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The application of a non-stationary regime of temperature modulation in metal oxide semiconductor sensor based on SnO2–Ag leads not only to a strongly increased sensor response, but also to a considerably improved sensor selectivity toward hydrogen sulfide. Selectivity with respect to other reducing gases (CO, NH3, H2) is about five orders of magnitude, enabling a correct selective determination of H2S in the presence of interfering gas components.

This work is an investigation of the properties of semiconductor materials based on metal oxides, their catalytic properties, and their application as gas sensors, which were shown to exhibit high sensitivity, stability, and selectivity to target gases. The aim of this work is the comparison of gas sensing properties of tin dioxide in the form of individual nanowires and nanopowders obtained by sol–gel synthesis. This comparison is necessary because the traditional synthesis procedures of small particle, metal oxide materials seem to be approaching their limit. Because of this, there is increasing interest in the fabrication of functional materials based on nanowires, i.e., quasi-one-dimensional objects. In this work, nanocrystalline tin dioxide samples with different morphology were synthesized. The gas-transport method was used for the fabrication of well-faceted wire-like crystals with diameters ranging between 15–100 nm. The sol–gel method allowed us to obtain fragile gels from powders with grain sizes of about 5 nm. By means of X-ray photoelectron spectroscopy (XPS) it was proven that the nanowires contain considerably smaller amounts of hydroxy groups compared to the nanopowders. This leads to a decrease in the parasitic sensitivity of the sensing materials to humidity. In addition, we demonstrated that the nanowires are characterized by a nearly single-crystalline structure, ensuring higher stability of the sensor response due to the unlikelihood of sample recrystallization. The results from the ammonia detection experiments showed that the ratio of the sensor response to the surface area exhibits similar values for both the individual nanowire and nanopowders-based sensor materials.

We have applied spark ablation technology for producing nanoparticles from platinum ingots (purity of 99.97 wt. %) as a feed material by using air as a carrier gas. A maximum production rate of about 400 mg/h was achieved with an energy per pulse of 0.5 J and a pulse repetition rate of 250 Hz. The synthesized nanomaterial, composed of an amorphous platinum oxide PtO (83 wt. %) and a crystalline metallic platinum (17 wt. %), was used for formulating functional colloidal ink. Annealing of the deposited ink at 750 &deg, C resulted in the formation of a polycrystalline material comprising 99.7 wt. % of platinum. To demonstrate the possibility of application of the formulated ink in printed electronics, we have patterned conductive lines and microheaters on alumina substrates and 20 &mu, m thick low-temperature co-fired ceramic (LTCC) membranes with the use of aerosol jet printing technology. The power consumption of microheaters fabricated on LTCC membranes was found to be about 140 mW at a temperature of the hot part of 500 &deg, C, thus allowing one to consider these structures as promising micro-hotplates for metal oxide semiconductor (MOS) gas sensors. The catalytic activity of the synthesized nanoparticles was demonstrated by measuring the resistance transients of the non-sintered microheaters upon exposure to 2500 ppm of hydrogen.

A combination of low limit of detection, low power consumption, and portability makes organic field-effect transistor (OFET) chemical sensors promising for various applications in the areas of indu...

The kinematic scheme of a two-stream transmission is considered, which makes it possible to implement the principle of using two engines (including those using different physical principles and having different energy characteristics) and to implement the idea of design a hybrid power plant, including one adapted for operation on a driverless ship. The result of the research is the structural diagram of the transmission, the kinematic diagram of the summing gear in its composition and proposals for the implementation of the main units of the summing gear. The gearbox allows for smooth connection or disconnection of selected motors to the payload. The considered power plant combines an internal combustion engine and a traction motor. The main benefit is increased reliability through redundant motors. Improvements in efficiency are expected by ensuring consistent engine performance. The composition, the kinematic diagram, the principle of the transmission are proposed. The equations describing the kinematic and force relations in the summing gear are considered. The used method of kinematic and force analysis has been tested in the machine-building industry in relation to planetary gears as part of highly loaded transmissions of wheeled and tracked vehicles. References are given to technical solutions that make it possible to implement the proposed transmission based on the technological capabilities mastered by Russian manufacturers. The proposed scheme seems to be promising for use on ships for various purposes, including military boats, in the power plant of which a gas turbine engine is used.

Two dimensional (2D) MXene decorated by the SnO2 nanoparticles has been successfully synthesized by the hydrothermal method. The formed MXene/SnO2 heterojunction based chemirestistive-type sensors exhibit an excellent sensitivity and selectivity to different concentrations of NH3 from 0.5 to 100 ppm at room temperature. The enhanced sensing properties can be attributed to two major factors. On one hand, 2D MXene provides a matrix which has a unique, selective adsorption ability to ammonia and good conductivity that makes the room-temperature sensing of the heterojunction based sensor feasible. On the other hand, the difference in the Fermi level of the 2D MXene and SnO2 drives the charge transfer at the interface of the heterojunctions enriching the electrons on the surface region of SnO2 and consequently enhancing the sensitivity. Furthermore, a wireless sensor made from an inductor-capacitor (LC) antenna and the as-synthesized MXene/SnO2 heterojunctions fabricated by the low-temperature-cofired ceramic technique (LTCC) was preliminary investigated. The wireless sensor shows a even faster response/recovery speeds (

We prepared platinum nanoparticle ink usable for the fabrication of MEMS microheatersof high-temperature gas sensors and thermoresistors operating up to 450 °C and present somepreliminary results on the application of the ink in sensor microheater manufacturing. The inkconsists of platinum particles (3⁻8 nm) suspended in ethylene glycol solution of polyvinylpyrrolidone.The ink is usable in both InkJet and AerosolJet printers. The annealing at temperature of about 600 °Cleads to the formation of uniform microheater structure. The experiments on microheater agingconfirm the stability of the printed microstructure at 450 °C for at least one year of operation. Thesubstrates used for printing were thin alumina and LTCC ceramics with thickness of 12⁻20 μm.

The perspective catalysts usable for the fabrication of thermocatalytic gas sensors were studied. The analysis of CO oxidation kinetics by Pd decorated Al2O3, ZSM-5, SnO2, CeO2/ZrO2 and some other carriers of catalysts showed that the application of these catalysts leads to the ambiguity of sensor response (light-off effect). It was demonstrated that a catalyst based on CeO2/ZrO2 carrier could be used for the fabrication of sensors characterized by the univocal correspondence between CO concentration and sensor response. The developed model of the CO oxidation on all Pd catalysts with inert carrier enabled the description of the CO oxidation using a single value of activation energy.

The online control of natural gas quality is important for customers, because for them the important value is calorific value of consumed gas, but not its volume. The application of thermoconductometric sensor gives simple possibility to fabricate imbedded intellectual plug-and-play device for this control. The ceramic MEMS sensor based on a combination of this ceramic LTCC membrane and aerosol jet printed platinum microheater was used as a sensing element of this unit. The electronic unit controlling the sensor was designed to stabilize the temperature of the microheater and to measure power necessary to maintain this temperature at different concentrations of N2and CO2 in natural gas. The application of this unit enables the measurement of admixtures of nitrogen and CO2 with detection limit of about 1 vol. % sufficient for the application in gas meter instruments.

We demonstrated the possibility of selective detection of hydrogen, ethanol, hydrogen sulfide, carbon monoxide, methane and ammonia gas using metal oxide gas sensor operating in non-stationary thermal regime. This non-stationary regime consists in fast heating of the sensing layer to high temperature followed by temperature stabilization at lower temperature. The analysis of the shape of the curve describing the sensor resistance as a function of time during this measurement cycle enables the quantitative analysis of gas mixture. The investigation of kinetics of the process in non-stationary regime permits to understand the mechanism of the processes on the surface of sensing material.

In this work gas sensing properties of Langmuir-Schaefer monolayer organic field-effect transistors (LS OFETs) prepared from organosilicon derivative of [1]benzothieno[3,2-b][1]-benzothiophene (BTBT) have been investigated. The monolayer has been deposited using Langmuir-Schaefer method, which results in a uniform low-defect monolayer with excellent electrical performance, hole mobility up to 7 × 10−2 cm2 V−1 s−1, the threshold voltage around 0 V and on-off ratio of 104. Developed sensors demonstrate a long-term stability of a half-year storage under ambient conditions. Preliminary investigations demonstrated that the LS OFETs give instantaneous response on ammonia and hydrogen sulfide at low concentrations. The results reported open new perspectives for the OFET-based gas-sensing technology.

Traditional methods of synthesis of metal-oxide gas sensing materials for semiconductor sensors are based on wet sol-gel processes. However, these processes lead to the formation of hydroxyl groups on the surface of oxide particles being responsible for the strong response of a sensing material to humidity. In this work, we investigated the possibility to synthesize metal-oxide materials with reduced sensitivity to water vapors. Dry synthesis of SnO2 nanoparticles was implemented in the gas phase by spark discharge, which allowed us to produce powder with specific surface area of about 40 m2/g after additional annealing at 610 °C. The drop of sensor resistance does not exceed 20%, when air humidity increases from 40 to 100%, whereas the response to 100 ppm of hydrogen is of a factor of 8 with very short response time of about 1 s.

During the topology creation by the selective laser sintering method experimental samples of microheater based on ruthenium dioxide micro-powder were made. The resulting structures were used as microheaters to measure changes in the thermal conductivity of gases. A power comparison of standard platinum spiral element widely used in catalytic thermal sensors and microheater produced by the new technology showed the advantage of the latter.

In this paper, a method of producing the metallization on the alumina ceramic substrate by micropowders of ruthenium dioxide sintering using laser radiation with 10.6 micrometers length (carbon dioxide laser) is described. During the work parameters of the mask, allowing to reduce the width of the laser spot as well as to get a mildly sloping profile of the radiation intensity, due to which more uniform sintering of the powders and pastes based on them takes place, are calculated.

We present a novel approach to the fabrication of MEMS devices, which can be used for gas sensors operating in harsh environment in wireless and autonomous information systems. MEMS platforms based on ZrO 2 /Y 2 O 3 (YSZ) are applied in these devices. The methods of ceramic MEMS devices fabrication with laser micromachining are considered. It is shown that the application of YSZ membranes permits a decrease in MEMS power consumption at 450 0 C down to ∼75 mW at continuous heating and down to ∼ 1 mW at pulse heating mode. The application of the platforms is not restricted by gas sensors: they can be used for fast thermometers, bolometric matrices, flowmeteres and other MEMS devices working under harsh environmental conditions.

The layout of experimental samples of microhotplate based on nanocomposite material consisting of ruthenium dioxide and borosilicate glass binder were formed by selective laser sintering method. The resulting structures were used as microhotplate to measure changes in thermal conductivity of gases. The comparison of power consumption of standard platinum wire coil element widely used in thermocatalytic (calorimetric) sensors and microhotplate produced by the new technology showed strong advantage of the latter one.

In this paper, we describe a novel cost-effective and simple technology for the production glass MEMS applied as microhotpalte platform for metal oxide gas sensors. The basis of the technology is magnetron sputtering of platinum heating layer followed by precise laser engraving and cutting used for heater patterning. As a result of the technology, we demonstrate the glass microhotplate cantilever with thickness of 30 μm equipped with platinum microheater with dimension of about 500×500 μm. The cantilever type MEMS microhotplate demonstrate very high stability at working temperatures up to 600 0C, which gives possibility to use it for the low-scale fabrication microhotplate of metal oxide gas sensors.

In this work we present the results on the application of additive technology that is aerosol and ink jet technique for the fabrication of high-temperature metal oxide gas sensors. The application of thin (12 μm) alumina membrane, aerosol jet printing of Pt microheater (line width 40–60 μm), printed sensing layer made of nanocristalline tin dioxide based material, laser cutting of the membrane enabled the fabrication of full-printed cantilever-shaped high-temperature sensor with optimal power consumption (~80 mW at 450 °C) applicable in wireless instruments for the detection of combustible and toxic gases including methane.

The application of thin LTCC is a very interesting and promising approach to the fabrication of ceramic MEMS gas sensors. The attempts to use this material were restricted till now by the thickness of commercial material (>50 μm). In this work, we found a possibility to fabricate thin LTCC membranes (20–30 μm) stretched on a frame made of 100 μm thick LTCC. Aerosol jet printed Pt microheater and laser cutting of the membrane gave a cantilever shaped microhotplate with hot spot of about 300 × 300 μm. Power consumption of the heater is ~150 mW at 450 °C.

In this paper, we describe a technique for the qualitative and quantitative analysis of such gas mixtures as &ldquo, hydrogen sulfide in air&rdquo, and &ldquo, methane in air&rdquo, using temperature modulation of a single metal oxide sensor. Using regression analysis in the principal components plane (PC1, PC2), we performed a selective determination of analytes on the minimum set of their concentrations in the training set, which is essential for solving practical problems. An important feature of this work is the difference in test gas concentrations from their concentrations in the training set. For the qualitative analysis of gas mixtures in a wide range of concentrations, we have developed an improved method for processing arrays of multidimensional data. For this improvement, we form a Mahalanobis neighborhood for polynomial regression lines constructed from the projection of training samples for each analyte on the (PC1, PC2) plane. Using the temperature modulation mode for the metal oxide sensor allowed us to increase its response when determining hydrogen sulfide by two to four orders of magnitude compared with the constant temperature mode.

The applicability of multisensor system based on a novel polymer nanocomposite material with parylene matrix including metal and/or semiconductive nanoparticles for the detection of low concentrations of ammonia gas, nitrogen dioxide, and hydrogen chloride is demonstrated. Nanocomposite films were synthesized by vacuum co-condensation method. It was shown that nanocomposite sensors demonstrate stable, fast, and reversible response at room temperature to target gases in ppm- and sub-ppm concentration ranges. Testing multisensor system using imitators of the odors of explosives (TNT) and drugs (heroin) showed the possibility of qualitative analysis of these odors as well.

The target of this paper is answering the question about the minimum response time of metal oxide semiconductor gas sensors. This question is very important at the monitoring of sudden explosive emission of high concentrations of combustible gases in mines, chemical and oil refinery factories, nuclear power stations, etc. To reach this target, we eliminated the influence of internal and external diffusion to the sensor response time by the optimization of the thickness of sensing layer, deposition conditions, material, and working temperature of the sensor. As a result, it was possible to fabricate the sensor with very short response time ∼ 160 ms (hexane) in a concentration range up to 12 vol%. The response time of the sensor was compared with the response time of IR optic sensor based on LED (λ = 3.4 μm) using testing gas mixing installation equipped with ultra-fast valves. The effect of sensing layer thickness and the conditions necessary to exclude the influence of reagent and product diffusion through the sensing layer to the response time were studied in detail. It was shown that, if the thickness of thin film sensing layer exceeds 200 nm, the sensor response rate is diffusion limited, the diffusion coefficient corresponding to inter-grain diffusion at 550 °C was estimated as (1.5 ± 0.5)·10−10 cm2/s. The results were proven in field experiment with spike emission of petrol aerosol.

SnO2 chemical sensors were fabricated by two different methods. The first one was based on contacting individual nanowires by in situ nanofabrication in a Focused Ion Beam (FIB) microscope. The second one, the traditional sol-gel method, was based on tin dioxide nanopowder thermal agglomeration. Both types of sensors were capable of detecting air-diluted H2S to the parts per million level. The responses to this gas were studied at different concentrations and operating temperatures, showing up reproducible characteristics. Their performances were discussed in relation to the accepted mechanisms for H2S sensing in n-type metal oxides. Investigations were made on sensitivity and device stability, demonstrating that these nanowires have some advantages in comparison with sol-gel sensors.

We elaborated a logically closed theory of the conductivity of nano-structured semiconductor material (NSSM) valid in a large range of grain sizes a . It is shown that high sensitivity to electronegative gases (O 2 , F 2 , etc.) is observed, when the grain size lies in a range of aSH a aCR , where aCR – is a critical size of a grain, below this size charge carrier self-exhaustion regime takes place; aSH – is a grain size, below which the mechanism of superficial hopping conductivity predominates. This hopping mechanism excludes gas sensitivity of the material. Theorem of gas sensitivity of NSSM and the rules of the selection of nano-structures prospective for the fabrication of sensing MOXlayers are formulated.

Hybrid nanomaterials based on oxygen plasma treated multiwall carbon nanotubes decorated with tin oxide nanoclusters were synthesised by the precipitation of a SnO 2 colloidal suspension in the presence of carbon nanotubes dispersed in the mother solution of precursor tin (II) acetate in a water free acetic acid. TEM analysis revealed that the size of tin oxide nanoclusters anchored at the carbon nanotube sidewalls is about 5 nm. Hybrid nanomaterials with different carbon nanotube to tin oxide ratios were prepared and their gas sensing properties when operated at room temperature and at 150 °C were investigated and compared against the properties of pure tin oxide or pure oxygen plasma treated multiwall carbon nanotube sensors. When an appropriate ratio between the amount of plasma treated nanotubes and tin oxide precursors is employed, hybrid sensors show superior performance in the detection of nitrogen dioxide in the ppb range and carbon monoxide in the low ppm range. Furthermore, these optimised sensors show a significantly reduced moisture cross-sensitivity. Detection mechanisms are discussed.

An increase in the number of gases detectable by sensors based on Pd-SiO2-Si (MIS) and Pt-LaF3-Si3N4 -SiO2-Si (MEIS) structures was achieved by the application of an external catalyst element (CE). It was shown that as a result of the decomposition of hydrocarbon and fluorocarbon molecules on a Ni coil (CE), the products detectable by metal-insulator-semiconductor (MIS) and metal-electrolyte-insulator-semiconductor (MEIS) sensors are formed. The simultaneous catalytic oxidation of hydrocarbons and their thermal decomposition result in an optimum CE temperature of about 1050 K for propane. The kinetics of the thermal decomposition of gases on Ni were investigated. The activation energy of the reaction for C3 H8 and the enthalpy in the case of CF3-CCl were estimated

A silicon based semiconductor sensor structure Pd/LaF3/Si3N4/SiO2/Si was prepared using thin layer technology. The sensor can be used for hydrogen detection at room temperature. Therefore, the power consumption is reduced by a factor 106 compared to the best low power consumption hydrogen sensors. In contrast to other sensors it can be used for measurements at very low and high hydrogen partial pressure. The limit of detection was determined to be 0.5 ppm. Measurements at high concentrations near to and above the Lower Explosion Level (LEL) of 4 % hydrogen in air are demonstrated. A method to achieve long lifetime of the sensor was developed.

An LaF3 layer was shown to improve the characteristics of field-effect gas sensors for room-temperature hydrogen monitoring. The Pt/LaF3 interface leads to a Nernst-type response and a detection limit of 10-ppm hydrogen in atmospheric air. The response time was shown to be about 110 s and was independent of hydrogen concentration. A method for the stabilization of a long-term behavior of the sensor was successfully demonstrated. The mechanism of the sensor's response to hydrogen was shown to be different from that of the metal/insulator/semiconductor (MIS)-type sensors

The target of this work is the demonstration of advanced approaches able to provide rapid prototyping by using laser technology ceramic MEMS platforms for chemical sensor operating under harsh environmental conditions and, on the other hand, to assure microhotplate stable at high temperature, which can be used for the deposition of high working temperature gas sensing materials, for example, oxides of tin, gallium, zirconium and hafnium. As substrate ceramic material in work using alumina oxide

In this work, we describe a new approach to the detection of pyrolysis gases produced at smoldering of organic materials using a single metal oxide gas sensors based on SnO 2 and operating in fast temperature scanning mode. The results of experimental comparison of the selectivity of standard electrochemical CO sensor and of the metal oxide gas sensors based on SnO 2 at smokeless pyrolysis of various organic materials are presented. The experiment showed high selectivity of metal oxide sensor at smoldering fire detection compared to the standard electrochemical sensor used in fire alarm system.

DC-biasing was applied as a method to enhance the performance of a capacitive type gas sensor with a polymer electrolyte layer. The sensor was constructed as a metal-electrolyte-insulator-semiconductor structure with a polymer electrolyte layer deposited on a Si-substrate with SiO2-dielectric layer and aluminum back electrode. The electrolyte was prepared from polyvinyl chloride polymer dissolved in water with adding H3PW12O40 to the mixture making it proton conductive. The device was finalized with a platinum top electrode. The sensor was shown to be sensitive to H2 with detection limit below 100-ppm concentrations in synthetic air at room temperature. The sensor was tested using ac voltages with 250-mV amplitude and frequency from 1 to 100 kHz. In addition, by dc biasing the device with voltages up to 2 V during the capacitive measurements, the response, and sensitivity of the sensor were increased by 70% and 50%, respectively, at the optimal measurement frequency (5 kHz).

The application of gas sensors in breath analysis is an important trend in the early diagnostics of different diseases including lung cancer, ulcers, and enteric infection. However, traditional methods of synthesis of metal oxide gas-sensing materials for semiconductor sensors based on wet sol-gel processes give relatively high sensitivity of the gas sensor to changing humidity. The sol-gel process leading to the formation of superficial hydroxyl groups on oxide particles is responsible for the strong response of the sensing material to this factor. In our work, we investigated the possibility to synthesize metal oxide materials with reduced sensitivity to water vapors. Dry synthesis of SnO2 nanoparticles was implemented in gas phase by spark discharge, enabling the reduction of the hydroxyl concentration on the surface and allowing the production of tin dioxide powder with specific surface area of about 40 m2/g after annealing at 610 &deg, C. The drop in sensor resistance does not exceed 20% when air humidity increases from 40 to 100%, whereas the response to 100 ppm of hydrogen is a factor of 8 with very short response time of about 1 s. The sensor response was tested in mixtures of air with hydrogen, which is the marker of enteric infections and the marker of early stage fire, and in a mixture of air with lactate (marker of stomach cancer) and ammonia gas (marker of Helicobacter pylori, responsible for stomach ulcers).