Weak Response of Metallic Single-Walled Carbon Nanotubes to C₆₀ Encapsulation Studied by Resonance Raman Spectroscopy

Metallic single-walled carbon nanotubes (SWCNTs) have been regarded as unique quasi-1D metallic systems. Their basic properties significantly differ from those of their semiconducting counterparts even though their chemical compositions and sizes are nearly identical to each other. In this study, we investigate the effects of C₆₀ fullerene encapsulation on the phonon and electronic properties of metallic SWCNTs by resonance Raman spectroscopy. The changes in the radial breathing mode frequencies and the optical transition energies after C₆₀ insertions show characteristic tube diameter dependences, as in the case of the corresponding semiconducting SWCNTs. Although the observed behaviors can be attributed to the intermolecular interaction between SWCNTs and the encapsulated C₆₀, similar to the corresponding semiconducting SWCNTs, the strength of the interaction is measurably weaker than that of semiconducting SWCNTs. The present findings provide important insight into the essential differences in the basic nature of metallic and semiconducting SWCNTs

Relationship between Mechanical and Electrical Properties of Continuous Polymer-Free Carbon Nanotube Fibers by Wet-Spinning Method and Nanotube-Length Estimated by Far-Infrared Spectroscopy

Neat carbon nanotube (CNT) fibers produced by wet spinning methods offers a potential for high-strength and electrically conductive lightweight materials. For improving their performances, it is necessary to understand how each manufacturing process affects the raw CNTs and implicates the effects in the fiber properties. Recently, we found that the lengths of the clean CNT channels can be estimated by far-infrared (FIR) spectroscopy based on the plasmon resonance model. In this paper, the relationship between the mechanical properties and electric conductivities of the neat CNT fibers, and the lengths of the constituent CNTs are systematically studied by using different types of single-walled CNTs (SWCNTs) with various diameters and different dispersing times. Irrespective of the type of CNTs or the tube diameters, Young moduli, fracture strengths, and electric conductivities of the CNT fibers were found to be related to the CNT lengths estimated from the FIR spectra. The results prove that the evaluation of CNT length by the FIR spectroscopy is a highly useful method to optimize the processing conditions as well as to select the proper CNTs for fabricating high-performance CNT-based materials

Self-Assembled Carbon Nanotube Honeycomb Networks Using a Butterfly Wing Template as a Multifunctional Nanobiohybrid

Insect wings have many unique and complex nano/microstructures that are presently beyond the capabilities of any current technology to reproduce them artificially. In particular, <i>Morpho</i> butterflies are an attractive type of insect because their multifunctional wings are composed of nano/microstructures. In this paper, we show that carbon nanotube-containing composite adopts honeycomb-shaped networks when simply self-assembled on <i>Morpho</i> butterfly wings used as a template. The unique nano/microstructure of the composites exhibits multifunctionalities such as laser-triggered remote-heating, high electrical conductivity, and repetitive DNA amplification. Our present study highlights the important progress that has been made toward the development of smart nanobiomaterials for various applications such as digital diagnosis, soft wearable electronic devices, photosensors, and photovoltaic cells

Length-Dependent Plasmon Resonance in Single-Walled Carbon Nanotubes

The optical response of single-walled carbon nanotubes (SWCNTs) to far-infrared (FIR) radiation was systematically studied using various SWCNTs with different tube-length distributions. The observed peak position in the FIR spectra linearly scaled with the inverse of tube length irrespective of diameter, which is consistent with the dispersion relation predicted by the one-dimensional plasmon resonance model. The effects of chemical doping on the FIR spectra of the separated metallic and semiconducting SWCNTs clearly indicate that the motion of plasmons in the electronic band structures is primarily responsible for the optical response in these spectral regions. The observed absorption peaks are naturally sensitive to the presence of defects on the tube wall and correlated with the electric resistance, suggesting that the plasmons resonate with the current path length of the SWCNTs

Immunoassay with Single-Walled Carbon Nanotubes as Near-Infrared Fluorescent Labels

The intrinsic photoluminescence of single-walled carbon nanotubes (CNTs) in the near-infrared (NIR) above 1000 nm makes them promising candidates for biological probes owing to low interference by bioorganic molecules and deep tissue penetration. We here demonstrate an immunoassay by using a NIR CNT labels conjugated to immunoglobulin G (IgG) antibodies. Most of the CNT-conjugated IgG was successfully immunoprecipitated with protein G-attached magnetic beads and eluted from them, which was confirmed by the NIR emission of the conjugated CNTs at 1000–1200 nm. The photoluminescence intensity of the CNT labels was strong enough to detect antigens at 600 pM by our simple procedures

Dimerization-Initiated Preferential Formation of Coronene-Based Graphene Nanoribbons in Carbon Nanotubes

We have investigated the growth mechanism of coronene-derived graphene nanoribbons (GNRs) using two different precursors: coronene and a dimer form of coronene, so-called dicoronylene (C₄₈H₂₀). For both of the precursors, the formation of nanoribbon-like materials inside carbon nanotubes (CNTs) was confirmed by transmission electron microscope observations. Experimental and theoretical Raman analysis reveals that the samples also encapsulated dicoronylene and linearly condensed other coronene oligomers, which can be regarded as analogues to GNRs. Interestingly, it was found that the present doping condition of coronene yields dicoronylene prior to encapsulation due to the thermal dimerization of coronene. These results indicate that the dimerization before the encapsulation drives the preferential formation of the coronene-based GNRs within CNTs

Spectroscopic Characterization of Nanohybrids Consisting of Single-walled Carbon Nanotubes and Fullerodendron

<div><p>Hydrogen gas, which can be used in fuel cells to generate electricity, is considered the ultimate clean energy source. Recently, it was reported that a photo-induced electron transfer system consisting of single-walled carbon nanotubes (SWCNTs) and fullerodendrons shows photo-catalytic activity with a very high quantum yield for splitting water under visible light irradiation. However, the mechanism of high efficiency hydrogen generation is not yet clearly understood. We report here the spectroscopic characterizations of the SWCNT-fullerodendron composites. The results indicate two important fundamental properties of the composite system. First, fullerodendrons preferentially interact with the semiconducting SWCNTs instead of with their metallic counterparts. Second, the photo-induced electron transfer process from the C₆₀ moiety of fullerodendrons to SWCNTs occurs more efficiently with an increasing tube diameter.</p> </div

Single Chirality Extraction of Single-Wall Carbon Nanotubes for the Encapsulation of Organic Molecules

The hollow inner spaces of single-wall carbon nanotubes (SWCNTs) can confine various types of molecules. Many remarkable phenomena have been observed inside SWCNTs while encapsulating organic molecules (peapods). However, a mixed electronic structure state of the surrounding SWCNTs has impeded a detailed understanding of the physical/chemical properties of peapods and their device applications. We present a single-chirality purification method for SWCNTs that can encapsulate organic molecules. A single-chiral state of (11,10) SWCNTs with a diameter of 1.44 nm, which is large enough for molecular encapsulation, was obtained after a two-step purification method: metal-semiconductor sorting and cesium-chloride sorting. The encapsulation of C₆₀ to the (11,10) SWCNTs was also succeeded, promising a route toward single-chirality peapod devices