Electronic States Of Single-walled Carbon Nanotubes Research Articles

Detecting the formation of single-walled carbon nanotube rings by photoabsorption spectroscopy

Photoabsorption spectroscopy was conducted on single-walled carbon nanotubes (SWNTs) during the formation of ring structures. The absorption bands observed before starting the formation gradually shifted while broadening in the middle. When they finally disappeared, it was found, via atomic force microscopy observations, that almost all SWNTs were transformed into rings. The spectral changes were assumed to be due to the changes in the electronic states of SWNTs. This idea was supported by the results of an investigation using a scanning tunneling microscope. It could be said that photoabsorption spectroscopy is useful for detecting ring formation in situ.

<i>In Situ </i>Photoluminescence Spectroelectrochemistry for Determination of Electronic States of Single-Walled Carbon Nanotubes

The determination of electronic states of single-walled carbon nanotubes (SWNTs) has been a central issue in nanoscience of carbon nanotubes. We have established an in situ photoluminescence (PL) spectroelectrochemistry to determine the electronic properties of the SWNTs. This review article focuses on the fundamentals of the in situ PL spectroelectrochmical method to determine electrochemical potentials of isolated SWNTs and microenviromental effects on the electronic states of the SWNTs, electronic states of SWNTs with a single chirality, and empirical prediction for the electronic potentials of the SWNTs. Such electronic state determination is important for detailed understanding about fundamental properties of the SWNTs and their applications, especially in electronic device applications of the nanotubes. [DOI: 10.1380/ejssnt.2015.179]

Electronic Structures of Single-Walled Carbon Nanotubes Encapsulating Ellipsoidal C70

The molecular orientation of ellipsoidal C(70) in single-walled carbon nanotubes (SWCNTs) depends on the tube diameter (d(t)). Photoluminescence (PL) studies reveal that the fullerene encapsulation effects on the optical transition energy of SWCNTs are significantly different for C(70) and C(60) at d(t) = 1.405-1.431 nm. This indicates that the transition from the "lying" alignment to the "standing" alignment occurs at d(t) ≈ 1.41 nm and the electronic states of SWCNTs are very sensitive to the interspacing between the encapsulated molecules and the SWCNTs. The present findings suggest that the electronic structure of SWCNTs is tunable not only by alternating the encapsulated molecules but also by controlling their molecular orientations, thus paving the way for development of novel SWCNT-based devices.

Diameter-Dependent Band Gap Modification of Single-Walled Carbon Nanotubes by Encapsulated Fullerenes

Band gap photoluminescence (PL) of single-walled carbon nanotubes (SWCNTs) encapsulating C60 fullerenes (nanopeapods) is examined over a wide range of diameters (∼1.25−1.55 nm). The encapsulated fullerenes induce characteristic PL peak shifts that strongly depend on the tube diameter (dt) and the “2n + m” family type {type I [mod(2n + m, 3) = 1] and type II [mod(2n + m, 3) = 2]}. This behavior can be explained by the strain-induced band gap shifts due to the C60 insertion and the hybridization between the electronic states of SWCNTs and C60. The present results provide significant insights into band gap engineering of SWCNTs in future nanodevices.

A Facile Strategy for Preparation of Fluorescent SWNT Complexes with High Quantum Yields Based on Ion Exchange

AbstractThe fluorescent imidazolium salt (1,3‐bis(9‐anthracenylmethyl)imidazolium chloride, [bamim]Cl) has been grafted onto the surfaces of single‐walled carbon nanotubes (SWNTs) using an ion exchange strategy based on metathesis of the K+ ion in CO2K derivatized SWNTs with [bamim]+. The resulting SWNT‐[bamim] complex has been characterized with high‐resolution transmission electron microscopy (HR‐TEM), X‐ray photoelectron spectroscopy (XPS), elemental mapping, and elemental linear profiles analysis. A blue light emission can be observed at 392, 414 and 438 nm for SWNT‐[bamim] upon being excited at 254 nm. The quantum yield (QY) of the SWNT‐[bamim] complex (0.40) is much higher than that of SWNT/[bamim]Cl (0.02), used as a control, and prepared using a π‐π stacking method, indicating that ion exchange is a far more effective strategy for retaining a high QY. Additionally, UV‐Vis‐NIR and Raman spectroscopy show that the SWNT‐[bamim] complex can maintain the one‐dimensional electronic states of SWNTs. Other imidazolium salts have also been successfully grafted onto SWNTs via the same strategy, indicating that the ion exchange process can serve as a universal strategy for the functionalization of SWNTs.

Raman Scattering of Single-Walled Carbon Nanotubes Implanted with Ultra-Low-Energy Oxygen Ions

Single-walled carbon nanotubes (SWNTs) implanted with ultra-low-energy oxygen (O+) ions have been studied by means of Raman scattering experiments. The relative intensities of the D-band related to some defects increase with the O+ dose in the Raman spectra of the implanted samples. Although no recognizable shift of phonon energies due to the ion implantation has been observed, the intensities of the Stokes and anti-Stokes lines originated from radial breathing modes of SWNTs which exhibit various behaviors due to degree of the implantation, indicating that the resonant energies are changed. To explain these findings, the structure and the electronic states of SWNTs with substitutional O impurities have been studied by applying theoretical calculations based on the first principle method and a tight-binding method. As a result, it has been suggested that the incorporation of oxygen atoms at carbon sites is plausible, and the experimental observation can thus be consistently explained on the basis of the O impurities in SWNTs.