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Time stability of carbon nanotube gas sensors
摘要： In this communication, we report on the long-term stability of a carbon nanotube (CNT) thin-film based NH3 gas sensor. These sensors were fabricated with a reproducible, large-scale, low-cost spray deposition process and are examined in terms of NH3 sensitivity and long-term stability. The devices are measured directly after fabrication; 1-year and 4-years post fabrication while being stored in ambient conditions without further encapsulation. The retainment of up to 96% of response demonstrates the stability of such CNT-based devices. Hence, it solves a critical issue for stepping beyond the proof of concept stage. Not only can CNT-based gas sensors be utilized for years, but such sensors also do not require any special recalibration over the years.
关键词： single-walled,NH3,CNT,aging,spray deposition
更新于2025-09-23 15:23:52
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Quantitative control and identification of copper species in Cu–SAPO-34: a combined UV–vis spectroscopic and H2-TPR analysis
摘要： A series of Cu–SAPO-34 catalysts with different copper contents were prepared using a modified ion-exchange method, i.e., impregnation–activation. Controlled amounts of well-dispersed active copper species and integrated physical properties were obtained by this method. The Cu–SAPO-34 catalysts retained the CHA structure, high specific surface area, and pore volume of the H–SAPO-34. Based on a combined analysis of UV–vis spectra and H2-TPR, these common laboratory techniques enabled the identification of the different copper species present in the catalysts. Only isolated copper ions balanced by two framework charges were present in the catalysts at copper contents ≤ 0.8 wt%. With increasing the Cu content, isolated Cu2+ ions charge-balanced by one negative charge became dominant. Further higher Cu contents could result in formation of copper oxides after consumption of all ion-exchange sites.
关键词： Cu–SAPO-34,Copper species,NH3-SCR,H2-TPR,Impregnation–activation
更新于2025-09-23 15:23:52
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Room temperature ammonia gas sensor based on Au/ graphene nanoribbon
摘要： Graphene nanoribbon (GNR) is a strip and 1D shape of graphene which can be an appropriate candidate for gas sensing application due to its significant electrical and chemical characteristic. In this study, graphene nanoribbon is employed for the NH3 detection process. The chemical approach is applied for unzipping MWCNTs by using KMnO4, as an oxidative material in graphene oxide nanoribbon synthesis process. The gold comb-like electrodes as a sensor structure is produced by standard deposition and photolithography methods. The quality of the synthesized GNRs is investigated by different analyses such as SEM, XRD, Raman Spectroscopy, and FTIR. In addition to GNR sensor preparation, AuGNR sensor is fabricated by gold sputtering deposition on a GNR sensor surface. The experimental results for sensors indicate that AuGNR and GNR sensors could be the appropriate choices for NH3 detection. The experimental tests for AuGNR and GNR sensors are performed for different NH3 concentration at room temperature which showed 34 % and 12.1% response for 25 ppm NH3 respectively. Furthermore, in 25 ppm for the AuGNR sensor, the sensor shows 224 s for response time, and 178 s for recovery time for a graphene-based sensor. All the tests are carried out at room temperature.
关键词： GNRs,gas sensor,AuGNR,NH3 detection
更新于2025-09-23 15:23:52
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Ammonia sensing properties of two-dimensional tin disulphide/tin oxides (SnS2/SnO2-x) mixed phases
摘要： 2D-SnS2 flakes were synthesized via a wet chemical route and deposited as a thin film onto the Pt-interdigitated contacts of a ceramic substrate with aim to fabricate a conductometric sensor. The 2D-SnS2 sensing film was then annealed "in situ" under controlled conditions at different temperatures up to 400 °C. The morphological, microstructural and electrical properties of the sensing film, before and after the thermal treatment, were characterized by "in situ" techniques. SEM analysis has shown that the 2D flake morphology was maintained after thermal treatments, whereas Raman and EDX analysis have highlighted the partial/total modification of the SnS2 phase towards the SnO2. As a consequence of the formation of 2D-SnS2/SnO2-x mixed phases, a dramatic change of the electrical properties of the sensing film has been also observed. Conductometric gas sensors based on hybrid SnS2-SnO2-x nanoflakes were then obtained by simple self-annealing treatments of 2D-SnS2 film directly on the sensor substrate. The fabricated sensors were tested toward ammonia (NH3) as target gas. Results evidence that increasing the annealing temperature of the 2D-SnS2 sensitive film, the electrical resistance of the sensing layer decreases while the response towards ammonia increases, showing the maximum at an annealing treatment of 250 °C. This behaviour was explained on the basis of the morphological, microstructural and electrical modifications observed, highlighting the role of 2D-SnS2/SnO2-x mixed phases in determining the sensing properties towards ammonia.
关键词： Heterostructure,Gas sensor,NH3,2D-SnS2 flakes,Ammonia
更新于2025-09-23 15:23:52
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Detection of NH<SUB>3</SUB> Using ZnO Thin Film Sensor Deposited on Si/SiO<SUB>2</SUB> Substrate Derived by RF Magnetron Sputtering
摘要： This paper reports the research results of Zinc Oxide (ZnO) thin film gas sensor which is able to detect low concentration of ammonia gas (NH3). Pure ZnO layer is deposited on Si/SiO2 substrate at room temperature by RF magnetron sputtering technique. Pt micro-heater, platinum resistance thermometer (PRT) and gold electrodes are also fabricated along with ZnO thin film to make a complete NH3 sensor device and the fabrication process is discussed in detail in this manuscript. The deposited ZnO thin film is annealed at different temperatures and the effect of annealing temperature on the properties of ZnO thin film is analyzed by using various characterization techniques such as surface profilometer, XRD, SEM, EDX, etc. A measurement set-up is established for the measurements of various sensor parameters. An operating temperature is optimized for the NH3 gas sensor to enhance the sensitivity of the device. The optimized operating temperature is achieved and measured by Pt heater and PRT, respectively. The measurements are also performed for Pt micro-heater and PRT to calibrate the temperature with respect to heater current. Finally, the gas sensing measurements are performed in the range of small NH3 concentration (below 10 ppm) and the results confirm very good sensitivity even in very small NH3 concentration.
关键词： NH3 Gas,Thin Film,Pt Microheater,NH3 Gas Sensor,RF Sputtering,ZnO
更新于2025-09-23 15:22:29
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Nitrogen Adsorption of Si(100) Surface by Plasma Excited Ammonia
摘要： Nitrogen adsorption on thermally cleaned Si(100) surfaces by pure and plasma excited NH3 is investigated by in situ IR absorption spectroscopy and ex-situ X-ray photoelectron spectroscopy with various temperatures from RT (25?C) to 800?C and with a treatment time of 5 min. The nitrogen coverage after the treatment varies according to the treatment temperature for both pure and plasma excited NH3. In case of the pure NH3, the nitrogen coverage is saturated as low as 0.13–0.25 mono layer (ML) while the growth of the nitride ?lm commenced at 550?C. For the plasma excited NH3, the saturation coverage was measured at 0.54 ML at RT and it remained unincreased from RT to 550?C. This indicates that the plasma excited NH3 enhances the nitrogen adsorption near at RT. It is found that main species of N is Si2 = NH in case of the plasma excited NH3 at RT while the pure NH3 treatment gives rise to the Si–NH2 passivation with Si–H at RT. We discuss the mechanism of the nitrogen adsorption on Si(100) surfaces with the plasma excited NH3 in comparison with the study on the pure NH3 treatment.
关键词： plasma excited NH3,Plasma,XPS,IR absorption spectroscopy
更新于2025-09-23 15:22:29
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Study of NH3 flow duty-ratio in pulsed-flow epitaxial growth of non-polar a-plane Al0.34Ga0.66N films
摘要： The effects of the modulation in the NH3 flow duty-ratio in a three-way pulsed-flow epitaxial growth process on the structural and optical properties of non-polar a-plane Al0.34Ga0.66N epi-layers were studied intensively. It was revealed that the typical pyramidal defects originated from the anisotropy in growth rate could be evidently reduced with an optimized NH3 flow duty-ratio. In fact, the root-mean-square value determined with atomic force microscope was decreased from 12.8 to 3.1 nm when the NH3 flow duty-ratio was increased from 0 to 0.57. Moreover, the LO-phonon-assisted exciton emission observed in the photoluminescence (PL) spectrum was remarkably suppressed, and the linewidth of the near band edge PL emission peak was decreased by 47%, implying the significantly enhanced optical properties of the non-polar a-plane Al0.34Ga0.66N epi-layer.
关键词： Pulsed-flow epitaxial growth,NH3 flow duty-ratio,Non-polar a-plane AlGaN epi-layers
更新于2025-09-23 15:21:21
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Wet NH3-Triggered NH2-MIL-125(Ti) Structural Switch for Visible Fluorescence Immunoassay Impregnated on Paper
摘要： This work has looked to explore an innovative and powerful visible fluorescence immunoassay method through wet NH3-triggered structural change of NH2-MIL-125(Ti) impregnated on paper for the detection of carcinoembryonic antigen (CEA). Gold nanoparticles heavily functionalized with glutamate dehydrogenase (GDH) and secondary antibody were used for generation of wet NH3 with a sandwiched immunoassay format. Paper-based analytical device (PAD) coated with NH2-MIL-125(Ti) exhibited good visible fluorescence intensity through wet NH3-triggeried structural change with high accuracy and reproducibility. Moreover, NH2-MIL-125(Ti)-based PAD displayed two visual modes of fluorescence color and physical color with naked eyes, and allowed the detection of CEA at a concentration as low as 0.041 ng mL-1. Importantly, the PAD-based assay provides promise for use in the mass production of miniaturized devices and opens new opportunities for protein diagnostics and biosecurity.
关键词： paper-based analytical device,NH2-MIL-125(Ti),visible fluorescence immunoassay,wet NH3,carcinoembryonic antigen
更新于2025-09-23 15:21:21
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The naked-eye NH3 sensor based on fluorinated graphene
摘要： Graphene has aroused continual and tremendous interest in gas sensing applications because of its unique properties. However, the graphene-based sensors still meet limitations such as inconvenient device fabrication, sustained power supply, specific measuring equipment, etc. Here, we find that fluorinated graphene (FG) shows an obvious color change (from white to dark yellow) in the presence of NH3 which can be observed directly by the naked eye. PL measurement shows that the sensitivity of color change can reach a high value of ca. 4.05 % ppm-1. The density functional theory calculations reveal that the F atoms on FG increase the adsorption ability and charge transfer of NH3 molecules, resulting in the efficient color change. This work develops a naked-eye sensor which needs no device fabrication, power supply or measuring equipment, thus, can be potentially used to manufacture a cheap, sensitive and miniaturized NH3 sensor.
关键词： fluorinated graphene,charge transfer,NH3 sensor,naked-eye color change,adsorption ability
更新于2025-09-23 15:21:01
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Influence of Ag NPs on Silicon Nanocolumns NH <sub/>3</sub> Gas Sensors
摘要： Two NH3 gas sensor devices, Al/Si nanocolumns/n-Si/Al and Al/Ag NPs/Si nanocolumns/n-Si/Al hybrid structures, have been fabricated and tested. A bare silicon nanocolumns layer was synthesized by a laser-assisted electrochemical etching process in HF solutions. The surface morphology of bare Si nanocolumns was modified by incorporating Ag NPs into Si nanocolumns by simple and fast immersions methods in an aqueous solution of AgNO3 to synthesize a hybrid structure. Characteristic features of bare Si nanocolumns and hybrid structure were investigated using scanning electron microscopy, EDS analysis, FTIR spectra, X-ray diffraction, and photoluminescence spectra (PL). The electrical characteristics of sensors with and without NH3 gas were measured at room temperature. The results showed that the nanoparticles grain size, nature, specific surface area (S.S.A) of Ag NPs, and morphological structure of the Si nanocolumns strongly affected the property characteristics. A significant enhancement in sensitivity, response, and recovery times of gas sensor for a hybrid structure was realized after compared with Al/Si nanocolumns/n-Si/Al gas sensor due to the high specific surface area.
关键词： silicon nanocolumns,response time,NH3 gas sensor,sensitivity,Ag NPs,hybrid structure,recovery time
更新于2025-09-23 15:21:01