丝网印刷碳纳米管阴极场发射点开启场强的分布统计

由于碳纳米管阴极场发射点数量巨大，分布无规律，无法单独测量各个场发射点的开启阈值，所以一直没有效的实验方法获得碳纳米管阴极中场发射点开启阈值的分布规律。本文采用丝网印刷碳纳米管点阵作为阴极，通过不同电压下该阴极场发射发光亮点的统计，间接地获得了丝网印刷碳纳米管阴极中场发射点开启阈值的分布规律。在此基础上，通过过压老炼的方法，有效地压缩了碳纳米管阴极场发射开启阈值的分布，显著提高了碳纳米管阴极场发射的均匀性。     

Chemical vapor deposition synthesis of self-aligned carbon nanotube arrays

A procedure for producing arrays of self-aligned carbon nanotubes (CNTs) using standard chemical vapor deposition (CVD) is reported. Using UV photolithography, silicon substrates are patterned with a thin layer of thermally evaporated iron as a CNT catalyst. The CVD synthesis was carried out over a small temperature range (700°C–800°C) using acetylene and methane gasses, producing aligned CNT towers. Scanning electron microscopy (SEM) analysis shows a relationship between CNT tower height and synthesis time. Additionally, results show that impurity particles dramatically effect CNT tower growth. These results indicate that aligned CNTs can be produced in a desired pattern with height control.     

3D Printable One-Part Carbon Nanotube-Elastomer Ink for Health Monitoring Applications

3D printing of conductive elastomers is a promising route to personalized health monitoring applications due to its flexibility and biocompatibility. Here, a one-part, highly conductive, flexible, stretchable, 3D printable carbon nanotube (CNT)-silicone composite is developed and thoroughly characterized. The one-part nature of the inks: i) enables printing without prior mixing and cures under ambient conditions; ii) allows direct dispensing at ≈100 µm resolution printability on nonpolar and polar substrates; iii) forms both self-supporting and high-aspect-ratio structures, key aspects in additive biomanufacturing that eliminate the need for sacrificial layers; and iv) lends efficient, reproducible, and highly sensitive responses to various tensile and compressive stimuli. The high electrical and thermal conductivity of the CNT-silicone composite is further extended to facilitate use as a flexible and stretchable heating element, with applications in body temperature regulation, water distillation, and dual temperature sensing and Joule heating. Overall, the facile fabrication of this composite points to excellent synergy with direct ink writing and can be used to prepare patient-specific wearable electronics for motion detection and cardiac and respiratory monitoring devices and toward advanced personal health tracking and bionic skin applications.     

The Effect of Nanotube Content and Orientation on the Mechanical Properties of Polymer–Nanotube Composite Fibers: Separating Intrinsic Reinforcement from Orientational Effects

We have measured the mechanical properties of coagulation‐spun polymer–nanotube composite fibers. Both the fiber modulus, Y, and strength, σ_B, scale linearly with volume fraction, V_f, up to V_f ～10%, after which these properties remain constant. We measured dY/dV_f = 254 GPa and dσ_B/dV_f = 2.8 GPa in the linear region. By drawing fibers with V_f < 10% to a draw ratio of ～60%, we can increase these values to dY/dV_f = 600 GPa and dσ_B/dV_f = 7 GPa. Raman measurements show the Herman's orientation parameter, S, to increase with drawing, indicating that significant nanotube alignment occurs. Raman spectroscopy also shows that the nanotube effective modulus, Y_Eff, also increases with drawing. We have calculated an empirical relationship between the nanotube orientation efficiency factor, η_o, and S. This allows us to fit the data for Y_Eff versus η_o, showing that the fiber modulus scales linearly with η_o, as predicted theoretically by Krenchel. From the fit, we estimate the nanotube modulus to be; Y_NT = 480 GPa. Finally, we show that the fiber strength also scales linearly with η_o, giving an effective interfacial stress transfer of τ = 40 MPa and a nanotube critical length of l_c=1250 nm. This work demonstrates the validity of the Cox‐Krenchel rule of mixtures and shows that continuum theory still applies at the near‐molecular level.     

精确测定碳纳米管螺旋度的电子衍射方法

本文介绍精确测定碳纳米管原子结构的电子衍射方法.电子衍射方法利用碳纳米管的电子衍射图与碳纳米管螺旋指数(u,v)间的内在关系,可以从(a)衍射层线上的电子散射强度分布或(b)衍射层线间距的比例测定碳纳米管的螺旋指数.电子衍射方法是迄今为止测定碳纳米管的螺旋指数的最有效方法.电子衍射方法除具有结果精度高外,亦可用于测定多层碳纳米管的每层的螺旋指数.     

新型前栅极CNT-FED的研究

传统的前栅极场致发射显示板由于介质层和栅极的制作在生成或制作阴极场致发射源之后，在制造过程中容易破坏场致发射源；另外阴极发射对介质层厚度、阳极电压和调制极开口等参数非常敏感，所以器件的发射均匀性难以保证。为了解决这些问题，引入了类似HOP玻璃的结构。阴极上只需要丝印碳纳米管，无需制作介质层和栅极，解决了场致发射源被破坏的问题。阴极与栅极之间真空取代了介质层，由于真空的绝缘性能高于介质层，所以阴极与栅极之间的距离可以减小，栅极的调制效果更显著。由于玻璃的平整度高于一般方法制作的介质层的平整度，所以器件的发射均匀性比较好。     

Increase in thermoelectric power factor of carbon-nanotube films after addition of polystyrene

We report the enhancement of the thermoelectric power factors of single-walled carbon-nanotube (SWCNT) films caused by the addition of polystyrene to the films as a binder. The Seebeck coefficient of the SWCNT films was increased by addition of polystyrene. On the other hand, the electrical conductivity gradually decreased with increasing amount of polystyrene. The power factor was maximum for a polystyrene concentration of 20 wt%; it was approximately 1.7 times higher than that of a pure SWCNT film. These results indicate that polystyrene is a superior binder polymer for synthesizing CNT/polymer thermoelectric composites.     

Solution processable PEDOT:PSS based hybrid electrodes for organic field effect transistors

We report high performance solution processed conductive inks used as contact electrodes for printed organic field effect transistors (OFETs). Poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) electrodes show highly improved very low sheet resistance of 65.8 ± 6.5 Ω/square (Ω/□) by addition of dimethyl sulfoxide (DMSO) and post treatment with methanol (MeOH) solvent. Sheet resistance was further improved to 33.8 ± 8.6 Ω/□ by blending silver nanowire (AgNW) with DMSO doped PEDOT:PSS. Printed OFETs with state of the art diketopyrrolopyrrole-thieno[3,2-b]thiophene (DPPT-TT) semiconducting polymer were demonstrated with various solution processable conductive inks, including bare, MeOH treated PEDOT:PSS, single wall carbon nanotubes, and hybrid PEDOT:PSS-AgNW, as the source and drain (S/D) electrode by spray printing using a metal shadow mask. The highest field effect mobility, 0.49 ± 0.03 cm² V⁻¹ s⁻¹ for DPPT-TT OFETs, was obtained using blended AgNW with DMSO doped PEDOT:PSS S/D electrode.     

硝酸镍催化裂解甲烷制备碳纳米管

以CH4为碳源,H2为还原气体,硝酸镍溶液为催化剂,在不同条件下催化热解制备多壁碳纳米管,对所得样品进行了提纯,并用透射电镜(TEM)和拉曼光谱对样品进行了表征。分析了不同温度,生长时间,气体流量和配比等实验参数对所制备样品结构和性能的影响,结果表明:在750℃,CH4/H2为1:6,总气体流量和生长温度合适时,碳纳米管的产率最高,温度升高至850℃后,样品中无定形碳等杂质增多,而且,高温下制备的碳纳米管含有较多缺陷,来源于管壁可能由大片石墨拼接而成。