Formation of well-packed TiO<Subscript>2</Subscript> nanoparticles on multiwall carbon nanotubes using CVD method to fabricate high sensitive gas sensors

Titanium oxide nanoparticles were coated on multiwall carbon nanotubes (MWCNTs) using an atmospheric pressure chemical vapor deposition (CVD) to achieve highly compact nanoparticles of about 5 nm on CNT structure. The CNTs with a diameter of about 50 nm were grown by plasma enhanced CVD. Gas sensitivity of the fabricated structure was investigated and compared with TiO₂/CNT composite-based gas sensors. The effect of the structural interaction between the nanoparticles and the CNT wall on sensing mechanism of the as-prepared gas sensors was investigated. Ultrasensitive gas sensors were obtained by TiO₂/CNT nanostructures with strong interaction between the MWCNT and the TiO₂ nanoparticles. The measurements show high chemical activity and exceptional electrical response of the as-prepared structure being exposed to gases. Scanning and transmission electron microscopy and X-ray diffraction analysis were used to obtain structural information.     

Preparation and characterisation of ZnFe2O4/ZnO polymer nanocomposite sensors for the detection of alcohol vapours

During the last 10 years, a large interest has developed in the preparation of nanocomposite structures by embedding inorganic nanoparticles into polymeric materials. These materials combine the properties of the inorganic fillers with the processability and flexibility of polymers. The versatility of polymer nanocomposite systems is of special interest to the gas sensor industry where arrays of polymer/carbon black composites have been used to identify gases and odours. These polymer gas sensors provide selectivity based on their chemical structures and operate at room temperature, which provide advantages over thick-film metal oxide gas sensors. ZnFe₂O₄ and ZnO have excellent stability, high sensitivity, low fabrication complexity and moderate operating temperatures, which are ideal properties for a gas sensing material. In this work, the development of a thick-film ZnFe₂O₄/ZnO sensor, which operates at room temperature and a drop-coated conducting polymer composite sensor containing 30 w/w% ZnFe₂O₄/ZnO nanoparticles is discussed. The sensors were tested in a fully automated test rig and showed promising results for the detection of alcohol vapours.     

Sono-synthesis approach of reduced graphene oxide for ammonia vapour detection at room temperature

In this paper, we report the sono-synthesis of reduced graphene oxide (rGO) using polyethyleneimine (PEI), and its performance for ammonia vapour detection at room temperature. Graphene oxide (GO) and reduced graphene oxide (rGO) were prepared by sonication method by using low-frequency ultrasound under ambient condition and films were deposited by Doctor Blade method. The rGO, which has vapour accessible structure showed a good sensing response with a minimum detection limit of 1 ppm and the detection range from 1 ppm to 100 ppm. The sensing response was found to be 2% at 1 ppm and 34% at 100 ppm of ammonia and the developed sensor operated at room temperature. The sensor displays a response time of 6 s and a recovery time of 45 s towards 100 ppm of ammonia vapour. The source for the highly sensitive, selective and stable detection of ammonia with negligible interference from other vapours is discussed and reported. We believe reduced graphene oxide (rGO) could potentially be used to manufacture a new generation of low-power portable ammonia sensors.     

碳纳米管/聚二甲基硅氧烷复合薄膜的制备及力敏特性研究

针对传感器的敏感单元发展需求,提出了一种碳纳米管复合材料.该材料是以碳纳米管作为填充粒子,结合聚二甲基硅氧烷(PDMS)有机基体,采用超声共混方法制备的一种新型传感器敏感元件.详细分析研究了复合材料的制备工艺参数,以及在不同工艺参数下该复合材料的力敏特性.扫描电镜测试表明碳纳米管在PDMS中分散均匀且镶嵌良好.通过对不同体积分数的碳纳米管与PDMS复合材料进行电学性能测试,研究薄膜的"力-电阻"和"力-电容"耦合性能,测试了薄膜结构的力敏效应.计算得到复合薄膜材料的压阻灵敏度因子达到40,压电容灵敏度因子达到70.实验研究表明,通过改变碳纳米管与PDMS的比例,可以很好地调节其电子输运特性以及电阻和电容的应力敏感特性,可以为该类型的力敏材料在不同的力敏传感技术领域提供新的研究思路.     

The role of defects in chemical sensing properties of carbon nanotube films

The electrical resistance of 24 different carbon nanotube (CNT) thin film samples in blowing ambient air and 10 different analyte vapor environments was measured. The effects of the CNT growth method, different chemical treatments, ball milling, sample preparation conditions and Ar⁺-ion irradiation are compared. Significant differences in the response signal curves as a function of time in the case of the studied sensor/vapor combinations show the important role of the defect structure and attached functional groups in the chemical sensing properties of CNTs.     

单根Sb掺杂ZnO微米线非平衡电桥式气敏传感器的制作与性能

通过使用化学气相沉积法,成功制备出超长、大尺寸的Sb掺杂ZnO微米线.基于非平衡电桥原理,利用单根Sb掺杂ZnO微米线作为非平衡电桥的一个桥臂,制作出了可以在室温环境下工作的气敏传感器原型器件.结果表明:室温下测得该传感器对20,50,100和200 ppm(1 ppm=10^-6)不同浓度的丙酮及乙醇气体的响应-恢复曲线均呈现为矩形形状,在空气及被测气体中均有稳定的电流值,并随着探测气体浓度的增大,器件的响应值也在逐渐增加.此外,还发现器件对丙酮气体具有更好的选择性,当丙酮气体浓度为200 ppm时,该传感器的响应时间为0.2 s,恢复时间为0.3 s,响应度高达243%.通过与普通电导式气敏传感器对比发现,采用这种非平衡电桥结构传感器可以明显地提高响应度,使响应和恢复时间更快.此外,还研究了器件的气体探测机理.     

International patenting activity in the field of carbon nanotubes

Carbon nanotubes (CNT) are unique nanostructures with remarkable electronic and mechanical properties and could be used, for example, in nanometre-sized electronics or to strengthen polymer materials. Today, both SWNT and MWNT are being used as key components in the production of high-strength composites, and advanced sensors, electronic and optical devices, catalysts, batteries and fuel cells.Patenting activity in this sub-field of nanotechnology registered a spurt during the last 12 years––implying a breakthrough bringing about a technological paradigm shift in the field of fullerene since carbon nanotubes are fullerene-related structures. CNT is, thus, one of the key technologies likely to revolutionize information technology, materials and medicine and the present study aim to examine technological developments in this field based on international patenting activity during the period of 1991–2003.     

Single and networked CuO nanowires for highly sensitive p‐type semiconductor gas sensor applications

Development of high‐performance p‐type semiconductor based gas sensors exhibiting fast‐response/recovery times with ultra‐high response are of major importance for gas sensing applications. Recent reports demonstrated the excellent properties of p‐type semiconducting oxide for various practical applications, especially for selective oxidation of volatile organic compounds (VOCs). In this work, sensors based on CuO nanowire (NW) networks have been successfully fabricated via a simple thermal oxidation process on pre‐patterned Au/Cr pads. Our investigation demonstrates high impact of the process temperature on aspect ratio and density of copper oxide NWs. An optimal temperature for growth of thin and densely packed NWs was found to be at 425 °C. The fabricated sensors demonstrated ultra‐high gas response by a factor of 313 to ethanol vapour (100 ppm) at an operating temperature of 250 °C. High stability and repeatability of these sensors indicate the efficiency of p‐type oxide based gas sensors for selective detection of VOCs. A high‐performance nanodevice was fabricated in a FIB‐SEM system using a single CuO NW, demonstrating an ethanol response of 202 and rapid response and recovery of ～198 ms at room temperature. The involved gas sensing mechanism of CuO NW networks has been described. We consider that the presented results will be of a great interest for the development of higher‐performance p‐type semiconductor based sensors and bottom‐up nanotechnologies. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Electrodeposition and characteristics of Ni80Fe20/Cu composite wires

Electrodeposited Ni₈₀Fe₂₀/Cu composite wire has significant advantages over amorphous wire as sensing element for weak magnetic field sensors, such as orthogonal fluxgate sensors, due to its non-ferromagnetic and conductive core structure. In this study, the key processing parameters are investigated, including electrodeposition current density, duty cycle, electrolyte solution, pH value, applied magnetic field, effect of seeded layers, and post annealing.     

Nano-porous indium oxide transistor sensor for the detection of ethanol vapours at room temperature

Porous indium oxide thin film prepared by the dip coating technique has been used in the construction of a field effect transistor. The coating solution was prepared from indium chloride precursor. The average particle size of the dip coated thin film was found to be 25 nm. Scanning electron microscopic images show the porous nature of the film, and the root mean square roughness of the film calculated using atomic force microscope was 24 nm. A transistor has been constructed by evaporating metal Aluminium as source and drain electrodes on the indium oxide active layer and employing the silicon substrate itself as a gate. The sensor response of the constructed transistor was tested with ethanol, ammonia and acetone vapours. The sensor showed good response to ethanol vapours even at 5-ppm level, and the time for response and recovery of the gas was nearly 1 min. Response to ammonia and acetone was comparatively poor. When the gate voltage was increased from 0 to 300 mV, a considerable increase in the source-drain current was observed. As the temperature of the sensing element increased, response to ethanol vapours also increased. There was nearly a linear variation in the transistor response for 100 ppm of ethanol vapours when the gate voltage was swept from 0 to 300 mV. The sensor response of the transistor increases with the gas concentration. The constructed transistor was found to be selectively sensitive to ethanol; therefore it can be implemented to work as a breath alcohol checker.     

二自由度反射式光纤传感探头的结构设计

采用五光纤特殊排列方式,研制了全自动补偿光纤二自由度传感探测器.分析了二自由度的探测方法,给出了可能的结构排列方案.理论上,给出了探测响应函数,与实验结果进行了对比.可用于二自由度非接触测量场合。     

Probing induced defects in individual carbon nanotubes using electrostatic force microscopy

Structural defects greatly affect the electronic properties of single wall carbon nanotubes (CNT’s), for instance by increasing the sensitivity to their environment; an effect which can be utilized for better performance of CNT based chemical sensors. Here we show that electrostatic force microscopy (EFM) can be used as a non-invasive technique for probing defects in individual CNT’s supported on insulating substrates. The technique is demonstrated by monitoring the change in EFM signal upon intentionally inducing defect by an oxygen plasma etch, and is applied to assess the quality of as-grown CNT samples and to study the effect of exposing CNT’s to the low energy electron irradiation of a scanning electron microscope (SEM). PACS 68.37.-d; 68.37.Ps; 61.46.Fg; 68.35.Dv     

Classical-Noise-Free Sensing Based on Quantum Correlation Measurement

Quantum sensing,using quantum properties of sensors,can enhance resolution,precision,and sensitivity of imaging,spectroscopy,and detection.An intriguing question is:Can the quantum nature(quantumness)of sensors and targets be exploited to enable schemes that are not possible for classical probes or classical targets?Here we show that measurement of the quantum correlations of a quantum target indeed allows for sensing schemes that have no classical counterparts.As a concrete example,in the case that the second-order classical correlation of a quantum target could be totally concealed by non-stationary classical noise,the higher-order quantum correlations can single out a quantum target from the classical noise background,regardless of the spectrum,statistics,or intensity of the noise.Hence a classical-noise-free sensing scheme is proposed.This finding suggests that the quantumness of sensors and targets is still to be explored to realize the full potential of quantum sensing.New opportunities include sensitivity beyond classical approaches,non-classical correlations as a new approach to quantum many-body physics,loophole-free tests of the quantum foundation,et cetera.     

DFT studies of CNT–functionalized uracil-acetate hybrids

Calculations based on density functional theory (DFT) have been performed to investigate the stabilities and properties of hybrid structures consisting of a molecular carbon nanotube (CNT) and uracil acetate (UA) counterparts. The investigated models have been relaxed to minimum energy structures and then various physical properties and nuclear magnetic resonance (NMR) properties have been evaluated. The results indicated the effects of functionalized CNT on the properties of hybrids through comparing the results of hybrids and individual structures. The oxygen atoms of uracil counterparts have been seen as the detection points of properties for the CNT–UA hybrids.     

金属基底光纤光栅应变传感器的传感特性研究

为了满足桥梁和大坝等民用建筑和航空航天飞行器等结构的健康监测与管理需要,设计并制作了两种分别用钛合金和不锈钢材料封装的光纤布拉格光栅应变传感器,并利用悬臂梁校准装置对两种传感器的应变特性进行测试。试验结果表明,钛合金封装的线性度及应变灵敏系数优于不锈钢材料封装的传感器。因此,在对结构的应变监测时,使用钛合金封装的传感器更能真实反映结构的应变变化,从而达到健康监测的目的。     

Micro traps for quantum information processing and precision force sensing

We review recent experimental progress towards quantum information processing and precision force sensing using neutral atoms in micro traps. Microscopic potential structures as generated by optical or electronic microstructures (micro traps) allow for a versatile manipulation of quantum states of atoms and of ultracold atomic quantum gases. Most recent experimental results include the implementation of single‐qubit‐operations in both, optical and magnetic micro traps, as well as in the demonstration of matter‐wave interferometer using Bose‐Einstein condensates coherently split in micro traps.     

Elucidating iron doping induced n- to p- characteristics of Strontium titanate based ethanol sensors

A series of pure and iron doped strontium titanate, (SrFe_xTi_1-xO₃; x = 0, 0.1 and 0.2) powders were synthesized, characterized and used to fabricate ethanol sensors for low concentration. X-Ray Diffraction (XRD) technique was used to confirm the single phase formation. Microstructural properties of the powders were investigated using scanning electron microscopy (SEM). Electrical conductivity of all the samples at room temperature (RT) was measured. Sensors were optimized for best responsiveness by varying the operating temperature from 350 °C to 500 °C.The sensor with doping x = 0.2 exhibited best sensing response at 400 °C for ethanol gas. The undoped sensor demonstrated a decrease in resistance on exposure to ethanol gas whereas Fe-doped sensors showed increase in resistance. The doping induced changeover from n to p behavior in the sensing response on doping has been investigated and corroborated with an observed shift in the Fermi level position by X-ray photoelectron spectroscopy (XPS). The disparity in gas sensing response clearly demonstrates inter-connection of multiple influencing factors such as electrical conductivity, morphology, porosity and change in chemical composition on doping. The sensors were exposed to ethanol, nitrogen dioxide, carbon monoxide, butane gases at concentration between 5 ppm and 50 ppm. The sensor exhibited much reduced relative response to all gases other than ethanol which can be utilized for wide range of applications.     

波分复用串联的布里渊散射分布式光纤传感器

在一定分辨率和响应时间要求下，应用波分复用技术来串联布里渊散射分布式光纤传感器，解决了同时进行传感和通信存在的信号干扰.具体是采用波分复用来隔离传感光信号与通信光信号，同时应用光相干外差接收来分离传感与通信之间的电信号频谱.实现了两台布里渊散射分布式光纤传感器之间的串联，单台传感器的传感距离为25 km，串联后达到50 km.     

保偏微纳光纤倏逝场传感器

近年来,保偏微纳光纤以其高双折射特性和强倏逝场效应引起了研究者的关注.本文从保偏微纳光纤的结构类型、制备方法和模式双折射特性等出发,介绍了目前不同类型保偏微纳光纤倏逝场传感器的构造特征与实现方法,利用保偏微纳光纤在两个垂直偏振方向的倏逝场对外界的不同响应,可制成偏振相关的干涉型或光栅型等传感器件.本文探究了包括超高折射率灵敏度特性和温度不敏感特性等的内在产生机理,并考察了保偏微纳光纤倏逝场传感器在折射率、湿度、磁场和特异性DNA分子探测等方面的应用,其结果对微纳光纤及其传感器的研究和应用具有重要的意义.     

ZnO纳米薄膜及其声表面波传感器的制备与特性研究

结合RF磁控溅射和水热合成法制备ZnO纳米结构薄膜,利用XRD及SEM分析ZnO薄膜的晶体结构和形貌、XPS分析薄膜的化学组分。结果表明,在适当的条件下,所制备的ZnO薄膜为具有良好c轴取向的纳米棒状结构,且ZnO纳米棒薄膜表面吸附的氧原子及晶格的氧空位缺陷增多。利用所制备ZnO纳米棒薄膜的上述特性,将其作为气体敏感材料。分别沉积于128°YX-LiNbO₃和36°YX-LiTaO₃基片,研制多层结构的声表面波(Rayleigh波和Love波)氢气传感器,并进行室温条件下氢气的实时传感检测,结果显示所研制的Love波传感器具有更高的灵敏度,性能更优化。