Role of Mechanical van der Waals Coupling in the G-Band Splitting of Individual Multiwall Carbon Nanotubes

Abstract

Characterization of multiwalled carbon nanotubes (MWCNT) by Raman spectroscopy is challenging due to their structural complexity, inhomogeneity, and complicated interlayer van der Waals (vdW) interactions. These latter effects can be however well investigated in individual MWCNTs, prepared by the on-chip purification of arc-discharge (AD) MWCNT powder, combining atomic force microscopy, polarized Raman imaging, and spectroscopy. In this work, we reveal the inhomogeneity of the Raman signal from individual AD-MWCNTs and attribute it to the extraction of inner layers during the sonication stage of the dispersion procedure. We report the splitting of the Raman-active G-band, describing it in terms of the variation of interlayer mechanical vdW coupling as a function of diameter and interlayer distance in the probed AD-MWCNTs. Finally, we present a practical method for investigating the polarization behavior of MWCNTs with a nonuniform Raman response based on Raman mapping and advanced data fitting. Our work gives additional insights into the characterization of structurally nonuniform MWCNTs and allows distinguishing between these MWCNTs and 1D moiré crystals based on collapsed SWCNTs or studying telescopic 1D vdW heterostructures with Raman spectroscopy.