This work demonstrates the promising performance of a nanostructured molybdenum oxide film deposited by rf-magnetron sputtering, as an ozone gas sensor. X-ray diffraction and scanning electron microscopy analyses revealed that the film comprises of alpha-MoO3/gamma-Mo4O11 nanostructures, exhibiting rice-like shape particles with an average length of 78 nm and a diameter of 25 nm. Gas-sensing measurements revealed that the nanostructures detected ozone levels ranging from 25 up to 225 ppb, operating optimally at 250 C-o, with a stable response, good repeatability, and total reversibility. At a 50 % relative humidity, the sensor response varied only similar to 1 % at low and similar to 12 % at high ozone concentrations compared to dry conditions, indicating low humidity interference. Moreover, the films exhibited selectivity toward ozone over NO2, NH3, CO2, and CO, even at low concentrations. These findings demonstrate the great potential of alpha-MoO3/gamma-Mo4O11 film for practical environmental monitoring applications.

In this study, mixed oxide gas sensors based on p-type CuO-SnO2: F thin films were prepared via the spray pyrolysis technique. The effect of dopant nature on the structural, optical, morphological, and ozone gas sensing properties was investigated. The results show that graphene-doped CuO-SnO2: F thin films have the best crystallinity and lowest band gap value (2.5 eV). The gas response of the homemade devices based on different dopant elements of CuO-SnO2: F nanocomposites toward O3 as a function of temperature, concentration, and different visible light sources was measured and compared with undoped CuO-SnO2: F films. Experiments indicated that Gr-doped CuO-SnO2: F-based sensor can detect minuscule traces of O3 gas with impressive sensitivity, even at room temperature, and show a fast response (53 s) and recovery time (225 s) at low O3 concentration (30 ppb) compared to undoped and other X-doped CuO-SnO2: F sensors (X = Al, Gr, and Fe). This enhancement can be justified by the increase of both porosity and crystallinity of the fabricated devices after doping with graphene that facilitate the charge transfer in the material. Furthermore, the Gr-doped CuO-SnO2: F showed excellent selectivity to ozone (four times higher) compared to other oxidizing and reducing gases (NO2, ethanol, and toluene). This study proves that the incorporation of graphene into the metal oxide semiconductor (MOSC) matrix can enhance the sensing capabilities of the material and improve its performance.

In this study, we present a dual Radio Frequency sensor coupled with a polymer sensitive material for Carbon dioxide gas detection. A commercially available polymer underwent functionalization to produce a derivative polymer with enhanced properties. The sensing performances of both polymers, when integrated with the RF transducer, were evaluated. The results demonstrate that functionalization led to an increased sensitivity to CO 2 while simultaneously reducing sensitivities to relative humidity (% RH) and temperature. The functionalized material exhibited good reversibility and repeatability, displaying a sensitivity of 17.3MHz/ppm to CO 2 at 0 % RH, in comparison to the commercial polymer with a sensitivity of 1.35 MHz/ppm. Nevertheless, it is important to note that the sensor’s CO 2 sensitivity is compromised when exposed to % RH levels exceeding 0. Moreover, the sensor demonstrated a high specificity during tests involving alternative gaseous compounds such as CO, NO 2 , and O 3 .

Thin films, owing to their versatility, are extensively employed in various applications, including solar cells and gas detection. In this study, CuO-SnO2:F thin films were fabricated using spray method. The influence of annealing temperature on their properties was examined. X-ray diffraction analysis of post-annealing at 300 degrees C revealed the emergence of the Cu2O phase, which disappeared at higher annealing temperatures of 500 degrees C. Substantial improvements in structural, optical, and electrical characteristics were observed, with the optimized films exhibiting heightened responsiveness at low NO2 gas concentration (4 ppm). The optimum operating temperature was determined at 150 degrees C, demonstrating small response and recovery times, and good reproducibility. Furthermore, Silvaco TCAD simulation was employed to model CIGS (Copper Indium Gallium Selenide) solar cells incorporating CuO-SnO2:F thin films as a buffer layer, yielding an impressive efficiency of 15.31 %.

In this current work, CuO–SnO2: F mixed oxide thin films were synthesized by spray pyrolysis technique on glass substrates. The structural and optical properties were optimized and improved by varying the substrate temperature from 300 to 350 °C by a step of 25 °C. By increasing the substrate temperature, in addition to the CuO monoclinic phase we notice the appearance of the SnO2: F tetragonal phase in the XRD spectrum. Therefore, CuO–SnO2: F coupled oxide thin film, where the ratio in the spray solution ( r=[Cu]/[Sn]=3) was successfully grown at the elevated temperature equals to 350 °C. This result was confirmed by Raman and FTIR analyses. SEM analysis of CuO–SnO2: F films elaborated at a substrate temperature equal to 350 °C endorsed the particle-like spherical shape structure with smooth surface. While EDS and Elemental mapping confirmed the presence of the expected elements. By using the transmission reflection spectra, we estimated the values of the refractive index n, the extinction coefficient k and the dielectric constant. In the visible area the refractive index (n) varies from 1.5 to 2.3 and the extinction coefficient k decreases from 0.8 for Ts = 300 °C, up to about 0.2 for Ts = 350 °C. Moreover, the photoluminescence spectra of the films was investigated and interpreted. The gas-sensing measurements revealed that CuO–SnO2: F thin films grown by spray-pyrolysis method at the substrate temperature equals to 350 °C, can detect minuscule traces of O3 gas (30 ppb) with good sensitivity, fast response and recovery times (60 s and 79 s respectively), at relatively low temperature (200 °C). This manuscript reports the effectiveness of our homemade device as promoter ozone gas sensor in many industrial applications.

Ozone detection is currently the subject of wide scientific and technological research, motivated by its harmful impact on human safety, environment and health.

The development of simple and reproducible synthesis techniques for obtaining one-dimensional semi-conducting nanostructures is essential for the advancement of gas sensor devices. We report a facile and versatile approach for the in-situ growth of vertically oriented hematite nanorods to be applied as a re-sistive ozone gas sensor. The alpha-Fe2O3 nanorods were grown via a hydrothermal treatment directly onto an Al2O3 substrate with interdigitated Pt electrodes, thus facilitating the integration of nanorods into the sensing platform. At 150 degrees C, the gas-sensing experiments revealed a good sensitivity of these nanorods to different ozone concentrations (10-570 ppb), besides a fast response time and repeatable response-r-ecovery cycles. The present study offers a promising way for designing high-performance gas sensors based on hematite nanorods.(c) 2023 Elsevier B.V. All rights reserved.

Although semiconducting metal oxide (SMOx) nanoparticles (NPs) have attracted attention as sensing materials, the methodologies available to synthesize them with desirable properties are quite limited and/or often require relatively high energy consumption. Thus, we report herein the processing of Zn-doped SnO2 NPs via a microwave-assisted nonaqueous route at a relatively low temperature (160 °C) and with a short treatment time (20 min). In addition, the effects of adding Zn in the structural, electronic, and gas-sensing properties of SnO2 NPs were investigated. X-ray diffraction and high-resolution transmission electron microscopy analyses revealed the single-phase of rutile SnO2, with an average crystal size of 7 nm. X-ray absorption near edge spectroscopy measurements revealed the homogenous incorporation of Zn ions into the SnO2 network. Gas sensing tests showed that Zn-doped SnO2 NPs were highly sensitive to sub-ppm levels of NO2 gas at 150 °C, with good recovery and stability even under ambient moisture. We observed an increase in the response of the Zn-doped sample of up to 100 times compared to the pristine one. This enhancement in the gas-sensing performance was linked to the Zn ions that provided more surface oxygen defects acting as active sites for the NO2 adsorption on the sensing material.

This work aims to compare two deposition methods to highlight the strong influence of the induced morphology on the sensitive film conductivity. Lanthanum oxycarbonate films have been deposited by drop coating and screen printing for carbon dioxide detection. The measurements are based on a change in resistance and provide sensitive responses to carbon dioxide concentrations in a humid environment maintained at 50%. Electrical measurements were made under 5 000 ppm of carbon dioxide in synthetic air. Our results highlighted the close link between the morphology of the sensitive layers and the electrical responses of the sensors, and therefore the need to master the deposition technique.

In this work, the conductance behavior of tungsten trioxide based chemoresistive ozone sensors under ultra violet illumination was investigated. The tungsten trioxide sensitive layers were deposited on a SiO2/Si substrate by reactive radio frequency magnetron sputtering with several Argon / Oxygen ratios. The detection principle is based on a change in the conductance of the semiconductor oxides when ozone is present around the surface. We demonstrate the influence of Argon / Oxygen during the deposition of the sensitive layer, on ozone detection at 50°C under light illumination. The sensor shows good sensitivity to ozone, with a stable baseline, fast response and recovery time. These results are promising for the detection of ozone at low temperature.

Over the past fifty years, gas sensors based on metal semiconducting oxides (MOXs) have drawn attention due to their performance in detecting various gases. Thus, we report herein on a BTEX gases sensor based on hematite (alpha-Fe2O3) microrhombuses synthesized via the hydrothermal method. X-ray diffraction and X-ray absorption spectroscopy analyses indicated the presence of a pristine hematite phase after hydrothermal treatment. Electron microscopy analyses revealed that the hematite sample consists of single-crystals with a rhombus-like shape and an average size of 140 nm. Electrical measurements pointed out that hematite microrhombuses were sensitive towards sub-ppm BTEX levels, in which the minimum detected level was 3 ppb and the long-term stability was 1 month. The results presented here demonstrate the potential of hematite microrhombuses as a sensing material to manufacture BTEX gas sensor devices.

Introduction Environmental safety is attracting significant attention due to the increase of dust particles, and toxic gas species (e.g. CO, NOx, etc.) [1]. CO is identified as a major threat for human health. Since CO is a colorless, odorless, and tasteless gas, it can't be detected by human senses. Therefore, sensitive sensor operating in humid air is required for CO gas detection [2]. For metal oxide (MOX) gas sensors, the humidity interferes with the low-level detection of reducing and oxidizing gases. The performances of MOX gas sensors such as SnO2 or CuO can be enhanced, by metal doping, material functionalization or MOX composite [3]. In this work, a comparison between resistive sensors based on CuO and on BaTiO3-CuO bi-layer film will be presented. The sensor responses to three CO gas concentrations in dry air and in 50% of relative humidity (RH) will be discussed. Method BaTiO3 nanoparticles (NPs) (<100nm) were dispersed in ethanol by stirring. Copper hydroxide Cu(OH)2 powder (0.2 g) was dissolved in acetic acid (5 ml), water (7 ml) and ethylene glycol (2ml). These two solutions were deposited by drop coating on a silicon oxide substrate provided with interdigitated platinum electrodes (figure 1). CuO films were prepared with one drop of Cu(OH)2 solution. BaTiO3-CuO films were fabricated with one drop of BaTiO3 NPs, an ambient drying for 5 minutes followed by one drop of Cu(OH)2 solution on the top of it. Then, the sensors were annealed at 500°C for 1 h. The sensing properties of these sensors were investigated by CO exposure. NI PXIe-4140 sourcemeter was used to measure the sensor resistance variations for an optimum operating temperature found at 280°C. Results and Conclusions Figure 2 shows the x-ray diffractograms of CuO and BaTiO3-CuO materials. The XRD patterns of CuO film indicate the existence of CuO nanoparticles in the monoclinic phase without CuO2 nanoparticles [4]. BaTiO3-CuO bilayer consists of a tetragonal phase of BaTiO3 in addition to monoclinic CuO [5]. Figure 3 presents the responses of CuO and BaTiO3-CuO to CO gas. In dry air, CuO gives a response equals to 1.22, while the response is more important for BaTiO3-CuO (1.41). In 50% RH, the sensor responses with CuO have almost disappeared while the sensors based on BaTiO3-CuO film gave a response equals to 1.32. Therefore, BaTiO3-CuO films have an enhanced response to CO in dry air as well as in the presence of 50% RH. The CO concentration effect on BaTiO3-CuO films was tested for 10, 50, and 100 ppm of CO in dry air and 50% RH (figure 4). Linear responses under CO in dry or wet air make BaTiO3-CuO bilayer films a potential candidate for the CO gas detection application. We have developed sensors based on BaTiO3-CuO composite for the CO gas detection under dry and wet air. The sensing properties are based on the resistance variation under CO gas. Our results show enhanced responses of BaTiO3-CuO concerning CuO in dry air and 50% RH. Future work will be focused on the proportion of BaTiO3 and CuO investigations to enhance the sensor response under CO. References [1] A. Kumar, A. Sanger, A. Kumar, et R. Chandra, « Highly sensitive and selective CO gas sensor based on a hydrophobic SnO2/CuO bilayer », RSC Adv., 6, 52, (2016), 47178–47184. doi: 10.1039/C6RA0653 [2] K. Sircar, J. Clower, M. Kyong Shin, C. Bailey, M. King, et F. Yip, « Carbon monoxide poisoning deaths in the United States, 1999 to 2012 », Am. J. Emerg. Med., 33, (2015), 1140–1145. doi: 10.1016/j.ajem.2015.05.002 [3] M. Hijazi, M. Rieu, V. Stambouli, G. Tournier, J.-P. Viricelle, et C. Pijolat, « Ambient temperature selective ammonia gas sensor based on SnO2 -APTES modifications », Sens. Actuators B Chem., 256, (2018), 440–447. doi: 10.1021/acsomega.9b02185 [4] K. Martin, G. McCarthy, North Dakota State Univ., Fargo, ND, USA., ICDD Grant-in-Aid, 1991. [5] S. B. Rudraswamy et N. Bhat, « Optimization of RF Sputtered Ag-Doped BaTiO3-CuO Mixed Oxide Thin Film as Carbon Dioxide Sensor for Environmental Pollution Monitoring Application », IEEE Sens. J., 16, (2016), 5145–5151. doi: 10.1109/Jsen.2016.2567220 Figure 1

A barium titanate thin film was deposited by drop coating for carbon dioxide detection. The measurements are based on a resistance change and provided a sensitive response to different CO2 concentrations under a humidity environment. The concentration measurement range was between 100 and 5000 ppm of CO2 in synthetic air, and likewise, the relative humidity was between 20 and 70%. The response and recovery times of the BaTiO3 based resistive sensors were determined to 2 min and 4 min, respectively, for 400 ppm of carbon dioxide and 50% relative humidity.

In this work, we report on a new evaluation of metal oxide based on carbon dioxide sensors, using barium titanate nano-powder. The sensing principle is based on a change in conductance of semiconducting oxides when carbon dioxide is present. The sensitive layer was deposited on a SiO 2 /Si substrate by screen printing technology. The sensor responses were studied between 100 and 5000 ppm of carbon dioxide in the air with 50% relative humidity. The sensor presents good sensitivity toward carbon dioxide, with a stable baseline, and fast response and recovery time. These results are promising for carbon dioxide sensing.

Tin dioxide is one of the most studied metal oxide thin film materials, thanks to its remarkable optical and electronic properties. It has attracted high attention for sensor and optoelectronic applications. Several techniques including spray, sol-gel coating, pulsed laser deposition, and radio-frequency (RF) reactive magnetron sputtering have been used for obtaining SnO2 thin films. This chapter, discusses the possibility of synthetizing thin films with a wide variety of structures and, consequently, presenting different properties. SnO2 properties are strongly dependent on the crystallographic nanostructuring and their modifications during annealing. In the gas-sensing area, the nanostructured film is a key challenging and a promising path. The nanostructures of the well-established metal oxide semiconductor (MOS) gas-sensing materials, such as SnO2, WO3, ZnO, and TiO2, have demonstrated high and fast response with improved sensitivity at low gas concentration. Among various MOS nanostructural materials, tin oxide (SnO2), a wide bandgap n-type semiconductor, has been the most popular gas sensors.

The effects of white-light irradiation on ∼15 nm diameter ZnO nanoparticles are investigated by means of electron paramagnetic resonance, near liquid-nitrogen and liquid-helium temperatures. Under dark conditions, usual core- and surface-defects are detected, respectively, at g = 1.960 and g = 2.003. Under white-light illumination, the core-defect signal intensity is strongly increased, which is to be correlated to the light-induced conductivity's augmentation. Beside, a four-lines structure appears, with the same gravity center as that of the surface defects. Simulations and intensity power-dependence measurements show that this four-line-structure is very likely to arise from a localized high spin S = 2, induced by light irradiation, and subjected to a weak axial anisotropy. At 85 K, this high-spin state can last several hours after the light-irradiation removal, probably due to highly spin-forbidden recombination process. The possible excited resonant complexes at the origin of this signal are discussed. Other light-induced S = 1/2-like centers are detected as well, which depend on the nanoparticles growth conditions.

Metal oxide semiconductors (MOS) have attracted considerable interest from many researchers due to their numerous technological applications such gas sensor, particularly, operated at room-temperature under UV-illumination. In this work, we report the preparation of the ZnO-SnO2 nanoheterostructures via microwave-assisted sol-gel route. The XRD measurements indicated the presence of both crystalline phases, i.e., ZnO and SnO2, without the evidence of solid solution formation. HRTEM analyses revealed that SnO2 nanoparticles (of ca. 5 nm) are attached onto ZnO rods, supporting the existence of junction between both oxides. Electrical measurements revealed that the heterostructures presented a high response to ppb levels of ozone and nitrogen dioxide at room temperature when kept under continuous UV-light illumination.

Chemiresistors are highly important for monitoring and detection of harmful gases produced from industrial processes and vehicle emissions. We report herein an experimental investigation of the gas-sensing properties of Zn0.95Co0.05O thin film deposited by spray pyrolysis technique. The X-ray photoelectron spectroscopy indicated the presence of Co2+ ions into de ZnO lattice. The gas-sensing measurements revealed the sensitivity of Zn0.95Co0.05O film towards ozone gas in a wide range of concentrations from 20 to 1040 ppb, exhibiting good repeatability and total reversibility after consecutive exposures. Selectivity for ozone is observed in comparison to NO2, NH3, and CO gases even at low levels. This manuscript reports the effectiveness of spray-pyrolysis method for obtaining nanostructured Zn1-xCoxO thin films for practical applications as an ozone gas sensor.