Junjun Wang

To clarify the distinct effects of Ru surface doping and loading on metal oxide semiconductor gas sensors, ZnO thin films were prepared by magnetron sputtering with Ru surface doping, surface loading, or combined modification. Structural and chemical analyses confirmed successful Ru incorporation or deposition. All Ru-modified sensors outperformed pristine ZnO in NH3 sensing, with surface loading yielding the best overall performance. At 325℃, the Ru-loaded sensor exhibited a response of 122 to 100 ppm NH3, approximately five times that of pristine ZnO, with a calculated limit of detection (LOD) of 11 ppb, a measurable response to 100 ppb NH3, and excellent selectivity. This enhancement was partly attributed to catalytic spillover and Schottky barrier formation at the Ru/ZnO interface. Density functional theory calculations further showed that surface loading balanced NH3 adsorption and desorption through moderate adsorption energy and efficient charge transfer. Conversely, surface doping bound NH3 too strongly, hindering desorption and limiting sensing performance. These findings identify the distinct roles of Ru doping and loading and offer guidance for designing high-performance NH3 sensors.

Sensitive low-concentration NH3 detection is critical for environmental monitoring and safety. Herein, MoO3/MoS2 hollow sphere array were fabricated for NH3 sensing. MoS2 hollow sphere array films were first fabricated by a combined colloidal template and magnetron sputtering method, and then controlled thermal oxidation at 320°C, 340°C and 360°C enabled partial in-situ conversion of MoS2 to MoO3. Multiple characterization techniques confirmed the hollow spherical morphology, interfacial electron transfer behavior, and tunable oxygen vacancy content regulated by the degree of oxidation. Gas sensing measurements revealed that the sensor subjected to oxidation at 340°C delivered superior sensing performance. When operated at 250°C, the sensor showed a response of 20.5 to 100 ppm NH3, representing an approximately 20-fold enhancement over pristine MoS2. while the response time was shortened from 107 s to 41 s and the limit of detection was lowered to 0.5 ppm. The sensing enhancement originates from the large accessible surface area of the hollow architecture, The modulation of sensor resistance by the depletion layer and potential barrier at the heterojunction interface, and the strong affinity between Lewis acid sites on MoO3 and alkaline NH3 molecules. The study demonstrates a viable route toward highly sensitive NH3 sensors with prospects for large-scale fabrication.

Real-time and highly selective monitoring of acetone (C3H6O) is crucial for industrial safety and occupational health. Herein, we report a Ce-doped BiFeO3 (BFO) sensing material synthesized via a sol–gel method, which enables simultaneous regulation of grain size, polarization strength, crystal phase composition, band structure, and defect. The optimized sensor (denoted as BC2FO, 2 mol% Ce-doped) exhibits excellent C3H6O sensing performance over a concentration range of 0.2–10 ppm at 220 °C, and its response value to 2 ppm C3H6O is twice that of the pure BFO sensor. Ex situ XPS and in situ Raman further revealed the sensitive reaction mechanism between C3H6O gas molecules and the BC2FO composite material. Furthermore, the machine learning classification algorithm was introduced for highly accurate identification of C3H6O against isopropanol (C3H8O). An intelligent warning system based on BC2FO micro-electro-mechanical system (MEMS) sensors has been developed, which successfully achieved continuous monitoring and automatic on-site alarm in simulated industrial leakage scenarios. This study presents a comprehensive and robust paradigm combining material engineering, machine learning-assisted recognition, and hardware integration for the detection of C3H6O.

Trace formaldehyde (HCHO) breath analysis requires sensors with ultra-low detection limits and high humidity tolerance. Achieving thermodynamically stabilized Ce3+ in conventional oxides remains challenging due to the strong dependence of Ce valence on synthesis conditions. Herein, we show that the multication lattice of CuBi2O4 enables site-dependent Ce valence regulation: Ce prefers +3 at Bi sites and +4 at Cu sites (DFT/XPS: 51% Ce3+ in CBO:Ce 0.25%). 1H SSNMR reveals that Ce doping disrupts the surface hydrogen-bonded network responsible for humidity-induced degradation. Consequently, CBO:Ce 0.25% achieves a response retention of 49.32% from 10% to 90% RH (vs. 11.13% for pristine CBO) while preserving a high response (3.91 at 90% RH toward 50 ppb HCHO) via active hydroxyl scavenging through the Ce3+/Ce4+ redox cycle—in contrast to the physical blocking approach of FAS modification, which attains higher retention but severely compromises sensitivity. This work establishes site-specific Ce3+ stabilization as a design strategy for humidity-tolerant MOS sensors.

Highly sensitive detection of formaldehyde (HCHO) under high relative humidity (RH) conditions is of great significance for the analysis of human exhaled breath and the monitoring of indoor air pollutants. In this study, a PTFE@Au@In2O3 hollow sphere film sensor for HCHO detection was successfully fabricated via a polystyrene (PS) template-assisted magnetron sputtering technique. Comprehensive material characterizations, including XRD, SEM and XPS, confirmed the formation of the PTFE@Au@In2O3 heterostructure with its unique microstructure. The gas-sensing performance of the sensor was found to be critically dependent on the PTFE sputtering time. At an operating temperature of 325 ℃ and 90% RH, the optimal sensor exhibited a response of 13.6 toward 100 ppm HCHO, along with a limit of detection of 10 ppb (corresponding to a response of 1.6). Notably, at an operating temperature of 325 ℃, this sensor demonstrated superior moisture resistance, retaining 93.3% of its initial response to 1 ppm HCHO when the RH increased from 10% to 90%, whereas the pure In2O3 sensor retained only 47.4%. This work provides a novel and feasible strategy for constructing high-performance HCHO sensors.

Owing to their high specific surface area, excellent electrical conductivity, and tunable surface functional groups, MXenes show great promise for room-temperature gas sensing. A key limitation, however, arises from the prevalent -F terminations in MXenes prepared by (in-situ) HF etching, which bind gas molecules weakly and result in low sensitivity. To address this, we tailored the surface chemistry using NaOH-assisted hydrothermal etching to synthesize single- or few-layer Ti3C2Tx. This method drastically reduces the -F fraction from 62.11% to 22.68% while elevating the -OH fraction from 12.84% to 63.01%. Consequently, the response to 100 ppm NH3 at 27℃ increases by approximately 30-fold, from 2.09% to 62.55%. Furthermore, we provide the experimental substantiation of proton-conduction and redox mechanisms in MXene-based sensors for NH3 and n-butyl alcohol, with DFT calculations elucidating the pivotal role of the -OH-rich surface in these sensitization mechanisms. This work establishes a clear and definitive correlation between the intrinsic surface functional groups and the gas-sensing performance of MXenes.

Flexible sensors are often constructed on polymeric or cellulosic substrates, which tend to compromise breathability for mechanical durability, leading to skin irritation and the limitation of long-term use. Here, we develop a monolithic breathable Ti₃C₂T_x@Spandex textile sensor that creates a continuous, gas-permeable conductive network for sensitive response transduction. Impregnated MXene nanosheets give 5.1% response to 300 ppm of NH₃ with a response time of 14 s under folding deformations, full selectivity against 14 interfering gases, and 4 order of magnitude lower resistance (∼5.7 × 10⁸ Ω) than that of bare Spandex (∼1.5 × 10¹² Ω), yielding a signal-to-noise ratio of 20.5 at room temperature. The continuous conductive pathways survive 100% strain, maintain a water-vapor transmission rate of 1149-1268 g m^-2 day^-1, and resolve joint bending angles via reversible Ti₃C₂T_x nanosheet slippage. This breathable, skin-conformable patch enables point-of-care screening of both renal-exhaled NH₃ and real-time joint kinematics.

Formaldehyde (HCHO), a key marker of lung cancer, is found in the exhaled breath of patients. Detecting low concentration HCHO (< 48 ppb) in highly relative humidity (RH) is crucial for HCHO gas sensors to be used in lung cancer detection. In this paper, we present a formaldehyde gas sensor based on CuO@In₂O₃ hollow sphere films, which were fabricated using a colloid template-assisted magnetron sputtering method. The characterization results indicate that the films are comprised of a single-layer, highly-ordered hollow-sphere structure, with CuO nanoparticles evenly distributed on the surface of In₂O₃ hollow sphere and forming a heterojunction with In₂O₃. The impact of CuO sputtering time on sensor performance was analyzed in detail. The sample with CuO sputtering time of 15 s exhibits the best performance. When the environment RH is 90%, 15-CuO@ In₂O₃ had a high response of 22.3 to 100 ppm HCHO and a 10 ppb detection limit. When the environmental RH increases from 10% to 90%, the response of sample 15-CuO@ In₂O₃ decreases with a decrease rate of about 27%, which is better than the decrease rate of sample In₂O₃ (46.9%). The sensors also have good selectivity and long-term stability, meeting the needs for detecting formaldehyde in lung cancer patients’ exhaled breath. Its superior performance is ascribed to its large specific surface area, the interface effect of CuO on the band structure, and the synergistic catalytic effect. This work offers a new approach for developing high performance diagnostic sensors.

This study systematically investigated the effects of oxygen plasma treatment on oxygen vacancy defects in sputtered β-gallium oxide (β-Ga₂O₃) films and their corresponding ultraviolet (UV) detection performance. The sputtered β-Ga₂O₃ film subjected to 1 min of oxygen plasma treatment exhibited optimal photodetection properties. Compared to the untreated sample, the dark current was reduced by approximately one order of magnitude to 0.378 pA at 10 V bias. It exhibited an 86% (from 2.92 s to 0.41 s) decrease in response time, a 41.6% increase in photocurrent, a very high photo-to-dark current ratio of 9.18 × 10⁵, and a specific detectivity of 2.62 × 10¹⁰ cm·Hz^1/2W⁻¹ under 254 nm UV illumination intensity of 799 μW/cm² at 10 V bias. Notably, appropriate oxygen plasma treatment minimizes electron capture, enhances the separation and collection of photogenerated carriers, and suppresses the persistent photoconductivity (PPC) effect, thus ultimately shortening the response time. Oxygen plasma processing thus provides an effective approach to fabricating high-performance β-Ga₂O₃ solar-blind photodetectors (SBPDs).