Palladium‐Decorated Silicon Nanomesh Fabricated by Nanosphere Lithography for High Performance,Room Temperature Hydrogen Sensing

A hydrogen (H₂) gas sensor based on a silicon (Si) nanomesh structure decorated with palladium (Pd) nanoparticles is fabricated via polystyrene nanosphere lithography and top‐down fabrication processes. The gas sensor shows dramatically improved H₂ gas sensitivity compared with an Si thin film sensor without nanopatterns. Furthermore, a buffered oxide etchant treatment of the Si nanomesh structure results in an additional performance improvement. The final sensor device shows fast H₂ response and high selectivity to H₂ gas among other gases. The sensing performance is stable and shows repeatable responses in both dry and high humidity ambient environments. The sensor also shows high stability without noticeable performance degradation after one month. This approach allows the facile fabrication of high performance H₂ sensors via a cost‐effective, complementary metal–oxide–semiconductor (CMOS) compatible, and scalable nanopatterning method.     

苯系物(BTEX)检测气敏材料研究进展

金属氧化物半导体传感器因具有体积小、成本低廉、使用方便等优点,越来越受到研究者的关注并被用于有毒有害气体的监测。传感材料是气敏传感器的核心,本文综述了近年来氧化物半导体BTEX气敏传感材料的研究进展,对传感材料的微结构、负载/掺杂改性、气敏性能、气敏机理及存在的问题进行了分析,并探讨了其下一步发展趋势。     

Detection of NO2 Down to One ppb Using Ion‐in‐Conjugation‐Inspired Polymer

Nitrogen dioxide (NO₂) emission has severe impact on human health and the ecological environment and effective monitoring of NO₂ requires the detection limit (limit of detection) of several parts‐per‐billion (ppb). All organic semiconductor‐based NO₂ sensors fail to reach such a level. In this work, using an ion‐in‐conjugation inspired‐polymer (poly(3,3′‐diaminobenzidine‐squarine, noted as PDBS) as the sensory material, NO₂ can be detected as low as 1 ppb, which is the lowest among all reported organic NO₂ sensors. In addition, the sensor has high sensitivity, good reversibility, and long‐time stability with a period longer than 120 d. Theoretical calculations reveal that PDBS offers unreacted amine and zwitterionic groups, which can offer both the H‐bonding and ion‐dipole interaction to NO₂. The moderate binding energies (≈0.6 eV) offer high sensitivity, selectivity as well as good reversibility. The results demonstrate that the ion‐in‐conjugation can be employed to greatly improve sensitivity and selectivity in organic gas sensors by inducing both H‐bonding and ion‐dipole attraction.     

Flexible Triboelectric Nanogenerator Based on High Surface Area TiO2 Nanotube Arrays

Triboelectric nanogenerators (TENGs) can harvest mechanical energy through coupling triboelectric effect and electrostatic induction. Typically, TENGs consist of organic materials, however on account of the potentially wide range of applications of TENGs as the self‐powered portable/wearable electronics, biomedical devices, and sensors; semiconductor metal oxide materials can be promising candidates to be incorporating in TENG structure. Here, flexible TENG based on self‐organized TiO₂ nanotube arrays (TNTAs) is fabricated via anodization method. The introduced flexible large area nanotubular electrode is employed as the moving electrode in contact with Kapton film in vertical contact separation mode of TENG. The fabricated TENG can deliver output voltage of 40 V with the current density of 1 μA cm^?2. To evaluate the role of nanostructured interface, its performance has been compared to the thin film flat compact TiO₂ electrode. The results of extracted charge measurements under short circuit condition indicate that larger triboelectric charge density formed in TNTA‐based electrode (about 110 nC per cycle of press and release) is in comparison to 15 nC in flat TiO₂ electrode. Due to the extensive range of applications of TiO₂, the introduced structure can potentially be applicable in various types of self‐powered systems such as photo‐detectors and environmental gas and bio‐sensors.

     

氧化钨基半导体气体传感器的研究进展

近年来,氧化钨(WO_3)基半导体气体传感器由于可用来检测低浓度二氧化氮、二氧化硫、臭氧和氨气等气体而受到广泛关注。将WO_3基材料分为4类:纯WO_3材料、氧化物-WO_3复合材料、贵金属-WO_3复合材料和有机物-WO_3复合材料,总结近年来中外文献中WO_3基材料对不同气体的响应性能,展现近年来国内外WO_3基半导体气体传感器的研究进展。最后根据已有的工作进展,提出合成新型纳米材料、降低工作温度、提高传感器选择性应成为WO_3基半导体气体传感器下一阶段的研究重点。     

A New Strategy for Humidity Independent Oxide Chemiresistors: Dynamic Self‐Refreshing of In2O3 Sensing Surface Assisted by Layer‐by‐Layer Coated CeO2 Nanoclusters

The humidity dependence of the gas sensing characteristics of metal oxide semiconductors has been one of the greatest obstacles for gas sensor applications during the last five decades because ambient humidity dynamically changes with the environmental conditions. Herein, a new and novel strategy is reported to eliminate the humidity dependence of the gas sensing characteristics of oxide chemiresistors via dynamic self‐refreshing of the sensing surface affected by water vapor chemisorption. The sensor resistance and gas response of pure In₂O₃ hollow spheres significantly change and deteriorate in humid atmospheres. In contrast, the humidity dependence becomes negligible when an optimal concentration of CeO₂ nanoclusters is uniformly loaded onto In₂O₃ hollow spheres via layer‐by‐layer (LBL) assembly. Moreover, In₂O₃ sensors LBL‐coated with CeO₂ nanoclusters show fast response/recovery, low detection limit (500 ppb), and high selectivity to acetone even in highly humid conditions (relative humidity 80%). The mechanism underlying the dynamic refreshing of the In₂O₃ sensing surfaces regardless of humidity variation is investigated in relation to the role of CeO₂ and the chemical interaction among CeO₂, In₂O₃, and water vapor. This strategy can be widely used to design high performance gas sensors including disease diagnosis via breath analysis and pollutant monitoring.     

Highly sensitive and rapidly responding room-temperature NO<Subscript>2</Subscript> gas sensors based on WO<Subscript>3</Subscript> nanorods/sulfonated graphene nanocomposites

Metal oxide/graphene nanocomposites are emerging as promising materials for developing room-temperature gas sensors. However, the unsatisfactory performances owing to the relatively low sensitivity, slow response, and recovery kinetics limit their applications. Herein, a highly sensitive and rapidly responding room-temperature NO₂ gas sensor based on WO₃ nanorods/sulfonated reduced graphene oxide (S-rGO) was prepared via a simple and cost-effective hydrothermal method. The optimal sensor response of the WO₃/S-rGO sensor toward 20 ppm NO₂ is 149% in 6 s, which is 4.7 times higher and 100 times faster than that of the corresponding WO₃/rGO sensors. In addition, the sensor exhibits excellent reproducibility, selectivity, and extremely fast recovery kinetics. The mechanism of the WO₃/S-rGO nanocomposite gas sensor is investigated in detail. In addition to the high transport capability of S-rGO as well as its excellent NO₂ adsorption ability, the superior sensing performance of the S-rGO/WO₃ sensor can be attributed to the favorable charge transfer occurring at the S-rGO/WO₃ interfaces. We believe that the strategy of compositing a metal oxide with functionalized graphene provides a new insight for the future development of room-temperature gas sensors.

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Ce-doped hollow In2O3 nanoboxes derived from metal–organic frameworks with excellent formaldehyde-sensing performance

In recent years, metal oxides derived from metal organic frameworks (MOFs) have been widely used in the gas-sensing direction due to their regular framework structure and large porosity. At the same time, rare earth ion doping can also effectively improve the gas-sensing properties of metal oxide semiconductors. Herein, we report the synthesis of MOFs-drived Ce-doped In₂O₃ samples by calcining precursors prepared by a simple oil bath method. The experimental characterization results show that the as-prepared samples exhibit uniform hollow nanoboxes with high surface area (48.5 m²/g) and abundant oxygen vacancies. Owing to the unique structures, the 1 wt% Ce-doped In₂O₃ nanobox-based gas sensor shows a fast response (1 s), quick recovery (1 s), and an ultralow detection limit (response of 13.4 for 1 ppm of formaldehyde) at the low operating temperature (140 °C). The excellent gas-sensing performance is mainly attributed to hollow structure and the incorporation of Ce, increasing the number of oxygen vacancies and adsorbed oxygen in improving formaldehyde sensing performance of In₂O₃ sensors. This kind of rare earth ion-doped hollow nanoboxes derived from MOFs provides a strategy for the design and development of high performance gas sensor.

     

UV–Ozone Interfacial Modification in Organic Transistors for High‐Sensitivity NO2 Detection

A new type of nitrogen dioxide (NO₂) gas sensor based on copper phthalocyanine (CuPc) thin film transistors (TFTs) with a simple, low‐cost UV–ozone (UVO)‐treated polymeric gate dielectric is reported here. The NO₂ sensitivity of these TFTs with the dielectric surface UVO treatment is ≈400× greater for [NO₂] = 30 ppm than for those without UVO treatment. Importantly, the sensitivity is ≈50× greater for [NO₂] = 1 ppm with the UVO‐treated TFTs, and a limit of detection of ≈400 ppb is achieved with this sensing platform. The morphology, microstructure, and chemical composition of the gate dielectric and CuPc films are analyzed by atomic force microscopy, grazing incident X‐ray diffraction, X‐ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy, revealing that the enhanced sensing performance originates from UVO‐derived hydroxylated species on the dielectric surface and not from chemical reactions between NO₂ and the dielectric/semiconductor components. This work demonstrates that dielectric/semiconductor interface engineering is essential for readily manufacturable high‐performance TFT‐based gas sensors.     

Molecules on Si: Electronics with Chemistry

Basic scientific interest in using a semiconducting electrode in molecule‐based electronics arises from the rich electrostatic landscape presented by semiconductor interfaces. Technological interest rests on the promise that combining existing semiconductor (primarily Si) electronics with (mostly organic) molecules will result in a whole that is larger than the sum of its parts. Such a hybrid approach appears presently particularly relevant for sensors and photovoltaics. Semiconductors, especially Si, present an important experimental test‐bed for assessing electronic transport behavior of molecules, because they allow varying the critical interface energetics without, to a first approximation, altering the interfacial chemistry. To investigate semiconductor‐molecule electronics we need reproducible, high‐yield preparations of samples that allow reliable and reproducible data collection. Only in that way can we explore how the molecule/electrode interfaces affect or even dictate charge transport, which may then provide a basis for models with predictive power. To consider these issues and questions we will, in this Progress Report,

• review junctions based on direct bonding of molecules to oxide‐free Si.
• describe the possible charge transport mechanisms across such interfaces and evaluate in how far they can be quantified.
• investigate to what extent imperfections in the monolayer are important for transport across the monolayer.
• revisit the concept of energy levels in such hybrid systems.

     

Multifunctional Organic‐Semiconductor Interfacial Layers for Solution‐Processed Oxide‐Semiconductor Thin‐Film Transistor

The stabilization and control of the electrical properties in solution‐processed amorphous‐oxide semiconductors (AOSs) is crucial for the realization of cost‐effective, high‐performance, large‐area electronics. In particular, impurity diffusion, electrical instability, and the lack of a general substitutional doping strategy for the active layer hinder the industrial implementation of copper electrodes and the fine tuning of the electrical parameters of AOS‐based thin‐film transistors (TFTs). In this study, the authors employ a multifunctional organic‐semiconductor (OSC) interlayer as a solution‐processed thin‐film passivation layer and a charge‐transfer dopant. As an electrically active impurity blocking layer, the OSC interlayer enhances the electrical stability of AOS TFTs by suppressing the adsorption of environmental gas species and copper‐ion diffusion. Moreover, charge transfer between the organic interlayer and the AOS allows the fine tuning of the electrical properties and the passivation of the electrical defects in the AOS TFTs. The development of a multifunctional solution‐processed organic interlayer enables the production of low‐cost, high‐performance oxide semiconductor‐based circuits.     

Metal oxide blended ZSM-5 nanocomposites as ethanol sensors

Nano-ZSM-5 is synthesized without organic template via microwave-assisted hydrothermal technique. The synthesized nano-ZSM-5 zeolite is blended with metal oxides (ZnO and TiO₂) to have novel composites as ethanol sensors. The composites are characterized by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) techniques. A study on ethanol sensing behaviour of metal oxide blended composite screen-printed thick films is carried out and the effect of metal oxide concentration on various ethanol sensing features, specifically operating temperature, response/recovery time and active region of the sensor, are investigated. XRD and FTIR confirm the blending of metal oxides in ZSM-5 matrix. Both, ZnO and TiO₂ blended, composite films are sensitive to ethanol. It can be concluded that metal oxide blending improves the preformance of sensor for ethanol detection. The response/recovery time and active sensing regions depend upon the concentration of metal oxide in host zeolite. The ZnO/ZSM-5 and TiO₂/ZSM-5 composite films are the excellent ethanol sensors.     

Energy Level Alignment at Metal/Solution‐Processed Organic Semiconductor Interfaces

Energy barriers between the metal Fermi energy and the molecular levels of organic semiconductor devoted to charge transport play a fundamental role in the performance of organic electronic devices. Typically, techniques such as electron photoemission spectroscopy, Kelvin probe measurements, and in‐device hot‐electron spectroscopy have been applied to study these interfacial energy barriers. However, so far there has not been any direct method available for the determination of energy barriers at metal interfaces with n‐type polymeric semiconductors. This study measures and compares metal/solution‐processed electron‐transporting polymer interface energy barriers by in‐device hot‐electron spectroscopy and ultraviolet photoemission spectroscopy. It not only demonstrates in‐device hot‐electron spectroscopy as a direct and reliable technique for these studies but also brings it closer to technological applications by working ex situ under ambient conditions. Moreover, this study determines that the contamination layer coming from air exposure does not play any significant role on the energy barrier alignment for charge transport. The theoretical model developed for this work confirms all the experimental observations.     

PdRh-Sensitized Iron Oxide Ultrathin Film Sensors and Mechanistic Investigation by Operando TEM and DFT Calculation

Metal oxide semiconductor (MOS) thin films are of critical importance to both fundamental research and practical applications of gas sensors. Herein, a high-performance H₂ sensor based on palladium (Pd) and rhodium (Rh) co-functionalized Fe₂O₃ films with an ultrathin thickness of 8.9 nm deposited by using atomic layer deposition is reported. The sensor delivers an exceptional response of 105.9 toward 10 ppm H₂ at 230 °C, as well as high selectivity, immunity to humidity, and low detection limit (43 ppb), which are superior to the reported MOS sensors. Importantly, the Fe₂O₃ film sensor under dynamic H₂ detection is for the first time observed by operando transmission electron microscopy, which provides deterministic evidence for structure evolution of MOS during sensing reactions. To further reveal the sensing mechanism, density functional theory calculations are performed to elucidate the sensitization effect of PdRh catalysts. Mechanistic studies suggest that Pd promotes the adsorption and dissociation of H₂ to generate PdH_x, while Rh promotes the dissociation of oxygen adsorbed on the surface, thereby jointly promoting the redox reactions on the films. A wireless H₂ detection system is also successfully demonstrated using the thin film sensors, certifying a great potential of the strategy to practical sensors.     

ZIF-67修饰WO3纳米片的制备及其气敏性能

金属氧化物半导体气敏传感器在有毒有害气体检测领域逐渐表现出巨大的应用前景,但是金属氧化物半导体传感器通常在检测时受环境湿度影响较大,这极大地限制了其应用。本文采用水热法成功在陶瓷管表面原位生长WO₃纳米片,并以此为基底,在其表面生长ZIF-67多孔材料,通过调控W和Co的比例制备了不同比例的ZIF-67/WO₃复合材料,利用XRD、SEM、FTIR和比表面积测试仪(BET)等方法对所制备的材料进行物相和形貌表征。针对其不同比例的复合材料的气敏性能进行了研究。结果表明:W∶Co摩尔比为 1∶1的ZIF-67/WO₃(1∶1)复合材料性能最好,在220℃对三乙胺表现出优异的选择性,对体积分数为100×10?6的三乙胺的响应值可达140.34,响应和恢复时间分别为9 s和7 s。研究了空气相对湿度(RH)对ZIF-67/WO₃(1∶1)传感器的影响,结果表明,在高达75%RH环境下该材料仍能保持较好的响应值,相对于纯WO₃气敏材料具有较好的抗湿性能。      

Designing Metallic and Insulating Nanocrystal Heterostructures to Fabricate Highly Sensitive and Solution Processed Strain Gauges for Wearable Sensors

All‐solution processed, high‐performance wearable strain sensors are demonstrated using heterostructure nanocrystal (NC) solids. By incorporating insulating artificial atoms of CdSe quantum dot NCs into metallic artificial atoms of Au NC thin film matrix, metal–insulator heterostructures are designed. This hybrid structure results in a shift close to the percolation threshold, modifying the charge transport mechanism and enhancing sensitivity in accordance with the site percolation theory. The number of electrical pathways is also manipulated by creating nanocracks to further increase its sensitivity, inspired from the bond percolation theory. The combination of the two strategies achieves gauge factor up to 5045, the highest sensitivity recorded among NC‐based strain gauges. These strain sensors show high reliability, durability, frequency stability, and negligible hysteresis. The fundamental charge transport behavior of these NC solids is investigated and the combined site and bond percolation theory is developed to illuminate the origin of their enhanced sensitivity. Finally, all NC‐based and solution‐processed strain gauge sensor arrays are fabricated, which effectively measure the motion of each finger joint, the pulse of heart rate, and the movement of vocal cords of human. This work provides a pathway for designing low‐cost and high‐performance electronic skin or wearable devices.     

Superior Self‐Powered Room‐Temperature Chemical Sensing with Light‐Activated Inorganic Halides Perovskites

Hybrid halide perovskite is one of the promising light absorber and is intensively investigated for many optoelectronic applications. Here, the first prototype of a self‐powered inorganic halides perovskite for chemical gas sensing at room temperature under visible‐light irradiation is presented. These devices consist of porous network of CsPbBr₃ (CPB) and can generate an open‐circuit voltage of 0.87 V under visible‐light irradiation, which can be used to detect various concentrations of O₂ and parts per million concentrations of medically relevant volatile organic compounds such as acetone and ethanol with very quick response and recovery time. It is observed that O₂ gas can passivate the surface trap sites in CPB and the ambipolar charge transport in the perovskite layer results in a distinct sensing mechanism compared with established semiconductors with symmetric electrical response to both oxidizing and reducing gases. The platform of CPB‐based gas sensor provides new insights for the emerging area of wearable sensors for personalized and preventive medicine.     

Isoindigo‐Based Polymers with Small Effective Masses for High‐Mobility Ambipolar Field‐Effect Transistors

So far, most of the reported high‐mobility conjugated polymers are p‐type semiconductors. By contrast, the advances in high‐mobility ambipolar polymers fall greatly behind those of p‐type counterparts. Instead of unipolar p‐type and n‐type materials, ambipolar polymers, especially balanced ambipolar polymers, are potentially serviceable for easy‐fabrication and low‐cost complementary metal‐oxide‐semiconductor circuits. Therefore, it is a critical issue to develop high‐mobility ambipolar polymers. Here, three isoindigo‐based polymers, PIID‐2FBT , P1FIID‐2FBT , and P2FIID‐2FBT are developed for high‐performance ambipolar organic field‐effect transistors. After the incorporation of fluorine atoms, the polymers exhibit enhanced coplanarity, lower energy levels, higher crystallinity, and thus increased µ _e. P2FIID‐2FBT exhibits n‐type dominant performance with a µ _e of 9.70 cm² V^?1 s^?1. Moreover, P1FIID‐2FBT exhibits a highly balanced µ _h and µ _e of 6.41 and 6.76 cm² V^?1 s^?1, respectively, which are among the highest values for balanced ambipolar polymers. Moreover, a concept “effective mass” is introduced to further study the reasons for the high performance of the polymers. All the polymers have small effective masses, indicating good intramolecular charge transport. The results demonstrate that high‐mobility ambipolar semiconductors can be obtained by designing polymers with fine‐tuned energy levels, small effective masses, and high crystallinity.     

A General and Straightforward Route to Noble Metal‐Decorated Mesoporous Transition‐Metal Oxides with Enhanced Gas Sensing Performance

Controllable and efficient synthesis of noble metal/transition‐metal oxide (TMO) composites with tailored nanostructures and precise components is essential for their application. Herein, a general mercaptosilane‐assisted one‐pot coassembly approach is developed to synthesize ordered mesoporous TMOs with agglomerated‐free noble metal nanoparticles, including Au/WO₃, Au/TiO₂, Au/NbO_x, and Pt/WO₃. 3‐mercaptopropyl trimethoxysilane is applied as a bridge agent to cohydrolyze with metal oxide precursors by alkoxysilane moieties and interact with the noble metal source (e.g., HAuCl₄ and H₂PtCl₄) by mercapto (? SH) groups, resulting in coassembly with poly(ethylene oxide)‐b‐polystyrene. The noble metal decorated TMO materials exhibit highly ordered mesoporous structure, large pore size (≈14–20 nm), high specific surface area (61–138 m² g^?1), and highly dispersed noble metal (e.g., Au and Pt) nanoparticles. In the system of Au/WO₃, in situ generated SiO₂ incorporation not only enhances their thermal stability but also induces the formation of ε‐phase WO₃ promoting gas sensing performance. Owning to its specific compositions and structure, the gas sensor based on Au/WO₃ materials possess enhanced ethanol sensing performance with a good response (R_air/R_gas = 36–50 ppm of ethanol), high selectivity, and excellent low‐concentration detection capability (down to 50 ppb) at low working temperature (200 °C).     

α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> based nanomaterials as gas sensors

Interest in detecting and determining concentrations of toxic and flammable gases has constantly been on the increase in recent years due to increase of modernization, industrialization and high standards of life. Detection of such gases is very important in many different fields such as industrial emission control, household and social security, vehicle emission control and environmental monitoring. Metal oxide gas sensors are among most important devices to detect a large variety of gases. α-Fe₂O₃, an environmental friendly semiconductor (E _g = 2.1 eV), is the most stable iron oxide under ambient atmosphere and because of its low cost, high stability, high resistance to corrosion, and its environmentally friendly properties is one of the most important metal oxides for gas sensing applications. This is the first review about gas sensing properties of α-Fe₂O₃ nanostructures. In this paper gas sensing properties of α-Fe₂O₃ are extensively reviewed. After a brief explanation about metal oxide gas sensors and α-Fe₂O₃, sensors based on α-Fe₂O₃ nanomaterials have been reviewed. Gas sensing section is divided into five subsections: pure α-Fe₂O₃ gas sensors, metal/α-Fe₂O₃ gas sensors, metal oxide/α-Fe₂O₃ gas sensors, polymer/α-Fe₂O₃ gas sensors and graphene/α-Fe₂O₃ gas sensors.