The adsorption and desorption of oxygen molecule on the surface of oxide semiconductors are the basis for sensing reactions between the surface oxygen species and the target gases molecules. Combined with experiments and theoretical calculations, we found that antimony impurities were conducive to the promotion of oxygen adsorption and dissociation on the surface of SnO₂. However, the narrow Debye length had an adverse effect on sensing properties of Sb doped SnO₂. On the contrary, the introduction of cobalt dopant will generate more oxygen vacancies and reduce the concentration of electrons and consequently the Debye length will become longer, which makes the transduction more significant. Namely, the same amount of charge transfer between surface and analyte gases can cause a larger change in resistance than pure metal oxide. The aforementioned inferences about doped metal oxides indicate that for optimizing their sensing properties, doped oxides with appropriate dopant and unique structure which can balance the recognition function and transduction function are required. Full article

Gas sensor as a device composed of sensing material coupled with signal transducer, has been acknowledged as an analytical tool for detection and quantification of inflammable, explosive or toxic gases. The gas sensors based on nanostructured oxide semiconductor endowed with excellent sensing properties have exhibited great potential application in the fields of environmental monitoring, resource exploration, medical welfare, etc. It is well known that the sensing mechanism of sensor employing oxide semiconductors is mainly that the interactions between the surface adsorbed oxygen species and target gases lead to a change in the electrical conductivity. Therefore, the gas sensing properties of oxide semiconductors are closely related with their composition, crystalline size, and microstructure. In this regard, design and preparation of oxides with novel architectures will be increasingly important in the construction of high performance gas sensors. Due to high specific surface area, low density, and good surface permeability, porous nanostructures oxide semiconductor sensing materials have attracted growing interest in recent years. In our work, we successfully prepared various porous nanostructures oxides and their composites to the construction of high performances gas sensors with enhanced sensitivity, selectivity, as well as lowered detection limit. The subsequent gas sensing measurements explicitly revealed that these oxides and composites manifested superior sensing behaviors (like much higher sensitivity and faster response speed), which can be ascribed to the porous architectures and the synergistic effects. Full article

Semiconductor functional materials play an increasingly important role in science and technology because of their unique optical, electrical, magnetic, catalytic and chemical properties. They are widely used in fields such as solar cell, photo-catalysts, optical coating, capacitors for large scale integrated devices, electrochromic systems and gas sensors. One important application for semiconductor gas sensors is the detection of pollutant gases for the control of the combustion process. Full article

In this work Ga doped ZnO thin films have been deposited by RF magnetron sputtering onto a silicon micro-hotplate and their structural, microstructural and gas sensing properties have been studied. ZnO:Ga thin film with a thickness of 50 nm has been deposited onto a silicon based micro-hotplates without any photolithography process thanks to a low cost and reliable stencil mask process. Sub-ppm sensing (500 ppb) of NO₂ gas at low temperature (50 °C) has been obtained with promising responses R/R0 up to 18. Full article

In this work, a new generation of gas sensing systems specially designed for breath analysis is presented. The developed system comprises a compact modular, low volume, temperature-controlled sensing chamber with three compartments that can host different sensor types. In the presented system, one compartment contains an array of 8 analog MOX sensors and the other two 10 digital MOX sensors each. Here, we test the system for the detection of low concentrations of several compounds. Full article

Aim of this work is to compare the electrical responses to 100–400 ppb NO₂ gas concentrations of WO₃ electrospun nanofibers both activated by thermal (in the temperature range 25–100 °C) and/or visible light at different wavelengths (Red λ = 670 nm, Green λ = 550 nm, and Purple-Blue λ = 430 nm). WO₃ nanofibers were prepared by mixing a W-O sol-gel transparent solution with a polymeric solution made of PVP and DMF, electospun and subsequently annealed at 450 °C. Regarding gas sensing measurements, Purple Blue light resulted the most effective light source as respect to the others. Light illumination at room temperature revealed to improve both base line recovery and response time, whereas temperature enhances relative response, with a maximum at 75 °C. Light-radiating room temperature gas detection yields a satisfactory response notwithstanding a slight reduction of sensor gas sensitivity. Light induced electrical response mechanisms is presented and discussed. Full article

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. Full article

The article describes the result of the use SnO₂-Pd thin films as a gate for structure measured ppb range of NO₂ gas by the capacitive method. The technological aspects of fabrication SnO₂-Pd gate and one comparison by metrological parameters with the classical Pd gate field effect sensor are discussed. The use of SnO₂-Pd material allows improvement in sensitivity of NO₂ by an order of magnitude compare the classical Pd based gate field effect sensors. Full article

Rare-earth oxycarbonates have been proposed as promising chemoresistive materials for CO₂ sensors. In this contribution we present the results of a broad investigation focused on selecting the best candidates in the rare-earth compounds and, in the case of the best performing material, preliminary results dealing with the understanding of sensing by the operando methods. Full article

We present flexible chemo-resistive sensors based on AACVD grown tungsten trioxide (WO₃) nanowires. The sensor response to gases, before and after a 50-cycle bending test, is reported. Thus, proving that reliable gas sensors, able to withstand repeated bending, have been achieved. Moreover, their integrity and durability have been tested under harsh bending conditions until break down. Full article

This work presents a practical application of an electronic nose to fast and efficient discrimination of different species of Amanita mushrooms. The electronic nose instrument were utilized for investigation of discrimination capability with respect to odour profile of these fungi. The home-made prototype was based on MOS-type chemical sensors and headspace sampling method. Samples were cut into thin sheets, placed in glass vials and maintained at a constant temperature using a thermostatic bath, the headspace of which was subjected to analysis. The data were analysed using multivariate methods: PCA, LDA and Artificial Neural Networks. The obtained results confirmed legitimacy of application of the electronic nose technique to identification and discrimination of fungi species. Results show a correct classification of the fungi species at the level of 80–100%. Full article

Chemical gas sensors were studied long ago and nowadays, for the advantageous role they provide to the environment, health condition monitoring and protection. The recent studies focus on the semiconductors sensing abilities, especially of non toxic and low cost compounds. The present work describes the steps to elaborate and perform a chemical sensor using intrinsic and doped semiconductor zinc oxide. First, we synthesized pure oxide using zinc powder, then, two other samples were established where we introduced the same doping percentage of Al and Sn respectively. Using low cost spray pyrolysis, and respecting the same conditions of preparation. The obtained samples were then characterized by X Ray Diffraction (XRD) that revealed the hexagonal wurzite structure and higher crystallite density towards the direction (002), besides the appearance of the vibration modes related to zinc oxide, confirmed by Raman spectroscopy. SEM spectroscopy showed that the surface morphology is ideal for oxidizing/reduction reactions, due to the porous structure and the low grain sizes, especially observed for the sample Sn doped ZnO. The gas testing confirms these predictions showing that the highest response is related to Sn doped ZnO compared to ZnO and followed by Al doped ZnO. The films exhibited responses towards: CO, acetone, methanol, H₂, ammonia and NO₂. The concentrations were varied from 10 to 500 ppm and the working temperatures from 250 to 500°C, the optimal working temperatures were 350 and 400 °C. Sn doped ZnO showed a high response towards H₂ gas target, with a sensitivity reaching 200 at 500 ppm, for 400 °C. Full article

Convenient and scalable single step flame spray pyrolysis (FSP) synthesis of bimetal AuPd sensitized nanocrystalline SnO₂ for gas sensor application is reported. The materials chemical composition, structure and morphology has been studied by XRD, XPS, HAADFSTEM, BET, ICP-MS techniques as well as thermo-programmed reduction with hydrogen (TPR-H₂). Superior gas sensor response of bimetal modified SnO₂ towards wide concentration range of reducing (CO, CH₄, C₃H₈, H₂S, NH₃) and oxidizing (NO₂) gases compared to pure and monometallic modified SnO₂ is reported. The observed enhanced gas sensor performance is concluded to arise from combination of facilitated oxygen molecule spillover on gold particles and electronic effect of Fermi level control by reoxidizing Pd-PdO clusters, homogeneously distributed over SnO₂ particles surface. Full article

Selective detection of hydrocarbons – methane and propane – in urban air for industrial safety properties by single metal oxide semiconductor gas sensor has been demonstrated. As sensors were fabricated on the basis of nanocrystalline SnO₂ and alumina micro-hotplates. Sensor working temperature modulation has been applied during raw sensor data collection. Pre-processing of acquired data – scaling, baseline extraction and exclusion of non-valid data points has been demonstrated to be critical procedures before application of machine learning algorithms. The achieved accuracy of 86% for correct gas identification in 40-200 ppm range has been demonstrated. Full article

By laser micromilling technology it is possible to fabricate custom MEMS microhotplate platform and also SMD package for MOX sensor, that gives complete solution for integration in mobile devices-smart phones, tablets and etc. The 3D design and fabrication of MEMS microhotplates and packages products occurs simultaneously that give opportunity for ultra-fast time making unique solutions for MOX sensors (number of microhotplates, hot spot size on microhotplates, diameter holes in package cap and etc.) without looking at standard solutions (primarily the package type). Full article

Abstract: Metal oxide semiconductor gas sensors are used in a various applications in environmental, industrial and medical field, for instance. They are relatively inexpensive compared to other sensing technologies, robust, lightweight, long lasting and benefit from high material sensitivity and quick response times. Copper oxide (CuO) thin film has been promisingly proposed for chemical sensing applications. Particularly, it has been recommended as a sensitive layer for monitoring harmful and combustible gases. It is an attractive material because of nontoxic, inexpensive, abundance advantages, and its fabrication is easy. In this work, we have synthesized CuO thin films by Spray pyrolysis method. The effect of the temperature deposition is investigated:to say 350 °C, 400 °C, and 450 °C while the deposition duration was kipped to 15 min. The samples were analyzed by X-ray diffraction, Raman spectroscopy, XPS analysis, UV-visible transmission and four points probe method. Full article