Role of nickel dopant on gas response and selectivity of electrospun indium oxide nanotubes

Gas Sensors Based on Semiconductor Metal Oxides Fabricated by Electrospinning: A Review

Electrospinning has revolutionized the field of semiconductor metal oxide (SMO) gas sensors, which are pivotal for gas detection. SMOs are known for their high sensitivity, rapid responsiveness, and exceptional selectivity towards various types of gases. When synthesized via electrospinning, they gain unmatched advantages. These include high porosity, large specific surface areas, adjustable morphologies and compositions, and diverse structural designs, improving gas-sensing performance. This review explores the application of variously structured and composed SMOs prepared by electrospinning in gas sensors. It highlights strategies to augment gas-sensing performance, such as noble metal modification and doping with transition metals, rare earth elements, and metal cations, all contributing to heightened sensitivity and selectivity. We also look at the fabrication of composite SMOs with polymers or carbon nanofibers, which addresses the challenge of high operating temperatures. Furthermore, this review discusses the advantages of hierarchical and core-shell structures. The use of spinel and perovskite structures is also explored for their unique chemical compositions and crystal structure. These structures are useful for high sensitivity and selectivity towards specific gases. These methodologies emphasize the critical role of innovative material integration and structural design in achieving high-performance gas sensors, pointing toward future research directions in this rapidly evolving field.

Development of Pd/In2O3 hybrid nanoclusters to optimize ethanol vapor sensing

In this study, we successfully synthesize palladium-decorated indium trioxide (Pd/In2O3) hybrid nanoclusters (NCs) using an advanced dual-target cluster beam deposition (CBD) method, a significant stride in developing high-performance ethanol sensors. The prepared Pd/In2O3 hybrid NCs exhibit exceptional sensitivity, stability, and selectivity to low concentrations of ethanol vapor, with a maximum response value of 101.2 at an optimal operating temperature of 260 °C for 6 at% Pd loading. The dynamic response of the Pd/In2O3-based sensor shows an increase in response with increasing ethanol vapor concentrations within the range of 50 to 1000 ppm. The limit of detection is as low as 24 ppb. The sensor exhibits a high sensitivity of 28.24 ppm-1/2, with response and recovery times of 2.7 and 4.4 seconds, respectively, for 100 ppm ethanol vapor. Additionally, the sensor demonstrates excellent repeatability and stability, with only a minor decrease in response observed over 30 days and notable selectivity for ethanol compared to other common volatile organic compounds. The study highlights the potential of Pd/In2O3 NCs as promising materials for ethanol gas sensors, leveraging the unique capabilities of CBD for controlled synthesis and the catalytic properties of Pd for enhanced gas-sensing performance.

Engineering of Mesoporous Cube-like In2O3 Products as Ethanol Detection Platform at Low Operating Temperature: Effects of Different Transition Metals as Dopant Ions

Although most semiconductor metal oxides including In2O3 show acceptable sensitivity to volatile organic compounds, it is difficult to detect ethanol effectively at low operating temperatures and detection levels. In this study, pure and Co-, Ni-, and Cu-doped In2O3 products with their doping content maintained at 1 mol % were successfully produced using a hydrothermal approach. Explicit contrast on the structural, microstructural, and textural properties of the synthesized In2O3 products was examined to determine their gas sensing performance. The Cu-doped In2O3 sensor demonstrated improved response of 15.3 to 50 ppm ethanol and has satisfactory selectivity, stability, low detection limit of 0.2, humidity resistance, and decreased working temperature of 80 °C compared to 150 °C of the pure In2O3 sensor. This optimal gas sensing performance is derived from the cube-like morphology assembled with interlinked nanoparticles, which favors trapping more target gas molecules and exposing more active sites, thereby greatly improving its sensing ability. This study showed that the Cu-doped In2O3 sensor with 1 mol % is suitable for monitoring ethanol gas for food safety applications.

Nitrogen doped In2O3-ZnO nanocomposite mesoporous thin film based highly sensitive and selective ethanol sensors

Nanocomposite metal oxide thin films exhibit promising qualities in the field of gas sensors due to the opportunities provided by the heterointerface formation. In this work, we present the synthesis of nitrogen doped mesoporous In₂O₃-ZnO nanocomposite thin films by a simple wet chemical method using urea as the nitrogen precursor. SEM investigation suggests the formation of mesoporous nanocomposite thin films, where the uniformity of the surface pore distribution depends on the relative proportion of In₂O₃ and ZnO in the composites. HRTEM investigation suggests the formation of sharp interfaces between N-In₂O₃ and N-ZnO grains in the nanocomposite thin films. The nanocomposite thin films have been tested for their ethanol sensing performance over an extensive range of temperatures, ethanol vapor concentrations and relative humidities. Nitrogen doped nanocomposite thin films with an equal proportion of In₂O₃ and ZnO exhibit excellent ethanol sensing performance at a reasonable operating temperature (∼94% at 200 °C for 50 ppm of ethanol), fast response time (∼two seconds), stability over time, enhanced resilience against humidity and selectivity to ethanol over various other volatile organic compounds. All the results indicated that nitrogen doped In₂O₃/ZnO nanocomposite thin films portray great possibilities in designing improved performance ethanol sensors.

Oxygen-Vacancy-Induced Synaptic Plasticity in an Electrospun InGdO Nanofiber Transistor for a Gas Sensory System with a Learning Function

The perceptual learning function of a simulating human body is very important for constructing a neural computing system and a brainlike computer in the future. The sense of smell is an important part of the human sensory nervous system. However, current gas sensors simply convert gas concentrations into electrical signals and do not have the same learning and memory function as synapses. To solve this problem, we propose a new sensing idea to induce and activate the synaptic properties of transistors by adjusting the oxygen vacancy in the active layer. This sensor combines gas detection with synaptic memory and learning and overcomes the disadvantage of the separation of synaptic transistors and sensors, thus greatly reducing the cost of production. This work combines the detection of N,N-dimethylformamide (DMF) gas with the synaptic mechanism of human olfactory nerves. We successfully fabricated an InGdO nanofiber field-effect transistor by electrostatic spinning and simulated the response of human olfactory synapses to target gas by regulating the oxygen vacancy of the InGdO nanofiber. The synaptic transistor response under different concentrations of unmodulated pulses is tested, and the pavlovian conditioned reflex experiment is simulated successfully. This work provides a new idea of a gas sensor device, which is very important for the development of high-performance gas sensors and bionic electronic devices in the future.

Chemical and Electronic Modulation via Atomic Layer Deposition of NiO on Porous In2O3 Films to Boost NO2 Detection

To achieve high sensitivity under low-temperature operation is currently a challenge for metal oxide semiconductor gas sensors. In this work, a unique NiO-functionalized macroporous In₂O₃ thin film is designed by atomic layer deposition (ALD), which demonstrates great potential in electronic sensors for detecting NO₂ at low temperature. This strategy allows for efficient engineering of the oxygen vacancy concentration and the formation of p-n heterojunctions in the hybrid In₂O₃/NiO thin films, which has been found to greatly impact the surface chemical and electrical properties of the sensing films. The sensor based on the optimized In₂O₃/NiO films exhibits a very high response of 532.2 to 10 ppm NO₂, which is 26 times higher than that of the In₂O₃, at a relatively low operating temperature of 145 °C. In addition, an ultralow detection limit of ca. 6.9 ppb has been obtained, which surpasses most reports based on metal oxide sensors. Mechanistic investigations disclose that the improved sensor properties are resultant from the paramount surface active sites and high carrier concentration enabled by the oxygen vacancies, while excessive NiO ALD leads to a decreased sensor response due to the formed p-n heterojunctions.

Investigation of doping effects of different noble metals for ethanol gas sensors based on mesoporous In2O3

Elaborating the sensitization effects of different noble metals on In₂O₃has great significance in providing an optimum method to improve ethanol sensing performance. In this study, long-range ordered mesoporous In₂O₃has been fabricated through replicating the structure of SBA-15. Different noble metals (Au, Ag, Pt and Pd) with the same doping amount (1 at%) have been introduced by anin situdoping routine. The results of the gas sensing investigation indicate that the gas responses towards ethanol can be obviously increased by doping different noble metals. In particular, the best sensing performance towards ethanol detection can be achieved through Pd doping, and the sensors based on Pd-doped In₂O₃not only possess the highest response (39.0-100 ppm ethanol) but also have the shortest response and recovery times at the optimal operating temperature of 250 °C. The sensing mechanism of noble metal doped materials can be attributed to the synergetic effect combining 'catalysis' and 'electronic and chemical sensitization' of noble metals. In particular, the chemical state of the noble metal also has a great influence on the gas sensing mechanism. A detailed explanation of the enhancement of gas sensing performance through noble metal doping is presented in the gas sensing mechanism part of the manuscript.

Inorganic-Diverse Nanostructured Materials for Volatile Organic Compound Sensing

Environmental pollution related to volatile organic compounds (VOCs) has become a global issue which attracts intensive work towards their controlling and monitoring. To this direction various regulations and research towards VOCs detection have been laid down and conducted by many countries. Distinct devices are proposed to monitor the VOCs pollution. Among them, chemiresistor devices comprised of inorganic-semiconducting materials with diverse nanostructures are most attractive because they are cost-effective and eco-friendly. These diverse nanostructured materials-based devices are usually made up of nanoparticles, nanowires/rods, nanocrystals, nanotubes, nanocages, nanocubes, nanocomposites, etc. They can be employed in monitoring the VOCs present in the reliable sources. This review outlines the device-based VOC detection using diverse semiconducting-nanostructured materials and covers more than 340 references that have been published since 2016.

Design of size-controlled Au nanoparticles loaded on the surface of ZnO for ethanol detection

Schematic diagram of the reaction mechanism of the sensor in air and ethanol.

Electrospun Yb-Doped In2O3 Nanofiber Field-Effect Transistors for Highly Sensitive Ethanol Sensors

Enhancing the reliability and sensitivity of gas sensors based on FETs has been of extensive concern for their practical application. However, few reports are available on nanofiber FET gas sensors fabricated by the electrospinning process. In this work, ethanol gas sensors based on Yb-doped In₂O₃ (InYbO) nanofiber FETs are fabricated by a simple and fast electrospinning method. The optimized In₂O₃ nanofiber FETs with a doping concentration of 4 mol % show a better electrical performance, including a high mobility of 6.67 cm²/Vs, an acceptable threshold voltage of 3.27 V, and a suitable on/off current ratio of 10⁷, especially the enhanced bias-stress stability. When employed in ethanol gas sensors, the gas sensors exhibit enhanced stability and improved sensitivity with a high response of 40-10 ppm, which is remarkably higher than that of previously reported ethanol gas sensors. Moreover, the InYbO nanofiber FET sensors also demonstrate a low limit of detection of 1 ppm and improved sensing performance ranging from sensitivity to the ability of selectivity. This work opens up a new prospect to achieve highly sensitive, selective, and reliable ethanol gas sensors using electrospun Yb-In₂O₃ nanofiber FETs with improved stability.