Carbon Nanotubes Based Devices and Sensors

The dimensionality of a system has a profound influence on its physical behavior, especially for nanostructured materials where at least one of the dimensions is less than 100 nm and, in many instances, the size is comparable with the size of many fundamental physical quantities. Carbon-based nanostructured materials exhibit unique mechanical, electrical, and optical characteristics that may result in many unique device designs. The materials are biocompatible, chemically inert, yet capable of altering electronic properties in presence of some chemical species, dimensionally compatible with bio-molecules, and have interesting electronic characteristics; hence, rendering them as potential chemical and biosensors. A recent heightened awareness of the potential for inadvertent or deliberate contamination of environment and food and agricultural products has made decentralized sensing an important issue for several federal agencies. Recent progress in nanostructured materials and its possible applications in chemical and biological sensors could have a significant impact on data collection, processing, and recognition. Our present and ongoing investigation is aimed towards evaluating the applications of carbon-based nanotubes, nanowires, and nanoporous materials in unique devices and sensors, based on its unique characteristics, morphological flexibility, and biocompatibility.     

碳纳米管的化学修饰

碳纳米管的化学修饰是纳米材料领域的一个重要研究方向.从有机化学修饰和无机化学修饰2个方面评述了碳纳米管化学修饰的发展过程和最新进展,讨论了碳纳米管化学修饰的方法及其对碳纳米管结构性能的影响,并对今后的研究方向进行了展望.     

Acoustic and Optical VOCs Sensors Incorporating Carbon Nanotubes

The authors investigate the sensing properties of single-walled carbon nanotubes (SWCNTs) films, which are used as nanostructured materials for chemical sensors onto three types of transducers using different principles of operation as surface acoustic waves (SAWs), quartz-crystal microbalance (QCM), and a standard silica optical fiber (SOF) for detection of volatile organic compounds at a room temperature. The sensing probes have been configured as 315- and 433-MHz SAW two-port resonator-based oscillator, 10-MHz QCM resonator, and SOF light-reflectometry-based system at a wavelength of 1310 nm. A nanocomposite film of SWCNTs embedded in a cadmium-arachidate matrix was deposited by Langmuir-Blodgett (LB) technique onto the SAW sensors. An LB multilayer of SWCNTs-onto-CdA buffer material was also deposited onto the QCM and SOF sensors. The experiments demonstrate that carbon-nanotubes acoustic and optical sensors are highly sensitive to a wide range of polar and nonpolar organic solvents up to a sub-ppm detection limit at a room temperature.     

Ultralow-Power Alcohol Vapor Sensors Using Chemically Functionalized Multiwalled Carbon Nanotubes

Alcohol sensors, batch fabricated by forming bundles of chemically functionalized multiwalled carbon nanotubes (f-CNTs) across Au electrodes on SiO₂/Si substrates using an AC electrophoretic technique, were developed for alcohol vapor detection using an ultralow input power of ~ 0.01 - 1 muW, which is lower than the power required for most commercially available alcohol sensors by more than four orders of magnitude. The multiwalled carbon nanotubes (MWCNTs) have been chemically functionalized with the COOH groups by oxidation. We found that the sensors are selective with respect to flow from air, water vapor, and alcohol vapor. The sensor response is linear for alcohol vapor concentrations from 1 to 21 ppm with a detection limit of 0.9 ppm. The transient response of these sensors is experimentally shown to be ~1 s and the variation of the responses at each concentration is within 10% for all of the tested sensors. The sensors could also easily be reset to their initial states by annealing the f-CNTs sensing elements at a current of 100-200 muA within ~ 100-200 s. We demonstrated that the response of the sensors can be increased by one order of magnitude after adding the functional group COOH onto the nanotubes, i.e., from ~0.9% of a bare MWCNTs sensor to ~9.6% of an f-CNTs sensor with a dose of 21 ppm alcohol vapor.     

化学气相沉积法制备碳纳米管

碳纳米管（CNTs）是一种具有独特理化性能和结构的一维纳米材料,也是当今纳米材料研究的焦点之一．在化学、生物、医药、能源、电子元件等诸多领域具有极高的应用价值．本文以有机溶剂环己烷为碳源．利用化学气相沉积法（CⅥ））在管式电阻炉内,以氩气为栽气,二茂铁为催化剂,一定温度条件下,制备了直径约为50nm,长度达几十微米以上的多壁碳纳米管（MWNTs）．采用拉曼光谱、扫描电镜、透射电镜、X-射线粉末衍射等测试手段,表征了碳纳米管的微观形貌和结构特征．通过对实验结果的分析和讨论,对CVD制备法中碳纳米管的生长机理进行了尝试性探讨。     

Noise-Enhanced Detection of Subthreshold Signals With Carbon Nanotubes

Electrical noise can help pulse-train signal detection at the nanolevel. Experiments on a single-walled carbon nanotube transistor confirmed that a threshold exhibited stochastic resonance (SR) for finite-variance and infinite-variance noise: small amounts of noise enhanced the nanotube detector's performance. The experiments used a carbon nanotube field-effect transistor to detect noisy subthreshold electrical signals. Two new SR hypothesis tests in the Appendix also confirmed the SR effect in the nanotube transistor. Three measures of detector performance showed the SR effect: Shannon's mutual information, the normalized correlation measure, and an inverted bit error rate compared the input and output discrete-time random sequences. The nanotube detector had a threshold-like input-output characteristic in its gate effect. It produced little current for subthreshold digital input voltages that fed the transistor's gate. Three types of synchronized white noise corrupted the subthreshold Bernoulli sequences that fed the detector. The Gaussian, the uniform, and the impulsive Cauchy noise combined with the random input voltage sequences to help the detector produce random output current sequences. The experiments observed the SR effect by measuring how well an output sequence matched its input sequence. Shannon's mutual information used histograms to estimate the probability densities and computed the entropies. The correlation measure was a scalar inner product of the input and output sequences. The inverted bit error rate computed how often the bits matched between the input and output sequences. The observed nanotube SR effect was robust: it persisted even when infinite-variance Cauchy noise corrupted the signal stream. Such noise-enhanced signal processing at the nanolevel promises applications to signal detection in wideband communication systems and biological and artificial neural networks     

碳纳米管

概述了碳纳米材料的发展及它们的性能和应用,同时介绍了一些比较成熟的制备纳米材料的技术。在此基础上分析了碳纳米管的形成过程和碳纳米管的微观结构,以及碳纳米管制备工艺对微观结构的影响。     

定向碳纳米管薄膜的制备

以二茂铁为催化剂前驱体,氢气为载气,乙炔为碳源,硅片作衬底,用化学气相沉积法,采用不同的催化剂引入方式,在700℃下分别制备出定向碳纳米管薄膜及非定向碳纳米管薄膜.并基于实验结果对影响生长定向碳纳米管的因素进行分析,表明催化剂颗粒的诱导作用是导致生长定向碳纳米管的重要原因.     

化学气相沉积法合成碳纳米管及其导电性能研究

以二甲硫醚为碳源前驱体,Co/MgO为催化剂,采用化学气相沉积法生长出碳纳米管及Y形碳纳米管,此法稳定性及重现性较好.通过扫描电子显微镜、透射电子显微镜、拉曼光谱及X射线衍射对产品形态和结构进行了分析和表征,结果表明,所制备的碳纳米管形态较规整、纯度较高,具有较好的石墨微晶结构;导电性能测试结果显示,Y形碳纳米管各分支均呈现出典型的金属性导电性能.     

Chemical Detection in Water by Single-Walled Carbon Nanotubes-Based Optical Fiber Sensors

In this letter, the possibility to use single-walled carbon nanotubes (SWCNTs) as sensitive nanostructured material for the development of an optoelectronic sensor that can perform chemical detection in water has been investigated and demonstrated for the first time. The fabricated sensor has been employed in a reflectometric system involving single wavelength reflectance measurements. The good stability of the steady-state signal, the high sensitivity, as well as the good response dynamics obtained in the case of toluene detection confirm the potentiality of SWCNTs to be employed in a water environment.     

Polymer-Coated Fiber Bragg Grating Sensors for Simultaneous Monitoring of Soluble Analytes and Temperature

A new fiber-optic sensor for simultaneous measurement of water-soluble analytes and temperature with polymer-coated fiber Bragg gratings (FBGs) is proposed. As an application of the approach, simultaneous monitoring of the concentration of sugar or potassium chloride (KCl) and temperature has been achieved. Changes in these environmental parameters result in different extents of either red- or blue-shifts of the Bragg resonance wavelengths of the gratings. It has been found that polyimide-coated FBG responds to variations of both temperature and concentrations of soluble analytes, while acrylate-coated FBG is sensitive to environmental temperature only. The experimental results showed that the temperature sensitivity of the acrylate-coated FBG, temperature, sugar, and KCl concentration sensitivities of the polyimide-coated FBG are 0.0102 $~hbox{nm}/^{circ}hbox{C}$ , 0.0094 $hbox{nm}/^{circ}hbox{C}$, 0.0012 $hbox{nm}/^{circ}hbox{Bx}$ , and 0.0126 nm/M, respectively. The sensing mechanism of the polyimide-coated FBG lies in the hygroscopic properties of the polyimide coating, which result in the change of the strain of the fiber and, thus, the optical properties of the grating. Since the sensor detects the analytes that swell the polyimide coating and different analytes induce different swelling effects, the sensor can detect different analytes without prior knowledge once a calibration curve is developed.      

预置镍化学气相沉积法制备定向碳纳米管(英文)

采用化学气相沉积法(CVD),在溅射了镍薄膜的硅基底上制备了定向碳纳米管薄膜。对镍薄膜的氨气预处理过程及其机理进行了研究。结果发现预处理后的岛状区域随着薄膜厚度的增加而增加,纳米粒子区域的变化则与之相反。对5nm的镍薄膜进行预处理能获得细化和均匀分布的纳米粒子,有利于定向碳纳米管的生长。碳纳米管的生长过程及其细微结构与温度有很大关系。碳源的分解、碳原子在催化剂内部的扩散以及催化剂粒子的团聚三者之间的竞争决定了碳纳米管的生长情况。本文分析了碳纳米管的顶部生长模式及该模式下催化剂粒子的形态变化。     

化学气相沉积法合成碳纳米管的研究进展

本文主要评述了化学气相沉积法合成碳纳米管的最新研究进展，结合我们在这方面的工作，重点讨论了催化剂、碳源、反应温度对合成碳纳米管质量和产率的影响，并对这一领域的发展趋势作了展望。     

稀土酞菁化学修饰竹节状的多壁碳纳米管

采用氨基稀土酞菁与纯化的竹节状碳纳米管发生酰胺反应的方法制备了稀土酞菁化学修饰的碳纳米管,并采用红外吸收光谱和热分析方法对产物的化学结构进行了表征,证明了复合体系中酰胺反应的发生.紫外可见光谱分析表明稀土酞菁与碳纳米管间存在强烈的电子相互作用.通过透射电镜观察化学修饰后的碳纳米管的形貌特征时,发现稀土酞菁大多呈竹节状分布在碳管壁上,其原因是由于竹节状碳管的结构特征和化学修饰的选择性造成的.     

Carbon Nanotubes Coated Acoustic and Optical VOCs Sensors: Towards the Tailoring of the Sensing Performances

This work is focused on the room temperature sensitivities and response times analysis against aromatic volatile organic compounds of both silica optical fiber and quartz crystal microbalance sensors, coated by single-walled carbon nanotubes (SWCNTs) Langmuir-Blodgett multilayers as highly sensitive nanomaterials. The fabricated samples have been characterized by means of X-ray diffraction, high-resolution transmission electron microscopy and scanning electron microscopy, silica optical fiber, and quartz crystal microbalance transducers have been simultaneously exposed at room temperature to toluene and xylene individual vapors in the ppm range. For each transducer type, a time division multiplexing approach has been exploited, enabling the simultaneous interrogation of up to 8 optical and 6 acoustic probes, respectively. The results obtained indicate that both optical and acoustic sensors provide very high reproducibility and sensitivity either towards toluene or xylene, with a resolution of few hundreds of ppb. Furthermore, sensitivities and response times turned out to be dependent on the particular analytes used for the vapors testing. Both transducer types demonstrate a similar response time, while with regard the recovery time, the optical detection seems to be significantly faster than the electrical counterpart. The effect of the SWCNTs monolayers number on sensors sensitivity and response time has also been investigated, demonstrating the possibility to enhance the performances of the proposed transducers by tailoring the geometric properties of the sensitive nanomaterial.     

纳米碳管的纯化

纳米碳管是一种新型的纳米材料和碳分子 ,其独特的分子结构和性能引起了人们的广泛关注。纳米碳管的纯化是纳米碳管研究领域的一个重要课题。本文综述了纳米碳管的几种纯化方法及其相关机理。     

纳米碳管的研究发展概况

从材料学的角度简要地介绍了新型纳米材料──纳米碳等的发现、结构、制各方法、性能以及在物理学、化学、材料学等领域的可能应用。     

钴/碳纳米管催化剂CVD法制备碳纳米管

以乙烯为碳源、多壁碳纳米管为载体负载钴作为催化剂,利用CVD法制备出了高质量的多壁碳纳米管.利用扫描电子显微镜(SEM)对催化剂的形貌进行了表征,利用透射电子显微镜(TEM)、X射线衍射仪(XRD)以及差热-热重(TG-DTA)方法对产物进行了表征.发现在最佳裂解温度770℃下制备的多壁碳纳米管直径分布均匀、曲率小、纯净、产率高,更重要的是不具有难处理的氧化物(如Al2O3)载体,充分体现了碳纳米管作为载体的优越性.     

化学修饰对多壁碳纳米管电学性质的影响

采用混酸和二甲亚砜对碳纳米管进行官能化修饰，实验发现经化学修饰后对多壁碳纳米管膜的电学性质有明显影响。经化学修饰后的碳纳米管膜电阻由结电阻和管电阻组成，未经化学修饰的碳纳米管膜电阻主要由碳纳米管管电阻决定。碳纳米管经化学修饰后，碳纳米管结增多，碳纳米管管电阻降低而碳纳米管结电阻增大。未经修饰的碳纳米管膜电阻随着温度的升高而略有增大，呈金属性；经混酸修饰的碳纳米管膜电阻随着温度的升高而减小，呈半导体性。