Excitation energy dependence of Raman bands in multiwalled carbon nanotubes

Abstract

Vertically aligned multiwalled carbon nanotubes (MWCNTs) were grown on 1-and 3-nm cobalt (Co) films, at various growth times by microwave plasma enhanced chemical vapor deposition technique and their microstructural properties were analyzed with the help of Raman spectra that were obtained from different sources of laser excitation energies (E L : 2.41, 1.96 and 1.58 eV). The variation of D and G band positions in MWCNTs grown on 1-and 3-nm Co films follows a similar behavior, and an anomalous behavior was observed in the E L dependence of the D -band wavenumber. In the second-order spectra, the G band varied strongly according to structure with the laser excitation energy (E L ). The I D /I G ratio decreased with the increase of E L for all MWCNTs; however, for a fixed E L , the I D /I G dispersion is higher at lower E L . The crystallite sizes were estimated using I D I G and E L . We have shown that, for all MWCNTs, I D /I G ratio is inversely proportional to E 4 L .

Carbon nanotube-nanoporous anodic alumina composite membranes with controllable inner diameters and surface chemistry: Influence on molecular transport and chemical selectivity

“…This ID/IG ratio is comparable to the ID/IG ratio of CNTs obtained by other CVD synthesis approaches using NAAMs as templates while using ethylene and acetylene as carbon sources (ID/IG = 0.79 and 1.38 respectively) [22,39]. However, it should be taken into account that the ID/IG ratio is dependent on the excitation energy [40]. It is worth stressing that CNTs prepared through template-directed method using a catalyst-free CVD approach can be easily graphitized by further thermal treatment at temperatures as high as 2000°C, which in turn drops the ID/IG ratio to a minimum of 0.27 [38].…”

Recent advances in linear and nonlinear Raman spectroscopy. Part V

“…Vertically aligned multiwalled CNTs were grown by Sion et al . on 1‐ and 3‐nm cobalt films with various growth times by a microwave plasma‐enhanced chemical vapor deposition technique, and their microstructural properties were analyzed with the help of Raman spectra that were obtained from different sources of laser excitation energies …”

Ex-situRaman spectroscopy to optimize the manufacturing process for a structural MWNT nanocomposite

“…Monitoring defects during this resin infusion process is more complicated and may require multiple laser excitations to fully understand the effects of the modified band gap of the MWNT-POSS-resin structure. Using multiple laser excitation in studying the double resonance Raman relationships has been the focus of many researchers recently [18,37], and should be used to study similar manufacturing processes in the future.…”

“…The disorder induced D-band in the Raman spectra indicates the presence of a variety of defects [14,15] and amorphous carbon [16] on the CNT. The D/G ratio has been reported to yield crystallite size (L a ) with a given excitation energy [17,18], using both intensity and integrated intensity ratios [17]. However, a study comparing it to data obtained via X-ray diffraction suggests the relation should be used with care [19].…”

“…However, a study comparing it to data obtained via X-ray diffraction suggests the relation should be used with care [19]. Despite this, the D/G ratio remains a popular choice in relating defect density for CNTs [12,14,18]. In this study, we introduce a method of using Raman spectra to qualitatively relate defect density on the MWNT surface across the different stages of the manufacturing process.…”