Direct Conversion of Single‐Layer SnO Nanoplates to Multi‐Layer SnO2 Nanoplates with Enhanced Ethanol Sensing Properties

Direct conversion of single‐layer SnO nanoplates to multi‐layer SnO₂ nanoplates is achieved by annealing in an O₂ ambient at 700 °C. For 50 ppm ethanol, the sensitivities of the multi‐layer SnO₂ nanoplates are more than double that of single‐layer SnO₂ nanoplates, which are also formed from the single‐layer SnO. The higher sensitivity of the multi‐layer nanoplates is attributed to their larger surface/volume ratio. The facile fabrication of interconnected multi‐layer SnO₂ nanoplates at low temperature directly on a Si substrate and sensing chip without the aid of catalysts offers vast advantages over competing methods for the fabrication of high‐sensitivity SnO₂ sensors.     

电纺SnO2纳米纤维的制备及其气敏特性

采用聚乙烯醇（PVA，Mw=80000g/mol）和五水合四氯化锡（SnCl4.5H2O）作为静电纺丝前驱液，着重研究了纺丝电压、前驱液中PVA浓度及煅烧温度等因素对纺丝过程及纤维特性的影响，并用扫描电镜（SEM）和X射线衍射（XRD）等分析手段对纤维的微观结构、表面形貌和结晶状态进行了表征。结果表明，当纺丝电压为4kV、纺丝液中PVA质量分数为7%、退火温度为700℃时，可以得到平均直径为300nm的连续SnO2纳米纤维。该纤维对乙醇的响应恢复时间小于15s，检测极限低于10×10^-9。     

退火处理对二氧化锡纳米线性能的影响

采用化学气相沉积法在硅衬底上生长二氧化锡(SnO2)纳米线,并对其进行热处理.扫描电子显微镜、X射线衍射仪和拉曼光谱测试分析表明所合成的SnO2蚋米线为单一四方金红石相,且结晶性能良好.光致发光测试显示在576 nm附近有明显的黄色发光峰,但在氧气氛环境退火处理后该发光峰逐渐减弱,表明576 nm处的发光峰为氧空位缺陷引起的发光.同时,退火处理能有效提高材料的场发射性能,SnO2纳米线的最低开启和阚值电场分别约为4.6和6.2 V/μm.     

Observation of a 2D Electron Gas and the Tuning of the Electrical Conductance of ZnO Nanowires by Controllable Surface Band‐Bending

Direct experimental evidence for the existence of a 2D electron gas in devices based on ZnO nanowires (NWs) is presented. A two‐channel core/shell model is proposed for the interpretation of the temperature‐dependent current–voltage (I–V) characteristics of the ZnO NW, where a mixed metallic–semiconducting behavior is observed. The experimental results are quantitatively analyzed using a weak‐localization theory, and suggest that the NW is composed of a “bulk” semiconducting core with a metallic surface accumulation layer, which is basically a 2D electron gas in which the electron–phonon inelastic scattering is much weaker than the electron–electron inelastic scattering. A series of I–V measurements on a single NW device are carried out by alternating the atmosphere (vacuum, H₂, vacuum, O₂), and a reversible change in the conductance from metallic to semiconducting is achieved, indicating the surface accumulation layer is likely hydroxide‐induced. Such results strongly support the two‐channel model and demonstrate the controllable tuning of the ZnO NW electrical behavior via surface band‐bending.     

Anti-Corrosive SnS2/SnO2 Heterostructured Support for Pt Nanoparticles Enables Remarkable Oxygen Reduction Catalysis via Interfacial Enhancement

The stability of Pt-based catalysts for oxygen reduction reaction (ORR) in hydrogen fuel cells is seriously handicapped by the corrosion of their carbon supports at high potentials and acidic environments. Herein, a novel SnS₂/SnO₂ hetero-structured support is reported for Pt nanoparticles (NPs) as the ORR catalyst, where Pt NPs are mainly deposited at the interfaces of SnS₂ and SnO₂ moieties. The Pt-support interactions, which can be tuned by the concentration of the heterointerfaces, can accelerate the electronic transfer and enrich the electron density of Pt with a favorable shift of the d-band center. In electrochemical measurements, the ORR mass activity (MA) of the optimal Pt-SnS₂/SnO₂ catalyst at 0.9 V versus RHE (0.40 A mg_Pt⁻¹) is four times higher than that of Pt/C. As for the stability, the electrochemical active surface area and MA of Pt-SnS₂/SnO₂ are only decreased by 18.2% and 23.7% after 50 000 potential cycles at a high potential region (1.0–1.6 V), representing the best ORR stability among the reported Pt-based catalysts. Density functional theory calculations indicate that the binding energy and migration barrier of Pt atom/cluster on the SnS₂/SnO₂ heterojunction are much higher relative to other supports, accounting for the outstanding stability of the catalyst.     

Band‐Edge Engineered Hybrid Structures for Dye‐Sensitized Solar Cells Based on SnO2 Nanowires

In this report, we show for the first time that SnO₂ nanowire based dye sensitized solar cells exhibit an open circuit voltage of 560 mV, which is 200 mV higher than that using SnO₂ nanoparticle based cells. This is attributed to the more negative flat band potential of nanowires compared to the nanoparticles as determined by open circuit photo voltage measurements made at high light intensities. The nanowires were employed in hybrid structures consisting of highly interconnected SnO₂ nanowire matrix coated with TiO₂ nanoparticles, which showed an open circuit voltage of 720 mV and an efficiency of 4.1% compared to 2.1% obtained with pure SnO₂ nanowire matrix. The electron transport time constants for SnO₂ nanowire matrix were an order of magnitude lower and the recombination time constants are about 100 times higher than that of TiO₂ nanoparticles. The higher efficiency observed for DSSCs based on hybrid structure is attributed to the band edge positions of SnO₂ relative to that of TiO₂ and faster electron transport in SnO₂ nanowires.     

Thin‐Wall Assembled SnO2 Fibers Functionalized by Catalytic Pt Nanoparticles and their Superior Exhaled‐Breath‐Sensing Properties for the Diagnosis of Diabetes

Hierarchical SnO₂ fibers assembled from wrinkled thin tubes are synthesized by controlling the microphase separation between tin precursors and polymers, by varying flow rates during electrospinning and a subsequent heat treatment. The inner and outer SnO₂ tubes have a number of elongated open pores ranging from 10 nm to 500 nm in length along the fiber direction, enabling fast transport of gas molecules to the entire thin‐walled sensing layers. These features admit exhaled gases such as acetone and toluene, which are markers used for the diagnosis of diabetes and lung cancer. The open tubular structures facilitated the uniform coating of catalytic Pt nanoparticles onto the inner SnO₂ layers. Highly porous SnO₂ fibers synthesized at a high flow rate show five‐fold higher acetone responses than densely packed SnO₂ fibers synthesized at a low flow rate. Interestingly, thin‐wall assembled SnO₂ fibers functionalized by Pt particles exhibit a dramatically shortened gas response time compared to that of un‐doped SnO₂ fibers, even at low acetone concentrations. Moreover, Pt‐decorated SnO₂ fibers significantly enhance toluene response. These results demonstrate the novel and practical feasibility of thin‐wall assembled metal oxide based breath sensors for the accurate diagnosis of diabetes and potential detection of lung cancer.     

Deconvoluting Energy Transport Mechanisms in Metal Halide Perovskites Using CsPbBr3 Nanowires as a Model System

Understanding energy transport in metal halide perovskites is essential to effectively guide further optimization of materials and device designs. However, difficulties to disentangle charge carrier diffusion, photon recycling, and photon transport have led to contradicting reports and uncertainty regarding which mechanism dominates. In this study, monocrystalline CsPbBr₃ nanowires serve as 1D model systems to help unravel the respective contribution of energy transport processes in metal-halide perovskites. Spatially, temporally, and spectrally resolved photoluminescence (PL) microscopy reveals characteristic signatures of each transport mechanism from which a robust model describing the PL signal accounting for carrier diffusion, photon propagation, and photon recycling is developed. For the investigated CsPbBr₃ nanowires, an ambipolar carrier mobility of μ = 35 cm² V⁻¹ s⁻¹ is determined, and is found that charge carrier diffusion dominates the energy transport process over photon recycling. Moreover, the general applicability of the developed model is demonstrated on different perovskite compounds by applying it to data provided in previous related reports, from which clarity is gained as to why conflicting reports exist. These findings, therefore, serve as a useful tool to assist future studies aimed at characterizing energy transport mechanisms in semiconductor nanowires using PL.     

Boosting the Efficiency of SnO2‐Triple Cation Perovskite System Beyond 20% Using Nonhalogenated Antisolvent

Solution‐processed triple‐cation perovskite solar cells (PSCs) rely on complex compositional engineering or delicate interfacial passivation to balance the trade‐off between cell efficiency and long‐term stability. Herein, the facile fabrication of highly efficient, stable, and hysteresis‐free tin oxide (SnO₂)‐based PSCs is demonstrated with a champion cell efficiency of 20.06% using a green, halogen‐free antisolvent. The antisolvent, composed of ethyl acetate (EA) solvent and hexane (Hex) in different proportions, works exquisitely in regulating perovskite crystal growth and passivating grain boundaries, leading to the formation of a crack‐free perovskite film with enlarged grain size. The high quality perovskite film inhibits carrier recombination and substantially improves the cell efficiency, without requiring an additional enhancer/passivation layer. Furthermore, these PSCs also demonstrate remarkable long‐term stability, whereby unencapsulated cells exhibit a power conversion efficiency (PCE) retention of ≈71% after >1500 hours of storage under ambient condition. For encapsulated cells, an astounding PCE retention of >98% is recorded after >3000 hours of storage in air. Overall, this work realizes the fabrication of SnO₂‐based PSCs with a performance greater or comparable to the state‐of‐the‐art PSCs produced with halogenated antisolvents. Evidently, EA–Hex antisolvent can be an extraordinary halogen‐free alternative in maximizing the performance of PSCs.     

Oxygen Vacancy-Mediated Catalysts toward Selective H2O2 Reduction in Cellular Environment

Abnormal hydrogen peroxide (H₂O₂) levels in the cellular environment are closely related to cell dysfunction and serious diseases. Thus, selective and sensitive H₂O₂ detections are urgently needed for clinical diagnosis and therapy. Herein, via surface defect engineering, an oxygen-tolerant electrocatalyst based on tin oxide for selective H₂O₂ reduction and detection with exceptional stability and activity is designed and developed. When introduced at an appropriate level (≈5.3%), surface oxygen vacancies help lower the charge transfer resistance for enhancing the H₂O₂ reduction reaction, while maintain the weak oxygen (O₂) adsorption, which enables a constant H₂O₂ reduction (sensing) response in the electrolyte at variable oxygen levels. Moreover, the tin oxide-based assay system exhibits outstanding stability over a wide pH range of 4–9, as well as selectivity in the presence of interferent endogenous and exogenous electroactive species, which is suitable for trace H₂O₂ monitoring secreted from NB4 cells, a model cancer cell. The oxygen vacancy-mediated tin oxide achieves the highest stability as well as high selectivity compared to reported electrochemical probes for specific H₂O₂ detection in biological environments, with the potential for biological and biomedical applications.     

电纺SnO_2纳米纤维的制备及其气敏特性

采用聚乙烯醇(PVA,Mw=80000g/mol)和五水合四氯化锡(SnCl4.5H2O)作为静电纺丝前驱液,着重研究了纺丝电压、前驱液中PVA浓度及煅烧温度等因素对纺丝过程及纤维特性的影响,并用扫描电镜(SEM)和X射线衍射(XRD)等分析手段对纤维的微观结构、表面形貌和结晶状态进行了表征。结果表明,当纺丝电压为4kV、纺丝液中PVA质量分数为7%、退火温度为700℃时,可以得到平均直径为300nm的连续SnO2纳米纤维。该纤维对乙醇的响应恢复时间小于15s,检测极限低于10×10-9。     

Templating Synthesis of SnO2 Nanotubes Loaded with Ag2O Nanoparticles and Their Enhanced Gas Sensing Properties

A new kind of SnO₂ nanotubes loaded with Ag₂O nanoparticles can be synthesized by using Ag@C coaxial nanocables as sacrificial templates. The composition of silver in SnO₂ nanotubes can be controlled by tuning the compositions of metallic Ag in Ag@C sacrificial templates, and the morphology of tubular structures can be changed by use of nanocables with different thicknesses of carbonaceous layer. This simple strategy is expected to be extended for the fabrication of similar metal‐oxide doped nanotubes using different nanocable templates. In contrast to SnO₂@Ag@C nanocables as well as to other types of SnO₂ reported previously, the Ag₂O‐doped SnO₂ nanotubes exhibit excellent gas sensing behaviors. The dynamic transients of the sensors demonstrated both their ultra‐fast response (1–2 s) and ultra‐fast recovery (2–4 s) towards ethanol, and response (1–4 s) and recovery (4–5 s) towards butanone. The combination of SnO₂ tubular structure and catalytic activity of Ag₂O dopants gives a very attractive sensing behavior for applications as real‐time monitoring gas sensors with ultra‐fast responding and recovering speed.     

溶剂热法制备纳米SnO2及其气敏性能研究

以SnCl2·2H2O为原料,采用溶剂热法,分别在体积分数为95%的乙醇及95%乙醇–油酸体系中制备了单分散的SnO2纳米粉。利用XRD和TEM等手段,对产物进行了表征,并对其气敏性能进行了测定。结果表明:在95%乙醇–油酸体系中制备的SnO2,粒径约为15nm,在4V的工作电压下,对体积分数为100×10–6的氯气灵敏度为370,响应–恢复时间仅为1s。     

Insights into Fullerene Passivation of SnO2 Electron Transport Layers in Perovskite Solar Cells

Interfaces between the photoactive and charge transport layers are crucial for the performance of perovskite solar cells. Surface passivation of SnO₂ as electron transport layer (ETL) by fullerene derivatives is known to improve the performance of n–i–p devices, yet organic passivation layers are susceptible to removal during perovskite deposition. Understanding the nature of the passivation is important for further optimization of SnO₂ ETLs. X‐ray photoelectron spectroscopy depth profiling is a convenient tool to monitor the fullerene concentration in passivation layers at a SnO₂ interface. Through a comparative study using [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) and [6,6]‐phenyl‐C₆₁‐butyric acid (PCBA) passivation layers, a direct correlation is established between the formation of interfacial chemical bonds and the retention of passivating fullerene molecules at the SnO₂ interface that effectively reduces the number of defects and enhances electron mobility. Devices with only a PCBA‐monolayer‐passivated SnO₂ ETL exhibit significantly improved performance and reproducibility, achieving an efficiency of 18.8%. Investigating thick and solvent‐resistant C₆₀ and PCBM‐dimer layers demonstrates that the charge transport in the ETL is only improved by chemisorption of the fullerene at the SnO₂ surface.     

Hydrogen‐Terminated Si Nanowires as Label‐Free Colorimetric Sensors in the Ultrasensitive and Highly Selective Detection of Fluoride Anions in Pure Water Phase

The detection of anions in pure water phase with colorimetric sensor is a long standing challenge. As one of the most important anions, F^– is associated with nerve gases and the refinement of uranium for nuclear weapons. However, limited by its anions nature, few of the reported colorimetric sensors can successfully applied to detect F^–1 in pure water phase. This work designs a colorimetric sensor for F^–1 pure water phase detection by taking the advantages of the strong specific binding between F and Si, as well as the color‐changing property of H‐terminated Si nanowires (SiNWs). The sensor demonstrates ultra‐sensitivity, high selectivity, and good stability. The results reveal particular interest for the development of new type aqueous phase anions sensors with SiNWs.     

White‐Light Emitting Diode Array of p+‐Si/Aligned n‐SnO2 Nanowires Heterojunctions

We report on the fabrication and optoelectronic properties of p‐n heterojunction arrays of p⁺‐type Si and aligned n‐type SnO₂ nanowires with high rectification ratios of >10⁴ at ±15 V. The electrical stability of the p‐n heterojunction devices was improved by coating the junction with poly(methylmethacrylate) to minimize the degradation of the interface layer at the junction. As a photodiode an enhanced UV photosensitivity higher than 10² was recorded under reverse bias. Using a large forward bias in the light‐emitting diode mode white light was emitted from the large‐scale heterojunction devices with at least three broad peaks in the visible range, which can be attributed to the interband transitions of the injected electrons or holes mediated by an interfacial SiO₂ layer with a contribution of trap‐level energies. These results indicate the high potential of Si/SnO₂ nanowires heterojunctions as optoelectronic devices with proper tuning of the recombination center at the junctions.     

MOEMS气体传感技术研究进展

微光电子机械系统(MOEMS)气体传感技术是光学式气体传感器技术与MOEMS技术、新材料技术相结合的创新型技术方案。MOEMS气体传感器具有更低的价格、更高的集成度、更强的抗干扰能力,以及更高的测试精度。文章首先阐述了主要的光学气体传感系统的工作原理及系统结构,随后介绍了MOEMS气体传感技术中最新的微光学器件及微光学系统。通过对MOEMS气体传感器的主要研究成果和进展的综述,对未来MOEMS气体传感器的研究重点和研究挑战等进行了展望。     

Catalytically Doped Semiconductors for Chemical Gas Sensing: Aerogel‐Like Aluminum‐Containing Zinc Oxide Materials Prepared in the Gas Phase

Atmospheric contamination with organic compounds is undesired in industry and in society because of odor nuisance or potential toxicity. Resistive gas sensors made of semiconducting metal oxides are effective in the detection of gases even at low concentration. Major drawbacks are low selectivity and missing sensitivity toward a targeted compound. Acetaldehyde is selected due to its high relevance in chemical industry and its toxic character. Considering the similarity between gas‐sensing and heterogeneous catalysis (surface reactions, activity, selectivity), it is tempting to transfer concepts. A question of importance is how doping and the resulting change in electronic properties of a metal‐oxide support with semiconducting properties alters reactivity of the surfaces and the functionality in gas‐sensing and in heterogeneous catalysis. A gas‐phase synthesis method is employed for aerogel‐like zinc oxide materials with a defined content of aluminum (n‐doping), which were then used for the assembly of gas sensors. It is shown that only Al‐doped ZnO represents an effective sensor material that is sensitive down to very low concentrations (<350 ppb). The advance in properties relates to a catalytic effect for the doped semiconductor nanomaterial.     

Reliable Monolayer‐Template Patterning of SnO2 Thin Films from Aqueous Solution and Their Hydrogen‐Sensing Properties

We demonstrate a novel lithographic technique utilizing a solvent to fabricate a chemically based semiconductor microdevice from an aqueous solution. According to this technique, SnO₂ thin film could be integrated onto predefined sites on a SiO₂/Si wafer. A patterned octadecyltrimethoxysilane self‐assembled monolayer (ODS‐SAM) was prepared by vacuum ultraviolet (VUV) irradiation through a photomask to use as a template for the fabrication of a micropatterned SnO₂ thin film on the SiO₂/Si surface. A Sn‐based thin film was then deposited onto the entire surface of the ODS template from an aqueous solution containing 0.03 mol L^–1 of SnCl₂·2H₂O at 60 °C for 16 h in an ambient atmosphere. The thin film deposited on the methyl‐terminated area of the template was then peeled using an ultrasonic rinse in anhydrous toluene for 30 min, while the film deposited on the silanol area remained intact and undamaged. Rinsing in hydrophilic solvents did not facilitate peeling of the thin film from the methyl‐terminated area. We succeeded by this process in obtaining a high‐resolution, micropatterned Sn‐based thin film on an ODS‐SAM template on Si. The as‐deposited film was composed of fine Sn‐based particles. The sensitivity of this SnO₂ thin film to H₂ gas increases linearly with improving crystallinity. The effectiveness of anhydrous toluene as a rinse in solution lithography is discussed from the viewpoint of the high hydrophobic affinity between the rinse solvent and the terminal groups in the monolayer template.