Dillon A C, Yudasaka M, Dresselhaus M S
National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, Colorado 80401, USA.
J Nanosci Nanotechnol. 2004 Sep;4(7):691-703. doi: 10.1166/jnn.2004.116.
Carbon single-wall nanotubes (SWNTs) have highly unique electronic, mechanical and adsorption properties, making them interesting for a variety of applications. Raman spectroscopy has been demonstrated to be one of the most important methods for characterizing SWNTs. For example, Raman spectroscopy may be employed to differentiate between metallic and semi-conducting nanotubes, and may also be employed to determine SWNT diameters and even the nanotube chirality. Single-wall carbon nanotubes are generated in a variety of ways, including arc-discharge, laser vaporization and various chemical vapor deposition (CVD) techniques. In all of these methods, a metal catalyst must be employed to observe SWNT formation. Also, all of the current synthesis techniques generate various non-nanotube carbon impurities, including amorphous carbon, fullerenes, multi-wall nanotubes (MWNTs) and nano-crystalline graphite, as well as larger micro-sized particles of graphite. For any of the potential nanotube applications to be realized, it is, therefore, necessary that purification techniques resulting in the recovery of predominantly SWNTs at high-yields be developed. It is, of course, equally important that a method for determining nanotube wt.% purity levels be developed and standardized. Moreover, a rapid method for qualitatively measuring nanotube purity could facilitate many laboratory research efforts. This review article discusses the application of Raman spectroscopy to rapidly determine if large quantities of carbon impurities are present in nanotube materials. Raman spectra of crude SWNT materials reveal tangential bands between 1500-1600 cm(-1), as well as a broad band at approximately 1350 cm(-1), attributed to a convolution of the disorder-induced band (D-band) of carbon impurities and the D-band of the SWNTs themselves. Since the full-width-at-half-maximum (FWHM) intensity of the various carbon impurity D-bands is generally much broader than that of the nanotube D-band, an indication of the SWNT purity level may be obtained by simply examining the line-width of the D-band. We also briefly discuss the effect of nanotube bundling on SWNT Raman spectra. Finally, sections on employing Raman spectroscopy, and Raman spectroscopy coupled with additional techniques, to identify the separation and possible isolation of a specific nanotube within purified SWNT materials is provided. Every SWNT can be considered to be a unique molecule, with different physical properties, depending on its (n, m) indices. The production of phase-pure (n, m) SWNTs may be essential for some nanotube applications.
碳单壁纳米管（SWNTs）具有高度独特的电子、机械和吸附特性，这使得它们在各种应用中备受关注。拉曼光谱已被证明是表征SWNTs最重要的方法之一。例如，拉曼光谱可用于区分金属型和半导体型纳米管，还可用于确定SWNT的直径甚至纳米管的手性。单壁碳纳米管通过多种方式生成，包括电弧放电、激光蒸发和各种化学气相沉积（CVD）技术。在所有这些方法中，都必须使用金属催化剂来观察SWNT的形成。此外，目前所有的合成技术都会产生各种非纳米管碳杂质，包括无定形碳、富勒烯、多壁纳米管（MWNTs）和纳米晶石墨，以及更大的微米级石墨颗粒。因此，为了实现任何潜在的纳米管应用，有必要开发能够高产率回收主要为SWNTs的纯化技术。当然，同样重要的是要开发并标准化一种确定纳米管重量百分比纯度水平的方法。此外，一种快速定性测量纳米管纯度的方法可以促进许多实验室研究工作。这篇综述文章讨论了拉曼光谱在快速确定纳米管材料中是否存在大量碳杂质方面的应用。粗SWNT材料的拉曼光谱显示在1500 - 1600 cm⁻¹之间有切向带，以及在约1350 cm⁻¹处有一个宽带，这归因于碳杂质的无序诱导带（D带）和SWNTs自身的D带的卷积。由于各种碳杂质D带的半高宽（FWHM）强度通常比纳米管D带的宽得多，通过简单检查D带的线宽就可以获得SWNT纯度水平的指示。我们还简要讨论了纳米管束对SWNT拉曼光谱的影响。最后，提供了关于使用拉曼光谱以及拉曼光谱与其他技术相结合来识别纯化的SWNT材料中特定纳米管的分离和可能的分离的章节。每个SWNT都可以被视为一个独特的分子，根据其（n，m）指数具有不同的物理性质。对于某些纳米管应用，生产相纯的（n，m）SWNTs可能至关重要。
