碳湿敏膜的非线性感湿特性和导电机理

采用羟乙基纤维素（HEC）和导电炭黑并添加山梨醇增湿剂制备碳湿敏膜,研究了膜在偏离结露区的非线性感湿特性和导电机理.扫描电镜观测到,膜中炭黑粒子形成网链状的空间导电结构;2%炭黑含量使膜的导电通路处于渗流区,膜电阻在80%RH附近对湿度有较强的非线性特性.分析I-V曲线认为,是导电网链中炭黑粒子的间距使膜电阻对湿度变化和测量电压的变化都非常敏感,非线性感湿特性与导电机理密切相关.复阻抗谱表明,碳湿敏样品在33%RH时只出现与炭黑体电阻有关的半圆弧,在80%RH时出现与炭黑粒界电 关键词： 碳湿敏膜 逾渗阈值 I-V特性')" href="#">I-V特性 复阻抗谱     

The state of the carbon vapour in the regenerative sooting discharge

Formation of the regenerative soot is the process of recycling and introduction of the cathode deposited carbon clusters into the discharge. The agglomerates of carbon clusters on the cathode release their constituents into the plasma that goes from the pure sputtering mode to the sooting one. The process of the regeneration of the soot that emits large carbon clusters is discussed by evaluating the state of the carbon vapour by using the characteristic line emissions from the discharge. Received 17 April 2001 and Received in final form 13 June 2001     

Synthesis and growth mechanism of carbon nanotubes and nanofibers from ethanol flames

The ethanol flame was successfully used to synthesize highly graphitic hollow-cored carbon nanotubes (CNTs) and novel disorder solid-cored carbon nanofibers (CNFs). Their morphologies were characterized by using scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy. It was found that the mixture of CNTs and CNFs were grown on Ni-contained substrates, whereas only the CNFs were produced on carbon steel and low alloy steel substrates. It has been established that Ni and its compounds play a key role in CNTs growth and Fe and its compounds in CNFs growth. The models of 'hollow-cored mechanism' and 'solid-cored mechanism' were proposed to explain the present CNTs and CNFs formations, based on the theory that 'Fe has a strong affinity for carbon and Ni has a weak affinity for carbon'. It is expected that the present ethanol flame may provide a much simpler and more economic approach for mass-production of CNTs and CNFs by using large flame or multi-flames.     

Quantum-mechanical investigation of field-emission mechanism of a micrometer-long single-walled carbon nanotube

A quantum-mechanical simulation is carried out to investigate the charge distribution and electrostatic potential along a 1 microm long (5,5) single-walled carbon nanotube under realistic field-emission experimental conditions. A single layer of carbon atoms is found sufficient to shield most of the electric field except at the tip where strong field penetration occurs. The penetration leads to a nonlinear decrease of potential barrier for emission, which is equally responsible for the low threshold voltage besides the well-known geometrical field enhancement factor.     

空心微球/网络复合型碳泡沫材料制备与机理分析

在Klett等人于2000年制备的韧带网络型碳泡沫和Bruneten等人在2002年制备了一种空心微球碳泡沫材料结构的基础上,分别经过微观结构优化、碳化、石墨化处理,制备出了一种空心微球/网络复合型碳泡沫材料.扫描电镜和体视显微镜测试结果显示网络韧带和球形空腔呈现明显的空间周期性.X射线衍射(X-ray diffraction,XRD)图谱中,26°处的衍射峰表明该试样具有较高的石墨化特征.同时,对该材料的形成机理进行了分析. 关键词： 碳泡沫 微观结构优化 扫描电镜 X射线衍射     

Humidity sensing properties of different single-walled carbon nanotube composite films fabricated by layer-by-layer self-assembly technique

Poly(diallyldimethylammonium chloride)/single-walled carbon nanotube (PDDA/SWNT) multilayered thin films were prepared on quartz crystal microbalance by layer-by-layer self-assembly technique, and their sensing properties to humidity were studied. The SWNTs were characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The composite films were observed by field-emission scanning electron microscope. Two types of SWNT humidity sensors were fabricated using SWNTs and carboxyl (COOH) modified SWNTs as sensitive material, respectively. The results showed that the sensitivity of the PDDA/SWNT?CCOOH humidity sensor was 20.23?% higher than that of the PDDA/SWNT sensor. In contrast, the latter had a much superior hysteresis property, and the reason to cause this phenomenon was discussed.     

The pick-up mechanism in composite particle emission processes

The pick-up mechanism has been included in the exciton model for the light composite particle emissions. Based on the cluster phase space integration method the formation probabilities of α,d, t,³He are obtained. The calculation results of (n, t) cross sections indicate that this theoretical method can reproduce the experimental data nicely. For triton emissions in pre-equilibrium reaction processes, the semi-direct reactions are the dominant terms which are just omitted in the previous model calculation.     

Morphology of carbon nanotubes prepared via chemical vapour deposition technique using acetylene: A small angle neutron scattering investigation

Small angle neutron scattering (SANS) has been utilized to study the morphology of the multi-walled carbon nanotubes prepared by chemical vapour deposition of acetylene. The effects of various synthesis parameters like temperature, catalyst concentration and catalyst support on the size distribution of the nanotubes are investigated. Distribution of nanotube radii in two length scales has been observed. The number density of the smaller diameter tubes was found more in number compared to the bigger one for all the cases studied. No prominent scaling of the structure factor was observed for the different synthesis conditions.      

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.     

Synthesis and ethanol sensing properties of Al-doped ZnO nanofibers

Undoped and Al-doped ZnO nanofibers were synthesized via a simple electrospinning method, and then characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman scattering and photoluminescence (PL) spectroscopy. The ethanol sensing properties of the sensor based on the nanofibers were also investigated. The results show that the sensor fabricated from Al-doped ZnO nanofibers exhibits better gas sensing performance than that fabricated from the undoped ZnO nanofibers, and the gas sensing mechanism is discussed.     

Synthesis of SnO2/ZnO composite nanofibers by electrospinning method and study of its ethanol sensing properties

In this paper, we report the synthesis of SnO₂/ZnO composite nanofibers via electrospinning method. Polyvinyl alcohol (PVA)/zinc acetate/stannous chloride nanofibers were electrospun using a solution containing PVA, zinc acetate and stannous chloride in distilled-water followed by calcination at 650 °C for 2 h, obtaining the related composite nanofibers. The nanofibers were characterized by simultaneous thermal analysis (STA), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and Fourier Transform Infrared spectroscopy (FTIR). Ethanol sensing of the nanofibers showed a good and desirable sensing behavior such as high sensitivity, quick response and recovery times.     

单壁碳纳米管储氢研究

摘要 利用Gaussian03程序计算出C-H键的键能是1.88eV,键长是0.113nm。已知H-H键能是4.748eV,键长是0.074nm。显然, H-H键能大于C-H键的键能,所以在常温常压下碳纳米管储氢时,以物理吸附H2分子为主,化学形式的C-H键吸附为辅。另外,利用LJ势能函数,计算了H2分子在碳纳米管中C原子所成的六边形中心正上方、C原子正上方以及相邻两C原子中间正上方时H2分子与碳纳米管之间的势能。得到无论管内、管外或者两端,都是H2分子在C原子所成的六边形中心正上方时能量最低。且在管内时H2分子距离管壁的距离是0.320nm,在管外时距离管壁的距离是0.309nm;在两端的管内时距离管壁的距离是0.324nm,在两端的管外时距离管壁的距离是0.313nm。     

单壁碳纳米管储氢研究

利用Gaussian03程序计算出C-H键的键能是1.88 eV,键长是0.113 nm.已知H-H键能是4.748 eV,键长是0.074 nm.显然,H-H键能大于C-H键的键能,所以在常温常压下碳纳米管储氢时,以物理吸附H_2分子为主,化学形式的C-H键吸附为辅.另外,利用LJ势能函数,计算了H_2分子在碳纳米管中C原子所成的六边形中心正上方、C原子正上方以及相邻两C原子中间正上方时H_2分子与碳纳米管之间的势能.得到无论H_2分子是被吸附到管内或管外,还是被吸附到中间区域或两端区域,都是H_2分子在C原子所成的六边形中心正上方时能量最低.当H_2分子被吸附到碳纳米管中间区域时,管内和管外的H_2分子距管壁的距离分别是0.320 nm和0.309 nm;而当H_2分子被吸附到碳纳米管两端区域时,这两个距离分别是0.324 nm和0.313 nm.     

TEM investigation on the growth mechanism of carbon nanotubes synthesized by hot-filament chemical vapor deposition

Carbon nanotubes (CNTs) were synthesized using hot-filament chemical vapor deposition on Ni film-coated Si substrate. The CNTs were well-aligned perpendicular to the substrate. The as-grown CNTs were bamboo-like in their morphology, and were investigated using SEM and high-resolution transmission electron microscopy (HRTEM). The SEM and HRTEM studies show that the both ends of a CNT contain metallic catalytic particles, which is different from results previously reported. Our analysis results provide strong evidence that the metallic catalyst remains in a liquid state during nanotube growth. The upward-growth pulling force of the CNT layer elongates the liquid nanoparticles, which are finally broken into two parts. One part remains at the substrate surface (base of the CNTs) and is responsible for the catalytic growth of the CNTs. The other part is enclosed at the tip of the CNTs and is inactive during CNT growth.     

Plasmonic effects in composite metal nanostructures for sensing applications

We have investigated numerically the plasmonic effect on a two-dimensional periodic array of metallic nanostructures. The unit cell of the array has an Ag nanosphere and nanorod pair formed in a single structure. Three-dimensional finite element method is used for the study on the sensing performance within the optical spectra. The study takes into account the influences of the structural and material parameters, the rotational angle of the metal nanostructure, the number of metal nanostructure per unit cell, and the localized surface plasmon resonances. The proposed nanostructures function as a refractive index sensor with a sensitivity of 400 nm/RIU (RIU is the refractive index unit), showing the characteristics of low transmittance (T?=?3.90%), high absorptance (A?=?94.5%), and near-zero reflectance (R?=?0.15%), could be achieved by a triangular arrangement of nanostructures within a unit cell. We also show how the tailoring of the structural parameters relates to the specific sensing schematics of the sensor.

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Graphical abstract x-y sectional plane of electric field intensity, electric force lines (pink lines), energy flows (green arrows) and surface charge density of type 2, corresponding to the surrounding testing medium of (a) n=1.00 and (b) n=1.33 around the PMNSs.

     

Spectrally dispersed femtosecond CARS investigation of vibrational characteristics in ethanol

Spectrally dispersed femtosecond time‐resolved coherent anti‐Stokes Raman spectroscopy is applied to study the ultrafast vibrational dynamics in ethanol at room temperature. The anti‐Stokes intensities were monitored as a function of delay time and wavenumber. By simply changing the timing of the laser pulses, the vibrational dynamics between the excited Raman transitions in ethanol molecules can be tracked and detected. Copyright © 2014 John Wiley & Sons, Ltd.     

Spectroscopic investigation of the mechanism of C2 formation in various types of discharges in a carbon dioxide atmosphere

Discharges in hollow carbon and molybdenum cathodes have been studied in atmospheres of O₂, CO₂, and also of He and Ar mixed with air. The experimental data and results of other studies provide the basis for a discussion of the most probable mechanism of C₂ radical formation.     

乙醇-水团簇分子形成激基缔合物及荧光发射机理研究

紫外光照射具有特殊结构的长链式乙醇-水团簇分子时,处于激发态和基态的分子形成了分子间激基缔合物,并发射荧光.根据实验结果分析和能量转移理论可知,激发态单分子和激基缔合物间形成了电子迁移洛合物并发生了能量转移.根据Mulliken理论对电子迁移洛合物进行量子力学处理,得出了团簇分子在基态和激发态能量E^b_N和E^b_E以及由于电子迁移而引起的静电相互作用能E^s;根 关键词： 荧光光谱 激基缔合物 电子迁移 乙醇-水团簇     

The investigation of carbon nitride films annealed at different temperatures

The effects of thermal annealing on the component and microstructure of carbon nitride films deposited by vacuum cathodic arc method are reported. The bonding structure of the films is investigated by Raman spectroscopy, FTIR, XPS and valence band XPS. Upon annealing, the N content of the film drops gradually from original 31.0 to 17.0 at.% at 600 °C. The results of Raman spectroscopy, FTIR and valence XPS demonstrate that the films below 500 °C mainly consist of aromatic cluster component and polymeric component, which is rather stable upon the increasing of anealing temperatures. With the further increasing of the annealing temperatures from 400 to 600 °C, the fraction of polymeric component decreases and the aromatic component develops greatly. Meanwhile the films tend to transform towards the fullerene-like microstructure, which can be seen from the large separation of the N 1s peaks (>2.0 eV). As a result the N sp³ C bonds increase due to the rising of cross-linking between the graphite plane.