Ni催化剂在N2O／N2／NH3中退火对碳纳米管表面结构及场发射特性的影响

研究在N2O/N2/NH3氛围中对Ni催化剂进行退火处理,旨在探讨退火处理对所生成碳纳米管的表面结构及其发射特性的影响.从表面结构及表面元素分析结果发现:Ni催化剂在N2O/N2/NH3氛围中退火处理之后,Ni催化剂的颗粒大小及催化剂的化学成分发生改变,进而影响所合成的碳纳米管的表面结构及场发射特性.扫描电镜显示:经过N2O退火前处理后,催化金属薄膜在成核时较易形成均匀性的金属颗粒,且金属颗粒较小.比较经N2O/N2/NH3氛围退火处理之后所合成的碳纳米管结果,经过N2O前处理可以有效抑制非品质碳的成长,使所成长出的碳纳米管数量最多、场发射电流最大.原因主要是因为N2O对催化剂镍膜金属前处理过程中分解出的氮原子及氧原子会活化及氧化催化剂Ni金属,并使所形成的Ni金属颗粒较小且更为均匀,造成表面型态上的显著改变,有助于使合成的碳纳米管场发射电流变大.     

有机溶剂高压气流法改善碳纳米管阴极场发射特性

针对丝网印刷碳纳米管阴极,提出有机溶剂高压气流法进行表面后处理,有效改善碳纳米管阴极场发射特性.利用表面轮廓仪、扫描电子显微镜及高分辨透射电子显微镜表征有机溶剂高压法处理前后CNT阴极表面形貌变化,并对处理前后CNT阴极进行场发射特性测试.结果表明,有机溶剂高压法处理后CNT阴极表面整洁无包覆,开启电场下降,场发射电流密度大幅度提升,发射点密度明显增大,均匀性提高,处理前后场增强因子比值为1:2.8.     

热化学气相沉积法在硅纳米丝上合成碳纳米管

利用热化学气相沉积法在负载不同厚度催化剂的硅纳米丝(SiNW)表面生长碳纳米管(CNTs),探讨了生长条件对所合成SiNW-CNT的结构和场发射特性的影响.这种类似树状的三维结构具有较高碳纳米管表面密度及降低的电场筛除效应等潜在优势.使用拉曼光谱( Raman)、电子显微镜(SEM)、透射电子显微镜(TEM)、能量扩散分光仪(EDS)分析了碳纳米管的结构性质,并在高真空下施加电场测得碳纳米管的场发射特性.结果表明:随硅纳米丝上负载催化剂镍膜厚度的变化,所合成碳纳米管的表面特性、结晶结构及功函数改变,导致电子发射难易程度的改变,进一步影响碳纳米管的场发射特性.     

碳纳米管表面化学镀银及场发射性能研究

利用化学镀方法对碳纳米管(carbon nano-tubes,CNTs)表面金属化镀银,研究表面化学镀银碳纳米管的场发射性能。碳纳米管经氧化处理后,表面存在一些羰基(CO)、羧基(—COOH)和羟基(—OH)等活性基团,经敏化、活化处理后,形成金属钯活化中心,进而还原金属银离子,从而获得表面化学镀银的碳纳米管。表面化学镀银碳纳米管阴极的开启电场约为0.19V/μm,当电场强度为0.37V/μm时,最大发射电流达6mA/cm2,场增强因子约为25565。实验结果表明,化学镀银层可以提高碳纳米管的电子传输和热传输能力,提高碳纳米管的场发射电流和发射稳定性,有利于碳纳米管在场发射平板显示领域的应用。     

表面态对碳纳米管场发射的影响

采用CVD法在Ni丝上直接沉积碳纳米管,并应用二极管结构测试表面态(突出尖端和吸附)对碳纳米管场发射的影响。测试表明,突出尖端主要影响碳纳米管场发射的开启电场以及场发射电流稳定性;吸附作用的影响表现在改变碳纳米管能带结构进而改变其场发射性能。     

碳纳米管/二氧化硅复合材料制备及场发射特性研究

采用溶胶-凝胶法制备了碳纳米管/二氧化硅复合材料,并对复合材料的场发射特性进行了研究,结果表明:复合材料有很好的场发射特性,含有10%(质量分数)CNTs的复合材料开启场较低(0.98V/μm).研究了用稀HF溶液处理复合材料表面后场发射性能,发现场发射性能明显改善,开启场由0.98V/μm下降到0.73V/μm,发射电流为1mA/cm2时的电场由2.1V/μm下降到1.0V/μm.研究表明碳纳米管/二氧化硅复合材料非常适用于场发射平面显示器中的阴极.     

电泳淀积图形化碳纳米管场发射阴极及其场发射特性研究

基于电泳和半导体工艺,制备了图形化的碳纳米管场发射阴极。用较高的电场激活碳纳米管薄膜,使得碳纳米管的场发射特性有了很大的改善,讨论了这一激活过程的物理机制。研究表明,这一激活过程可能的物理机制一方面是由于碳纳米管薄膜表面形貌发生了变化,增大了碳纳米管的场增强因子;另一方面是由于碳纳米管表面吸附的气体脱附,降低了碳纳米管的表面功函数。电场激活处理后,碳纳米管薄膜的开启电场为2.1 V/μm,应用电场为6 V/μm时,电流密度达到1.19mA/cm2。该图形化的碳纳米管场发射阴极可以应用到高分辨率场发射显示器。     

用玻璃粉作粘结剂制备碳纳米管厚膜及其场发射特性

研究了用涂敷法制备的碳纳米管（CNT）厚膜及其场发射特性,裂解法获得的碳纳米管与玻璃粉等混合、研磨,直接涂敷在Si基底上,经烧结后制成碳纳米管厚膜,二极结构测量的结果表明,碳纳米管厚膜有较低的开启电场（1.0～1.25V/μm）,场强为5V/μm时,电流密度达到了50μA/cm^2.该工艺的烧结过程应控制好,加热时间稍长会使CNT厚膜的场发射性能很快下降,时间过长会使CNT处在厚膜表面之下,无法有效发射电子.浆料中的玻璃粉比例增大时,碳纳米管阴极的场发射性能会有所降低.     

碳纳米管电极电催化氧化降解染料溶液的研究

研究了经高温焙烧结合高速球磨处理后的碳纳米管的结构及形貌, 测定了其相应的比表面积. 对碳纳米管冷压成形制得的电催化电极的表面形貌进行了分析. 分别以活性炭、石墨、碳纳米管作为电催化阳极, 处理模拟染料废水活性艳红X-3B溶液, 实验结果表明: 碳纳米管电极电催化稳定性较好, 经电催化氧化反应20min后, X-3B染料的降解率达到96.55%, 其电催化降解效率明显优于活性炭和石墨电极.     

图形化的衬底电极改善碳纳米管的场发射特性

用电泳法将碳纳米管分别淀积到图形的和平面的ITO(铟锡氧化物)电极上作为场发射阴极并比较性的研究了它们的场发射特性.实验结果显示,相对于平面的衬底电极,斑条的ITO电极能够有效的改善碳纳米管的场发射特性.通过电场的数值计算,场发射特性的改善起源于斑条的ITO电极自身的表面电场增强引起了碳纳米管表面电场的两级放大.采用图形化衬底电极去制备碳纳米管阴极是改善碳纳米管场发射特性的一个简单、有效途径.     

碳纳米管的表面修饰及其对碳纳米管/氟橡胶复合材料导电性能的影响

分别采用混酸和四氟化碳(CF4 ) 等离子体处理技术对碳纳米管(MWCNTs) 进行了表面修饰, 将处理前后的碳纳米管进行了XPS 和SEM 测试, 获得了处理后前的表面形貌和结构, 并采用溶液浇注的方式制备了MWCNTs/氟橡胶(FE) 复合材料, 探讨了不同碳纳米管状态(未处理、混酸处理、CF4等离子体处理) 的导电性能, 结果表明两种表面处理方式可以使MWCNTs 表面接上极性官能团。而且在相同的碳纳米管添加量下(质量分数分别为0. 1 %、0. 5 %、1. 0 %、2. 0 %) , 酸处理MWCNTs/ FE 的渗流阈值最小, 达0. 5 %。      

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.     

Growth and characterization of bamboo-like multiwalled carbon nanotubes over Cu/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

The growth of bamboo-like multiwalled carbon nanotubes (MWCNTs) over Cu/Al₂O₃ catalyst by chemical vapor deposition under atmospheric pressure using ethanol as the carbon source has been demonstrated. The obtained MWCNTs are dominant with bamboo-like morphology. The morphologies, graphitization degree, and microstructures of the products were characterized by transmission electron microscopy, X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, high-resolution transmission electron microscopy, and selected area electron diffraction. The results show that the combination of Cu/Al₂O₃ catalyst and ethanol was critical for the growth of bamboo-like MWCNTs. The possible factors causing the formation of bamboo-like structures were also discussed.     

Preparation of a MWCNT/ZnO nanocomposite and its photocatalytic activity for the removal of cyanide from water using a laser

Nano-zinc oxide (n-ZnO) was loaded onto multi-walled carbon nanotubes (MWCNTs) via a hydrothermal process. Here pure n-ZnO used for loading was synthesized by the pulsed-laser ablation technique while MWCNTs were used as received. The synthesized MWCNT/ZnO nanocomposites were characterized using x-ray diffraction, field emission scanning electron microscopy, high resolution transmission electron microscopy and Fourier transform infrared spectrometry. A model has been proposed for the structural nature of the alignment of ZnO on the surface of MWCNTs. The photocatalytic activity in the removal of highly toxic substances like cyanide (CN) was carried out in a special reactor using pulsed 355 nm UV generated by the third harmonic of an Nd:YAG laser. In order to understand the cyanide removal process, the study was carried out at different laser irradiation times, incident laser energies, pH of the solution and dosage of the MWCNT/ZnO nanocomposite. The study demonstrated that the CN removal process by MWCNT/ZnO composite has higher photocatalytic activity than pure n-ZnO and MWCNTs alone. The mechanism for the degradation using MWCNT/ZnO has been schematically explained. It was noticed that the oxidation process activity is affected by the pH of the solution, and after 20 min of UV laser irradiation, approximately 90% of CN had been degraded.     

Decoration of multi-walled carbon nanotubes with silver nanoparticles and investigation on its colloid stability

In this paper, multi-walled carbon nanotubes (MWCNTs) were decorated with silver nanoparticles which have been successfully synthesized by chemical reduction of Ag cations on the acid treated MWCNTs surface by sodium hydroxide. Ag/MWCNTs were characterized by TEM and XRD. The results indicated that silver nanoparticles were homogeneously dispersed on the outer surface of MWCNTs. The dispersibility of pristine, acid treated and decorated carbon nanotubes in distilled water were investigated by zeta potential and optical image. The results revealed that the dispersion of acid treated carbon nanotubes in distilled water was better than those of pristine MWCNTs and Ag/MWCNTs.     

Morphological and compositional engineering of Ni/carbon nanotube composite film via a novel cyclic voltammetric route

Ni/multi-walled carbon nanotubes (MWCNTs) composite films were deposited on the glassy carbon electrode (GCE) by a Ni plating bath containing homogeneously dispersed MWCNTs using polyvinylpyrrolidone (PVP) as dispersion additive. Incorporation of MWCNTs into Ni matrix was greatly enhanced by the application of cyclic voltammetric (CV) deposition technique. The structure and nature of the Ni/MWCNT were characterized by field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD). The results show that the content of MWCNT and the morphology of the deposited Ni/MWCNT composite film can be controlled by selecting the appropriate electroplating conditions. Further study indicates that the obtained Ni/MWCNT showed excellent electro-catalytic activity for the oxidation of ethanol in alkaline solution.     

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.     

Influence of catalyst particles on multi-walled carbon nanotubes morphology and structure

Multi-walled carbon nanotubes (MWCNTs) have been successfully grown by Chemical Vapor Deposition (CVD) method. Elucidating the key characteristics of catalyst sources that affect carbon nanotubes growth is of great importance for improving and control MWCNTs morphology and structure. In this work we present a systematically study of CVD parameters, such as catalyst source, substrate morphology and temperature and how it affects carbon nanotubes synthesis. The novelty of this work lies on the catalyst composition. Two specific catalyst sources were analyzed: (i) Fe₂Co and (ii) Fe₂Co with ferrocene. Cyclic Voltammetry results confirmed the presence of Fe²⁺ in the Fe₂Co with ferrocene solution. X-Ray Diffraction analysis confirmed the presence of iron particles on the substrate surface after its submission to growth conditions. Raman results suggested an improvement in carbon nanotubes crystalline quality catalyzed by Fe₂Co with ferrocene. For tridimensional substrates such as fibers, the Fe₂Co with ferrocene provided aligned CNTs with lower defects density noticed in Raman spectra and SEM micrographs. Finally, we corroborated the Fe²⁺ encapsulation relation with the growth mechanism and MWCNTs formation.     

Ageing effect on the field emission reproducibility of multiwalled carbon nanotubes

The ageing effect on the field emission (FE) reproducibility of multiwalleded carbon nanotubes (MWCNTs) synthesised by plasma enhanced chemical vapour deposition was investigated by scanning electron microscopy. To investigate the ageing effect on the physical state of the MWCNTs, a scanning electron microscope (SEM), a Raman spectrometer, an X-ray photoelectron spectroscope and an X-ray diffractometer were used to characterise the MWCNTs comprehensively before and after the ageing. Through ageing, the FE reproducibility became better because the larger number and more evenly distributed shorter MWCNTs – (resulted from the local vacuum breakdown of higher MWCNTs due to Joule heating and oxidisation) – became the dominating emitters.     

The perovskite CdSnO3 micro-particles modified by multi-walled carbon nanotubes enhance the ethanol gas sensing property

Cubic CdSnO3 and it modified by multi-walled carbon nanotubes (CdSnO3/MWCNTs) have been synthesized by following a mild hydrothermal method. CdSnO3/MWCNTs were characterized by using field emission scanning electron microscope (FE-SEM) and X-ray diffractometer (XRD) techniques. The results show that adding MWCNTs in the processing of synthesis had advantage to the growth of the CdSnO3 crystalline. Meanwhile, a comparative study of gas sensing property of CdSnO3 and CdSnO3/MWCNTs to ethanol vapor has been reported. CdSnO3 and CdSnO3/MWCNTs samples were deposited as thick films to act as gas sensors and their comparative response to ethanol vapor was investigated at different temperatures and concentrations. The results reveal that gas response of CdSnO3/MWCNTs is exceptionally higher than that of CdSnO3. The improvement of the gas sensing property of CdSnO3/MWCNTs might due to the bigger surface area and the better crystalline of CdSnO3/MWCNTs.