Analysis of Oxidation State of Multilayered Catalyst Thin Films for Carbon Nanotube Growth Using Plasma-Enhanced Chemical Vapor Deposition
Analysis of Oxidation State of Multilayered Catalyst Thin Films for Carbon Nanotube Growth Using Plasma-Enhanced Chemical Vapor Deposition
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DOI：
10.1143/jjap.45.8323
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发表时间：
2006-10
影响因子：
1.5
通讯作者：
A. Okita;Atsushi Ozeki;Y. Suda;J. Nakamura;A. Oda;K. Bhattacharyya;H. Sugawara;Y. Sakai
中科院分区：
文献类型：
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作者：
A. Okita;Atsushi Ozeki;Y. Suda;J. Nakamura;A. Oda;K. Bhattacharyya;H. Sugawara;Y. Sakai
采用射频（13.56 MHz） CH4/H2/Ar等离子体增强化学气相沉积技术，利用多层催化剂薄膜（Fe/Al2O3和Al2O3/Fe/Al2O3）合成了垂直排列的碳纳米管（CNTs）。催化剂的预处理是碳纳米管生长的关键。本文分析了催化剂还原对碳纳米管生长的影响。在550℃条件下，通过H2等离子体预处理将基底上的催化剂薄膜还原成纳米级催化剂颗粒。对多层薄膜进行了分析；通过x射线光电子能谱（XPS）和扫描电子显微镜（SEM）分析了材料的化学成分和氧化状态。XPS光谱的fe2p峰表明，预处理时间为4 min后，沉积催化剂中的FexOy被有效还原为Fe。使用这种催化剂，我们得到的碳纳米管的平均直径为10.7 nm，平均长度为5.3µm。然而，预处理时间超过4 min， CNTs变短，Fe峰从Fe转移到Fe3O4。这些转变（Fe2O3→Fe3O4→Fe→Fe3O4）可以用氧化物的焓来解释。这一结果表明，存在一个最佳的比例之间的铁和feexoy最大化碳纳米管的长度。
We synthesized vertically aligned carbon nanotubes (CNTs) using multilayered catalyst thin films (Fe/Al2O3 and Al2O3/Fe/Al2O3) by RF (13.56 MHz) CH4/H2/Ar plasma-enhanced chemical vapor deposition. Pretreatment of the catalyst is crucial for CNT growth. In this paper, we analyzed the effect of catalyst reduction on CNT growth. Catalyst thin films on substrates were reduced by H2 plasma pretreatment at 550 °C to form nanometer-sized catalyst particles. The multilayered thin films were analyzed; the chemical composition and oxidation state by X-ray photoelectron spectroscopy (XPS) and the surface morphology by scanning electron microscopy (SEM). The Fe 2p peak of the XPS spectra showed that FexOy in the as-deposited catalyst was effectively reduced to Fe by a pretreatment of duration 4 min. Using this catalyst, we obtained CNTs with an average diameter of 10.7 nm and an average length of 5.3 µm. However, pretreatment longer than 4 min resulted in shorter CNTs and the Fe peak was shifted from Fe to Fe3O4. These transitions (Fe2O3→Fe3O4→Fe→Fe3O4) can be explained by the enthalpy of the oxides. This result indicates the presence of an optimum ratio between Fe and FexOy to maximize the CNT lengths.