Multi-walled CNTs

Studies on the electronic structure of carbon nanotube (CNT) is of much importance toward its efficient utilisation in electronic devices. It is well known that the early prediction of its peculiar electronic structure [1-3] right after the lijima s observation of multi-walled CNT (MWCNT) [4] seems to have actually triggered the subsequent and explosive series of experimental researches of CNT. In that prediction, alternative appearance of metallic and semiconductive nature in CNT depending on the combination of diameter and pitch or, more specifically, chiral vector of CNT expressed by two kinds of non-negative integers (a, b) as described later (see Fig. 1). 

Realistic samples contain CNTs with different layer numbers, circumferences, and orientations. If effects of small interlayer interactions are neglected, the magnetic properties of a multi-walled CNT (MWCNT) are given by those of an ensemble of single-walled CNTs (SWCNTs). The distribution function for the circumference, p(L), is not known and therefore we shall consider following two different kinds. The first is the rectangular distribution, p(L) = mn)... 

Multi-walled CNTs (MWCNTs) are produced by arc discharge between graphite electrodes but other carbonaceous materials are always formed simultaneously. The main by-product, nanoparticles, can be removed utilizing the difference in oxidation reaction rates between CNTs and nanoparticles [9]. Then, it was reported that CNTs can be aligned by dispersion in a polymer resin matrix [10]. However, the parameters of CNTs are uncontrollable, such as the diameter, length, chirality and so on, at present. Furthermore, although the CNTs are observed like cylinders by transmission electron microscopy (TEM), some reports have pointed out the possibility of non-cylindrical structures and the existence of defects [11-14]. 

For multi-walled CNT (MWCNT), as for the case of graphites, some specific aspects need to be considered ... 

The formation of fullerenes and CNTs has also been affected by their environmental atmosphere [22] and, in particular, a hydrogen atmosphere plays an important role in forming graphitic structures of multi-walled CNTs (MWCNTs) in the form of buckybundles [24]. Intercalation into MWCNTs has been difficult or impossible, because there is no space for intercalants to enter into a Russian-doll-type structure of the nanotubes. However, the buckybundles formed in the hydrogen arc discharge were found to be successfully intercalated with potassium and ferric chloride (FeCl3) without breaking the... 

For the first time, a-Mn02nH20 based composites have been studied in real two electrode capacitors. The a-Mn02nH20/CNTs electrodes demonstrate an ideal capacitive behavior and high values of capacitance. Compared to the conventional carbon black, multi-walled CNTs are a very promising conductivity additive for capacitor or battery electrodes. 

CNTs have a different porous structure than activated carbon. The specific surface area of CNTs can range from 50 m2/g (multi-walled CNTs with 50 graphene walls) to 1315 m2/g (single-walled CNTs). Theoretically, the porous structure of CNTs is identical to the tubular structure of CNTs and the pore sizes of CNTs correspond to the inner diameters of opened CNTs and should have a narrow distribution. Activated carbons usually have a broad pore distribution covering micropore, meso-pore and macropore ... 

The upscaling of nanocarbon production, while considering purity and homogeneity aspects in the kilogram scale, is a very important factor. Except for multi-walled CNTs no such process has been industrialized so far. If commercially available, high-purity nanocarbon materials provide exorbitant costs of up to several hundred Euro per milligram, which in most cases is inacceptable for applied research. As a consequence, nanocarbons are often synthesized in-house, which substantially lowers the comparability among different studies. Synthesis, characterization, and application must go hand-in-hand to exploit the full potential of nanocarbons. 

For the ordered carbon phase, i.e., for nanographite and multi-walled CNT, we consider the mechanism of conductivity similar to that existing in the highly oriented pyrolytic graphite... 

A multi-walled CNT is a coaxial assembly of single-walled CNTs, normally encased by 10 to 30 consecutive layers of carbon atoms. Multi-walled CNTs are more synthesized than single-walled CNTs. In most cases multi-walled CNT contain many structural defects. Recently the synthesis of double-walled CNTs has been reported7 (Figure lc). 

Quantum dots have been widely explored during the last few years for their interesting optical properties and for their possible applications in diode lasers, amplifiers, and detectors. Quantum dot behaviour, observed both in single- and in multi-walled CNTs,17 18 is determined by the unique electronic structure of these particles. Moreover, a CNT can act as a quantum wire capable of... 

Induced Controlled Dispersion of Multi wall CNTs 387... 

CNTs in n-Si/Si02/Ni nanoporous structure were synthesized in accordance with the above techniques and their arrays have been fabricated. This was confirmed by SEM investigations (Fig. 3). Raman spectroscopy characterization of the obtained structures have confirmed the formation of multi wall CNTs. 

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