substrate, the dimensions of the stable temperature-cut (ST-cut) quartz substrate, and the electrode thickness. The output variable of the IANFIS model is composed of the resonant frequency shift performance. The results predicted by the proposed IANFIS are compared with those obtained by the back-propagation neural network. The comparison has shown that the performance prediction of resonant frequency shift using the proposed IANFIS is effective. In addition, the sensitivity analyses of the five design parameters have also shown that both the electrode overlap and the dimensions of the ST-cut quartz substrate have the most influence on the resonant frequency shift performance.
关键词： Adaptive neuro-fuzzy inference system,surface acoustic wave (SAW) gas sensors,Taguchi-genetic learning algorithm
更新于2025-09-19 17:13:59
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Laser method of microscopic sensor synthesis for liquid and gas analysis using glucose and H2S as an example
摘要： Laser-induced deposition of metals from a solution has been used as a new method for the synthesis of microcomposite materials in the copper-silver system. It was shown that the obtained materials have good sensory properties with respect to the determination of D-glucose in aqueous solutions. It is also shown that it can be used for gas sensors. Control of sensory properties can be done by changing the method of deposition. X-ray diffraction, EDX, and impedance spectroscopy were used to characterize the materials obtained and it was shown that laser sequential deposition and coprecipitation of two metals give different results. An explanation of the results was proposed. It explains them by the eutectic nature of the interaction in the copper-silver system.
关键词： copper-silver system,impedance spectroscopy,D-glucose,EDX,sensory properties,X-ray diffraction,Laser-induced deposition,microcomposite materials,gas sensors
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Adjustable Optical Path Length Compact Spherical Mirrors Multipass Cell Optimized with Genetic Algorithm
摘要： Numerous practical applications, including health and environmental protection, need compact and high sensitivity gas sensors. This work reports an experimental investigation on a compact multipass cell (MPC) designed and optimized with a genetic algorithm (GA) with long, adjustable optical path length (OPL) using only inexpensive spherical mirrors. A four-mirror based MPC with the GA developed here, offers great design flexibility in comparison to a two-mirror solution. As an example, a stable 24 m OPL was reached within only 80 cc volume. Moreover, by changing the mirror positions various stable OPLs can be achieved in a controllable way. The presented MPC consists of four mirrors in a configuration similar to a bow-tie. As a result, the symmetry between the mirrors is broken (mirrors are not parallel to each other) and an astigmatic spot pattern with a high fill factor is obtained. Additionally, the use of the folded optical path geometry causes higher compactness in contrast to an astigmatic mirror-based MPC. Compared to other dense-pattern or folded spherical mirrors MPCs reported previously, longer OPL in the same volume can be obtained. In order to accurately calculate the line-sphere intersection points and reflection angles based on algorithms reported in custom ray tracing software was developed. It also allows to determine the optimal MPC configuration with specified design constraints (mirror diameters, their focal lengths and desirable OPL) by using a GA. To verify the simulation results, we assembled a MPC with four 1” in diameter, 25 mm focal length mirrors mounted in kinematic holders and fixed them to an aluminum base. By changing the angle and distance between the mirrors, different MPC configurations were tested. Several OPLs ranging from 4.5 m to 28 m were achieved with the GA. The longest OPL, with sufficient output beam quality for such mirrors, was 24 m. In order to prove the agreement between the simulation and experiment, a 16 m and 24 m OPL configurations were prepared and the time-of-flight inside the MPC was measured by injecting a 10 ns pulse laser into the cavity. The first pulse (registered at 0 ns delay in Fig. 1c) corresponds to light partially reflected from the optical plate situated near the MPC input, whereas the second one arrives from the output of MPC. By measuring the time delay between both pulses, the actual OPL was calculated. The experimentally obtained OPLs were 16.11 m and 23.88 m, which is in good agreement with the simulated values of 16.1 m and 23.82 m respectively. In conclusion, we present a compact, four-mirror MPC, designed and optimized with a GA in several OPL variants. Then two of them were experimentally verified through time-of-flight measurement inside the MPC.
关键词： optical path length,genetic algorithm,spherical mirrors,multipass cell,gas sensors
更新于2025-09-12 10:27:22
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Nitrogen oxides sensing performance of thiols and dithiols self-assembled monolayer functionalized Au/GaAs-based Schottky diodes
摘要： In this work, GaAs-based Schottky diodes, functionalized by alkanethiolates, were used to fabricate NOx gas sensors with high-selectivity and low-power. Alkanethiolates were employed to form a self-assembled monolayer (SAM) on the surface of the Au (111) Schottky contacts of the n-GaAs substrate using immersion method. The adsorption behaviors between SAM and Au (111) with different terminal (functional) groups, carbon numbers (CN), immersion times (tim), and alkanedithiol concentrations were characterized by cyclic voltammetry (CV) measurement. The interaction between NOx molecules and SAM was determined by an ultraviolet/visible (UV-Vis) spectrophotometer. The NOx sensing performance of the studied device under proper conditions was investigated at different temperatures and NOx gas concentrations. Experimentally, at 25℃, good sensing responses of 49.6 and 35.5 in 100 ppm NO2 and NO ambiences were obtained, respectively. Furthermore, similar sensing properties of the studied device were found in air and in N2 ambience. Therefore, the studied device can be considered a promising candidate for NOx sensing applications.
关键词： Alkanedithiol,Nitrogen oxides,Gas sensors,Schottky diode,GaAs,Self-assembled monolayers (SAM)
更新于2025-09-12 10:27:22
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High-selectivity NOx sensors based on an Au/InGaP Schottky diode functionalized with self-assembled monolayer of alkanedithiols
摘要： This work was devoted to fabricating high-selectivity NOx gas sensors based on an Au/InGaP Schottky diode. In order to enhance the sensing selectivity and sensing response, a self-assembled monolayer (SAM) of alkanedithiol was used to modify the Schottky contact with an S-Au covalent bond based on the self-assembled property and terminal functional group. The studied SAM/Au/InGaP Schottky diodes were fabricated by semiconductor processes and immersion treatment. The effects of the carbon number (CN) of SAM, the SAM immersion time, and immersion dithiol concentrations were comprehensively studied in this work. In addition, the selectivity and sensing performance of dithiol functionalized Au/InGaP Schottky diodes under different temperatures and NOx concentrations were studied for comparison. In order to obtain the optimal NOx sensing performance, cyclic voltammetry (CV) was employed to study the self-assembled performance of the dithiol monolayer on the Au surface. The sensing responses of 16.5 and 7.2 were obtained under 100 ppm NO2/N2 and NO/N2 at 30oC, respectively, for the studied 1,10-decanedithiol (DDT)/Au/InGaP device. Moreover, compared to other sensing gases, the DDT/Au/InGaP sensing device showed high selectivity toward NOx gas. Furthermore, the theoretical first-order kinetic and thermodynamic theoretical analysis were consistent with the experimental transient and steady-state sensing results. Therefore, the studied SAM/Au/InGaP Schottky diode demonstrated promising results for NOx sensing applications.
关键词： Nitrogen oxides,Gas sensors,Schottky diode,Self-assembled monolayers (SAM),InGaP,Alkanedithiol
更新于2025-09-12 10:27:22
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2D Plasmonic Tungsten Oxide Enabled Ultrasensitive Fiber Optics Gas Sensor
摘要： Functional materials coated on optical fibers have demonstrated great potential for optical gas sensing applications. However, their sensitivity is typically limited to the sub-parts per million (sub-ppm) range. Here, for the first time a 2D near-infrared plasmonic tungsten oxide (WOx) enabled ultrasensitive fiber optics gas sensor on a side-polished D-shape single mode optical fiber is presented. The plasmon resonance wavelength range of 2D WOx is matched with a conventional telecommunications wavelength of 1550 nm for driving the optical fiber, therefore inducing a strong light–matter interaction. Upon the surface adsorption of gas molecules, free electrons in the 2D WOx body are redistributed changing the plasmon resonance properties and hence the transmission through the optical fiber. The sensor is selectively responsive to NO2 at concentrations down to 44 parts per billion (ppb) with a limit of detection of 8 ppb at a relatively low elevated temperature. Such an excellent sensing performance is significantly improved over the previously reported fiber optics NO2 sensors, which suggests the integration of 2D plasmonic degenerated semiconductors as a viable approach to develop high-performance fiber optics gas sensors.
关键词： fiber optics,2D materials,NO2 gas sensors,plasmonic materials
更新于2025-09-11 14:15:04
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Gas Sensing Performances of ZnO Hierarchical Structures for Detecting Dissolved Gases in Transformer Oil: A Mini Review
摘要： Power transformer is one of the critical and expensive apparatus in high voltage power system. Hence, using highly efficient gas sensors to real-time monitor the fault characteristic gases dissolved in transformer oil is in pressing need to ensure the smooth functionalization of the power system. Till date, as a semiconductor metal oxide, zinc oxide (ZnO) is considered as the promising resistive-type gas sensing material. However, the elevated operating temperature, slow response, poor selectivity and stability limit its extensive applications in the field of dissolved gases monitoring. In this respect, rigorous efforts have been made to offset the above-mentioned shortcomings by multiple strategies. In this review, we first introduce the various ZnO hierarchical structures which possess high surface areas and less aggregation, as well as their corresponding gas sensing performances. Then, the primary parameters (sensitivity, selectivity and stability) which affect the performances of ZnO hierarchical structures based gas sensors are discussed in detail. Much more attention is particularly paid to the improvement strategies of enhancing these parameters, mainly including surface modification, additive doping and ultraviolet (UV) light activation. We finally review gas sensing mechanism of ZnO hierarchical structure based gas sensor. Such a detailed study may open up an avenue to fabricate sensor which achieve high sensitivity, good selectivity and long-term stability, making it a promising candidate for transformer oil monitor.
关键词： ZnO,sensitivity,gas sensors,hierarchical structures,stability,gas sensing mechanism,selectivity
更新于2025-09-10 09:29:36
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Constructing hierarchical SnO2 nanofiber/nanosheets for efficient formaldehyde detection
摘要： SnO2 nanofiber/nanosheets with hierarchical nanostructures were successfully synthesized via a facile hydrothermal method by using hollow SnO2 nanofibers as the backbone. The microstructure, morphology, chemical composition, oxidation states and surface areas of SnO2 nanofibers, SnO2 nanofiber/nanosheets and SnO2 nanosheets were comparatively studied by X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET). The characterization results indicated that the hierarchical SnO2 nanofiber/nanosheets were constructed by nanosheets arrays uniform growth on the surface of nanofibers. Sensing performances of SnO2-based nanomaterials were investigated utilizing formaldehyde (HCHO) as a target gas. Compared to SnO2 nanofibers, nanosheets and the physical mixture of nanofibers and nanosheets, the gas sensor based on SnO2 nanofiber/nanosheets exhibited better response, more excellent selectivity, transient response and trace detection ability to HCHO gas. The response (Ra/Rg) of the gas sensor is 57 toward 100 ppm HCHO at 120 °C, which is about 300% and 200% higher than that of pure SnO2 nanofibers sensors and SnO2 nanosheets sensors, respectively. Furthermore, the sensor has an excellent response/recovery performance with 4.7 s and 11.6 s for detecting 100 ppm HCHO. Both the growth process and the gas sensing mechanism of SnO2 hierarchical nanostructures were discussed. Successful preparation of SnO2 nanofiber/nanosheets is attributed to uniform decoration of seeds on the nanofibers and suitable growth conditions of nanosheets. Enhanced sensing performance mainly result from the synergistic effect of nanofibers and nanosheets, hierarchical structures and larger specific surface areas. The synthetic strategy can also be applied in preparing hierarchical materials of different constituent materials.
关键词： Homogeneous materials,SnO2 nanofiber/nanosheets,Formaldehyde gas sensors,Hierarchical structure
更新于2025-09-10 09:29:36