金红石相TiO_2(110)面吸附H_2S分子光学气敏效应的微观机制与特性

光学气敏材料吸附气体分子后导致光学性质发生变化,运用这一原理来检测环境中的气体成分,称为光学气敏效应。采用基于密度泛函理论(DFT)体系下的第一性原理平面波超软赝势方法,研究了光学气敏材料金红石相TiO2(110)表面吸附H2S分子的微观特性,计算了TiO2(110)表面吸附能、电荷密度、态密度和光学性质的变化。结果表明,TiO2最稳定的表面是终止于二配位O原子的(110)面,只有含有氧空位的表面才能稳定吸附H2S,且氧空位比例越高,越有助于H2S吸附于表面;表面吸附H2S以水平吸附方式为主,在氧空位比例达到33%时,吸附能为0.7985eV;吸附的实质是表面氧空位具有氧化性,氧化了H2S分子。在可见光400~760nm范围内,存在氧空位的TiO2(110)表面吸附H2S后都可改善表面的光学性质。氧空位缺陷浓度越高,改善材料对可见光的吸收和反射能力越强,光学气敏响应能力越佳。     

氧化钨基室温气敏传感器的研究进展

氧化钨(WO_3)基半导体气体传感器对NO_2等气体具有较好的气敏特性。为了将传感器工作温度降低至室温,研究者们尝试了各种方法,如合成新型纳米材料、紫外光和可见光照射等。主要介绍了近年来WO_3基气敏材料在室温条件下其气敏性能的最新研究进展,展现了近年来WO_3基室温气体传感器的最新研究成果。并提出通过合成具有p-n异质结构的材料、开发新型纳米结构、增加材料中氧空位浓度以减小材料带隙宽度有可能是WO_3室温气体传感器下一下阶段的研究重点。     

CeO2气敏材料的研究进展

二氧化铈(CeO2)具有独特的萤石型晶体结构、优秀的储放氧能力、良好的化学稳定性以及高温下氧空位的快速扩散能力,在有毒有害气体检测方面被广泛关注和研究。然而,纯CeO2气敏传感器工作温度偏高且响应恢复时间长,无法满足越发严苛的实际环境监测需求。综述了近年来国内外关于纳米CeO2气敏材料相关研究进展,根据不同的机理从结构调控、掺杂复合两个方面重点对CeO2的改性进行分析,简述了其在柔性传感领域的应用,为高性能气敏传感器的深入研究提供参考。     

电压敏电容双功能元件制备

为提高元件半导化原理并提高元件的氧气灵敏度,对以SrTiO3为基材的样品分别在强还原气体条件和大气条件下的N型电压敏、电容双功能元件和P型氧气敏感元件,分别测试了N型元件的压敏电压U1mA等电参数和P型元件在不同的温度下的阻温特性、氧敏特性,并进行了TPD测量。研究表明氧空位是在SrTiO3晶体中杂质扩散、实现半导化的重要条件,因此控制氧空位的浓度成为制备钙钛矿型半导体功能陶瓷元件的重要因素;还原气氛烧结产生的氧空位是材料实现N型半导化的重要手段;受主杂质所产生的氧空位促进了环境氧与晶格氧的交换,是材料实现P型半导化的重要手段,也提高了元件的氧气灵敏度。     

N/Rh共掺杂金红石TiO_2表面对CO气体光学气敏传感特性的影响

采用基于密度泛函理论的第一性原理平面波超软赝势方法计算了金红石TiO_2(110)纯净表面以及掺杂N、掺杂Rh和N/Rh共掺表面吸附CO分子后的光学气敏传感特性。研究发现:纯净和掺杂表面吸附CO分子后均表现出光学气敏传感特性,其原因是表面氧空位的氧化作用;而N/Rh共掺杂对表面氧化性改善得最多,吸附CO分子后吸附距离最小,吸附能最大,稳定性最好,且易于实现。因此,相比于纯净及单掺杂体系,N/Rh共掺杂表面对气体有更好的光学气敏传感效应,是一种改进TiO_2光学气敏传感材料的良好方式。     

Cr对钙钛矿型氧敏材料性能的影响

利用固相合成法制备了不同Cr含量的氧敏陶瓷样品,研究了添加剂Cr对钙钛矿型氧敏材料性能的影响,测量了不同氧分压下的阻–温特性和氧敏特性。结果表明:在SrTiO3中Cr离子替钛位可使SrTiO3实现p型掺杂;Cr掺杂促进了氧空位的产生,加强环境氧与晶格氧的交换,提高了氧灵敏度,使其达到9;Cr离子变价增加了空穴载流子浓度,提高了材料的电导率,使电阻值降低到几千欧。     

氧化锌纳米纤维的制备及其氨气气敏特性

采用静电纺丝技术制备了具有多孔结构的ZnO纳米纤维，通过扫描电子显微镜(SEM)、X射线衍射(XRD)和X射线能量色散谱(EDS)对ZnO纳米纤维的形貌、晶体结构和组成成分进行了表征。将上述材料制成气体传感器，对氨气进行了气敏性能测试。实验结果表明，由ZnO纳米纤维制成的气体传感器在室温下对氨气具有较高的灵敏度和较低的检测限，对300ppm氨气的响应值约为65%,响应时间和恢复时间分别为70 s和60 s,对10ppm氨气的响应值约为3.3%,并且具有良好的选择性和长期稳定性。由于ZnO纳米纤维表面形成了特殊的多孔结构，为氧化还原反应提供了更多的氧空位和活性位点，有利于气体的吸附，提高了传感器对氨气的气敏性能，使其在实际应用中极具前景。     

锐钛矿型TiO2(101)面吸附CO2分子的光学气敏传感机理

对金属氧化物光学气敏传感材料TiO2的探索与应用是当前研究的热点问题。采用基于密度泛函理论(DFT)中的平面波超软赝势方法, 模拟计算CO2分子在锐钛矿型TiO2(101)表面的吸附行为, 对吸附能, 吸附距离, 电子态密度以及光学性质进行分析。结果表明: CO2分子在含O空位表面的吸附效果优于无氧空位表面, 且表面O空位的浓度越高, 吸附效果越明显;分子平行于表面放置模型的吸附能为正值, 吸附后的结构稳定, 且以O端吸附为主, 为此, 分子平行于表面放置O端吸附于含两个O空位表面为最可能吸附模型;对电子态密度分析发现, 当最佳模型吸附稳定后, 含O空位表面为P型杂质, 又有CO2分子中的2p电子掺入, 在费米能级附近出现新峰值, 改善了TiO2材料的光学性质, 体现出较好的光学气敏传感特性。     

离子注入技术在气敏材料上的应用

离子注入技术已被应用于气敏材料的开发研究，这是离子注入技术的一个较新的应用领域。本文介绍离子注入技术对气敏材料表面层组分、结构、电导率及气敏特性进行改性的研究进展。     

掺杂纳米SnO2气敏传感器的研究进展

介绍了半导体气敏传感器的发展历史和掺杂纳米SnO2气敏传感器的特性与应用；详细分析了掺杂金属单质、金属氧化物和稀土元素对SnO2气敏性的影响，通过掺杂可以显著改善其对特定气体的灵敏度、稳定性和选择性等参数；利用元件表面的氧吸附理论分析掺杂纳米SnO2的气敏机理；展望了SnO2气敏传感器的发展前景。     

Semiconducting-oxide chemical sensors

The Taguchi and thick-film forms of semiconducting metal-oxide sensors and their reproducibility and stability problems are discussed. An attempt to circumvent these problems by producing a modified thin-film sensor based on oxygen absorption rather than adsorption is described. The sensor is made with evaporated bismuth molybdate, which has a very high diffusion constant for oxygen vacancies. The combustion gas to be sensed extracts lattice oxygen from the bismuth molybdate; atmospheric oxygen restores the lattice oxygen. Because the oxygen vacancies move rapidly in the material, the bulk stoichiometry (i.e. metal/oxygen ratio) follows the surface stoichiometry and controls the resistance. Bismuth molybdate films are stable and, as prepared, are highly sensitive to alcohols. Techniques for improving selectivity are considered. The use of electronic circuitry to circumvent inherent sensor problems is examined     

ZnO Nanotetrapods: Controlled Vapor‐Phase Synthesis and Application for Humidity Sensing

A systematic study on controlled synthesis of ZnO nanotetrapods by combining metal‐vapor transport, oxidative nucleation/growth, fast‐flow quenching, and water‐assisted cleaning is reported. The technique developed in this work makes possible the fabrication of ZnO nanotetrapods with different morphologies, with arm diameters down to 17 nm, and with arm lengths ranging from 50 nm up to a few micrometers. The octa‐twin model is verified for the growth of the ZnO nanotetrapods. Photoluminescence (PL) studies indicate a higher level of surface and subsurface oxygen vacancies for smaller ZnO nanotetrapods. The ZnO nanotetrapods are first used for the fabrication of resistor‐type humidity sensors, which show high sensitivity, quick response/recovery, long lifetime, and a wide range of humidity response. These favorite characteristics of the humidity sensors are ascribed to the unique morphology of the nanotetrapods, which can create a film with faceted pores and large internal surfaces.     

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.     

水溶性聚苯胺/SmBaCuMO_(5+δ)(M=Cu,Zn)材料的制备与氨敏性能研究

采用化学氧化法制备了水溶性聚苯胺(PANI),溶胶–凝胶法制备了SmBaCuMO5+δ(M=Cu,Zn;SBCM)粉体,用微粒填充法制备了PANI/SBCM复合材料。利用傅里叶变换红外光谱法(FT-IR)、XRD、TEM对产物进行了分析表征,研究了PANI/SBCM元件的氨敏性能。结果表明,PANI/SBCM元件在室温下对NH3具有良好的灵敏性,同条件下PANI/SmBaCuCuO5+δ(SBCC)元件的氨敏性能优于PANI/SmBaCuZnO5+δ(SBCZ)元件。室温条件下,PANI/SBCC元件对体积分数为100×10–6的NH3的最大灵敏度为7.29,具有高的灵敏度和选择性,且性能稳定。     

Ce:YIG薄膜中氧空位对光吸收性能的影响

讨论了Ce替代石榴石薄膜制备条件对其光吸收性能的影响.通过引入氧空位概念,提出了溅射气氛中的氧含量对薄膜中Ce元素价态影响的理论模型.基于该模型,讨论了Ce：YIG晶体中氧空位的产生机理.研究表明,当晶格中存在过量氧空位时,会导致部分Fe^3＋被还原成Fe^2＋,使得薄膜的光吸收显著增大.实验结果证实,在Ce：YIG薄膜的晶化过程中,采用富氧气氛可以使得薄膜中Ce元素的价态以Ce^3＋离子为主而Ce^4＋离子含量较少,从而有效降低薄膜的光吸收.溅射气氛中的氧含量及后续热处理过程中氧含量的大小均会直接影响Ce：YIG薄膜的光吸收特性.     

Epitaxial graphene gas sensors on SiC substrate with high sensitivity

2D material of graphene has inspired huge interest in fabricating of solid state gas sensors.In this work,epitaxial graphene,quasi-free-standing graphene,and CVD epitaxial graphene samples on SiC substrates are used to fabricate gas sensors.Defects are introduced into graphene using SF6 plasma treatment to improve the performance of the gas sensors.The epitaxial graphene shows high sensitivity to NO2 with response of 105.1%to 4 ppm NO2 and detection limit of 1 ppb.The higher sensitivity of epitaxial graphene compared to quasi-free-standing graphene,and CVD epitaxial graphene was found to be related to the different doping types of the samples.     

Manipulating the Sensitivity and Selectivity of OECT‐Based Biosensors via the Surface Engineering of Carbon Cloth Gate Electrodes

Organic electrochemical transistors (OECTs) provide the opportunity to fabricate flexible biosensors with high sensitivity. However, there are currently very few methods to improve the selectivity of OECT sensors. In this work, nitrogen/oxygen‐codoped carbon cloths (NOCCs) are prepared by the carbonization of polyaniline‐wrapped carbon cloths at 750 °C under different atmospheres. The resulting NOCC electrodes exhibit different electrochemical sensing behaviors toward ascorbic acid (AA) and dopamine (DA), enabling the fabrication of OECT sensors with high sensitivity and selectivity that are comparable to the state‐of‐the‐art OECT sensors for AA and DA. The structural characterization and theoretical calculation reveal that the electrochemical sensing behaviors of the NOCC electrodes are closely related to their surface compositions, providing an unprecedented strategy for the design of flexible OECT sensors with high sensitivity and selectivity.     

Regulating the Unhybridized O 2p Orbitals of High-Performance Li-Rich Mn-Based Layered Oxide Cathode by Gd-Doping Induced Bulk Oxygen Vacancies

Li-rich Mn-based layered oxides (LRLOs) with ultrahigh specific capacities are promising cathode materials for high energy density lithium-ion batteries. Nevertheless, severe irreversible oxygen release, structure degradation, capacity and voltage attenuation hinder their commercialization due to the uncontrollable oxygen redox chemistry originated from unhybridized O 2p orbitals. Herein, a strategy to generate bulk oxygen vacancies is proposed. And bulk oxygen vacancies are constructed by lowering the formation energy of oxygen vacancies in LRLOs via Gd-doping. The energy level and the amount of unhybridized O 2p states are reduced to partly inhibit the oxygen redox activity. Surprisingly, the oxygen redox is not fully activated in the first cycle and is further activated in the second cycle. Moreover, the reduced oxygen redox activity significantly suppresses the oxygen release, lattice volume change, layered-to-spinel phase transition. As a result, the amount of oxygen gas release is reduced from 98.80 to ≈0 nmol mg⁻¹ in the first cycle. Superior cycle stability of 90.4% capacity retention after 300 cycles and small voltage decay of only 1.013 mV per cycle are achieved. This study provides a valuable bulk oxygen vacancies strategy to regulate the unhybridized O 2p orbitals for designing high-performance Li-rich Mn-based layered oxide cathode materials.