高场发射性能碳纳米管薄膜的沉积与表征

利用电泳法将碳纳米管（CNTs）沉积在表面镀覆了50～150 nm Ti薄膜的Si基底表面,900℃真空退火后形成了具有良好场发射性能的Ti-CNTs薄膜阴极.利用X射线衍射和扫描电子显微镜对制备的Ti-CNTs薄膜进行了表征.结果表明,高温退火过程中,CNTs的C原子和基底表面的Ti原子发生化学反应,在CNTs与基底之间形成了导电性钛碳化物,明显改善了CNTs与基底之间的电导性和附着力等界面接触性能;与Si基底表面直接电泳沉积的CNTs薄膜相比,制备的Ti-CNTs薄膜的开启电场从1.31 V/μm降低到1.19 V/μm;当电场强度为2.50 V/μm时,Ti-CNTs薄膜的场发射电流密度可达13.91 mA/cm^2;制备的Ti-CNTs薄膜显示出改善的发射稳定性.     

衬底电极对丝网印刷CNT阴极场发射性能的影响

通过丝网印刷技术,将碳纳米管(carbon nanotube,CNT)浆料直接转移到CrCuCr薄膜衬底电极、掺Sn的In_2O_3(indium tin oxides,ITO)透明导电薄膜衬底电极和Ag浆导电厚膜衬底电极上,高温烧结后得到CNT阴极,并对CNT阴极进行表面形貌和场发射性能的研究.结果表明,不同衬底电极对CNT阴极场发射性能的影响不一样,CrCuCr薄膜衬底电极CNT阴极、ITO透明导电薄膜衬底电极CNT阴极及Ag浆厚膜导电衬底电极CNT阴极场发射的开启电场分别为0.99、2.05和2.46V/μm;当电场为3.0V/μm时,它们的亮度分别为2472、1889、587cd/m~2.CrCuCr薄膜衬底电极CNT阴极的场发射性能最优,ITO透明导电薄膜衬底电极CNT阴极次之,Ag浆厚膜导电衬底电极CNT阴极最差,并根据金属-半导体理论模型分析了原因.     

一种应用于PDP显示单元的CNT辅助电极制备方法及其性能评价

建立了一种应用于等离子显示器(PDP)显示单元的碳纳米管(CNT)辅助电极制备工艺方法,创新性提出了场发射作为PDP平板显示的辅助性应用,并对制备的CNT辅助电极样片进行了性能评价。文章通过三维轮廓和SEM微观形貌测试手段,表征工艺过程中CNT辅助电极的宏观尺度和微观形貌。通过拉曼光谱、傅里叶红外光谱、粒径分布和ZETA电位表征与其性能直接相关的体系分散性。通过对荷电盐浓度、电泳电压、电泳时间和阴阳极板间距的系统分析和优化,获得优化电泳参数。通过关键参数对比确定了前后处理工艺及其效果。对CNT辅助电极的场发射性能进行测试,初步评价其辅助性能并考察其与PDP单元制备流程的兼容性。优化工艺制备的CNT辅助电极场发射开启电压在10μA/cm2的电流密度时低至1.2 V/μm。虽然在MgO保护层制备后增大至1.6 V/μm,但仍可保证其作为PDP辅助电极的典型功能。所建立的CNT辅助电极制备方法具备与PDP显示单元制备工艺有良好兼容性。     

电泳沉积碳纳米管的微波等离子体改性

采用电泳法在Si基底上沉积了碳纳米管(CNTs)薄膜, 并利用Ar微波等离子体对CNTs薄膜进行了改性处理, 研究了改性前后CNTs的微观结构和场发射性能. 高分辨透射电子显微镜(HRTEM)和拉曼光谱的表征结果表明, 等离子体改性明显改变了CNTs的微观结构, 形成了大量的管壁结构缺陷、纳米级突起和“针形”尖端; 场发射测试结果表明, CNTs经Ar等离子体改性处理后开启电场较改性前?略有增大, 等离子体改性10min的CNTs薄膜表现出最佳的场发射J-E特性, 阈值电场由改性前的3.12V/μm降低到2.54V/μm, 当电场强度为3.3V/μm时, 场发射电流密度由改性前的18.4mA/cm²增大到60.7mA/cm². 对Ar微波等离子体改性增强CNTs薄膜场发射性能的机理进行了分析.     

电泳和电镀法增强碳纳米管场发射特性的研究

碳纳米管(CNT)和衬底的电学接触问题是获得高性能CNT电子器件的一个关键性的问题。本文采用电泳电镀方法制备CNT冷阴极,有效改善了CNT与衬底间接触电阻,增强了碳纳米管场发射性能。电泳电镀法制备的碳纳米管冷阴极场发射的开启电场(电流密度为10μA.cm-2时的电场)由2.95 V.μm-1降低到1.0V.μm-1,在电场为8V.μm-1时电流密度由0.224增加到0.8112mA.cm-2。在电流密度为800μA.cm-2时进行1h的场发射稳定性测试,结果表明,电泳电镀法所得CNT场发射电子源电流密度几乎不变,而且电流密度比较稳定;而只有电泳的方法获得的CNT场发射电子源电流密度波动较大,电流不稳定且呈较快的衰减趋势,1h后减少到原来的75%。采用电泳电镀方法制备CNT阴极,CNT的根部被纳米银颗粒覆盖和包裹,使CNT与衬底接触更加牢固而紧密,又由于银具有很好的导电性,从而大大减小了接触电阻,因此电泳电镀法能大大改善CNT与衬底的电学接触性能。     

碳纳米管和镓掺杂碳纳米管场发射性能研究

采用催化热解方法分别 制备出碳纳米管和镓掺杂碳纳米管, 并利用丝网印刷工艺将其制备成纳米管薄膜. 对此薄膜进行低场致电子发射测试表明, 碳纳米管和镓掺杂纳米管开启电场分别为2.22和1.0V/μm, 当外加电场为2.4V/μm, 碳纳米管发射电流密度为400μA/cm², 镓掺杂纳米管发射电流密度为4000μA/cm². 可见镓掺杂碳纳米管的场发射性能优于同样条件下未掺杂时的碳纳米管. 对镓掺杂纳米管场发射机理进行了探讨.     

类金刚石薄膜作为阴极阵列的场发射显示器研制

采用真空磁过滤弧沉积（FAD）的方法制备的金刚石（DLC）薄膜具有良好的场发射性能。通过离子束技术和微细加工技术可以实现DLC薄膜的图形化并能大大提高薄膜的场发射性能。测试表明，DLC薄膜孔洞阵列具有很好的电子场发射性能，阈值电场达到了2.1V/μm，当场强为14.3V/μm时，电流密度达到了1.23mA/cm^2。利用图形化的DLC薄膜作为阴极，设计和制作了矩阵选址单色场发射显示器（FED）样管。     

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.     

ZnO纳米棒/CNTs复合阴极的制备及其场发射性能的研究

采用水热法和喷涂法制备ZnO纳米棒/CNTs复合材料,并测试其场发射性能。首先采用水热法在ITO电极基面生长ZnO纳米棒阵列,随后通过喷涂技术在ZnO纳米棒阵列表面沉积碳纳米管(CNTs)。使用扫描电子显微镜和X-射线衍射分别表征样品的结构和形貌特征。结果表明,经喷涂沉积的CNT薄膜均匀地包裹在ZnO纳米棒尖端。对该复合材料采用二极结构测试其场发射性能,通过测试结果发现,ZnO纳米棒/CNTs复合材料可明显改善ZnO纳米棒阵列及CNT薄膜的场发射性能,该复合材料具有低开启电场强度(约0.96V/μm),高场增强因子(9881)。因此,ZnO纳米棒/CNTs复合材料是最有前景的场发射阴极材料之一。     

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.     

电泳沉积制备氧化钇稳定的二氧化锆薄膜

采用恒压电泳沉积方法在Ni-YSZ(氧化钇稳定的氧化锆)阳极基体上制备YSZ电解质膜,研究了悬浮体系YSZ含量、外加电压、沉积时间对电泳过程及YSZ膜层质量的影响,结果表明,YSZ含量为20 g/L,沉积电压为10 V,沉积时间5 min时,恒压电泳一次即可得到均匀致密的YSZ膜:膜层与基体结合紧密,厚度约为10 μm.     

Enhanced field emission characteristics of nitrogen-doped carbon nanotube films grown by microwave plasma enhanced chemical vapor deposition process

Nitrogen-doped carbon nanotube (CNT) films have been synthesized by simple microwave plasma enhanced chemical vapor deposition technique. The morphology and structures were investigated by scanning electron microscopy and high resolution transmission electron microscopy. Morphology of the films was found to be greatly affected by the nature of the substrates. Vertically aligned CNTs were observed on mirror polished Si substrates. On the other hand, randomly oriented flower like morphology of CNTs was found on mechanically polished ones. All the CNTs were found to have bamboo structure with very sharp tips. These films showed very good field emission characteristics with threshold field in the range of 2.65-3.55 V/μm. CNT film with flower like morphology showed lower threshold field as compared to vertically aligned structures. Open graphite edges on the side surface of the bamboo-shaped CNT are suggested to enhance the field emission characteristics which may act as additional emission sites.     

电泳沉积PNN-PZT陶瓷厚膜及其电学性能研究

利用电泳沉积法分别在Al₂O₃/Pt和Pt金属基底上制备了厚度为10~40μm的0.3Pb(Ni_1/3Nb_2/3)O₃-0.7Pb(Zr,Ti)O₃(PNN-PZT)厚膜, 研究了pH值、Zeta电位与PNN-PZT悬浮液稳定性的关系, 探索了沉积电压、沉积时间与电泳沉积量的关系. 结果表明, 当添加少量分散剂聚乙二醇时, pH值在3.5~5.5较宽的范围内, 悬浮液具有较高的Zeta电位, 容易制得稳定的悬浮液. 沉积电压为21V, 沉积时间为5min时, 在Pt金属基底上电泳沉积得到的PNN-PZT厚膜, 经过1200℃烧结30min后, SEM显微结构分析表明, 厚膜致密, 晶粒得到充分生长. 电学性能测试显示此厚膜具有良好的铁电介电性能, 其剩余极化强度Pr可达20.8μC/cm², 介电损耗tanδ为3.2%.     

Study of electrophoretic deposition of ZnS:Ag/CNT composites for luminescent applications

In present work, electrophoretic deposition of novel photoluminescence (PL) composites of ZnS:Ag/carbon nano tube (CNT) on the surface of Al substrates was investigated. In deposition process, CNT concentration and applied coating voltage were studied as the effective parameters. Deposition weight showed the reverse relationship with the amount of concentration and direct dependence to the applied voltages. Furthermore, current densities were decreased with increasing CNT concentrations up to 12.5 wt%, and increased strongly with further CNT concentrations. Moreover, applied voltage and current density show the same positive trends. Other results revealed that PL emission intensities were significantly quenched with increasing the CNT concentration. Nevertheless, PL intensities were improved with increasing applied voltage up to 300 V, but reduced with further voltage increase. Morphological studies of ZnS:Ag/CNT composites confirmed that the intertwined architecture was formed by wrapping of CNTs on the surfaces of ZnS microsize particles.     

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.     

X-ray images obtained from cold cathodes using carbon nanotubes coated with gallium-doped zinc oxide thin films

X-ray imaging data obtained from cold cathodes using gallium-doped zinc oxide (GZO)-coated CNT emitters are presented. Multi-walled CNTs were directly grown on conical-type (250 μm-diameter) tungsten-tip substrates at 700 °C via inductively coupled plasma-chemical vapor deposition (ICP-CVD). GZO films were deposited on the grown CNTs at room temperature using a pulsed laser deposition (PLD) technique. Field-emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM) were used to monitor the variations in the morphology and microstructure of the CNTs before and after GZO coating. The formation of the GZO layers on the CNTs was confirmed using energy-dispersive X-ray spectroscopy (EDX). The CNT-emitter that was coated with a 10-nm-thick GZO film displayed an excellent performance, such as a maximum emission current of 258 μA (at an applied field of 4 V/μm) and a threshold field of 2.20 V/μm (at an emission current of 1.0 μA). The electric-field emission characteristics of the GZO-coated CNT emitter and of the pristine (i.e., non-coated) CNT emitter were compared, and the images from an X-ray system were obtained by using the GZO-coated CNT emitter as the cold cathode for X-ray generation.     

Preparation of flat and dense conjugated polymer films from dilute solutions by means of electrophoretic deposition

Some experimental results on the electrophoretic deposition of conjugated polymer are reported. The scanning electron micrographs clearly indicate that the the morphology of filmsof a fluorene-based polymer PDOF-MEHPV by the electrophoretic deposition strongly depends on the toluene/acetonitrile ratio of the parent suspensions. It is also shown that the suspension prepared from a 0.1 g/l toluene solution of the polymer, can give flat and dense polymer films with a thickness in the order of 100 nm by using the electrophoretic deposition. The electrical current originating from the movement of colloial particles has been measured for the suspensions containing polymer more than 0.2 g/l. However, the current due to impurities in the solvent makes it difficult to detect the electrical current corresponding to the particle movement in the suspensions containing smaller amount of the polymer. Polymer light-emitting devices having PDOF-MEHPV films with various thickness prepared by electrophoretic deposition have also been demonstrated.     

Cathodic electrophoretic deposition of barium titanate films from aqueous solution

Cathodic electrophoretic deposition (EPD) of barium titanate from aqueous suspensions was performed on nickel substrate. Cathodic deposition allows preparation of thin layers from aqueous solution on base metal electrodes, such as Ni or Cu, without creating an intermediate oxide layer during the deposition. This opens the opportunity to prepare complex shapes of dielectric layers onto base metals for co-firing, using relatively cheap and environmentally benign aqueous EPD. Stable barium titanate colloidal suspension with a concentration of 10 g/100 mL at pH of 9.2 has been prepared for the deposition. The characteristics of electrophoretic deposition of those positively charged particles onto cathode were investigated. A uniform and dense layer was obtained for films deposited at 3 V for 2 min. The calculated film thickness for the sintered layer at these conditions was ∼1 μm. The morphology can be controlled, and in particular the pore size and distribution can be controlled via the applied voltage. At low voltage a uniform layer can be obtained whereas at high voltage a large number of macropores appears in the deposit and their size increase with the increasing of the voltage due to gas bubble formation.