Ultrasensitive Detection of VOCs Using a High‐Resolution CuO/Cu2O/Ag Nanopattern Sensor

The p‐type semiconducting copper oxides (CuO and Cu₂O) are promising materials for gas sensors, owing to their characteristic oxygen adsorption properties and low operation temperature. In this study, the sensing performance of a CuO‐based chemiresistor is significantly enhanced by incorporating Ag nanoparticles on high‐resolution p‐type CuO/Cu₂O nanopattern channels. The high‐resolution CuO/Cu₂O/Ag nanochannel is fabricated using a unique top‐down nanolithographic approach. The gas response (ΔR/R_a) of the CuO/Cu₂O/Ag gas sensor increases by a maximum factor of 7.3 for various volatile organic compounds compared with a pristine CuO/Cu₂O gas sensor. The sensors exhibit remarkable sensitivity (ΔR/R_a = 8.04) at 125 parts per billion (ppb) for acetone analytes. As far as it is known, this is the highest sensitivity achieved for p‐type metal oxide semiconductor (MOS)‐based gas sensors compared to previous studies. Furthermore, the outstanding gas responses observed in this study are superior to the most of n‐type MOS‐based gas sensors. The high sensitivity of the sensor is attributed to i) the high resolution (≈30 nm), high aspect ratio (≈12), and ultrasmall grain boundaries (≈10 nm) of the CuO/Cu₂O nanopatterns and ii) the electronic sensitization and chemical sensitization effects induced by incorporating Ag nanoparticles on the CuO/Cu₂O channels.     

氧化铜纳米棒的水热合成及其气敏性能研究

以Cu(NO3)2·3H2O为铜源,氢氧化钠为pH调节剂,CTAB为表面活性剂,在150℃下水热反应24h成功制备出氧化铜纳米棒。通过TEM,XRD对其进行了表征。结果表明:所制得的材料为具有单斜晶系的氧化铜纳米棒,其长度为300～500nm,直径为40～50nm。通过静态配气法,对其在不同工作温度下的气敏性能进行了研究。发现:采用p型氧化铜纳米棒所制得的元件在250℃下,对体积分数为50×10–6的氯气有较好的气敏性能,灵敏度为4.5,响应/恢复时间为8s/40s。     

Tuning the Morphology of Isoindigo Donor–Acceptor Polymer Film for High Sensitivity Ammonia Sensor

Monitoring the ammonia gas is of great interest to both environmental benefits and human health. The recent advance in polymer thin film transistors (TFTs) can realize high sensitivity and low‐cost gas sensors. Ammonia gas interacts with charge carrier channels and polymer/dielectrics interface through Coulomb force. This is the first report of high sensitivity and reusable ammonia sensor fabricated from thiophene‐isoindigo donor–acceptor conducting polymer. This kind of polymer has advantages of simple synthesis and excellent air stability. The systematic study is carried out to investigate relationship among chemical structure variation and morphology control of polymer to the performance of ammonia sensor. High crystallinity, favored crystal orientation, and direct percolation routes for analytes are found to be essential to increase the susceptibility of polymers to ammonia gas. By strengthening edge‐on morphology, the sensitivity can be enhanced fivefold for the same polymer. The idea can put forward the development of sensor array in a time‐efficient manner by employing the morphology effect.     

Effect of silver additive on electrical conductivity and methane sensitivity of SnO2

A composite powder of tin oxide (SnO₂) and silver (Ag) clusters was prepared by a simple and cost effective method of reducing their aqueous mixture with sodium borohydride (NaBH₄). Gas sensors based on the composite were made by powder pressing procedure and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrical conductivity and gas sensing behavior of the sensors for methane (CH₄) gas were studied as a function of Ag concentration (0.3, 0.5, 0.8 and 1.5 wt%). The Ag additive is found to improve sensor response and widen its working temperature range with notable sensor response. The best sensor response was achieved by the sensor with 0.5 wt% Ag. The enhanced response was proved to be due to both electrical and chemical mechanisms.     

Mo Doping Induced More Active Sites in Urchin‐Like W18O49 Nanostructure with Remarkably Enhanced Performance for Hydrogen Evolution Reaction

Exploring highly efficient and inexpensive hydrogen evolution reaction (HER) electrocatalysts for various electrochemical energy conversion technologies is actively encouraged. Herein, a 3D urchin‐like Mo‐W₁₈O₄₉ nanostructure as an efficient HER catalyst is reported for the first time. The obtained Mo‐W₁₈O₄₉ catalyst exhibits excellent electrocatalytic activity toward HER with small onset potential and Tafel slope. The prepared Mo‐W₁₈O₄₉ electrode shows excellent durability after a long period. Density functional theory calculations reveal that the remarkably enhanced performance of Mo‐W₁₈O₄₉ can be due to the ability of Mo dopant to increase the number of active sites, leading to optimal hydrogen adsorption on the active sites because of the electronic and geometric modulation. In addition, the urchin‐like 3D morphology with a high surface area and abundant 1D nanowires promotes electron transfer, thereby ensuring fast interfacial charge transfer to improve electrocatalytic reactions. All these experimental and theoretical results clearly reveal that Mo‐W₁₈O₄₉ intrinsically improves HER activity and thus has potential applications in water splitting.     

金属氧化物气敏元件的研究进展

气敏传感器在现代工农业、信息技术、环境监测等领域都有重要应用。随着这几个领域的发展,人类对其综合性能要求越来越强,进而不断积极改良气敏传感器的性能。金属氧化物气敏元件是利用金属氧化物半导体的表面电阻遇到被测气体发生变化的原理制成的电子器件,其选择性和稳定性是研究气敏元件的两项重要指标。文章概述了金属氧化物元件气敏特性的研究进展,介绍了基体材料、掺杂材料、气敏材料的制备工艺、电极材料及结构等几个因素对元件气敏特性的主要影响,并对各种因素的作用机理进行了分析。最后展望了金属氧化物气敏元件的发展前景。     

Label‐Free Bioanalysis Based on Low‐Q Whispering Gallery Modes: Rapid Preparation of Microsensors by Means of Layer‐by‐Layer Technology

Low‐Q‐whispering gallery modes (low‐Q‐WGM) can be used for label‐free detection of interactions between biomolecules, measuring their binding and release kinetics or for analysis of changes in the medium in real‐time. The main advantage of the low‐Q‐WGM approach over other label‐free methods is the possibility of measurements in small cavities as the method uses microparticles down to 6 µm as sensors. Commercially available dye‐doped microparticles that are used as low‐Q‐WGM sensors exhibit several drawbacks. Therefore, alternative particle types are developed and optimized as low‐Q‐WGM sensors. First, dye‐doped particles made of different materials are screened. The most critical parameter for WGM performance is the refractive index (RI) of sensor particles. Furthermore, surface roughness of particles, determined by scanning electron microscopy and atomic force microscopy, affects their performance as WGM microsensors. In the second test, fluorescent dyes immobilized on nonfluorescent particles by means of nanometer thick layer‐by‐layer (LbL) films are shown to generate a strong WGM signal. The LbL‐coated particles show remarkably less background fluorescence than dye‐doped particles and are easier to prepare. Finally, this article proposes rapid preparation methods for WGM microparticle sensors based on various parameters such as material type, RI, surface roughness, and number of coated polymer layers.     

基于单片机的分布式无线气体监测装置

针对目前市场上气体检测设备存在检测种类单一、可调性差、适用性较低等问题,设计了一种根据实际需要,用户可自由选择检测气体种类的无线气体检测系统。该系统由MQ系列气体传感器、ADC0809、STC89C52、NRF905无线收发模块和LCD显示等构成。测试证明,当传感器检测到气体浓度超标时,实现系统自动报警。     

The Role of Sulfur in the Synthesis of Novel Carbon Morphologies: From Covalent Y‐Junctions to Sea‐Urchin‐Like Structures

A detailed characterization, using high resolution electron microscopy/microanalysis (SEM, TEM, HRTEM, and EDX), reveals tubular carbon nanostructures exhibiting complex and fascinating morphologies. The materials were obtained by sulfur‐assisted chemical vapor deposition. It is demonstrated that S not only acts on the catalyst, but also can be detected in the carbon lattice of the nanostructures. The experimental data presented here confirms the critical role of S, which is responsible for inducing curvature and therefore influencing the final carbon nanostructure morphology. In particular, different types of covalent Y‐junctions of CNTs and even sea urchin‐like nanostructures were produced and their experimental conditions are listed and discussed.     

MoS2 Van der Waals p–n Junctions Enabling Highly Selective Room‐Temperature NO2 Sensor

Van der Waals p–n junctions of 2D materials present great potential for electronic devices due to the fascinating properties at the junction interface. In this work, an efficient gas sensor based on planar 2D van der Waals junctions is reported by stacking n‐type and p‐type atomically thin MoS₂ films, which are synthesized by chemical vapor deposition (CVD) and soft‐chemistry route, respectively. The electrical conductivity of the van der Waals p–n junctions is found to be strongly affected by the exposure to NO₂ at room temperature (RT). The MoS₂ p–n junction sensor exhibits an outstanding sensitivity and selectivity to NO₂ at RT, which are unavailable in sensors based on individual n‐type or p‐type MoS₂. The sensitivity of 20 ppm NO₂ is improved by 60 times compared to a p‐type MoS₂ sensor, and an extremely low limit of detection of 8 ppb is obtained under ultraviolet irradiation. Complete and very fast sensor recovery is achieved within 30 s. These results are superior to most of the previous reports related to NO₂ detection. This work establishes an entirely new sensing platform and proves the feasibility of using such materials for the high‐performance detection of gaseous molecules at RT.     

Low‐Temperature Growth of SnO2 Nanorod Arrays and Tunable n–p–n Sensing Response of a ZnO/SnO2 Heterojunction for Exclusive Hydrogen Sensors

Uniform SnO₂ nanorod arrays have been deposited at low temperature by plasma‐enhanced chemical vapor deposition (PECVD). ZnO surface modification is used to improve the selectivity of the SnO₂ nanorod sensor to H₂ gas. The ZnO‐modified SnO₂ nanorod sensor shows a normal n‐type response to 100 ppm CO, NH₃, and CH₄ reducing gas whereas it exhibits concentration‐dependent n–p–n transitions for its sensing response to H₂ gas. This abnormal sensing behavior can be explained by the formation of n‐ZnO/p‐Zn‐O‐Sn/n‐SnO₂ heterojunction structures. The gas sensors can be used in highly selective H₂ sensing and this study also opens up a general approach for tailoring the selectivity of gas sensors by surface modification.     

Highly Selective SAM–Nanowire Hybrid NO2 Sensor: Insight into Charge Transfer Dynamics and Alignment of Frontier Molecular Orbitals

Organic–inorganic hybrid gas sensors can offer outstanding performance in terms of selectivity and sensitivity towards single gas species. The enormous variety of organic functionalities enables novel flexibility of active sensor surfaces compared to commonly used pure inorganic materials, but goes along with an increase of system complexity that usually hinders a predictable sensor design. In this work, an ultra‐selective NO₂ sensor is realized based on self‐assembled monolayer (SAM)‐modified semiconductor nanowires (NWs). The crucial chemical and electronic parameters for an effective interaction between the sensor and different gas species are identified using density functional theory simulations. The theoretical findings are consistent with the experimentally observed extraordinary selectivity and sensitivity of the amine‐terminated SnO₂ NW towards NO₂. The energetic position of the SAM–gas frontier orbitals with respect to the NW Fermi level is the key to ensure or impede an efficient charge transfer between the NW and the gas. As this condition strongly depends on the gas species and the sensor system, these insights into the charge transfer mechanisms can have a substantial impact on the development of highly selective hybrid gas sensors.     

High‐Performance,Transparent Thin Film Hydrogen Gas Sensor Using 2D Electron Gas at Interface of Oxide Thin Film Heterostructure Grown by Atomic Layer Deposition

A high‐performance, transparent, and extremely thin (<15 nm) hydrogen (H₂) gas sensor is developed using 2D electron gas (2DEG) at the interface of an Al₂O₃/TiO₂ thin film heterostructure grown by atomic layer deposition (ALD), without using an epitaxial layer or a single crystalline substrate. Palladium nanoparticles (≈2 nm in thickness) are used on the surface of the Al₂O₃/TiO₂ thin film heterostructure to detect H₂. This extremely thin gas sensor can be fabricated on general substrates such as a quartz, enabling its practical application. Interestingly, the electron density of the Al₂O₃/TiO₂ thin film heterostructure can be tailored using ALD process temperature in contrast to 2DEG at the epitaxial interfaces of the oxide heterostructures such as LaAlO₃/SrTiO₃. This tunability provides the optimal electron density for H₂ detection. The Pd/Al₂O₃/TiO₂ sensor detects H₂ gas quickly with a short response time of <30 s at 300 K which outperforms conventional H₂ gas sensors, indicating that heating modules are not required for the rapid detection of H₂. A wide bandgap (>3.2 eV) with the extremely thin film thickness allows for a transparent sensor (transmittance of 83% in the visible spectrum) and this fabrication scheme enables the development of flexible gas sensors.     

High Performance Three‐Dimensional Chemical Sensor Platform Using Reduced Graphene Oxide Formed on High Aspect‐Ratio Micro‐Pillars

The sensing performance of chemical sensors can be achieved not only by modification or hybridization of sensing materials but also through new design in device geometry. The performance of a chemical sensing device can be enhenced from a simple three‐dimensional (3D) chemiresistor‐based gas sensor platform with an increased surface area by forming networked, self‐assembled reduced graphene oxide (R‐GO) nanosheets on 3D SU8 micro‐pillar arrays. The 3D R‐GO sensor is highly responsive to low concentration of ammonia (NH₃) and nitrogen dioxide (NO₂) diluted in dry air at room temperature. Compared to the two‐dimensional planar R‐GO sensor structure, as the result of the increase in sensing area and interaction cross‐section of R‐GO on the same device area, the 3D R‐GO gas sensors show improved sensing performance with faster response (about 2%/s exposure), higher sensitivity, and even a possibly lower limit of detection towards NH₃ at room temperature.     

Zn/Co金属有机框架的制备及其对正丁醇的气敏特性

采用水热法合成了Co3O4、ZnO和Zn/Co金属有机框架(Zn/Co-MOF)纳米结构。利用扫描电子显微镜(SEM)和X射线衍射仪(XRD)对其形貌和晶体结构进行了表征,分析结果表明制备的Zn/Co-MOF为边长约300 nm的立方体结构。制备了基于Co3O4、ZnO和Zn/Co-MOF纳米结构的气体传感器,并对正丁醇进行了气敏性能研究。实验结果表明:三种气体传感器对正丁醇均有明显的响应,其中Zn/Co-MOF气体传感器的气敏性能最优。Zn/Co-MOF气体传感器最佳工作温度为200℃,其对体积分数为1×10^-4正丁醇气体的灵敏度为59.18,响应/恢复时间分别约为39 s和40 s。同时,Zn/Co-MOF传感器还具有良好的选择性、重复性和长期稳定性。     

Synthesis and Characterization of Chromium‐Doped Mesoporous Tungsten Oxide for Gas Sensing Applications

SBA‐15 (2D hexagonal structure) and KIT‐6 (3D cubic structure) silica materials are used as templates for the synthesis of two different crystalline mesoporous WO₃ replicas usable as NO₂ gas sensors. High‐resolution transmission electron microscopy (HRTEM) studies reveal that single‐crystal hexagonal rings set up the atomic morphology of the WO₃ KIT‐6 replica, whereas the SBA‐15 replica is composed of randomly oriented nanoparticles. A model capable of explaining the KIT‐6 replica mesostructure is described. A small amount of chromium is added to the WO₃ matrix in order to enhance sensor response. It is demonstrated that chromium does not form clusters, but well‐distributed centers. Pure WO₃ KIT‐6 replica displays a higher response rate as well as a lower response time to NO₂ gas than the SBA‐15 replica. This behavior is explained by taking into account that the KIT‐6 replica has a higher surface area as demonstrated by Brunauer–Emmett–Teller analyses and its mesostructure is fully maintained after the screen‐printing step involved in sensors preparation. The presence of chromium in the material results in a shorter response time and improved sensor response to the lowest NO₂ concentrations tested. Electrical differences related to mesostructure are reduced as a result of additive introduction.     

Synthesis and characterization of CuO–SnO2 nanocomposite and its application as liquefied petroleum gas sensor

Present paper reports the synthesis of CuO–SnO₂ nanocomposite via sol–gel route as a sensing material for a liquefied petroleum gas (LPG). X-ray diffraction analysis confirmed the formation of CuO–SnO₂ nanocomposite. Crystallite size was found 5 nm. The optical band gap of the nanocomposite was found 4.1 eV. The thin/thick films were fabricated using spin coating and screen printing technology respectively and investigated with the exposition of LPG at room temperature (25 °C). Surface morphology of the thin film exhibits that it has a number of gas adsorption sites. The sensitivities of the thick and thin film sensors were found 4.1 and 42 respectively. The response and recovery times of the fabricated film sensor were 180 and 200 s respectively. Maximum sensor response of thin film sensor was found 4100. Better sensitivity and percentage sensor response, small response and recovery times, and good reproducibility and stability recognize the fabricated thin film of CuO–SnO₂ as a challenging material for the detection of LPG.     

Bubble‐Decorated Honeycomb‐Like Graphene Film as Ultrahigh Sensitivity Pressure Sensors

Recently, macroporous graphene monoliths (MGMs), with ultralow density and good electrical conductivity, have been considered as excellent pressure sensors due to their excellent elasticity with a rapid rate of recovery. However, MGMs can only exhibit good sensitivity when the strain is higher than 20%, which is undesirable for touch‐type pressure sensors, such as artificial skin. Here, an innovative method for the fabrication of freestanding flexible graphene film with bubbles decorated on honeycomb‐like network is demonstrated. Due to the switching effect depended on “point‐to‐point” and “point‐to‐face” contact modes, the graphene pressure sensor has an ultrahigh sensitivity of 161.6 kPa^?1 at a strain less than 4%, several hundred times higher than most previously reported pressure sensors. Moreover, the graphene pressure sensor can monitor human motions such as finger bending and pulse with a very low operating voltage of 10 mV, which is sufficiently low to allow for powering by energy‐harvesting devices, such as triboelectric generators. Therefore, the high sensitivity, low operating voltage, long cycling life, and large‐scale fabrication of the pressure sensors make it a promising candidate for manufacturing low‐cost artificial skin.     

一种提高气敏元件热稳定性的优化设计

本文提出一种新的具有较好热稳定性的气敏元件结构。在这种结构里,气敏元件的输出无需外接取样电阻即可获得。文中对现有气敏元件和新型结构气敏元件的热稳定性作了理论分析和实验对比。本设计也适用于其它类型半导体气敏元件。     

H2S气体传感器的进展

综述了Ｈ２Ｓ半导体气体传感器的制备及敏感机理，添加剂ＣｕＯ化合物可以明显提高对Ｈ２Ｓ气体的灵敏度与选择性，最后，介绍了一种似乎合理的敏感机制。