Semiconductor Gas Sensors: Materials, Technology, Design, and Application

This paper presents an overview of semiconductor materials used in gas sensors, their technology, design, and application. Semiconductor materials include metal oxides, conducting polymers, carbon nanotubes, and 2D materials. Metal oxides are most often the first choice due to their ease of fabrication, low cost, high sensitivity, and stability. Some of their disadvantages are low selectivity and high operating temperature. Conducting polymers have the advantage of a low operating temperature and can detect many organic vapors. They are flexible but affected by humidity. Carbon nanotubes are chemically and mechanically stable and are sensitive towards NO and NH3, but need dopants or modifications to sense other gases. Graphene, transition metal chalcogenides, boron nitride, transition metal carbides/nitrides, metal organic frameworks, and metal oxide nanosheets as 2D materials represent gas-sensing materials of the future, especially in medical devices, such as breath sensing. This overview covers the most used semiconducting materials in gas sensing, their synthesis methods and morphology, especially oxide nanostructures, heterostructures, and 2D materials, as well as sensor technology and design, application in advance electronic circuits and systems, and research challenges from the perspective of emerging technologies. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

Nanostructured Fe2O3/TiO2 thick films prepared by screen printing

Nanostructured single layered (pure TiO2 , pure α-Fe2O3 and mixed Fe2O3 /TiO2 with two different oxide ratios, 2 : 3 and 3 : 2) and double layered (TiO2 layer over a Fe2O3 layer) thick films have been fabricated by screen printing technology on a glass substrate. The pastes used for film preparation were obtained by adding an organic vehicle to the oxide powders together with a small percentage of binding glass frit. Samples were dried up to 100 °C and sintered at 650 °C/60 minutes. Structural, morphological and optical studies have been carried out using XRD, SEM analyses and UV/Vis spectroscopy. The prepared pure and mixed Fe2O3 /TiO2 thick films had a homogenous nanostructure without secondary phases. Indirect band gaps were determined from the measured transmission spectra and the obtained values are in the range of literature data. [Projekat Ministarstva nauke Republike Srbije, br. III45007

Far infrared and photoacoustic characterization of iodine doped PbTe

Single crystal samples of PbTe doped with PbI2 were made using the Bridgman technique. Far infrared reflectivity diagrams of PbTe doped with 0.4 at% and 0.6 at% Iodine were measured and numerically analyzed. A plasma resonance at about 650 cm(-1) with the reflectivity minima very close to zero was observed for both samples. Thermal diffusivity was determined for the same samples using the photoacoustic method with a transmission detection configuration and the values of the minority free carrier (holes) mobility were calculated

Far infrared and photoacoustic characterization of iodine doped PbTe

Single crystal samples of PbTe doped with PbI2 were made using the Bridgman technique. Far infrared reflectivity diagrams of PbTe doped with 0.4 at% and 0.6 at% Iodine were measured and numerically analyzed. A plasma resonance at about 650 cm(-1) with the reflectivity minima very close to zero was observed for both samples. Thermal diffusivity was determined for the same samples using the photoacoustic method with a transmission detection configuration and the values of the minority free carrier (holes) mobility were calculated

Discutindo a educação ambiental no cotidiano escolar: desenvolvimento de projetos na escola formação inicial e continuada de professores

A presente pesquisa buscou discutir como a Educação Ambiental (EA) vem sendo trabalhada, no Ensino Fundamental e como os docentes desta escola compreendem e vem inserindo a EA no cotidiano escolar., em uma escola estadual do município de Tangará da Serra/MT, Brasil. Para tanto, realizou-se entrevistas com os professores que fazem parte de um projeto interdisciplinar de EA na escola pesquisada. Verificou-se que o projeto da escola não vem conseguindo alcançar os objetivos propostos por: desconhecimento do mesmo, pelos professores; formação deficiente dos professores, não entendimento da EA como processo de ensino-aprendizagem, falta de recursos didáticos, planejamento inadequado das atividades. A partir dessa constatação, procurou-se debater a impossibilidade de tratar do tema fora do trabalho interdisciplinar, bem como, e principalmente, a importância de um estudo mais aprofundado de EA, vinculando teoria e prática, tanto na formação docente, como em projetos escolares, a fim de fugir do tradicional vínculo “EA e ecologia, lixo e horta”.Facultad de Humanidades y Ciencias de la Educació

Semicondcuting metal oxide nanoparticles in sensors, optoelectronics and electronic devices

The Internet of Things (IoT) represents a multi-layer technology connecting diverse hardware (smart appliances, smart gadgets, and wearable, biocompatible, and mobile consumer devices) by middleware to the cloud of things (CoT). It is changing how electronics interface with our physical world in terms of sensing, information display and communication. Gas sensors and sensor nodes are a vital component of the IoT. Modern electronic systems are flexible, transparent, biocompatible and wearable. Semiconducting metal oxides are earth abundant multifunctional materials. Their multifunctionality stems from their complex and widely varied electronic structure and properties. They include a wide range of band gaps, high surface activity, and electrical properties making them the subject of continuous research, especially in the form of nanoparticles for application in sensors, optoelectronics and electronic devices. Metal oxides are stable materials, easy to synthesize and process. In nanostructure form they show a wide range of enhanced properties, such as a suitable band gap, conduction properties and confined conduction pathways for photoelectric electronic devices. They are excellent candidates, in crystalline or amorphous form, for optoelectronic devices, such as flat panel displays, solar cells, organic light-emitting diode displays (OLEDs) and emerging flexible and transparent electronics, as they can exhibit high electrical performance and excellent visible range transparency. The high growing demand for flexible electronics requires low temperature and high-throughput synthesis of oxide thin films on flexible plastic substrates. High sensitivity, fast response/recovery and good selectivity are generally required of a good sensing material. Metal oxides still remain the first choice for application in sensors, especially gas sensors due to their ease of fabrication, low cost, high sensitivity, and stability. Some of their disadvantages are low selectivity and high operating temperature. Over time commercially produced metal oxide gas sensors have reduced in size being produced in different technologies, starting with tube-type sensors in the eighties of the last century, through screen-printed sensors produced in the nineties and completing with state-of-the art micro-electro-mechanical system (MEMS) sensors produced today. Development of low cost, reduced power consumption and reliable sensing devices for the detection of gases for environmental and industrial applications, especially at room temperature remains a significant scientific and technological challenge

Multipolar anisotropy and domain semicircular alignment in sintered strontium hexaferrite shaped by PIM technology

Multipolar anisotropy was induced in strontium hexaferrite green samples in a high intensity magnetic field during feedstock injection by PIM (powder injection molding) technology. Strontium hexaferrite particles in the melted feedstock were multipolarly aligned into four semi-circular paths that were circularly closed through a multipolar electromagnet. After debinding (with acetone and thermally) and sintering (optimized to obtain maximal values of the (BH)max product), samples were multipolarly magnetized again to form four poles on the outer surface of the sample. Multipolar anisotropy of the samples was observed and analyzed in detail by SEM and AFM (crystalline alignment) and by MFM (magnetical alignment)

Multipolar anisotropy and domain semicircular alignment in sintered strontium hexaferrite shaped by PIM technology

Multipolar anisotropy was induced in strontium hexaferrite green samples in a high intensity magnetic field during feedstock injection by PIM (powder injection molding) technology. Strontium hexaferrite particles in the melted feedstock were multipolarly aligned into four semi-circular paths that were circularly closed through a multipolar electromagnet. After debinding (with acetone and thermally) and sintering (optimized to obtain maximal values of the (BH)max product), samples were multipolarly magnetized again to form four poles on the outer surface of the sample. Multipolar anisotropy of the samples was observed and analyzed in detail by SEM and AFM (crystalline alignment) and by MFM (magnetical alignment)

Multipolar anisotropy and domain semicircular alignment in sintered strontium hexaferrite shaped by PIM technology

Multipolar anisotropy was induced in strontium hexaferrite green samples in a high intensity magnetic field during feedstock injection by PIM (powder injection molding) technology. Strontium hexaferrite particles in the melted feedstock were multipolarly aligned into four semi-circular paths that were circularly closed through a multipolar electromagnet. After debinding (with acetone and thermally) and sintering (optimized to obtain maximal values of the (BH)max product), samples were multipolarly magnetized again to form four poles on the outer surface of the sample. Multipolar anisotropy of the samples was observed and analyzed in detail by SEM and AFM (crystalline alignment) and by MFM (magnetical alignment)

Influence of MgO addition on the synthesis and electrical properties of sintered zinc-titanate ceramics

Starting mixtures of ZnO, TiO(2) and MgO (0, 1.25 and 2.5 wt.% MgO) powders were mechanically activated for 15 min in a planetary ball mill. The powders obtained were sintered non-isothermally to temperatures between 800 and 1100 degrees C and then held at those temperatures for 120 min. Analysis of the influence of MgO addition on the synthesis of zinc-titanate ceramics showed that its addition increased slightly the temperature at which the reaction process started, accelerated the reaction and resulted in higher sample densities. These results were correlated with the results of structural characterization using X-ray powder diffraction method and SEM analysis. Also, the results of electric resistivity, capacitance and loss tangent of the sintered samples were obtained. (C) 2008 Elsevier B.V. All rights reserved