Effect of patterned and aligned carbon nanotubes on field emission properties

The field emission (FE) properties of carbon nanotubes (CNTs) films with different morphologies were simulated and examined. Based on the FE mechanism of aligned CNTs’ emitter the theoretical analysis exhibited the following relations: the FE enhancement factor with the distance between the emitters, the electric field with work function, and the work function with FE enhancement factor. Using the structure-induced CNTs growing method and theoretical results the direction of aligned CNTs could be controlled and the special morphology with different aligned CNTs’ film could be fabricated. Comparing to the experimental results (the medium density and patterned CNTs’ emitters) with the theoretically calculating results the I-V curves had the same trend with only 0.05 mA deviation. Based on the better experimental methods and means the accurate of formula could be further improved by modified the FE properties (Φ, β).     

Effect of hydrogen plasma pretreatment on growth of carbon nanotubes by MPECVD

We have grown carbon nanotubes (CNTs) with a microwave (μW) plasma enhanced chemical vapor deposition (MPECVD) method, which has been regarded as one of the most promising candidates for the synthesis of CNTs due to the vertical alignment, the low temperature and the large area growth. We use methane (CH₄) and hydrogen (H₂) gas for the growth of CNTs. Ni catalytic layer (10 nm thick) were deposited on the Ti-coated Si substrate by RF magnetron sputtering method. In this work, we report the effects of pretreatment μW power on the growth of CNTs. We have pretreated the Ni catalytic layer in different μW power (600, 700, and 800 W) and grown same μW power (800 W). Scanning electron microscopy (SEM) images show Ni catalytic layer diameter and density are varied dependent with their pretreatment conditions. Raman spectroscopy of CNTs shows that I_D/I_G ratios and G-peak positions vary with pretreatment conditions.     

不同强酸氧化对碳纳米管场发射特性的影响

研究了强HNO3和HNO3-H2SO4氧化对碳纳米管(carbon nanotubes,CNTs)场发射特性的影响,采用TEM、Raman、XPS和J-E进行了表征。实验结果表明,HNO3和HNO3-H2SO4可去除碳纳米管中的催化剂颗粒、无定形碳及碳纳米微粒等杂质;由于H2SO4具有协同氧化和脱水作用,使得混酸氧化后的碳纳米管具有更高的无序程度和缺陷密度,且表面存在C—OH,CO,OCOH等氧化基团。HNO3和HNO3-H2SO4氧化碳纳米管的开启电场分别为1.7和1.1V/μm,当电场增大至3.0V/μm的电场下对应的发射电流密度分别为1.8和4.2mA/cm2。     

Time-dependent resonating plasma treatment of carbon nanotubes for enhancing the electron field emission properties

Journal of Materials Science: Materials in Electronics - Vertically aligned carbon nanotubes having the advanced atomic configuration, structural properties, and electronic conductivity, which...     

真空度对纳米碳管场发射性能的影响

研究了单壁纳米碳管(SWNTs)、双壁纳米碳管(DWNTs)和多壁纳米碳管(MWNTs)在不同真空度下的场发射性能。在超高真空条件下(2.0×10-7Pa),以上三种材料均表现出良好的稳定性;而在高真空条件下(1.0×10-4Pa),三种材料的场发射稳定性有不同程度的下降。通过控制系统真空度在2.0×10-7Pa～1.3×10-3Pa范围内逐渐变化,考察了真空度对纳米碳管场发射性能的影响及其机制,提出适合于SWNTs、DWNTs和MWNTs场发射性能测试和应用的真空度下限分别为6.0×10-5Pa、1.0×10-4Pa和5.7×10-4Pa。     

测试环境对碳纳米管场发射性能的影响

采用CVD法在Ni丝上直接沉积碳纳米管,并应用二极管结构对其场发射性能进行测试,测试结果表明:(1)碳管表面态对其场发射稳定性影响明显,运用密度泛函平面波赝势方法(PWP)和广义梯度近似(GGA)对碳管表面吸附水分子前后电子能带结构和态密度作比较,发现吸附水分子后碳管功函数降低,费米能级处电子态密度增大,有利于增大碳管场发射电流;(2)高真空是获得碳管场发射稳定性一个必要条件;(3)荧光粉对碳管场发射电流也有一定贡献,但大的场发射电流情形下可忽略其影响。     

链状碳纳米管薄膜的制备及场发射特性研究

以镀有Ti层的Al2O3为衬底,在微波等离子体化学气相沉积系统中,以CH4和H2为反应气体,快速制备了链状碳纳米管薄膜(沉积时间仅1 min).通过SEM、TEM和Raman光谱观察了薄膜的表面形貌,分析了薄膜的微观结构.在高真空室中测试了薄膜场发射特性,其开启电场为0.81 V/μm,在3.15 V/μm 电场下,其场发射电流密度达到9 mA/cm2,发射稳定,是一种良好的电子发射体.     

Hydrogen-acetylene gas ratio and catalyst thickness effect on the growth of uniform layer of carbon nanotubes

Effect of catalyst thickness (2, 4, and 6 nm) and acetylene-hydrogen gas ratio (1/4, 2/4, and 3/4) on the synthesis of carbon nanotubes is reported in this article. Synthesized nanotubes are characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy, and Raman effect. From SEM results, nanotubes growth is less for higher thickness, as at higher thickness catalyst nanoparticles agglomerate which suppress the growth of nanotubes. Raman spectroscopy results reveal that at higher thickness defects density increases. Nanotube of better crystallinity and graphitic outer walls grows for lower acetylene-hydrogen gas ratio and at smaller thickness of catalyst layer. The sheet resistance of carbon nanotube thin film is measured by using Hall effect measurement systems. Smallest sheet resistance among synthesized multi-walled carbon nanotubes sample is obtained for nanotubes grown on 2 nm thick catalyst film and is 0.9 kΩ/square.     

非晶碳包覆碳纳米管复合结构电泳沉积及其场发射性能研究

利用电泳法在镀镍的聚酰亚胺薄膜上制备了非晶碳包覆碳纳米管复合结构柔性冷阴极.利用扫描电镜观察了结构形貌.并对其场发射性能进行了研究.结果显示,该复合结构柔性冷阴极具有较低的开启电场和较高的发射电流密度.     

Synthesis of straight multi-walled carbon nanotubes by arc discharge in air and their field emission properties

The possibility of preparing straight multi-walled carbon nanotubes (MWCNTs) on a large scale is demonstrated using direct current arc discharge with a rotating graphite anode in low pressure air. The process is time-saving, economical, and non-hazardous. It is found that the optimum air pressure for the highest yield of MWCNTs is about 60 Torr. Investigation of the internal organization of the cathode deposit reveals that many columns about 40 μm in diameter are closely packed and mechanically stable. The highest content of MWCNTs is found in the intercolumnar spaces between columns. Emitters made of the cathode deposits that contain a large number of straight nanotubes exhibit outstanding field emission properties. The turn-on electric field decreases from 1.44 to 0.93 V/μm and the field enhancement factor β increases from about 3,190 to 7,830 only after simple burning at 750 °C for 30 min in air. The results indicate that MWCNTs prepared by arc discharge in air are promising for field emission application.     

碳纳米管场发射阴极的制备及其场发射特性

采用电泳法将碳纳米管组装到电化学淀积的银台阵列上作为场发射阴极并研究了它的场发射特性.场发射特性测试结果表明:该阴极具有优异的场发射特性,开启电场为2.8V/μm,在应用电场为5.5V/μm时,发射电流密度达到1.7mA/cm2.具有优异的发射性能的原因可以归结到银台的边缘和银台类山状的表面增强了碳纳米管的场致电子发射.该阴极制备工艺简单、发射特性优异,且容易实现大面积制备,可以应用到大面积场发射显示器件中.     

Synthesis and field electron emission properties of hybrid carbon nanotubes and nanoparticles

Hybrid ZnO-carbon nanotubes as well as nanodiamond-carbon nanotubes were synthesized via a straightforward process of plasma enhanced chemical vapor deposition. For the former, ZnO nanoparticles were instantly coated on the tube surface in the final growing process of carbon nanotubes, while for the latter diamond nanoparticles were grown using pretreatment of a silicon substrate with Ni(NO(3))(2)·6H(2)O/Mg(NO(3))(2)·6H(2)O alcohol solution prior to deposition and a high H(2)/CH(4) gas flow ratio in the deposition process. The morphology and microstructure of the obtained hybrid materials were characterized by transmission electron microscopy. Both hybrid ZnO-carbon nanotubes and nanodiamond-carbon nanotubes exhibited excellent field emission properties.     

Optimization of field emission properties of carbon nanotubes by Taguchi method

It is the purpose of this study to evaluate the field emission property of carbon nanotubes (CNTs) prepared by microwave plasma-enhanced chemical vapor deposition (MPCVD) method. Nickel layer of 5 nm in thickness on 20-nm thickness titanium nitride film was transformed into discrete islands after hydrogen plasma pretreatment. CNTs were then grown up on Ni-coated areas by MPCVD. Through the practice of Taguchi method, superior CNT films with very low emission onset electric field, about 0.7 V/μm (at J = 10 μA/cm²), are attained without post-deposition treatment. It is found that microwave power has the most important influence on the field emission characteristics of CNT films. The increase of methane flow ratio will downgrade the degree of graphitization of CNT and thus its field emission characteristics. Scanning electron microscope and transmission electron microscopy (TEM) observation and energy dispersive X-ray spectrometer analysis reveal that CNT growth by MPCVD is based on tip-growth mechanism. TEM micrographs validate the hollow, bamboo-like structure of the multi-walled CNTs.     

Dispersion and field emission properties of multi-walled carbon nanotubes by high-energy milling

Multi-walled carbon nanotubes (MWNTs) were high-energy milled for 2 h in texanol after a polycarboxylic acid polymeric dispersant had been added in order to enhance the dispersion. The degree of MWNT dispersion was significantly enhanced by high-energy milling compared to the intact sample, which increased the density of surface-exposed MWNTs with a screen-printed paste. However, the emission properties of high-energy milled MWNTs did not show such a high emission current density relative to their increased surface-exposed density. Further investigation using Raman spectroscopy and X-ray diffraction evidenced the milling-induced MWNT damage, which explained the relatively lower emission current density of high-energy milled MWNTs.     

Improved field emission properties of carbon nanotubes by dual layer deposition

In this paper, we tried to increase the current density of carbon nanotubes (CNTs) by depositing double layer of CNTs instead of single layer. Both the layers of CNTs are deposited by the low pressure chemical vapour deposition technique on silicon substrate with Fe catalyst. Scanning electron microscopic images show the surface morphology of single and double layer of CNTs. Dual layer deposition of CNTs is a very simple and easy method to increase the current density of CNTs based field emitters than other conventional methods. Excellent field emission properties of double layer of CNTs are exhibited with large field enhancement factor and low turn-on voltage as compared to those for single layer of CNTs. High current density of CNTs is required for field-emission-based display devices associated with field enhancement factor and number of emitting electrons. Therefore, we may say that dual layer deposition of CNTs can be utilised as an alternative approach to improve the current density for field emitters. Stability measurement of the samples was also performed for 3 h (180 min) with current at constant applied voltage, and it was found that the stability of dual layer of CNTs is remarkable than that of single layer of CNTs.     

催化剂对爆炸法合成碳纳米管的影响

通过热引发方式使炸药-催化剂前驱体-碳氢化合物体系在密闭反应管中发生爆炸合成碳纳米管。采用TEM,HRTEM,XRD和TG等方法研究了以二茂铁、甲酸镍和乙酸钴作为催化剂前驱体对所合成碳纳米管产物的形貌、微观结构和纯度的影响。以乙酸钴为前驱体可以得到纯度较高(约80%～90%)、微观结构较好的管腔中空的碳纳米管。以二茂铁为前驱体,只有约10%～20%的碳管生成且多呈竹节状形貌。以甲酸镍为前驱体,得到的碳管纯度也不高(约10%～20%),碳管管壁富含结构缺陷,相当多的碳管端口膨胀成直径约为160nm的纳米泡。XRD分析表明这些催化剂前驱体在爆炸反应后均被分解、还原为金属单质。通过对生成的碳纳米管的质量和纯度进行比较,得出本方法中催化剂的催化活性依次为:钴>铁>镍,并对本方法中高碳源浓度环境下不同催化剂的活性差异作了简要分析。     

Improved field emission properties of thiolated multi-wall carbon nanotubes on a flexible carbon cloth substrate

In this paper we report the observation of enhanced field emission properties from thiolated multi-wall carbon nanotubes (MWCNTs) produced by a simple and effective two-step chemical surface modification technique. This technique implements carboxylation and thiolation on the MWCNTs synthesized by microwave plasma chemical vapor deposition (MPCVD) on the flexible carbon cloth substrate. The resulting thiolated MWCNTs were found to have a very low threshold field value of 1.25?V?μm(-1) and a rather high field enhancement factor of 1.93 × 10(4), which are crucial for applications in versatile vacuum microelectronics.     

一种基于CVD法的纳米碳管微观分析及场致发射特性的研究

将化学气相沉积法（CVD）制备的纳米碳管提纯后，用透射电镜（TEM）观测了它的微观结构，通过实验对纳米碳管在不同温度下生长的结构特性进行了分析比较，得出了纳米碳管生长的最佳温度为750℃；并对纳米碳管粉体的拉曼（Raman）光谱进行了分析，得到了与透射电镜观测相一致的结论；最后测试了纳米碳管的场致发射特性．     

Optimization of field emission properties of carbon nanotubes cathodes by electrophoretic deposition

Cold cathodes of carbon nanotubes (CNTs) were deposited on the glass substrate by the electrophoretic deposition (EPD) method. The cathodes were tested in the diode construction with the cathode–anode gap of 170 μm in vacuum. The emission characteristics of the CNTs film cathodes have as good properties as those by screen printing and better emission uniformity. The influence of the voltage between electrodes in the electrophoretic process of flat cold cathode fabrication on the uniformity of the CNTs film distribution was studied. The results indicate that the uniformity of CNTs film cathode by EPD depends on the voltage between electrodes during the electrophoretic deposition. The uniformity of CNTs film and optimized emission properties of the cathode have been achieved when the voltage is 25 V.