Influence of the growth temperature on the first and second-order Raman band ratios and widths of carbon nanotubes and fibers

Multi-walled carbon nanotubes (MWCNT) and carbon nanofibers (CNF) were created using chemical vapor deposition at growth temperatures between 500 and 750 °C, which have increasing crystallinity with increasing growth temperature. We used Raman spectroscopy to analyze the samples. The intensity ratios compared to the G-band, and full-width at half-maximum, of all observable Raman bands in both the first and second-order region were investigated. Good match was observed for the defect related bands of the MWCNT samples and data found in the literature. Several second-order bands display a strong dependency to growth temperature. Similar growth temperature (and thus defect) dependencies were found between several first and second-order bands, which might aid in determining the physical causes of these bands. CNF show much weaker Raman features due to their low crystallinity, making them more difficult to analyse. The results of this work are used to give recommendations on how to investigate MWCNT and CNF crystallinity using Raman spectroscopy. Finally, we demonstrate that Raman spectroscopy can be used to distinguish between the MWCNT root and tip growth mechanism.