The chirality (n,m) determines all structures and properties of a single-walled carbon nanotube (SWNT), therefore, accurate and convenient (n,m) assignments are vital in nanotube-related science and technology. Previously, a so-called Kataura plot that protracts the excitonic transition energies (Eii’s) of SWNTs with various (n,m) with respect to the tube diameter (dt) has been widely utilized by researchers in the nanotube community for all (n,m)-related studies. However, the facts that both Eii and the calculated dt are subject to interactions with the environments make it inconvenient to accurately determine the (n,m) under complex environments. Here, we propose a series of bilayer plots that take into account the interactions between the SWNTs and the environments so that the (n,m) of SWNTs can be accurately determined. These plots have more advantages than the Kataura plot in concision, less data overlapping, and the suitability to be used in complex environments. We strongly encourage the researchers in the carbon nanotube community to utilize the bilayer plots for all (n,m)-related studies, especially for accurate and convenient (n,m) determination.Keywords: bilayer plots; chirality assignments; Kataura plot; Raman spectroscopy; single-walled carbon nanotubes;

Graphene oxides (GO) can be considered as polyelectrolytes with surfactant-like characteristics. On one hand, due to the electrical repulsion between the negatively charged ionized edges, GO exhibits great water solubility; on the other hand, its hydrophobic central plane retains the potential of strong π–π interaction with other conjugated sp2 network structures. Therefore, it is expected that GO can serve as an excellent dispersing agent for dispersion of various carbon-based nanomaterials in aqueous phase. Here we report a systematic study of dispersing various carbon-based nanomaterials, including SWNTs, C60, and graphene, by aqueous GO. The GO-dispersed all-carbon nanocomposites are characterized using various spectroscopic methods and electron microscopies, and their stabilities are tested. Compared to other dispersing agents, the GO concentration is much lower than the concentrations of other dispersing agents used when similar contents of carbon-based nanomaterials are dispersed. Involving only simple ultrasonication and centrifugation processes, GO dispersion thus offers an easy manipulation for large-scale solution-dispersed all-carbon nanocomposites.

In this work, we report an accurate and convenient method that can be used to assign the chirality of all metallic single-walled carbon nanotubes (M-SWNTs). This method is designed based on the electronic Raman scattering (ERS) features, which are resonantly enhanced at the corresponding excitonic transition energies (Mii+ and Mii–). Using this method, we are able to accurately determine the electronic property Mii with the resolution of a vibrational Raman spectroscopy (∼0.3 meV), which is significantly higher than that of the electronic spectroscopies (∼3 meV). We use the Mii splitting value, which is found insensitive to environmental changes, as a universal criteria for (n,m) assignments in various environments. As an illustrative example, simply using a commercialized Raman spectrometer with two laser lines (1.959 and 2.330 eV), we are able to unambiguously assign 18 metallic chiralities with M11 in the 1.6–2.3 eV range in our samples. This method provides an accurate database of Mii’s in a similar way as photoluminescence excitation spectroscopy does for Sii’s. It can facilitate further systematic studies on the properties of M-SWNTs with defined chirality.Keywords: chirality assignments; electronic Raman scattering; Mii splitting; resonant Raman spectroscopy; single-walled carbon nanotubes;

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 ωRBM = 235.9/dt + 5.5 for SWNTs grown by Ni, Co, and Fe catalysts on SiO2/Si substrates in the dt 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.

Graphene oxides (GO) can be considered as polyelectrolytes with surfactant-like characteristics. On one hand, due to the electrical repulsion between the negatively charged ionized edges, GO exhibits great water solubility; on the other hand, its hydrophobic central plane retains the potential of strong π–π interaction with other conjugated sp2 network structures. Therefore, it is expected that GO can serve as an excellent dispersing agent for dispersion of various carbon-based nanomaterials in aqueous phase. Here we report a systematic study of dispersing various carbon-based nanomaterials, including SWNTs, C60, and graphene, by aqueous GO. The GO-dispersed all-carbon nanocomposites are characterized using various spectroscopic methods and electron microscopies, and their stabilities are tested. Compared to other dispersing agents, the GO concentration is much lower than the concentrations of other dispersing agents used when similar contents of carbon-based nanomaterials are dispersed. Involving only simple ultrasonication and centrifugation processes, GO dispersion thus offers an easy manipulation for large-scale solution-dispersed all-carbon nanocomposites.

To explore poly(phenylacetylene) (PPA) derivatives as the dispersing agent of single-walled carbon nanotubes (SWNTs), we synthesized a new series of side chain PPAs (denoted as PPA-m, m = 2, 1, 0). The side chains of PPA-m bear a soluble 3,4,5-tris(octyloxy)phenyl moiety at the end, and a biphenyl (m = 2), a phenyl (m = 1), or no phenyl ring (m = 0) in the middle linked to the PPA main-chain through an ether linkage. All the three PPA-ms can efficiently disperse SWNTs in organic solvents forming stable SWNTs/PPA-m composites. The composites were characterized by microscopy method, absorbance and photoluminescence spectroscopy. Quantitative analysis shows that there is a tendency for PPA-m to preferentially disperse SWNTs with large diameters in tetrahydrofuran and toluene when compared with the normally used surfactant of sodium dodecyl sulfate. The effective interactions between PPA-m and SWNTs should be ascribed to the helical wrapping of the PPA-m backbone on SWNTs and the π–π interactions between the phenyl groups and SWNTs. The long alkyl tails on the side-chains also prevent individual SWNTs from reaggregation. Additionally, the near-infrared (nIR) photoresponsive electrical conductivity of the SWNTs/PPA-2 composite is measured, indicating a 12% increase of the photocurrent upon the nIR irradiation, which is greater compared with that of the reported pure SWNTs film.

Resonance Raman spectra in the intermediate-frequency mode (IFM) region have been studied for isolated single-walled carbon nanotubes (SWNTs) at the single-nanotube level. The SWNT samples with diameter in the range of 0.8–2.0 nm are first grown on quartz substrate and then transferred to silicon substrate by nanotransfer printing technique. A specific linear relation of ωRBM = 222.0/dt + 8.0 is found to best suit for our transferred isolated SWNTs. By measuring more than 80 isolated SWNTs with 36 different assigned chiralities using five different excitation lasers, the dependence of the nondispersive out-of-plane transverse optical (oTO) and the dispersive IFM– and IFM+ features on the nanotube structure has been determined. It is found that the oTO, IFM–, and IFM+ frequencies decrease slightly, decrease significantly, and increase slightly with decreasing nanotube diameter, respectively. The appearance of the oTO band is indifferent to SWNT chirality or type, while the IFM– feature can only be observed in metallic or MOD1 semiconducting nanotubes with small chiral angles. The IFM– feature in resonance Raman spectra thus offers a method to distinguish small θ nanotubes from large θ nanotubes and distinguish MOD1 semiconducting nanotubes from MOD2 semiconducting nanotubes.