(n,m) Assignments and quantification for single-walled carbon nanotubes on SiO2/Si substrates by resonant Raman spectroscopy

The single-walled carbon nanotubes (SWNTs) on silicon substrates are a promising candidate for the next generation of electronic and photoelectronic devices, therefore an easy, convenient, and nondestructive method for characterizing such samples is quite important and strongly needed. In this study, we provide in detail such a method to assign (n,m) indices with considerable accuracy through resonant Raman spectra analysis. We developed an equation of omega(RBM) = 235.9/d(t) + 5.5 for SWNTs grown by Ni, Co, and Fe catalysts on SiO2/Si substrates in the d(t) range of 1.2-2.1 nm. This method was further utilized to make (n,m) assignments and quantification for our SWNTs catalyzed by W6Co7, which is highly enriched with (12,6). The less abundant chiralities in the samples were also assigned and the contents were analyzed using a counting-based method. Moreover, these chirality-specified samples allowed us to collect 1330 RBM data for the single chirality (12,6) and the RBM variation was found to be no larger than +/- 2.5 cm(-1). A step-by-step procedure is also provided as a general guide for (n,m) assignments.