Stable and highly sensitive gas sensors based on semiconducting oxide nanobelts

©2002 American Institute of Physics. The electronic version of this article is the complete one and can be found online at: : http://link.aip.org/link/?APPLAB/81/1869/1DOI:10.1063/1.1504867Gas sensors have been fabricated using the single-crystalline SnO₂ nanobelts. Electrical characterization showed that the contacts were ohmic and the nanobelts were sensitive to environmental polluting species like CO and NO₂ , as well as to ethanol for breath analyzers and food control applications. The sensor response, defined as the relative variation in conductance due to the introduction of the gas, is 4160% for 250 ppm of ethanol and 21550% for 0.5 ppm NO₂ at 400 °C. The results demonstrate the potential of fabricating nanosized sensors using the integrity of a single nanobelt with a sensitivity at the level of a few ppb

Recent Advancements in TiO2 Nanostructures: Sustainable Synthesis and Gas Sensing

The search for sustainable technology-driven advancements in material synthesis is a new norm, which ensures a low impact on the environment, production cost, and workers' health. In this context, non-toxic, non-hazardous, and low-cost materials and their synthesis methods are integrated to compete with existing physical and chemical methods. From this perspective, titanium oxide (TiO2) is one of the fascinating materials because of its non-toxicity, biocompatibility, and potential of growing by sustainable methods. Accordingly, TiO2 is extensively used in gas-sensing devices. Yet, many TiO2 nanostructures are still synthesized with a lack of mindfulness of environmental impact and sustainable methods, which results in a serious burden on practical commercialization. This review provides a general outline of the advantages and disadvantages of conventional and sustainable methods of TiO2 preparation. Additionally, a detailed discussion on sustainable growth methods for green synthesis is included. Furthermore, gas-sensing applications and approaches to improve the key functionality of sensors, including response time, recovery time, repeatability, and stability, are discussed in detail in the latter parts of the review. At the end, a concluding discussion is included to provide guidelines for the selection of sustainable synthesis methods and techniques to improve the gas-sensing properties of TiO2

Uncertainties of synchrotron microCT-based digital volume correlation bone strain measurements under simulated deformation

Digital Volume Correlation (DVC) is used to measure internal displacements and strains in bone. Recent studies have shown that synchrotron radiation micro-computed tomography (SR-microCT) can improve the accuracy and precision of DVC. However, only zero-strain or virtually-moved test have been used to quantify the DVC uncertainties, leading to potential underestimation of the measurement errors. In this study, for the first time, the uncertainties of a global DVC approach have been evaluated on repeated SR-microCT scans of bovine cortical bone (voxel size: 1.6μm), which were virtually deformed for different magnitudes and along different directions. The results showed that systematic and random errors of the normal strain components along the deformation direction were higher than the errors along unstrained directions. The systematic percentage errors were smaller for larger virtual deformations. The random percentage error was in the order of 10% of the virtual deformation. However, higher errors were localized at the boundary of the volumes of interest, perpendicular to the deformation direction. When only the central region of the samples was considered (100 micrometers layers removed from the borders where the deformation was applied), the errors in the direction of virtual deformation were comparable to the errors in the unstrained directions. In conclusion, the method presented to estimate the uncertainties of DVC is suitable for testing anisotropic specimens as cortical bone. The good agreement between the uncertainties in measurements of strain components obtained with this approach and with the simpler zero-strain-test suggests that the latter is adequate in the tested deformation scenarios

What happens at the aroma of coffee beans after roasting?

The coffee aroma is one of the most important quality evaluation criteria employed for coffee commercialization and consumption. The purpose of this study was following the roasting process VOCs creations with the novel Electronic Nose equipped whit 2 of 6 MOX nanowire sensors. The nanowires exhibit exceptional crystalline quality and a very high length-to-width ratio, resulting in enhanced sensing capability as well as long-term material stability for prolonged operation. Four different methods of roasting, made by ROSTAMATIC (Table 1) machine, were applied to gain a clearer picture of the differences in roasted coffee aromas by means of a volatile compound analysis. Different methods applied on four different origins of green coffee (India, Indonesia, Honduras, Santos and Nicaragua). The commercial coffees products are made from a blending from minimum five different kinds of coffee and the consumers have developed an addiction/expectation to a specific flavor and taste. Different methods of roasting process will provide the coffee different aroma that will add flexibility to those one that already posses the matrix due to different origins. This work tests and illustrates the broad spectrum of potential uses of the EN technique in food quality control

K-ATP channel gene expression is induced by urocortin and mediates its cardioprotective effect

Background-Urocortin is a novel cardioprotective agent that can protect cardiac myocytes from the damaging effects of ischemia/reperfusion both in culture and in the intact heart and is effective when given at reperfusion.Methods and Results-We have analyzed global changes in gone expression in cardiac myocytes after urocortin treatment using gene chip technology. We report that urocortin specifically induces enhanced expression of the Kir 6.1 cardiac potassium channel subunit. On the basis of this finding, we showed that the cardioprotective effect of urocortin both in isolated cardiac cells and in the intact heart is specifically blocked by both generalized and mitochondrial-specific K-ATP channel blockers, whereas the cardioprotective effect of cardiotrophin-1 is unaffected. Conversely, inhibiting the Kir 6.1 channel subunit greatly enhances cardiac cell death after ischemia.Conclusions-This is, to our knowledge, the first report of the altered expression of a K-ATP. channel subunit induced by a cardioprotective agent and demonstrates that K-ATP, channel opening is essential for the effect of this novel cardioprotective agent

Copper oxide nanowires prepared by thermal oxidation for chemical sensing

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Response dynamics of metal oxide gas sensors working with temperature profile protocols

Abstract In this work we present the analysis of gas sensors working in modulated temperature mode with temperature varying according to exponential law. We integrate conductometric gas sensor based on semiconducting metal oxide layers and an ad-hoc developed electronics to present a sensing system based on a single sensor featuring a degree of selectivity arising from the exploitation of response dynamics features. In particular, a set of parameters is used to summarize the deviation of the response shape from the single exponential law

Zinc Oxide Nanowires Deposited on Polymeric Hotplates for Low-power Gas Sensors

Zinc oxides (ZnO) nanowires were successfully deposited on plastic low-power micro-hotplates using the thermal oxidation technique. Metallic zinc layer was deposited on the sensing transducer by RF magnetron sputtering and then oxidized in a controlled atmosphere in order to obtain ZnO nanostructures. Morphological investigations confirmed the nanometric dimensions of the fabricated nanostructures. The n-type behavior of the nanostructured material was evaluated towards different chemical species to highlight the electrical properties of the materials. Calibration curves for the detection of several chemical species were defined. © 2012 The Authors. Published by Elsevier Ltd

Characterization and testing of Pt/TiO2/SiC thin film layered structure for gas sensing

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Synthesis and characterization of mixed oxide nanowires for gas sensing

A healthy and long-lasting life is the utmost wish of any living being thus aging. The aging phenomenon cannot be stopped but may be controlled to some extent when we live in appropriate environments. Usually, the outdoor environment is polluted by two means natural events (windblown dust, volcano eruptions, etc.) and man-made ones (burning of facile fuels, factories, volatile organic compounds, etc.). Pollution due to harmful air such as sulfur oxides (SO2), nitrogen oxides (NOX), carbon monoxide (CO), ammonia (NH3), methane (CH4), and volatile organic compounds (VOCs) is one of the significant issues since it is more sensitive to compromising the natural ecosystem and environment. So, exposure to these compounds worsens the aging phenomena of the living being (headache, fainting, skin and eye irradiation, respiratory infections, heart disease, lung cancer, and even superficial death). Therefore, it is necessary the detection these compounds in the environment. Accordingly, metal oxides (MOXs) gas sensors have conventionally been employed to detect and quantify harmful gases in both indoor and outdoor environments. However, one of the major problems with these sensors is achieving selective detection. Herein, we propose a novel design with two metal oxides (ZnO and Co3O4) that provide very high gas response together with superior selectivity. The proposed structure is a one-dimensional (1D) metal oxide composite; Co3O4/ZnO nanowires. The composite was prepared by in-situ thermal oxidation of metallic Co thin layer (50 nm) and evaporation of ZnO powder at a temperature of 800 ᵒC at a pressure of 0.15 mbar. The pressure was maintained by a controlled mixture of O2 and Ar. The morphological, compositional, and structural analyses are evidence of the successful growth of the Co3O4/ZnO composite nanowire with the root of Co3O4 and the tip with Pt (catalyzer) and Co3O4. The gas sensing characterization shows exciting sensing functionality towards acetone (C3H6O) compared to that of tested gases (C2H5OH, H2S, NH3, CO, NO2, and H2). The reported highest response (ΔG/G; G is the conductance) was above the value of 5000 toward 50 ppm (parts per million) C3H6O at 40 RH% air when working at 250 °C with the potential of detecting sub ppb (parts per billion) concentration levels of C3H6O. The very high C3H6O sensing performance together with exceptionally high selectivity of the sensor ascribed to Pt nanoparticle and the Co3O4 section on the tip of the Co3O4/ZnO. Moreover, the formation of heterojunctions, synergistic gas sensing, and the catalytic activity of the proposed design enhances the response of the sensors. Accordingly, scanning electron microscopic (SEM), transmission electron microscope (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) characterization, and the sensing mechanisms are comprehensively discussed at the conference