碳纳米管膜的制备及场发射特性研究
摘要
碳纳米管作为冷阴极场致电子发射材料的应用还有很多问题需要解决，如发射点密度及发射点均匀性、场发射的稳定性、碳纳米管的场发射机理、场发射显示器(FED)样管制做的工艺、由周围碳纳米管和导电材料引起的屏蔽效应等问题。这些问题大大限制了这项技术的应用范围，因此，上述问题的解决，必然会导致碳纳米管发射器件的快速产业化，从而在平板显示的市场领域占据重要地位。
本研究工作尝试了几种改善碳纳米管薄膜场致发射性能的方法，研究了沉积工艺参数等对碳纳米管薄膜场致电子发射特性的影响规律，得到了一些新的研究结果。在此基础上，利用在不锈钢衬底上制备的碳纳米管薄膜作为阴极研制了三极管结构的发光管。
1) 刻线镍膜上沉积的碳纳米管场发射特性研究
利用微波等离子体化学气相沉积(MPCVD)方法，在刻线的镍膜上沉积了碳纳米管膜。通过扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射光谱(XRD)和拉曼光谱表征研究了其微观结构，并讨论了催化剂厚度、制备温度、反应时间以及甲烷浓度对碳纳米管质量和场发射性能的影响。结果表明：甲烷浓度、生长时间、镍膜厚度以及反应温度对碳纳米管的生长都有影响，在一定条件下，可在镍膜上沉积垂直于衬底的高度取向的碳纳米管膜；不同条件下制备的碳纳米管的场发射性能有很大差异，保持氢气的流量(100 sccm)不变，当甲烷流量为5 sccm、生长时间为5 min、催化剂膜厚为150 nm、温度为700～800℃时，场发射性能最好，开启场强为1.3 V／μm，最大发射电流密度达到6.8mA／cm~2。而平板显示器要求的电流密度为1 mA／cm~2。
2) 不锈钢衬底直接沉积碳纳米管薄膜的场发射特性研究
利用微波等离子体化学气相沉积(MPCVD)方法，在不外加催化剂的不锈钢衬底上直接制备了碳纳米管膜，研究了其场发射特性。通过SEM和TEM观察、XRD和Raman光谱分析及场发射性能测试，可得出如下结论：
多壁碳纳米管在衬底上生长；碳纳米管取向无序。
直接将它作为场电子发射体，呈现良好的场电子发射特性。直接用ITO玻
璃作阳极时，开启场强为1.67 Vlpm，最大电流密度可达到31 nLA/c扩，且稳定，
最大电流时的场强为6.67 V/ pm。用荧光粉涂履的ITO玻璃作阳极时，开启场
强仅为2.86v/协m，在6VI协m的场强下，电流密度可达到3.75饥AjcmZ;这种
场电子发射体材料的来源广，制备方法简便且成本低，性能稳定，具有很高的应
用价值。
研究表明，不锈钢衬底的预处理条件影响碳纳米管的场发射性能。抛光和酸
洗可降低开启场强，提高发射电流密度，用荧光粉涂覆的ITO玻璃作阳极，衬
底未处理、衬底抛光、衬底既抛光又酸洗的样品的开启场强(对应于电流密度10
协川呱2)分别为2.92、1.67和2.5v/，m。当场强为6.25 v/pm时，三个样品的
电流密度分别达到1 .2、3.2和2.75In习七扩;三个样品的场强增强因子刀分别为
2446，12192，3787。以上数据说明抛光样品的开启场强低、发射电流密度大是
因为它的场强增强因子刀大。因此得出结论:基底的抛光预处理导致刀的增加，
在MPCVD系统中成功合成碳纳米管，基底的抛光预处理是必要的。文中对样
品预处理与刀因子之关系进行了分析讨论，认为不锈钢衬底的机械抛光使基底产
生不规则的突起，这些突起导致刀值的二次增强，使碳纳米管的场增强因子大大
增加;若抛光后进一步酸洗，则催化剂颗粒的活性增强，导致聚集成团，失去催
化剂活性，影响碳纳米管的生长，从而影响它的场发射性能。
沉积工艺参数影响碳纳米管薄膜的质量，从而影响它的场发射性能。在其他
沉积条件相同的情况下，甲烷浓度为8%，基体温度为700-800℃时，碳纳米管
膜较厚，碳纳米管分布均匀，这导致碳纳米管均匀电子发射;另一方面，管子的
弯曲和管中分布的催化剂颗粒引起了大量缺陷，也导致碳纳米管具有低的开启场
强和高的发射电流密度。
3)碳纳米管薄膜场发射器件制备的研究
对碳纳米管薄膜作为阴极的真空三极结构发光管器件进行了初步研制。研
究了器件结构及场发射特性。研究证明了碳纳米管薄膜是一种性能优良的冷阴极
材料。在阳极电压为5.skV，栅压为750v时，在3emZ发射面积上，可获得1.lmA
的电流值。器件的发射电流较稳定，且亮度达到1 .8 xl护ed/扩。这对进一步研
和究高清晰度、高亮度的大屏幕平板显示像素管，提供了有价值的实验基础。
Carbon nanotubes(CNTs) have attracted much attention because of their unique structure and properties since their discovery. One important potential application for the CNTs is as electron field emission sources in cold cathode flat panel displays and electron guns. In order to allow electron field emission to achieve a high electron current density, the number density of electron emission sites must be as large as possible, the emission current from each emission site must be as large as each carbon nanotube can tolerate, the emission current must be as uniform as possible among all emission sites, and the electric field screening effect caused by surrounding carbon nanotubes and other conductive structures must be reduced to an optimized level.
In this work, Carbon nanotubes films were deposited on Ni films and stainless steel substrates by microwave plasma CVD (MPCVD) method. We improved the field emission properties of carbon nanotubes films by optimizing the deposition conditions. Meantime, we fabricated cathode-ray tube (CRT) type lighting-elements.
1) Field emission properties of carbon nanotubes films grown on patterned Ni lines
Carbon nanotubes (CNTs) films were grown on patterned Ni lines coated substrate by microwave plasma chemical vapour deposition (MWPCVD). Ni films deposited on ceramics substrates by d.c. magnetron sputtering are used as catalysts for growing the CNTs. The ceramics substrates were mechanically polished using various grinding and polishing powders in order to uniform Ni film. Before growing CNTs, the Ni films were patterned to be lines by laser writing technology and then the CNTs were deposited on the catalyst patterns. The source gas for growing the CNTs was a mixture of H2 and CH4. The gas flow rate of H2 is 100 sccm, and the growth pressure was 6.5x103 Pa, various deposition times were applied to control the length of the carbon nanotubes. Scanning electron microscopy (SEM) was used to determine the morphology of carbon nanotubes. Raman spectroscopy was used to analyze the structure of carbon nanotubes. The field emission characteristics of the samples were measured by using a diode structure. The transpar
ent anode was made of coating phosphor onto an ITO coated glass plate. The CNT samples as the cathode were separated from the anode by a mica sheet with a suitable hole as the emission area. The gap between the anode and the cathode was 500 um. The measurement was conducted under pressure of 3.6x10-5 Pa.. By varying process conditions such as Ni layer
thickness, gas flow rate, deposition time, reactive temperature, the optimum conditions for field electron emission were found. When gas flow rate of CH4 was 5 sccm, Ni film thickness was 150 nm, deposition time was 5 min, and reactive temperature was 700-800C, the field emission properties are best. At this condition, all nanotubes are well aligned as characterized by SEM. Turn-on field of 1.3 V/u m, emission current density of 6.8 mA/cm2 and field enhancement factor of 8477 were achieved.
2) Field emission properties of carbon nanotubes films on stainless steel substrates Carbon nanotubes (CNTs) were synthesized from methane and hydrogen gas mixture directly
on stainless steel plates by microwave plasma chemical vapor deposition (MWPCVD). The SEM images show that the CNTs are of uniform with high density and lest amorphous carbon quantity, and their diameters are ranged from 30 to 60 nm, they are multi-wall nanotubes. The Raman spectrum shows more defect density in nanotube . In the field emission test, when anode was made of an ITO coated glass plate, the current density of sample attains 31 mA/cm2, at the electric field of 6.67 V/ u m, but when anode was made of coating phosphor onto an ITO coated glass plate, the current density attains 3.75 mA/cm2, at the electric field of 6 V/u m. The CNTs film could be a good cold cathode for flat panel display applications.
Pretreatment conditions of stainless steel substrates influence on field emission properties of carbon nanotubes. By varying pretreatment conditions of the subs
本研究工作尝试了几种改善碳纳米管薄膜场致发射性能的方法，研究了沉积工艺参数等对碳纳米管薄膜场致电子发射特性的影响规律，得到了一些新的研究结果。在此基础上，利用在不锈钢衬底上制备的碳纳米管薄膜作为阴极研制了三极管结构的发光管。
1) 刻线镍膜上沉积的碳纳米管场发射特性研究
利用微波等离子体化学气相沉积(MPCVD)方法，在刻线的镍膜上沉积了碳纳米管膜。通过扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射光谱(XRD)和拉曼光谱表征研究了其微观结构，并讨论了催化剂厚度、制备温度、反应时间以及甲烷浓度对碳纳米管质量和场发射性能的影响。结果表明：甲烷浓度、生长时间、镍膜厚度以及反应温度对碳纳米管的生长都有影响，在一定条件下，可在镍膜上沉积垂直于衬底的高度取向的碳纳米管膜；不同条件下制备的碳纳米管的场发射性能有很大差异，保持氢气的流量(100 sccm)不变，当甲烷流量为5 sccm、生长时间为5 min、催化剂膜厚为150 nm、温度为700～800℃时，场发射性能最好，开启场强为1.3 V／μm，最大发射电流密度达到6.8mA／cm~2。而平板显示器要求的电流密度为1 mA／cm~2。
2) 不锈钢衬底直接沉积碳纳米管薄膜的场发射特性研究
利用微波等离子体化学气相沉积(MPCVD)方法，在不外加催化剂的不锈钢衬底上直接制备了碳纳米管膜，研究了其场发射特性。通过SEM和TEM观察、XRD和Raman光谱分析及场发射性能测试，可得出如下结论：
多壁碳纳米管在衬底上生长；碳纳米管取向无序。
直接将它作为场电子发射体，呈现良好的场电子发射特性。直接用ITO玻
璃作阳极时，开启场强为1.67 Vlpm，最大电流密度可达到31 nLA/c扩，且稳定，
最大电流时的场强为6.67 V/ pm。用荧光粉涂履的ITO玻璃作阳极时，开启场
强仅为2.86v/协m，在6VI协m的场强下，电流密度可达到3.75饥AjcmZ;这种
场电子发射体材料的来源广，制备方法简便且成本低，性能稳定，具有很高的应
用价值。
研究表明，不锈钢衬底的预处理条件影响碳纳米管的场发射性能。抛光和酸
洗可降低开启场强，提高发射电流密度，用荧光粉涂覆的ITO玻璃作阳极，衬
底未处理、衬底抛光、衬底既抛光又酸洗的样品的开启场强(对应于电流密度10
协川呱2)分别为2.92、1.67和2.5v/，m。当场强为6.25 v/pm时，三个样品的
电流密度分别达到1 .2、3.2和2.75In习七扩;三个样品的场强增强因子刀分别为
2446，12192，3787。以上数据说明抛光样品的开启场强低、发射电流密度大是
因为它的场强增强因子刀大。因此得出结论:基底的抛光预处理导致刀的增加，
在MPCVD系统中成功合成碳纳米管，基底的抛光预处理是必要的。文中对样
品预处理与刀因子之关系进行了分析讨论，认为不锈钢衬底的机械抛光使基底产
生不规则的突起，这些突起导致刀值的二次增强，使碳纳米管的场增强因子大大
增加;若抛光后进一步酸洗，则催化剂颗粒的活性增强，导致聚集成团，失去催
化剂活性，影响碳纳米管的生长，从而影响它的场发射性能。
沉积工艺参数影响碳纳米管薄膜的质量，从而影响它的场发射性能。在其他
沉积条件相同的情况下，甲烷浓度为8%，基体温度为700-800℃时，碳纳米管
膜较厚，碳纳米管分布均匀，这导致碳纳米管均匀电子发射;另一方面，管子的
弯曲和管中分布的催化剂颗粒引起了大量缺陷，也导致碳纳米管具有低的开启场
强和高的发射电流密度。
3)碳纳米管薄膜场发射器件制备的研究
对碳纳米管薄膜作为阴极的真空三极结构发光管器件进行了初步研制。研
究了器件结构及场发射特性。研究证明了碳纳米管薄膜是一种性能优良的冷阴极
材料。在阳极电压为5.skV，栅压为750v时，在3emZ发射面积上，可获得1.lmA
的电流值。器件的发射电流较稳定，且亮度达到1 .8 xl护ed/扩。这对进一步研
和究高清晰度、高亮度的大屏幕平板显示像素管，提供了有价值的实验基础。
Carbon nanotubes(CNTs) have attracted much attention because of their unique structure and properties since their discovery. One important potential application for the CNTs is as electron field emission sources in cold cathode flat panel displays and electron guns. In order to allow electron field emission to achieve a high electron current density, the number density of electron emission sites must be as large as possible, the emission current from each emission site must be as large as each carbon nanotube can tolerate, the emission current must be as uniform as possible among all emission sites, and the electric field screening effect caused by surrounding carbon nanotubes and other conductive structures must be reduced to an optimized level.
In this work, Carbon nanotubes films were deposited on Ni films and stainless steel substrates by microwave plasma CVD (MPCVD) method. We improved the field emission properties of carbon nanotubes films by optimizing the deposition conditions. Meantime, we fabricated cathode-ray tube (CRT) type lighting-elements.
1) Field emission properties of carbon nanotubes films grown on patterned Ni lines
Carbon nanotubes (CNTs) films were grown on patterned Ni lines coated substrate by microwave plasma chemical vapour deposition (MWPCVD). Ni films deposited on ceramics substrates by d.c. magnetron sputtering are used as catalysts for growing the CNTs. The ceramics substrates were mechanically polished using various grinding and polishing powders in order to uniform Ni film. Before growing CNTs, the Ni films were patterned to be lines by laser writing technology and then the CNTs were deposited on the catalyst patterns. The source gas for growing the CNTs was a mixture of H2 and CH4. The gas flow rate of H2 is 100 sccm, and the growth pressure was 6.5x103 Pa, various deposition times were applied to control the length of the carbon nanotubes. Scanning electron microscopy (SEM) was used to determine the morphology of carbon nanotubes. Raman spectroscopy was used to analyze the structure of carbon nanotubes. The field emission characteristics of the samples were measured by using a diode structure. The transpar
ent anode was made of coating phosphor onto an ITO coated glass plate. The CNT samples as the cathode were separated from the anode by a mica sheet with a suitable hole as the emission area. The gap between the anode and the cathode was 500 um. The measurement was conducted under pressure of 3.6x10-5 Pa.. By varying process conditions such as Ni layer
thickness, gas flow rate, deposition time, reactive temperature, the optimum conditions for field electron emission were found. When gas flow rate of CH4 was 5 sccm, Ni film thickness was 150 nm, deposition time was 5 min, and reactive temperature was 700-800C, the field emission properties are best. At this condition, all nanotubes are well aligned as characterized by SEM. Turn-on field of 1.3 V/u m, emission current density of 6.8 mA/cm2 and field enhancement factor of 8477 were achieved.
2) Field emission properties of carbon nanotubes films on stainless steel substrates Carbon nanotubes (CNTs) were synthesized from methane and hydrogen gas mixture directly
on stainless steel plates by microwave plasma chemical vapor deposition (MWPCVD). The SEM images show that the CNTs are of uniform with high density and lest amorphous carbon quantity, and their diameters are ranged from 30 to 60 nm, they are multi-wall nanotubes. The Raman spectrum shows more defect density in nanotube . In the field emission test, when anode was made of an ITO coated glass plate, the current density of sample attains 31 mA/cm2, at the electric field of 6.67 V/ u m, but when anode was made of coating phosphor onto an ITO coated glass plate, the current density attains 3.75 mA/cm2, at the electric field of 6 V/u m. The CNTs film could be a good cold cathode for flat panel display applications.
Pretreatment conditions of stainless steel substrates influence on field emission properties of carbon nanotubes. By varying pretreatment conditions of the subs
引文
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[2]Liao M Y, Zhang Z G, Wang W L, et al. Field Emission Current from Diamond Film Deposited on Molybdenum. J. Appl. Phys., 1998; 84(2):1081.
[3]C A. Spindt, J Appl. Phys., 1968, 39:3504
[4]王保平，雷威，编著．真空微电子学及其应用．东南大学出版社，南京，2002．
[5]陈献忠，姚汉民，陈旭南，等．纳米光刻技术的现状和未来．物理，2002，31(11)：691．
[6]Spallas J P, Hawryluk A M, Kania D R. Field Emitter Array Mask Pattering Using Laser Interference Lithography. J Vac Sci Technol, 1995, B13:1973.
[7]陈光华，邵乐喜，贺德衍，刘小平．物理，2000，Vol．29，no5．
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