Deeper insights into the structure of multi-walled carbon nanotubes

Although Raman spectroscopy is a robust, non-destructive chemical analysis, its application to characterize multi-walled carbon nanotubes (MWCNTs) is challenging due to its inhomogeneity, structural complexity, and complex van der Waals interactions.

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​​​​​​Stady: The role of mechanical van der Waals coupling in the G-band splitting of single multi-walled carbon nanotubes. Image Credit: lucadp / Shutterstock.com

However, heterogeneity and vdW interactions in single multiwalled carbon nanotubes can be investigated by common analytical techniques, including atomic force microscopy (AFM), polarized Raman imaging, and spectroscopy through a multiple arc-discharge (AD) purification setup. on the chip. – Parietal carbon nanotube powder.

Article published in Journal of Physical Chemistry c Discuss the heterogeneity in individual AD multiwalled carbon nanotubes which is determined by Raman signal by extracting the inner layers of multiwalled carbon nanotubes during the sonication phase of the dispersion procedure.

Active Raman G-band splitting was observed and described in terms of the interlayer variable vdW coupling as a function of interlayer distance and diameter in the tested multiwalled carbon nanotubes.

Moreover, Raman maps and advanced data synthesis were used to investigate the polarization behavior of multi-walled carbon nanotubes that resulted in a non-uniform Raman response. Thus, the present work has given insights into heterogeneous multiwalled carbon nanotubes and distinguished between one-dimensional (1D) ripple crystals and multiwalled carbon nanotubes based on disjointed single-walled carbon nanotubes (SWCNTs) or by investigating the 1D vdW heterostructures via Raman spectroscopy.

Study of multiwalled carbon nanotubes using Raman spectroscopy

Multi-walled carbon nanotubes is a special form of carbon nanotubes in which several single-walled carbon nanotubes are nested inside each other. They are mechanically strong due to sp2 The type of carbon-carbon bond. It has a large surface area on the outer side and a wide cavity on the inner side and is often applied for packaging and molecular grafting.

The optical and electronic properties of multi-walled carbon nanotubes are determined by the metallic and semiconducting nature of the individual walls depending on the varying bandgap given by the diameter and the chiral (chiral) angle. Besides, the electronic band structure of multiwalled carbon nanotubes has flat bands or pseudo-caps due to tunable vdW electronic coupling and moiré interference.

Raman spectroscopy is an analytical technique where scattered light is used to measure the vibrational energy modes of a sample. The Raman effect arises from the inelastic scattering of light and can directly examine the vibrational/rotational vibration states in the samples.

Raman spectroscopy yields information about purity, defects, and tube alignment and helps distinguish the presence of multiwalled carbon nanotubes relative to other carbon allotropes. Raman spectroscopy has been strikingly successful in characterizing the structural properties of polynitrogen sulfur nanotubes (SWCNTs). Unfortunately, the interpretation of the spectra for multiwalled carbon nanotubes is often very complex and has not yet yielded a band output similar to what was achieved by Raman spectroscopy of carbon nanotubes.

Characterization of multiwalled carbon nanotubes

Identification of multiwalled carbon nanotubes is a prerequisite for many basic studies. Resonant Raman spectroscopy (RRS) can be a powerful technique in this framework, which previously provided substantial information on SWCNTs. However, the heterogeneity, structural complexity and complex interlayer interactions with vdW in multiwalled carbon nanotubes restrict the application of the RRS technique and do not yield similar outputs.

In the present work, the role of structural heterogeneity and vdW mechanical coupling for characterization of single multiwalled carbon nanotubes was investigated via combined AFM and RRS measurements and polarized Raman imaging.

Single pure multi-walled carbon nanotubes were obtained from their AD composite versions via the on-chip purification method. The results revealed that the irregularity of the Raman signal of AD multiwalled carbon nanotubes was due to extraction or damage to the inner layers by the scattering sonication step.

Single multi-walled carbon nanotubes isolated with active Raman G-band splitting have been reported, which is described in terms of the interlayer mechanical vdW coupling and a function of the interlayer distance and diameter. Thus, the present work has added insights into structurally heterogeneous multiwalled carbon nanotubes, allowing the distinction between multiwalled carbon nanotubes and one-dimensional ripple crystals.

conclusion

In conclusion, the heterogeneity of the Raman signal obtained from AD multiwalled carbon nanotubes is attributed to the extraction or damage of the inner layers during the scattering procedure. Furthermore, the splitting of the active G band Raman in single multiwalled carbon nanotubes was explained in relation to the effect of mechanical vdW coupling of the interlayer.

Ultimately, the present work revealed a practical approach to determine the polarization behavior of multiwalled carbon nanotubes via the non-uniform Raman response through Raman mapping and advanced data synthesis that also helped determine the antenna effect. Thus, the present work gave an insight into the structure of multiwalled carbon nanotubes and distinguished between multiwalled carbon nanotubes and one-dimensional ripple crystals.

reference

Avramenko, M. V., Hokkanen, M. J., Slabodyan, Y., Ahlskog, M., Levshov, D.I. (2022). The role of the mechanical van der Waals coupling in GScale division of individual multi-walled carbon nanotubes. Journal of Physical Chemistry c.

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