Fullerene tubular structures

The other example is related to fullerene tubular structures [8-30], Such structures have been generated by vapor condensation of carbon on atomically flat graphite surfaces. Due to a misorientation of the top layer relative to the second layer, a Moir pattern is created whose lattice parameter is determined by the angle of misorientation. The structural model of the superpattern produced by two misoriented sheets is illustrated by Figure 8-44. 

Let us note in addition that the layered sulfides M0S2 and WS2 have been found to form nanotubes and other fullerene-type structures, on account of their highly folded and distorted nature that favors the formation of rag and tubular structures. Such materials have been synthesized by a variety of methods [78] and exhibit morphologies, which were described as inorganic fiillerenes (IF), single sheets, folded sheets, nanocrystals, and nested IFs (also known as onion crystals or Russian dolls ). 

Carbon nanotubes (CNTs) constitute a nanostructured carbon material that consists of rolled up layers of sp2 hybridized carbon atoms forming a honeycomb lattice. After diamond, graphite and fullerenes, the one-dimensional tubular structure of CNTs is considered the 4th allotrope of carbon (graphene is the 5th). 

Layered dichalcogenides with highly folded and disordered structure have been recognized for several decades. The so-called rag and tubular structures in selected MS2 compounds were first reported in 1979, and they gained wider interest following the discovery of fullerene and carbon nanotubes [53]. Fundamentally, the composition of the IF materials are similar to those of the bulk layered MS2. 

It was shown how both endohedral and exohedral fullerenes can be inserted in nanotubes. In the peapods containing endohedral fullerenes (for instance Ce Cg2), HRTEM images showed interesting rotation and translation motion of the trapped spheroids. Exohedral metallofullerenes, CsC io have been synthesized and successfully encapsulated into SWCNTs via a new chemical reduction of Cgo molecules into anions. The addition of iodine to already prepared peapods allowed the coalescence of Cgo directly inside the nanotubes. Indeed, after heating at 550 C, iodine-doped peapods, inside the Cgo molecules molecules have been transformed in a tubular structure. Khlobystov et al. were able to perform reactions on the inner surface of carbon nanotubes in the presence of catalyti-cally active atoms of rhenium and monitor the whole process via HRTEM. ... 

More recently, a new frontier was opened up by filling single-walled carbon nanotubes with Cso to form the so-called fullerene peapods [23]. In 2003, Terrones et al. studied fullerene coalescence to a polyfullerene induced by electron irradiation on pristine nanotube peapods [24], paving the way to new highly conducting and semiconducting tubular structures with specific electronic characteristics (Figure 1.3). 

Another important group of fullerene-related compounds are the carbon nanotubes, the reference compounds of the carbon nano-science. They may be obtained by convenient variations of the preparation procedure mentioned. These are long tubular fullerenes with a concentric shell structure a few nanometres wide and often capped with C60-like hemisphere or faceted tips. They are mechanically very strong and either metallic conducting or semiconducting types have been obtained. 

Onion-like structures analogous to nested fullerenes were also obtained in considerable yields (Fig. 5). The heating arrangement with a tubular furnace employed for the preparation of MoS2 nanotubes is shown in Fig. 7. MoOj being sublimable, the Furnace ... 

Despite the tremendous interest recently in the physics and chemistry of and other fiillerenes and their solid forms, little is known about fuiierene growth. Neither the onset of nucleation nor the progression toward the fuiierene network is understood. The structure of giant fullerenes (containing hundreds of carbon atoms) is also controversial experimental evidence exists to support two possibilities, spherical molecules versus tubular cages. 

New carbon modifications, which consist of discrete polyhedral molecules, have been intensively investigated since the early 1990 s. The structures of these fullerenes range from the highly symmetrical buckminsterfullerenes, C50, to the chiral fullerenes, 7, to larger tubular or carbon particles built up of onionscale-shaped molecules. Possible applications, such as the manufacture of superconducting alkali metal-doped fullerenes or their utilization as a support for catalysts, are being developed, but are not yet market ripe. 

This is indeed close to reality as actually hemispheric caps are observed rather seldom. In most cases conical structures are found. These bear defects at the tip itself as well as at the transition to the nanotube. They aU have in common that the required curvature is brought about by pentagonal defects. The bevel angle of such conical caps depends on the number of five-membered rings present at their tips, as demonstrated by the values in Table 3.1. A cap with six pentagonal defects, for instance a hemispheric fullerene fragment, enables a direct transition to the tubular part, while a smaller number of five-membered rings causes a more or less conical shape. 

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