Changes in the vibrational modes of carbon nanotubes induced by electron-beam irradiation: Resonance Raman spectroscopy
Changes in the vibrational modes of carbon nanotubes induced by electron-beam irradiation: Resonance Raman spectroscopy
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DOI：
10.1002/jrs.1622
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发表时间：
2007-02-01
影响因子：
2.5
通讯作者：
Patel, R. J.
中科院分区：
文献类型：
--
作者：
Gupta, S.;Patel, R. J.
研究了电子束（e-beam）辐照对微波化学气相沉积技术生长的多壁（MW）和单壁（SW）碳纳米管薄膜的影响。这些薄膜在扫描电子显微镜下承受 50 keV 的电子束能量 2.5、5.5、8.0 和 15 小时，并在透射电子显微镜下承受 100 和 200 keV 的电子束能量几分钟至大约 2 小时。这种条件类似于增加温度和压力的状态，从而实现一定程度的结构流动性。为了评估结构修饰，除了通过电子显微镜进行原位监测之外，还使用共振拉曼光谱（RRS）在照射之前和之后对它们进行了分析。实验表明，随着长时间的暴露，两种类型的纳米管都表现出各种局部结构不稳定性，包括收缩、石墨化/非晶化，以及可能通过无定形碳聚集体在电子束聚焦区域内形成分子内结（IMJ）。 RRS揭示了辐射在晶格中产生的缺陷，通过以下方式量化：（1）径向呼吸模式（RBM）强度的变化，（2）D与G带的强度比（I-D/I-G），以及（3）D和G带的位置及其谐波（D*和G*）和组合带（D + G）。其中一些影响包括缺陷引起的 D 带强度的增加、RBM 强度的淬灭以及 G 带强度的轻微增加。 MW纳米管在长时间暴露下往往会达到饱和状态，而SW纳米管则从半导体特性转变为准金属特性。建议软化 q = 0 选择规则作为解释这些结果的可能原因。此外，这些研究还提供了 MW 和 SW 纳米管之间的对比。版权所有 (C) 2006 John Wiley & Sons, Ltd.
Influence of electron-beam (e-beam) irradiation on multi-walled (MW) and single-walled (SW) carbon nanotube films grown by microwave chemical vapor deposition technique is investigated. These films were subjected to an e-beam energy of 50 keV from a scanning electron microscope for 2.5, 5.5, 8.0, and 15 h, and to 100 and 200 keV from a transmission electron microscope for a few minutes to similar to 2 h continuously. Such conditions resemble an increased temperature and pressure regime enabling a degree of structural fluidity. To assess structural modifications, they were analyzed prior to and after irradiation using resonance Raman spectroscopy (RRS) in addition to in situ monitoring by electron microscopy. The experiments showed that with extended exposures, both types of nanotubes displayed various local structural instabilities including pinching, graphitization/amorphization, and formation of an intramolecular junction (IMJ) within the area of electron beam focus possibly through amorphous carbon aggregates. RRS revealed that irradiation generated defects in the lattice as quantified through (1) variation of the intensity of radial breathing mode (RBM), (2) intensity ratio of D to G band (I-D/I-G), and (3) positions of the D and G bands and their harmonics (D* and G*) and combination bands (D + G). The increase in the defect-induced D band intensity, quenching of RBM intensity, and only a slight increase in G band intensity are some of the implications. The MW nanotubes tend to reach a state of saturation for prolonged exposures, while the SW ones transform from a semiconducting to a quasi-metallic character. Softening of the q = 0 selection rule is suggested as a possible reason to explain these results. Furthermore, these studies provide a contrasting comparison between MW and SW nanotubes. Copyright (C) 2006 John Wiley & Sons, Ltd.