1,721,057 research outputs found
Catalyst – Assisted vapor liquid solid growth of α-Bi2O3 nanowires for acetone and ethanol detection
No full textIn this study, conductometric gas sensors based on p-type α-Bi2O3 nanowires for the detection of low concentrations of acetone and ethanol were investigated. Excellent sensing performances in terms of high response, fast kinetics and long-term stability at different humidity levels together with good selectivity were found. The synthesis of α-Bi2O3 nanowires was successfully achieved using a simple Vapor-Liquid-Solid (VLS) method. Nanowires were prepared using different catalysts (Au, Pt and Cu) as seed layers but the highest aspect ratio was obtained using Au. The excellent sensing performances were explained by the extra-sensitization caused by spillover effect of gold nanoparticles on the top of the nanowires. The sensing results showed good selectivity and high response towards low concentrations of acetone and ethanol. In particular, the recorded responses were 6.85, 14.4 and 34.1 towards 10, 20 and 40 ppm of ethanol, respectively, and 0.67, 2.11 and 2.93 towards 4, 6 and 10 ppm of acetone, respectively. Stable response towards low acetone concentrations was observed even after increasing the relative humidity level from 50 % to 90 % @ 20 °C. The results achieved in this work for α-Bi2O3 nanowires demonstrate their promising functionalities in chemical/gas sensing applications
P‐Type Metal Oxide Semiconductor Thin Films: Synthesis and Chemical Sensor Applications
Full text linkThis review focuses on the synthesis of p‐type metal‐oxide (p‐type MOX) semiconductor thin films, such as CuO, NiO, Co3O4, and Cr2O3, used for chemical‐sensing applications. P‐type MOX thin films exhibit several advantages over n‐type MOX, including a higher catalytic effect, low humidity dependence, and improved recovery speed. However, the sensing performance of CuO, NiO, Co3O4, and Cr2O3 thin films is strongly related to the intrinsic physicochemical properties of the material and the thickness of these MOX thin films. The latter is heavily dependent on synthesis techniques. Many techniques used for growing p‐MOX thin films are reviewed herein. Physical vapor‐deposition techniques (PVD), such as magnetron sputtering, thermal evaporation, thermal oxidation, and molecular‐beam epitaxial (MBE) growth were investigated, along with chemical vapor deposition (CVD). Liquid‐phase routes, including sol–gel‐assisted dip‐and‐spin coating, spray pyrolysis, and electrodeposition, are also discussed. A review of each technique, as well as factors that affect the physicochemical properties of p‐type MOX thin films, such as morphology, crystallinity, defects, and grain size, is presented. The sensing mechanism describing the surface reaction of gases with MOX is also discussed. The sensing characteristics of CuO, NiO, Co3O4, and Cr2O3 thin films, including their response, sensor kinetics, stability, selectivity, and repeatability are reviewed. Different chemical compounds, including reducing gases (such as volatile organic compounds (VOCs), H2, and NH3) and oxidizing gases, such as CO2, NO2, and O3, were analyzed. Bulk doping, surface decoration, and heterostructures are some of the strategies for improving the sensing capabilities of the suggested pristine p‐type MOX thin films. Future trends to overcome the challenges of p‐type MOX thin‐film chemical sensors are also presented
Progress towards chemical gas sensors: Nanowires and 2D semiconductors
No full textThere is a great interest in portable gas sensing technologies to provide real-time monitoring of indoor and outdoor air quality as well as the human health diagnostics. One-dimensional metal oxide nanowires have demonstrated improved properties compared to the conventional thick film gas sensors. Furthermore, two-dimensional semiconductor nanomaterials have shown great promise for the development of high performance functional devices owing to their unique physical, chemical and electrical characteristics. Hence, they become one of the most investigated structures for the fabrication of detection systems. Herein, we present an overview of the synthesis and sensing properties of metal oxide nanowires and two-dimensional semiconductor nanostructures such as metal-organic frameworks, graphene and transition metal dichalcogenides. We discuss the current achievements and issues in the preparation of pure, doped and composite materials comprising metal oxide nanowires and two-dimensional semiconductors. Then, we discuss the advances in gas sensing performances of the aforementioned materials considering their morphology, compositions and structure. Afterward, we provide a brief summary along with the opportunities and challenges for future fabrication of high performance and small size gas sensing devices
1D titanium dioxide: Achievements in chemical sensing
No full textFor the last two decades, titanium dioxide (TiO2) has received wide attention in several areas such as in medicine, sensor technology and solar cell industries. TiO2-based gas sensors have attracted significant attention in past decades due to their excellent physical/chemical properties, low cost and high abundance on Earth. In recent years, more and more efforts have been invested for the further improvement in sensing properties of TiO2 by implementing new strategies such as growth of TiO2 in different morphologies. Indeed, in the last five to seven years, 1D nanostructures and heterostructures of TiO2 have been synthesized using different growth techniques and integrated in chemical/gas sensing. Thus, in this review article, we briefly summarize the most important contributions by different researchers within the last five to seven years in fabrication of 1D nanostructures of TiO2-based chemical/gas sensors and the different strategies applied for the improvements of their performances. Moreover, the crystal structure of TiO2, different fabrication techniques used for the growth of TiO2-based 1D nanostructures, their chemical sensing mechanism and sensing performances towards reducing and oxidizing gases have been discussed in detail
One dimensional ZnO nanostructures: Growth and chemical sensing performances
No full textRecently, one-dimensional (1D) nanostructures have attracted the scientific community attention as sensitive materials for conductometric chemical sensors. However, finding facile and low-cost techniques for their production, controlling the morphology and the aspect ratio of these nanostructures is still challenging. In this study, we report the vapor-liquid-solid (VLS) synthesis of one dimensional (1D) zinc oxide (ZnO) nanorods (NRs) and nanowires (NWs) by using different metal catalysts and their impact on the performances of conductometric chemical sensors. In VLS mechanism, catalysts are of great interest due to their role in the nucleation and the crystallization of 1D nanostructures. Here, Au, Pt, Ag and Cu nanoparticles (NPs) were used to grow 1D ZnO. Depending on catalyst nature, different morphology, geometry, size and nanowires/nanorods abundance were established. The mechanism leading to the VLS growth of 1D ZnO nanostructures and the transition from nanorods to nanowires have been interpreted. The formation of ZnO crystals exhibiting a hexagonal crystal structure was confirmed by X-ray diffraction (XRD) and ZnO composition was identified using transmission electron microscopy (TEM) mapping. The chemical sensing characteristics showed that 1D ZnO has good and fast response, good stability and selectivity. ZnO (Au) showed the best performances towards hydrogen (H2). At the optimal working temperature of 350◦ C, the measured response towards 500 ppm of H2 was 300 for ZnO NWs and 50 for ZnO NRs. Moreover, a good selectivity to hydrogen was demonstrated over CO, acetone and ethanol
Metal Oxide Nanowire-Based Sensor Array for Hydrogen Detection
No full textAccurate hydrogen leakage detection is a major requirement for the safe and widespread integration of this fuel in modern energy production devices, such as fuel cells. Quasi-1D nanowires of seven different metal oxides (CuO, WO3, Nb-added WO3, SnO2, ZnO, alpha-Bi2O3, NiO) were integrated into a conductometric sensor array to evaluate the hydrogen-sensing performances in the presence of interfering gaseous compounds, namely carbon monoxide, nitrogen dioxide, methane, acetone, and ethanol, at different operating temperatures (200-400 degrees C). Principal component analysis (PCA) was applied to data extracted from the array, demonstrating the ability to discriminate hydrogen over other interferent compounds. Moreover, a reduced array formed by only five sensors is proposed. This compact array may be easily implementable into artificial olfaction systems used in real hydrogen detection applications
The effect of structural characteristics of ZnO and NiO thin films on the performance of NiO/ZnO photodetectors
No full textMaterial properties play an important role in the fabrication of optoelectronic devices such as photodetectors because it is ultimately reflected in their efficiency and performance. To fabricate a NiO/ZnO heterojunction with better structural properties using a low-cost and uncomplicated deposition process, we studied the influence of NiO and ZnO thickness by taking different volumes of spray solution (5, 10, and 15 ml) on the structural and morphological properties that were investigated using the spray pyrolysis technique. When the films' thickness increased, the crystalline structure of both films improved. The deposited ZnO layers have a hexagonal Wurtzite structure with preferable growth orientations along (002). The NiO X-ray diffraction patterns showed that the films were in cubic phase with orientation (111) and the peak density increased with the film thickness. According to our experimental conditions and XRD results, we suggest that thicker NiO and ZnO are the optimal films to fabricate a NiO/ZnO heterostructure. It is found that Raman and XRD results confirm the formation of NiO/ZnO heterostructure. The morphology of NiO/ZnO is smooth and completely covers the substrate without any pinholes. The further investigation related to the effect of NiO and ZnO thin films' structural properties on NiO/ZnO heterostructure photodetector performance is presented using the simulations. It is worth mentioning that based on the suggested transport models, the results confirm that the origin of the dark current has been attributed to the tunneling and thermionic emission at the interface while bulk defects, leading to the increase Shockley-Read-Hall recombination and generation, control the carrier transport. Furthermore, we studied the effect of Gaussian and tail acceptor/donor defects on the current-voltage (J-V) characteristics and responsivity. The obtained results showed that increasing NiO tail states cause an increase in tunneling current. In contrast, the deep defects density in both ZnO and NiO affects the photodetection characteristics, resulting in a decrease in responsivity and photocurrent when these defects increase
Evaporation Condensation Growth of One-Dimensional Metal Oxide at SENSOR Lab in Brescia for Chemical Sensors Applications
No full textEven though several classes of materials have been investigated for chemical sensors applications, one-dimensional metal oxides (1D MOX) have considerable advantages. Especially, MOX nanowires (NWs) show physicochemical properties that allow them to overcome the drawbacks of traditional thick and thin film-based gas sensors such as low sensitivity and signal drifting due to the grain coalescence. As a result, nanosized 1D MOX are considered one of the best materials to fabricate new generation of chemical/gas sensors. This review attempts to collect the significant results achieved at SENSOR Lab, Brescia (Italy) on the synthesis of 1D MOX for chemical sensors applications. In particular, the bottom-up strategy to grow 1D MOXs (nanowires-like structures) mainly adopted by SENSOR Lab is the evaporation condensation technique. 1D MOX may be produced by using two different mechanisms, Vapor Liquid Solid (VLS) which employs a seed catalyst to assist the 1D growth and, Vapor Solid (VS). The synthesized nanowires are uniform, dense and have a high aspect ratio with diameters as low as few nanometers and length of tens of micrometers. Many gas sensors based on 1D MOX are produced including p-type semiconductors such as NiO and n-type such as ZnO, SnO2, WO3 and In2O3. They exhibit excellent sensitivity, high stability and fast response towards hazardous gases including toxic and flammable compounds such as NO2, NH3, acetone, ethanol and H2
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