This study presents a novel gas/vapor sensing system utilizing electronic gas microsensors to detect water stress in grapevines. The system incorporates state-of-the-art microfabricated sensor arrays comprising micromachined transducing platforms with integrated, surface-modified metal oxide nanowires. Experiments are conducted in a semi-controlled environment using climate chambers to assess the system’s performance. Results demonstrate the effects of water deficit in the grapevines and confirm the feasibility of detecting early plant stress responses with the gas/vapor sensing system. These results are attributed to the plant’s initial adaptive response to water stress, characterized by stomatal closure, which leads to reduced gaseous exchange and therefore noticeable changes in the response of the gas/vapor sensors. These findings highlight the viability of this gas sensing technology as a non-invasive tool for early water stress detection in grapevines.

Copper sulfide (Cu2S) thin films are synthesized via aerosol-assisted chemical vapor deposition (AACVD) of [Cu(Et4P2S2)Cl](2) complex. These films are directly integrated on silicon-based micromachined substrates and are tested as gas sensing materials. Results demonstrate the AACVD of crystalline flake-like Cu2S structures, while surface analysis indicate the presence of other copper species, including CuS2 and metal sulfides. The integrated microsensors reveal selective response to nitrogen dioxide (NO2) detection under photoactivation at room temperature.

Iron oxide (Fe 2 O 3 ) structures with various morphologies are synthesized by aerosol -assisted chemical vapor deposition (AACVD) method. The structures are formed reproducibly by tuning different AACVD synthesis parameters, including temperatures, solvents, and samples ' position in the reaction chamber. The properties of these structures are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Results demonstrate the formation of six types of crystalline Fe 2 O 3 structures - flattened pyramids (fPy), pyramids (Py), porous pyramids (pPy), sheets (Sh), bricks (Br), and quasi -spherical particles (qsP). The formation of these structures is mainly connected with the use of acetone or acetone/ethanol mixture as solvents and their effect on boosting the influence of the temperature or sample ' s position, respectively, on the properties of the structures. The gas sensing tests of the structures with higher aspect ratios or porosity (pPy, Py, fPy, and Sh) showed responses to various gases (acetone, ethanol, toluene, carbon monoxide, hydrogen, methane, ammonia, and nitrous oxide), reporting maximum sensitivity and selectivity to acetone and ethanol. The best results recorded are for the porous pyramids which show sensitivities of 5.1 % ppm -1 and 3.9 % ppm -1 (in the range of 10 - 40 ppm) to acetone and ethanol, respectively.

Electron-assisted oxidation of Co–Si-based focused electron beam induced deposition (FEBID) materials is shown to form an oxide bilayer with a total thickness of less than 15 nm by phase separation.

The investigation of precursor classes for the fabrication of nanostructures is of specific interest for maskless fabrication and direct nanoprinting. In this study, the differences in material composition depending on the employed process are illustrated for focused-ion-beam- and focused-electron-beam-induced deposition (FIBID/FEBID) and compared to the thermal decomposition in chemical vapor deposition (CVD). This article reports on specific differences in the deposit composition and microstructure when the (H3Si)2Fe(CO)4 precursor is converted into an inorganic material. Maximum metal/metalloid contents of up to 90 at. % are obtained in FIBID deposits and higher than 90 at. % in CVD films, while FEBID with the same precursor provides material containing less than 45 at. % total metal/metalloid content. Moreover, the Fe:Si ratio is retained well in FEBID and CVD processes, but FIBID using Ga+ ions liberates more than 50% of the initial Si provided by the precursor. This suggests that precursors for FIBID processes targeting binary materials should include multiple bonding such as bridging positions for nonmetals. In addition, an in situ method for investigations of supporting thermal effects of precursor fragmentation during the direct-writing processes is presented, and the applicability of the precursor for nanoscale 3D FEBID writing is demonstrated.

Methyl salicylate (MeSal) is an organic compound present in plants during stress events and is therefore a key marker for early plant disease detection. It has usually been detected by conventional methods that require bulky and costly equipment, such as gas chromatography or mass spectrometry. Currently, however, chemical sensors provide an alternative for MeSal monitoring, showing good performance for its determination in the vapour or liquid phase. The most promising concepts used in MeSal determination include sensors based on electrochemical and conductometric principles, although other technologies based on mass-sensitive, microwave, or spectrophotometric principles also show promise. The receptor elements or sensitive materials are shown to be part of the key elements in these sensing technologies. A literature survey identified a significant contribution of bioreceptors, including enzymes, odourant-binding proteins or peptides, as well as receptors based on polymers or inorganic materials in MeSal determination. This work reviews these concepts and materials and discusses their future prospects and limitations for application in plant health monitoring.

In this work we present a methodology for the localized growth of nanowires on prespecified areas of micro -hotplates that allows to independently adjust the device's resistance and its response to the gas. This is achieved through the fabrication stripes containing the nanowires, with or without the presence of a gap in the stripe, giving rise that the nanowires bridge the current. The methodology is demonstrated growing SnO2 nanowire-based chemoresistors and the fabricated sensors have been characterized against CO and NO2. The results show the capability of tailoring nanowire stripe sizes from 1 to 100 mu m, including empty areas of the same sizes along the sensing material, and a response increase by a factor of up to 500. We attribute the response enhancement to the absence of nucleation seeds in the gap area, where only arching nanowires can allow the current to flow between electrodes. In this way, the current flow along the bridge of nanowires is restricted principally to the surface conduction, which is controlled by the interaction of the nanowires with gases.

Aerosol assisted chemical vapour deposited ZnO nanostructured films integrated into Si-based transducing platforms are modified with preformed Au nanoparticles (NPs) via impregnation. The morphological, structural, and chemical characterization of these films using different characterisation techniques shows the incorporation of well-distributed and stable Au nanoparticles (NPs) at the surface of ZnO. Photoactivated gas sensing tests at room temperature (RT) demonstrate enhanced sensitivity and better speed of response for the Au modified ZnO films (AuZn) providing 3 times higher response to ethanol and acetone as compared to the non-modified ZnO films (Zn).

We report the growth of micrometer-sized In 2 O 3 octahedral structures, which are next aligned in chains using dielectrophoresis on top of microhotplates with prepatterned electrodes and integrated heater to work as chemoresistive gas sensors. The devices are relatively fast (180 s), highly sensitive (response up to ~256%), and selective toward NO 2 in humid environments, showing little response to O 2 and ethanol, and being completely insensitive to CO and CH 4 . The here-presented fabrication method can be easily extended as a cost-effective post-process in CMOS-compatible microhotplate fabrication and, thus, represents a promising candidate for indoor and outdoor air quality monitoring devices.

Zinc oxide rod structures are synthetized and subsequently modified with Au, Fe2O3, or Cu2O to form nanoscale interfaces at the rod surface. X-ray photoelectron spectroscopy corroborates the presence of Fe in the form of oxide—Fe2O3; Cu in the form of two oxides—CuO and Cu2O, with the major presence of Cu2O; and Au in three oxidation states—Au3+, Au+, and Au0, with the content of metallic Au being the highest among the other states. These structures are tested towards nitrogen dioxide, ethanol, acetone, carbon monoxide, and toluene, finding a remarkable increase in the response and sensitivity of the Au-modified ZnO films, especially towards nitrogen dioxide and ethanol. The results for the Au-modified ZnO films report about 47 times higher response to 10 ppm of nitrogen dioxide as compared to the non-modified structures with a sensitivity of 39.96% ppm−1 and a limit of detection of 26 ppb to this gas. These results are attributed to the cumulative effects of several factors, such as the presence of oxygen vacancies, the gas-sensing mechanism influenced by the nano-interfaces formed between ZnO and Au, and the catalytic nature of the Au nanoparticles.

The sensing properties of (3-aminopropyl)triethoxysilane modified tungsten oxide nanowires (APTES@WO3-x) based sensors towards several gases and vapors are reported in this work. The developed sensors show high sensitivity to ethanol and nitrogen dioxide under UV-irradiation at room temperature (24 degrees C). Gas sensing results demonstrate enhanced sensing properties for the APTES@WO3-x compared to non-modified WO3-x sensors, with the APTES@WO3-x sensors showing approximately 17 and 20 times more sensitivity to ethanol and nitrogen dioxide, respectively, compared to the non-modified WO3-x sensors. The APTES@WO3-x sensors also display improved selectivity to nitrogen dioxide (oxidizing gas) and ethanol (among other reducing gases including acetone, toluene, hydrogen, and carbon monoxide). These results are attributed to the presence of the reactive amino group at the APTES@WO3-x sensors, which facilitates the chemical interaction with nitrogen dioxide and ethanol and the electron transfer towards/from WO3-x under UV-light excitation.

As soon as we sever the connection of a fresh product from "mother earth," a race against the clock starts. It will transform due to metabolic mechanisms and finally decay due to microorganisms' action. Historically, humankind has stored food for long periods by transforming it into more stable products, that is, by renouncing to its freshness. If we insist in eating fresh, beating decay involves several approaches: fast consumption, cold chain, or controlled atmospheres. In all cases, a certain degree of monitoring is needed. Otherwise, unrestrained spoilage leads to adverse consequences such as tremendous food waste and unwanted foodborne diseases. Generally, food quality is occasionally monitored along the food supply chain by qualified food inspectors using analytical chemical instrumentation. Such systems offer accurate but off-site and time-consuming measurements that preclude prompt reaction. Since decay telltale species are often of gaseous/volatile nature, different gas-sensing schemes can be used leveraging on different optical or electrical transduction mechanisms that can be integrated in cost-effective small footprint devices. These sensors or indicators can be then placed close to the product along the food chain, or, for more complex measurements, can be further integrated into deployable or portable miniaturized systems than enable bringing the lab to the product.

first_page settings Order Article Reprints Font Type: Arial Georgia Verdana Font Size: Aa Aa Aa Line Spacing:    Column Width:    Background: Open AccessProceeding Paper Room Temperature Humidity Sensor Based on Single β-Ga2O3 Nanowires † by Guillem Domènech-Gil 1,2,*, Irmina Peiró 1, Elena López-Aymerich 1, Mauricio Moreno 1,2, Paolo Pellegrino 1,2, Isabel Gràcia 3, Carles Cané 3, Sven Barth 4 and Albert Romano-Rodríguez 1,2 1 Department of Electronic and Biomedical Engineering, Universitat de Barcelona (UB), 08028 Barcelona, Spain 2 Institute of Nanoscience and Nanotechnology (IN2UB), Universitat de Barcelona (UB), 08028 Barcelona, Spain 3 Institut de Microelectrònica de Barcelona-Centre Nacional de Microelectrònica, Consejo Superior de Investigaciones Científicas (CSIC), 08193 Bellaterra, Spain 4 Institute of Materials Chemistry, TU Wien, 1060 Vienna, Austria * Author to whom correspondence should be addressed. † Presented at the Eurosensors 2018 Conference, Graz, Austria, 9–12 September 2018. Proceedings 2018, 2(13), 958; https://doi.org/10.3390/proceedings2130958 Published: 8 January 2019 (This article belongs to the Proceedings of EUROSENSORS 2018) Download Download PDF Download PDF with Cover Download XML Browse Figure Versions Notes 1. SummaryMonoclinic gallium oxide (β-Ga2O3) nanowires were fabricated via a metal-assisted vapor-liquid-solid process using chemical vapor deposition techniques and carbothermal reduction. The fabricated nanowires were structurally and optically characterized, revealing a high crystalline nature, with strong photoluminescent emission and a bandgap of 4.2 eV. Using focused electron beam techniques, nanowires were individually contacted for their use as gas sensors. The fabricated devices were tested against different concentrations of gases up to temperatures of 200 °C. Fast, stable and reproducible responses were measured towards water vapor at room temperature, with a power consumption in the nW range. The reaction promoting this response is strongly related to pre-adsorbed oxygen, a tight requirement for the water vapor sensing. 2. Motivation and ResultsIn the early nineties β-Ga2O3 appeared as an interesting material for high-temperature oxygen and reducing gases sensors in form of thin films [1]. As gallium oxide requires temperature above 600 °C to sense oxygen, several alternative strategies were explored to lower this threshold: surface functionalization with metal-particles, dopants or the use of morphologies with higher surface-to- volume ratio, like nanowires. The β-Ga2O3 nanostructure-based sensors have shown enhanced sensing performance when compared to thin film gas sensors, being able to sense reducing gases and volatile organic compounds at considerably low temperatures or even at room temperature with less power consumption than their thin film counterparts [2].In this study, we present single β-Ga2O3 nanowire-based sensors, Figure 1a, and their behavior when exposed to different concentrations of water vapor at room temperature, Figure 1b. The response measured increased with concentration and was always fast, between 7 and 2 min to reach a steady state when exposed from 40 to 80% of relative humidity, respectively. The maximum response lies around 97%. With increasing temperature, the response decreased, disappearing at ~150 °C. This occurrence seems to indicate that the sensing process is due to physisorption.To study possible reaction paths, tests were repeated under nitrogen ambient, revealing that water vapor promotes the oxygen desorption from the β-Ga2O3 nanowires and, therefore, the presence of oxygen at the surface or the surrounding of the sensing material is necessary for effective sensing. The oxygen adsorption on the surface of the nanowires was very fast, around 1 min for varying oxygen concentration. ReferencesFleischer, M.; Meixner, H. Gallium oxide thin films: A new material for high-temperature oxygen sensors. Sens. Act. B Chem. 1991, 4, 437–441. [Google Scholar] [CrossRef]Park, S.; Kim, H.; Jin, C.; Lee, C. Synthesis, structure, and room-temperature gas sensing of multiple- networked Pd-doped Ga2O3 nanowires. J. Korean Phys. Soc. 2012, 60, 1560–1564. [Google Scholar] [CrossRef] Figure 1. (a) Gallium oxide nanowires grown via gold-assisted vapor-liquid-solid process using chemical vapor deposition techniques and carbothermal reduction at 800 °C; (b) Gallium oxide nanowire-based gas sensor's resistance evolution towards varying concentrations of relative humidity in synthetic air at room temperature. Figure 1. (a) Gallium oxide nanowires grown via gold-assisted vapor-liquid-solid process using chemical vapor deposition techniques and carbothermal reduction at 800 °C; (b) Gallium oxide nanowire-based gas sensor's resistance evolution towards varying concentrations of relative humidity in synthetic air at room temperature. Publisher's Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. © 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). Share and Cite MDPI and ACS Style Domènech-Gil, G.; Peiró, I.; López-Aymerich, E.; Moreno, M.; Pellegrino, P.; Gràcia, I.; Cané, C.; Barth, S.; Romano-Rodríguez, A. Room Temperature Humidity Sensor Based on Single β-Ga2O3 Nanowires. Proceedings 2018, 2, 958. https://doi.org/10.3390/proceedings2130958 AMA Style Domènech-Gil G, Peiró I, López-Aymerich E, Moreno M, Pellegrino P, Gràcia I, Cané C, Barth S, Romano-Rodríguez A. Room Temperature Humidity Sensor Based on Single β-Ga2O3 Nanowires. Proceedings. 2018; 2(13):958. https://doi.org/10.3390/proceedings2130958 Chicago/Turabian Style Domènech-Gil, Guillem, Irmina Peiró, Elena López-Aymerich, Mauricio Moreno, Paolo Pellegrino, Isabel Gràcia, Carles Cané, Sven Barth, and Albert Romano-Rodríguez. 2018. "Room Temperature Humidity Sensor Based on Single β-Ga2O3 Nanowires" Proceedings 2, no. 13: 958. https://doi.org/10.3390/proceedings2130958 Find Other Styles Note that from the first issue of 2016, MDPI journals use article numbers instead of page numbers. See further details here. Article Metrics No No Article Access Statistics Multiple requests from the same IP address are counted as one view.

Gas microsensors based on zinc oxide structures with rod- and needle-like morphology, both integrated via a non-catalyzed vapor-solid mechanism enabled using aerosol-assisted chemical vapor deposition, are developed. Analyses of the films via SEM, TEM, XPS, and water contact angle indicate a higher concentration of oxygen vacancies, higher aspect ratio and higher roughness factor for the needles than for the rods. Gas sensing tests towards hydrogen and carbon monoxide demonstrate reduced humidity-interference, and higher responses to the analytes for the needle-based systems compared to the rods. These results are attributed to the morphology of the sensitive materials, which not only affects the surface-area-to-volume-ratio of the films but also their surface chemistry. These findings indicate that a thorough optimization of morphology, structure and surface properties of gas sensitive metal oxides could allow for more reliable sensor operation in humid conditions.

In the near future, a multitude of wireless sensor nodes spread all around our environment and even our body will be continuously receiving and sending information, measuring data and working together to make more complex processes. This disruptive concept is known as Internet of Things (IoT). One of the main difficulties to make this vision real is the way of powering all these tiny devices. As alternative, energy harvesting from ambient sources becomes a tangible possibility thanks to the great reduction in power consumption of current electronic circuits. This work is mainly focused on energy harvesting from ambient vibrations by means of piezoelectric resonant devices. In this field, ENSOECSEL- H2020 project is dealing with this and other approaches (mechanical, thermal and solar harvesting, wireless charging, and flexible batteries) to develop new energy efficient systems for Smart Objects.

In this contribution we present a highly miniaturized device that integrates a photoactive material with a highly efficient LED light source. This so-called micro light plate configuration (µLP) allows for maximizing the irradiance impinging on the photoactive material, with a minimum power consumption, excellent uniformity and accurate control of the illumination. We demonstrate that, with the µLP approach, very efficient low power gas sensors can be built, and provide a detailed analysis of the rationales behind such improvement, as well as a quantitative model and a set of design rules to implement it in further integrated applications. As a demonstrator, we will describe a NO2 gas sensor operating in the part per billion range (ppb) with microwatt (µW) power consumption. These are the best figures reported to date in conductometric metal-oxides (MOX) sensors operated with light (instead of heat) at room temperature.

Based on the recently reported "micro-light-plate" configuration, we have implemented a light activated gas sensor for NO 2 operating at room temperature. With this conductometric device, we achieved detection limits down to a few parts per billion (ppb) with power consumption in the tens of microwatt range (μW). These are record values for conductometric metal-oxides (MOX) sensors activated with light (instead of heat).

A methodology based on the use of Electron Beam Lithography for contacting individual nanowires on top of non-flat micromembranes and microhotplates has been implemented, and the practical details have been exhaustively described. The different fabrication steps have been adapted to the substrate's topology, requiring specific holders and conditions. The methodology is demonstrated on individual SnO2 nanowires, which, after fabrication, have been characterized as functional resistive gas nanosensors towards NH3 and benchmarked against similar devices fabricated using more conventional Dual Beam Focused Ion Beam techniques, demonstrating the superior properties of the here presented methodology, which can be further extended to other non-conventional suspended substrates and nanomaterials.

A new method for the site-selective synthesis of nanowires has been developed to enable the material growth with specific morphology and different compositions on one single chip. Based on a modification of the chemical vapor deposition method, the growth of nanowires on top of micromembranes can be easily tuned and represents a simple and adjustable fabrication process for the direct integration of different nanowire-based resistive multifunctional devices. This proof-of-concept is exemplified by the deposition of SnO2, WO3 and Ge nanowires on the membranes of one single chip and their gas sensing responses towards different concentrations of CO, NO2 and humidity diluted in synthetic air are evaluated. The principal component analysis of the collected data allows gas identification and, thus, the system is suitable for environmental monitoring.

A film of gas sensitive ZnO nanoparticles has been coupled with a low-power micro light plate (μLP) to achieve a NO2-parts-per-billion conductometric gas sensor operating at room temperature. In this μLP configuration, an InGaN-based LED (emitting at 455 nm) is integrated at a few hundred nanometers distance from the sensor material, leading to sensor photoactivation with well controlled, uniform, and high irradiance conditions, and very low electrical power needs. The response curves to different NO2 concentrations as a function of the irradiance displayed a bell-like shape. Responses of 20% to 25 ppb of NO2 were already observed at irradiances of 5 mWatts·cm-2 (applying an electrical power as low as 30 μW). In the optimum illumination conditions (around 60 mWatts·cm-2, or 200 μW of electric power), responses of 94% to 25 ppb were achieved, corresponding to a lower detection limit of 1 ppb of NO2. Higher irradiance values worsened the sensor response in the parts-per-billion range of NO2 concentrations. The responses to other gases such as NH3, CO, and CH4 were much smaller, showing a certain selectivity toward NO2. The effects of humidity on the sensor response are also discussed.