Search Results (594)

In the current work, the microstructural evolution and CO₂ sensing performance of tungsten trioxide (WO₃) thin films synthesized by reactive DC magnetron sputtering are investigated. Three specific thicknesses of 42, 66, and 131 nm were obtained and annealed at 500 °C, resulting in a stable monoclinic P2₁/n phase with a strong (200) preferred orientation. Gas sensing tests toward 10,000 ppm of CO₂ revealed that the 42 nm film achieves the highest sensitivity (92%) at an optimal operating temperature of 300 °C. Rietveld refinement and texture analysis (texture index, J) demonstrate that the superior performance of the thinnest film is driven by a synergy between its high surface porosity, a grain size comparable to the Debye length, and a high density of active sites on the (200) plane. While all films exhibit n-type semiconductor behavior, increasing thickness leads to microstructural densification and reduced texture, which hinders gas diffusion and operational stability. These findings establish thickness control as a critical parameter for engineering high-performance WO₃-based CO₂ sensors. Full article

The growing demand for intelligent environmental monitoring is driving the advancement of high-performance, low-cost, and highly integrated gas sensors. Silicon-compatible semiconductor gas sensors provide a promising platform to achieve this goal by leveraging their compatibility with complementary metal–oxide semiconductor (CMOS) processes. The established mass-manufacturing capabilities of micro-electromechanical systems (MEMS) and the high sensitivity and signal amplification characteristics of field effect transistors (FETs) in recent years have made the development of next-generation sensing devices feasible. In this review, we systematically summarize the latest advances in silicon-compatible gas sensors, with a focus on MEMS and FET technologies. We discuss their sensing mechanisms and performance optimization strategies, and further highlight the evolution of gas sensor technology toward on-chip intelligent olfactory systems that integrate sensing, computing, and storage capabilities. Full article

The detection of low humidity levels remains a great challenge in relative humidity (RH) sensing technologies. In this work, methacryloxyethyl trimethyl ammonium chloride (DMC) was coated around SiO₂ microspheres to form DMC/SiO₂ composite microspheres, which were self-assembled into a three-dimensional (3D) network structure for low humidity detection. The hydrophilic nature of the DMC component enhances the adsorption capacity for water molecules even at ultra-low humidity levels (1–18.6% RH), while the 3D network structure provides abundant channels for fast water molecule transport, facilitating rapid response and recovery processes. The optimized sensor shows high response (13,544%) in 1–18.6% RH, with short response/recovery time (6 s/10 s) and a small humidity hysteresis (1.4% RH). Such high performance shows that this type of sensor has great potential for application in widespread fields, such as electricity, semiconductor manufacturing, pure gas supply, aerospace, and pharmaceutical formulations. Full article

This systematic review presents a critical analysis of multifunctional nanowire sensors, with explicit selection criteria for included studies: we focus on peer-reviewed research, prioritizing studies on semiconductor (ZnO, TiO₂, Si), metal (Ag, Au), and carbon-based (CNT) nanowires that report structural innovations, performance breakthroughs, or industrial scalability. We systematically analyze their structural characteristics, advanced fabrication techniques (hydrothermal synthesis, magnetron sputtering, PECVD), and application performance across biosensing, pressure sensing, and gas monitoring. Unlike existing reviews limited to single material classes or application scenarios, this work advances the field by integrating three novel perspectives: it delivers a cross-material comparison of nanowire structure–performance relationships, incorporates an analysis of fabrication strategy scalability for industrial translation, and synthesizes unresolved challenges and future directions. Nanowire sensors exhibit superior sensitivity, rapid response, and broad detection ranges compared to conventional sensors, with significant potential to advance healthcare, environmental monitoring, and flexible electronics. Full article

Gas sensors based on metal oxide semiconductors (MOS) have attracted significant attention in monitoring of methane emission and leakage monitoring due to their high sensitivity, fast response time, simple structure and low cost. However, the high power consumption caused by long-term high-temperature operation of MOS sensors restricts their application in mobile and portable devices. In this study, MOF-derived Co₃O₄ dodecahedrons for low-concentration methane detection at room temperature was prepared using Zeolitic Imidazolate Framework-67 (ZIF-67) as a template and with various calcination temperatures. Among them, the Co₃O₄-350 calcined at 350 °C exhibited the optimal CH₄ sensing performance at room temperature, with a response of R_g/R_a = 1.53 to 2000 ppm CH₄. This enhanced gas sensing performance is attributed to the highest Co³⁺ proportions and the largest specific surface area in Co₃O₄-350 nanomaterials, which provided more active sites for gas adsorption and reaction. To address the challenge of slow response speed and irrecoverability during CH₄ detection at room temperature, the Co₃O₄ nanomaterials were printed onto a micro-heater plate (MHP) to form a MEMS gas sensor. By introducing a pulse heating mode to the MEMS sensor, the response and recovery time were significantly reduced to 26 s and 21 s, respectively. This enhancement improves both the efficiency and reliability of the MEMS gas sensor for early-stage detection of CH₄ leaks in various industrial applications. Full article

Graphene-like 2D ZnO (g-ZnO), a wide-bandgap semiconductor, shows great potential for gas sensing, owing to its high surface area and carrier mobility. However, the practical use of it is hampered by its intrinsic chemical inertness. In this study, density functional theory was first used to study the effects of zinc vacancies (V_Zn), oxygen vacancies (V_O), and Au doping on formaldehyde (CH₂O) sensing. The results show that engineering of the defects and the Au doping both significantly improve the reactivity of the material. Specifically, the V_Zn system promotes dissociative chemisorption (E_ads = −5.55 eV) of CH₂O to CO and H atoms. Charge compensation effectively passivates the vacancy states and returns the direct bandgap semiconducting nature of the system. Furthermore, Au doping raises the conduction band and enlarges the bandgap, while the charge accumulation around Au atoms activates the surrounding sites, causing the adsorption mechanism to change from physisorption to chemisorption. Overall, the introduction of V_Zn and Au doping is an efficient way to overcome the surface inertness and improve sensing sensitivity, offering a theoretical framework for the design of high-performance 2D gas sensors. Full article

The accidental contamination of olives by mineral hydrocarbons, such as diesel, motor lubricants, and hydraulic fluids from agricultural machinery, has become a growing concern in the olive oil industry. In response, European regulatory bodies are working on establishing new standards to address this issue. This study explores the feasibility of using Metal Oxide Semiconductor (MOS) gas sensors as a non-invasive method for detecting such contaminants on freshly harvested olives across different maturity stages. By assessing the sensitivity and selectivity of MOS sensors, this research aims to identify hydrocarbons that may adhere to the olive surface during harvesting and processing. The study involves controlled laboratory contamination scenarios, with samples exposed to various hydrocarbons to evaluate the relative response of individual MOS sensors under reproducible conditions. Findings from this research may provide valuable insights into rapid and cost-effective detection systems, supporting quality control and regulatory compliance in olive oil production, and contributing to the safety and traceability of olive-derived products. As a feasibility study, the results provide a basis for future developments involving multivariate analysis, field-contaminated samples, and industrial implementation. Full article

Lithium-ion batteries (LIBs) face the safety hazard of thermal runaway (TR). Gas-sensing-based monitoring is one of the viable warning approaches for batteries during operation, and TR warning using semiconductor gas sensors has garnered widespread attention. This review presents a comprehensive analysis of the latest advances in this field. It details the gas release characteristics during the TR failure process and identifies H₂, electrolyte vapor, CO, CO₂, and CH₄ as effective TR warning markers. The core of this review lies in an in-depth critical analysis of gas-sensing materials designed for these target gases, systematically summarizing the design, performance, and application research of semiconductor gas-sensing materials for each aforementioned gas in battery monitoring. We further summarize the current challenges of this technology and provide an outlook on future development directions of gas-sensing materials, including improved selectivity, integration, and intelligent advancement. This review aims to provide a roadmap that directs the rational design of next-generation sensing materials and fast-tracks the implementation of gas-sensing technology for enhanced battery safety. Full article

This paper introduces a streamlined three-step synthesis method for crafting porous Fe₂O₃/ZnO nanofibers (NFs). Initially, Fe₂O₃ nanoparticles (NPs) were synthesized using the hydrothermal method. Subsequently, PVP NFs laden with Fe₂O₃ NPs and zinc salt were synthesized via an electrospinning method. Finally, porous Fe₂O₃/ZnO NFs were fabricated through calcination, resulting in an average diameter of approximately 100 nm. Gas-sensing experiments illuminate that the porous Fe₂O₃/ZnO NFs exhibit outstanding sensitivity, selectivity, and robust long-term stability. Although the response magnitude decreased under high relative humidity (RH) due to competitive adsorption, the sensor maintained distinct detectable responses towards NO₂ vapor at an optimum temperature of 225 °C. Particularly noteworthy is the substantial enhancement in NO₂ sensing properties observed in the Fe₂O₃/ZnO composite compared to pure ZnO NFs. This enhancement can be ascribed to the distinctive microstructure and heterojunction formed between Fe₂O₃ and ZnO. Full article

Volatile organic compounds (VOCs) released from automotive interior materials and exchanged with external air seriously compromise cabin air quality and pose health risks to occupants. Electronic noses (E-noses) based on metal oxide semiconductor (MOS) micro-electro-mechanical system (MEMS) sensor arrays provide an efficient, real-time solution for in-vehicle gas monitoring. This review examines the use of SnO₂-, ZnO-, and TiO₂-based MEMS sensor arrays for this purpose. The sensing mechanisms, performance characteristics, and current limitations of these core materials are critically analyzed. Key MEMS fabrication techniques, including magnetron sputtering, chemical vapor deposition, and atomic layer deposition, are presented. Commonly employed pattern recognition algorithms—principal component analysis (PCA), support vector machines (SVM), and artificial neural networks (ANN)—are evaluated in terms of principle and effectiveness. Recent advances in low-power, portable E-nose systems for detecting formaldehyde, benzene, toluene, and other target analytes inside vehicles are highlighted. Future directions, including circuit–algorithm co-optimization, enhanced portability, and neuromorphic computing integration, are discussed. MOS MEMS E-noses effectively overcome the drawbacks of conventional analytical methods and are poised for widespread adoption in automotive air-quality management. Full article

Food fraud, particularly in the olive oil sector, represents a pressing concern within the agri-food industry, with implications for consumer trust and product authenticity. Certified products like Protected Designation of Origin (PDO) Extra Virgin Olive Oil (EVOO) are premium products that undergo strict quality controls, must comply with specific production regulations, and generally have a higher market price. These characteristics make them particularly vulnerable to economically motivated adulteration. In this study, the adulteration of PDO EVOO with Olive Pomace Oil (POO) and Olive Oil (OO) was investigated through a combined analytical approach. A traditional technique, gas chromatography–mass spectrometry (GC-MS) combined with solid-phase microextraction (SPME), was employed alongside an innovative method based on an electronic nose equipped with metal oxide semiconductor (MOX) sensors. GC-MS analysis enabled the identification of characteristic volatile compounds, providing a detailed chemical fingerprint of the different oil samples. Concurrently, the MOX sensor array successfully detected variations in the volatile profiles released by the adulterated oils, demonstrating its potential as a rapid and cost-effective screening tool. The complementary use of both techniques highlighted the reliability of MOX sensors in differentiating authentic PDO EVOO from adulterated samples and underscored their applicability in routine quality control and fraud prevention strategies. Full article

Metal oxide semiconductor (MOS)-based chemiresistive gas sensors, attributable to their low cost, compact structure, and long operational lifetime, have been widely employed for the detection and monitoring of trace ozone (O₃) in environmental air. Moreover, as ozone is a highly reactive oxidizing species extensively used in medical device sterilization, hospital disinfection, and food processing and preservation, accurate monitoring of ozone concentration is also essential in medical sanitation and food safety inspection. However, their practical applications are often limited by insufficient sensitivity and the requirement for elevated operating temperatures. In this study, Au-modified indium oxide (Au-In₂O₃) nanocomposite sensing materials were synthesized via a hydrothermal route followed by surface modification. Structural and morphological characterizations confirmed the uniform dispersion of Au nanoparticles on the In₂O₃ surface, which is expected to enhance the interaction between the sensor and target gas molecules. The resulting Au-In₂O₃ sensor exhibited excellent O₃ sensing performance under room-temperature conditions. Compared with pristine In₂O₃, the Au-In₂O₃ sensor with 1.0 wt% Au modification demonstrated a remarkably enhanced response of 1398.4 toward 1 ppm O₃ at room temperature. Moreover, the corresponding response/recovery times were shortened to 102/358 s for Au-In₂O₃. The outstanding O₃ sensing performance can be attributed to the synergistic effects of Au nanoparticles, including the spillover effect and the formation of a Schottky junction at the Au-In₂O₃ interface. These results suggest that Au-modified In₂O₃ cauliflower represents a highly promising candidate material for high performance O₃ sensing at low operating temperatures. Full article

This review summarizes the use of Auger Electron Spectroscopy (AES) for microchemical analysis of two different types of dielectric/(Al,Ga)N-based systems: (i) extrinsic dielectric PECVD SiO₂, ALD Al₂O₃, and ECR-CVD SiN_x films on Al_xGa_1−xN/GaN structures in the context of their application in microelectronic power devices and (ii) intrinsic Al₂O₃ films on AlN epitaxial layers grown by high-temperature oxidation for nanostructured technology of various gas/ion sensors. Particular attention is given to AES depth profiling across complete multilayer cross-sections, combining qualitative analysis of spectral line shape and intensity evolution as well as kinetic energy shifts with quantitative elemental depth distributions. This approach enables identification of chemical states and oxidation-related transformations at dielectric/semiconductor interfaces. Reported results demonstrate that AES provides micro- to nanometer-scale chemical information essential for distinguishing interfacial from the bulk properties. The capabilities and inherent limitations of AES depth profiling, including sputter-induced artifacts are also addressed, highlighting the role of optimized experimental conditions in reliable interface analysis. Full article

Hazardous gas detection requires portable, low-power sensors with high sensitivity, where micro-heater design is critical for semiconductor metal oxide (SMO) sensors. This study presents a standardized evaluation framework for quantitatively comparing patterned micro-heaters under equal-power conditions, ensuring objective comparison across geometries. Two key metrics—power efficiency and temperature uniformity—were defined, normalized, and integrated into a single optimal score through weighted summation. The framework was validated through coupled electro-thermal simulations and experiments on six geometries, including spiral and meander patterns. Results demonstrated that the framework enables accurate identification of designs combining low power consumption with high temperature uniformity. Notably, the meander-based design showed superior efficiency and uniformity, demonstrating its suitability for practical applications. This framework thus offers a rational tool for micro-heater design, supporting the development of reliable, energy-efficient devices for portable and Internet of Things (IoT) applications. Full article

Accurate, real-time monitoring of meat freshness is essential for reducing food waste and safeguarding consumer health, yet conventional methods rely on costly, laboratory-grade spectroscopy or destructive analyses. This work presents a low-cost electronic-nose platform that integrates a compact array of metal-oxide gas sensors (Figaro TGS2602, TGS2603, and Sensirion SGP30) with a Gaussian Process Regression (GPR) model to estimate a continuous freshness index under refrigerated storage. The pipeline includes headspace sensing, baseline normalization and smoothing, history-window feature construction, and probabilistic prediction with uncertainty. Using factorial analysis and response-surface optimization, we identify history length and sampling interval as key design variables; longer temporal windows and faster sampling consistently improve accuracy and stability. The optimized configuration (≈143-min history, ≈3-min sampling) reduces mean absolute error from ~0.51 to ~0.05 on the normalized freshness scale and shifts the error distribution within specification limits, with marked gains in process capability and yield. Although it does not match the analytical precision or long-term robustness of spectrometric approaches, the proposed system offers an interpretable and energy-efficient option for short-term, laboratory-scale monitoring under controlled refrigeration conditions. By enabling probabilistic freshness estimation from low-cost sensors, this GPR-driven e-nose demonstrates a proof-of-concept pathway that could, after further validation under realistic cyclic loads and operational disturbances, support more sustainable meat management in future smart refrigeration and cold-chain applications. This study should be regarded as a methodological, laboratory-scale proof-of-concept that does not demonstrate real-world performance or operational deployment. The technical implications described herein are hypothetical and require extensive validation under realistic refrigeration conditions. Full article