新型有序纳米碳管阵列的合成、表征及电化学性能

用模板法合成纳米碳管阵列(ordered carbon nanotubes arrays,OCNT)。利用XRD、氮气吸附、电镜、 循环伏安技术对样品的结构和电化学性能进行表征。样品孔结构具有典型的二维六角(p6mm)有序分布,比 表面积高达1 703m2/g,中孔分布集中,最可儿直径3．5nm。OCNT由纳米碳管规整有序排列构成。OCNT具 有很好的电容特性,在高的电压扫描速度下比电容值不发生明显衰减,50mV/s的高电压扫描速度下,比电 容为181．2F/g;高频下仍能保持优异的电容特性,频率1Hz时样品的比电容大约100F/g。OCNT大的孔尺 寸和规整有序的孔结构是其优异电容性能的主要原因。

纳米碳管阵列场增强因子的计算

采用悬浮球模型,结合对称的镜像电荷层方法,对静电场中纳米碳管阵列的场增强因子进行了计算,并在考虑极板间距的情况下,对其计算结果做了修正.结果表明:纳米碳管阵列的间距对纳米碳管阵列的场发射性能影响很大.当纳米碳管阵列中碳管间距小于碳管高度时,场增强因子随间距的减小而急剧减小;而当碳管间距显著大于碳管高度时,场增强因子几乎不变.但当考虑阴阳极之间单位面积通过的场发射电流时,可论证当管间距与管高度相若时,能使场发射电流密度最佳(最大).另外,极板间距对场增强因子的影响很小,但是可以通过减小极板间距,来降低纳米碳管作为场发射体的场发射的开启电压,优化纳米碳管的场发射性能.

生长纳米碳管阵列用Cu纳(微)米催化颗粒的制备

以生长纳米碳管阵列用催化剂为应用对象,采用辉光放电等离子体增强氧化还原方法制备纳(微)米Cu催化剂颗粒.采用AFM和SEM对试样表面进行分析,结果表明,当气体流量不变时,温度和氧化时间对颗粒形貌和尺寸有明显的影响.温度过低,不能获得足够的颗粒,温度过高则颗粒聚集长大;400℃为较好的温度条件,氧化5min时颗粒尺寸达到纳米量级.

纳米碳管阵列

在概括纳米碳管阵列特异的场发射效应及在场发射器方面应用前景的基础上,介绍了合成纳米碳管阵列的研究历程以及化学气相沉积法在纳米碳管阵列合成方面的重要意义,就当前纳米碳管阵列的快速合成与低温合成两个发展方向进行了概述,并指出等离子体化学气相沉积法能有效地用于纳米碳管阵列的低温合成。

TiO2纳米碳管阵列--合成、性能和应用

本书主要介绍了高度有序垂直定向的TiO2纳米碳管的构成、性能和多方面应用。自从Gong等第一次报道TiO2纳米碳管阵列的高度有序性，该领域发展非常迅速，很难及时对相关研究工作进行总结。研究者借助一系列合成化学，使得纳米管具有不同的形态学。TiO2纳米管阵列已被证实具有重要的应用价值，如在大电容、太阳能电池、药物洗涤表面、氢气传感器与生物过滤膜等方面得到了大量的应用。

栅控纳米碳管冷阴极X线管

本发明涉及对现有X线管的工作原理结构材料及其供电电路的重大改进。其特征是由纳米碳管膜片作为X线管阴极电子发射体，在该膜片中心的发射面积上设置有纳米碳管阵列；在纳米碳管膜片相对应的位置上设置有栅极片，栅极片是固定在阴极组合体外壳上并与之相互导通，纳米碳管膜片与栅极片及阴极组合体外壳被绝缘垫片所隔离。

微孔对单壁纳米碳管储氢性能的影响

用巨正则蒙特卡罗分子模拟方法研究了单壁纳米碳管中的微孔即单壁纳米碳管基本孔-内管腔和管间孔对单壁纳米碳管储氢性能的影响.与低温下氮气吸附实验结果的比较发现单壁纳米碳管的内管腔是吸附的主要位置.分析单壁纳米碳管内管腔中吸附势的叠加和利用效率,发现管径为2nm左右时单壁纳米碳管内管腔的储氢容量最高.当单壁纳米碳管阵列的管间距增加时,单壁纳米碳管的管间孔也会成为有效的氢吸附位.

Effect of Anodization Parameters on Morphologies of TiO2 Nanotube Arrays and Their Surface Properties

This work presents the potentiostatic anodization study of titania nanotube array films fabricated in fluoride-based organic electrolytes including DEG （diethylene glycol） and EG （ethylene glycol）. The work focuses on the effect of important anodization parameters such as applied voltage, anodization time, and electrolyte type on nanotube morphologies and corresponding surface properties. Depending upon unique nanotube formation structures obtained from each anodizing electrolyte, wettability of the nanotube array layer has been determined by means of the contact angle measurement. The EG nanotube array films with close-packing cell orientation are found to show hydrophilic behavior. While the well separated DEG nanotube array films are found to exhibit hydrophobic behavior, with the characteristics of more discrete, wider cell separation obtained through manipulating the electrolyte conditions and the fabrication techniques offering considerable prospects for developing the superhydrophobic sample surface. Such formation structures observed for the DEG fabricated nanotube is believed to play a prominent role in determining the surface wettability of the anodized nanotube array film. The achieved result in this work is anticipated to pave the way to other relevant applications, where interfacial properties are critically concerned.

Large-area growth of ultra-high-density single-walled carbon nanotube arrays on sapphire surface

A scalable approach to obtaining high-density, large-area single-walled carbon nanotube （SWNT） arrays is essential for realizing the full potential of SWNTs in practical electronic devices; this is still a great challenge. Here, we report an improved synthetic method for large-area growth of ultra-high-density SWNT arrays on sapphire surfaces by combining Trojan catalysts （released from the substrate, to assure ultra-high density） with Mo nanoparticles （loaded on the surface, to stabilize the released Trojan catalysts） as cooperating catalysts. Dense and perfectly aligned SWNTs covered the entire substrate and the local density was as high as 160 tubes/pro. Field-effect transistors （FETs） built on such arrays gave an output current density of -488 μA/μm at the drain-source voltage （Vds） = the gate-source voltage （Vgs） = -2 V, corresponding to an on-conductance per width of 244 μS/μm. These results confirm the wide range of potential applications of Trojan-Mo catalysts in the structure-controlled growth of SWNTs.

Novel Photodetectors Based on Double-Walled Carbon Nanotube Film/TiO2 Nanotube Array Heterodimensional Contacts

A new kind of photodetector based on a double-walled carbon nanotube （DWCNT） film and a TiO2 nanotube array with hetrodimensional non-ohmic contacts has been fabricated. Due to the dimensionality difference effect, the DWCNT film/TiO2 nanotube array photodetector exhibits a much higher photocurrent-to-dark current ratio and photoresponse relative to an Au film/TiO2 nanotube array device, even at small bias voltage. The photocurrent-to-dark current ratio reached four orders of magnitude and a high photoresponse of 2467 A/W was found upon irradiation at 340 nm. Furthermore, the photosensitive regions could be extended into the visible range. The photocurrent-to-dark current ratio reached approximately three orders of magnitude upon irradiation at 532 nm, where the photon energy is much lower than the band gap of TiO2.

Heating graphene to incandescence and the measurement of its work function by the thermionic emission method

The work function （WF） of graphene is an essential parameter in graphene electronics. We have derived the WF of graphene by the thermionic emission method. Chemical vapor deposition （CVD）-grown single-layered polycrystalline graphene on copper foil is transferred to a cross-stacked carbon nanotube （CNT） film drawn from a super-aligned multiwalled CNT array. By decreasing the pore size of the CNT film, the as-prepared CNT-graphene film （CGF） can be Joule heated to a temperature as high as 1,800 K in vacuum without obvious destruction in the graphene structure. By studying the thermionic emission, we derive the WF of graphene, ranging from 4.7 to 4.8 eV with the average value being 4.74 eV. Because the substrate influence can be minimized by virtue of the porous nature of the CNT film and the influence of adsorbents can be excluded due to the high temperature during the thermionic emission, the measured WF of graphene can be regarded as intrinsic.

Ultrahigh Density Modulation of Aligned Single-Walled Carbon Nanotube Arrays

Controlling the densities of aligned single-walled carbon nanotube arrays （SWNTs） on ST-cut quartz is a critical step in various applications of these materials. However the growth mechanism for tuning SWNT density using the chemical vapor deposition （CVD） method is still not well understood, preventing the development of efficient ways to obtain the desired results. Here we report a general ＂periodic＂ approach that achieves ultrahigh density modulation of SWNT arrays on ST-cut quartz substrates--with densities increased by up to -60 times compared with conventional methods using the same catalyst densities--by varying the CH4 gas ＂off＂ time. This approach is applicable to a wide range of initial catalyst densities, substrates, catalyst types and growth conditions. We propose a general mechanism for the catalyst size-dependent nucleation of SWNTs associated with different free carbon concentrations, which explains all the observations. Moreover, the validity of the model is supported by systematic experiments involving the variation of key parameters in the ＂periodic＂ CVD approach.

Synthesis and Characterization of Niobium-doped TiO_2 Nanotube Arrays by Anodization of Ti-20Nb Alloys

Well crystallized niobium-doped TiO; nanotube arrays （TiNbO-NT） were successfully synthesized via the anodization of titanium/niobium alloy sheets, followed with a heat treatment at 550 ℃ for 2 h. Morphology analysis results demonstrated that both the titanium/niobium alloy microstructure and the dissolution strength of electrolyte played major roles in the formation of nanotube structure. A single-phase microstructure was more favorable to the formation of uniform nanotube arrays, while modulating the dissolution strength of electrolyte was required to obtain nanotube arrays from the alloys with multi-phase microstructures. X-ray diffraction （XRD） and X-ray photoelectron （XPS） analysis results clearly demonstrated that niobium dopants （Nb^5＋） were successfully doped into TiO2 anatase lattice by substituting Ti^4＋ in this approach.

In Situ TEM Observation of the Gasification and Growth of Carbon Nanotubes Using Iron Catalysts

We report the in situ transmission electron microscope (TEM) observation of the catalytic gasification and growth of carbon nanotubes (CNTs). It was found that iron catalysts can consume the CNTs when pumping out the precursor gas, acetylene, at the growth temperature, and reinitiate the growth when acetylene is re-introduced. The switching between gasification and growth of CNTs can be repeated many times with the same catalyst. To understand the phenomenon, thermogravimetric analysis (TGA) coupled with mass spectroscopy was used to study the mechanism involved. It was shown that the residual water molecules in the growth chamber of the TEM react with and remove carbon atoms of CNTs as carbon monoxide vapor under the action of the catalyst, when the precursor gas is pumped out. This result contributes to a better understanding of the water-assisted and oxygen-assisted synthesis of CNT arrays, and provides useful clues on how to extend the lifetime and improve the activity of the catalysts.

Effects of the local environment on plasmonic coupling of metallic nanotube arrays

We have theoretically investigated the effect of the dielectric core and the dielectric embedding medium separately on the transmission spectra and plasmonic properties of coupled metallic nanotube arrays.It is found that the plasmonic properties of the nanotube arrays are strongly influenced by the presence of the dielectric which induces additional screening charges.We show that instead of one single photonic bandgap for the hollow nanotube arrays placed in air,an additional photonic bandgap arises from the presence of dielectric media in the transmission spectra.Based on the localized nature of the electric field distributions,we also clearly show the presence of the local plasmonic resonant modes that originate from multipolar plasmon polaritons in the cross section of these nanotube arrays,and that a large amount of opposing surface charges are built up in the gap between adjacent nanotubes.

Preparation of horizontally aligned single-walled carbon nanotubes with floating catalyst

A strategy to prepare horizontally aligned single-walled carbon nanotubes(SWNTs) at moderate temperatures(≤600 ℃) were developed.Using ferocene as the catalyst precursor,Fe nanoparticles are formed in the gaseous phase and catalyze the nucleation and growth of SWNTs in situ.Then the resultant SWNTs are deposited onto the substrates downstream and aligned by the surface lattice of the ST-cut single crystal quartz.The preparation of SWNT arrays at moderate temperatures is important for combining the tube growth with device fabrication.

Laser tuned field emission of the carbon nanotube arrays grown on an optical fiber

Laser was coupled into an optical fiber,on which covered a layer of well-aligned carbon nanotubes(CNTs)serving as cathode,to tune the field emission of the cathode.CNT arrays as field emission cathode were synthesized by chemical vapor deposition(CVD)on a naked fiber core.When the laser was coupled into the fiber,the turn-on voltage(Vto at a current density of 1 mA cm?2)decreased from 1.0 to 0.9 kV and the emission current density increased from 0.83 mA cm?2(at a 1 kV bias voltage)to3.04 mA cm?2 on 40μm diameter fiber.A photon absorption mechanism is attributed to the field emission improvement.The estimated effective work function of CNT arrays on the optical fiber decrease from 4.89 to 4.29 eV.The results show the possibility of constructing a waveguide type laser modulated field emission cathode.

High-strength composite yarns derived from oxygen plasma modified super-aligned carbon nanotube arrays

Spinning carbon nanotube （CNT） yarns from super-aligned carbon nanotube （SACNT） arrays is a promising approach to fabricate high-strength fibers. However the reported tensile strengths of the as-prepared fibers are far below that of an individual CNT. It is therefore still a challenge to improve their mechanical strengths. Here we report that the tensile strengths and Young＇s moduli can be further improved to 2.2 GPa and 200 GPa respectively, if we first treat the SACNT array with oxygen plasma by using a reactive ion etching （RIE） facility, then dry spin yarns from it and make composite fibers with polyvinyl alcohol. According to the experimental results obtained using scanning electron microscopy （SEM）, Raman spectroscopy and X-ray photoelectron spectroscopy （XPS）, the improvement is attributed to the oxygen RIE process, as it can create functional groups on the outer walls of CNTs and thus improve the interaction between the CNTs and the polymer molecules.

Uniform arrays of carbon nanotubes applied in the field emission devices

Carbon nanotubes(CNTs)were grown into anodic aluminum oxide(AAO)channels by chemical vapor deposition(CVD)using C2H2/N2mixtures as feeding gas,which can be used as field emitters.The bottom surface of AAO template was etched slightly and the tips of CNTs were explored as the field emission arrays which were uniform and vertical.Field emission characterization showed a low turn-on field about 3.25 V/m and high emission current about 30 mA/cm2with the electric field about 4 V/m.These superior field emission characteristics could be attributed to low density of vertical CNTs and higher conductivity of the substrate.

Short channel carbon nanotube thin film transistors with high on/off ratio fabricated by two-step fringing field dielectrophoresis

A two-step fringing field dielectrophoretic assembly method for carbon nanotube thin film transistors （CNT-TFTs） fabrication was demonstrated. Densely aligned CNT arrays were assembled at the source and drain electrodes sequentially which form a cascade structure of the aligned CNT arrays. The cascade structure reduces the possibility of percolating metallic pathways in the channel, which is beneficial to device performance. In this way, both high on/off current ratio Ion/loft （up to 107） and high out-put current density （8.5μA/μm） were obtained in short channel length （1-2.5μm） CNT-TFTs. The reported CNT assem- bling strategy is site selective and highly efficient, which can be scaled up to large size substrates and leads to high throughput of CNT-TFTs fabrication.