Han Si-ping, Goddard William A
Materials and Properties Simulation Center, California Institute of Technology, Pasadena, California 91125.
J Phys Chem B. 2009 May 21;113(20):7199-204. doi: 10.1021/jp805828g.
Measurements of the radial breathing modes from Raman Spectroscopy have been most useful in characterizing the diameters of single-wall carbon nanotubes (SWNT), where there is a simple monotonic relationship between frequency and diameter. Similar correlations have also been used to predict sizes for double and multiple wall nanotubes and for bundles of SWNT. However this can lead to significant errors because the relationship between frequencies and diameter is much more complicated for DWNT. This is because of couplings between the vibrations of various walls. To provide guidance in such assignments we used the GraFF atomistic force field to predict the in-phase and counter-phase radial breathing modes (RBMs) of double wall carbon nanotubes (DWNTs) over a broad range of inner and outer diameters and chiralities. We then developed an analytical model to describe the RBMs of dispersed DWNTs. This enables the inner and outer shell diameters to be extracted from pairs of RBM peaks. We find that nanotubes bundles show significant dependent peak broadening and shifting compared to dispersed nanotubes. For bundles of SWNT and DWNT, the relationships are much more complicated.
通过拉曼光谱对径向呼吸模式进行测量，在表征单壁碳纳米管（SWNT）的直径方面最为有用，频率与直径之间存在简单的单调关系。类似的相关性也被用于预测双壁和多壁纳米管以及单壁碳纳米管束的尺寸。然而，这可能会导致显著误差，因为对于双壁纳米管（DWNT），频率与直径之间的关系要复杂得多。这是由于各壁振动之间的耦合。为了在这类任务中提供指导，我们使用GraFF原子力场来预测双壁碳纳米管（DWNT）在广泛的内径、外径和手性范围内的同相和反相径向呼吸模式（RBM）。然后我们开发了一个分析模型来描述分散的双壁纳米管的径向呼吸模式。这使得能够从成对的径向呼吸模式峰中提取内壳和外壳直径。我们发现，与分散的纳米管相比，纳米管束显示出显著的峰展宽和峰位移依赖性。对于单壁碳纳米管束和双壁碳纳米管束，其关系要复杂得多。
