Mechanical Properties of Carbon Nanotubes

An early motivation to study carbon nanotubes has been the expectance of extraordinary mechanical properties for both single- and multiwalled species. The perspective to obtain highly strain-resistant composites or fibrous materials liberated large resources in nanotube exploration. At the peak of nanotube euphoria, the catchphrase of the so called sky elevator created a sensation in the media and indicated what great expectations were set in the newly discovered material. The concept was based...

Absorption and Emission Spectroscopy of Carbon Nanotubes

Compared to the vibrational spectroscopy of carbon nanotubes, their absorption and luminescence spectroscopy kind of lives in the shadows. This is, however, not due to a lack of information these methods could provide to the understanding of the nanotubes' electronic structure. There are rather experimental complications that arise from the inhomogeneity of the available materials. These methods could especially elucidate the structure of bands farther distant from the Fermi level. Due to the...

Inorganic Chemistry of Fullerenes

Like in most other cases too, it is hard to distinguish inorganic from organic chemistry of fullerenes. This section primarily deals with aspects of structural chemistry, whereas reactions with metahorganic agents to organic derivatives of Figure 2.42 Examples of organometallic fullerene complexes with one metal center (a), two metal centers arranged at opposite sites (b) and neighbouring sites (c) and a complex comprising three metal centers in close proximity (d). Figure 2.42 Examples of...

Spectroscopic Properties

First fundamental investigations on the photophysical properties of fullerenes were performed as early as 1991. A comprehensive picture of possible transitions and photophysical characteristics have been collected since then. Figure 2.26 summarizes the essential processes. Solutions of C60 in organic media are colored dark violet, and those of C70 are deep red. These colors vary slightly with the individual solvents due to their different interactions with the fullerenes. Their specific...

Structure of Higher Fullerenes and Growth Mechanisms

C76 Fulleren

According to Euler's theorem on closed polyhedrons (refer to Section 4.2.1), every fullerene composed of five- and six-membered rings contains 2 (10 + M) C-atoms, and the resulting cage is made of exactly 12 penta- and M hexagons. The smallest conceivable fullerene accordingly is C20 (M 0). While this molecule could not be isolated experimentally so far, the related hydrocarbon C20H20 is known. It features the expected pentagon-dodecahedral structure. With M increasing, the number of possible...

Arc Discharge Methods

As early as i99i, carbon nanotubes have been prepared with an apparatus quite similar to the arc discharge reactor for fullerene production (Section 2.3.3). Here as well an electric arc is used to vaporize carbon introduced in the shape of graphite rods, and again deposition occurs on cooler parts of the installation. The decisive difference to fullerene preparation consists in the electrodes not touching each other during reaction and an arc evolving between them. The so- called contact arcing...

Hydrogenation and Halogenation

For being polyolefins, the fullerenes present a multitude of double bonds that can in principle be transformed into C-C-single bonds by hydrogenation. Depending on the method applied, the reaction can lead to singly or multiply hydrogenated species. Still the directed production of defined hydrofullerenes is a demanding task, and structure determination sometimes is not trivial, especially for multiply hydrogenated compounds. The reaction with molecular hydrogen is no suitable method to...

Graphite and Related Materials

Potassium Graphite Structure Distance

Graphite may be the thermodynamically most stable modification of carbon. Still it is chemically attacked more easily than diamond due to its layered structure and the comparatively weak interaction between the graphene sheets. Altogether the graphite's reactivity toward many chemicals is rather low nevertheless. With chlorine, for example, it does not react at all under usual conditions, and even with fluorine reaction occurs only at more than 400 C. Suitable performance yields the...

Electric Conductivity of Diamond Films

Diamond as a pure material is a very good insulator. Owing to its large bandgap of 5.46 eV, it is virtually impossible to generate charge carriers by thermal excitation. Even at 700 K, the bandgap is still 5.34 eV wide. The intrinsic density of charge carriers of 10'27cm-3 is so small that just a single electron-hole pair would exist in a diamond the size of the earth The resistance of diamond as determined experimentally is about 1016 Q- Hence, in the case of a doped diamond material,...

Graphite and Its Structure

The structure of graphite had been elucidated from 1917 on by Debye, Scherrer, Grimm, Otto, and Bernal. It is characterized by a succession of distinct so-called graphene layers that spread over an xy-plane. They are stacked in a z-direction, and there are only weak van der Waals interactions among them (Figure 1.7). Within one graphene layer, the carbon atoms are situated at the corners of regular hexagons that constitute a two -dimensional lattice. From each C -atom there are three o-bonds...

Growth Mechanisms of Carbon Onions Obtained by Thermal Treatment

A thermal treatment of different carbon forms can lead to the formation of onion-)ike species as well. As for diamond particles, their surface structure plays an important role for the actual outcome of the process. If it is covered with functional groups, the bonding sites are saturated which renders a graphitization more difficult. From dangling bonds, on the other hand, graphitized domains will arise that can serve as nucleation center to the formation of carbon onions. In this process, a...

Chemical Properties

Carbon is a fairly inert element and most of its modifications may only be reacted under rather harsh conditions. Nevertheless the entire Organic Chemistry, known exclusively to deal with its compounds alone, is founded on the chemistry of carbon. This apparent contradiction is resolved by the simple compounds being hard to obtain from the elements, but any further reaction being quite easy to achieve. They succeed in impressive variety, mainly due to the manifold ways of carbon bonding with...

Structure of Other Carbon Allotropes

There are a number of further carbon phases besides the classics graphite and diamond. In the 1960s, a white allotrope was found that was named chaoite. It was discovered in the Bavarian Ries (northeast of Ulm) in graphite gneiss that had molten under pressure. It may further be generated by heating pyrolytic graphite to about 2000 C in vacuo (about 1.9 x 10-6psi). The resulting hexagonal crystals grow as dendrites, the lattice parameters are a0 894.5 pm and c0 1407.1pm, and the material's...

Nucleophilic Addition to Fullerenes

C60 Iodine

The reactivity of fullerenes toward nucleophiles is caused by their electron deficiency. Numerous reactions with nucleophilic reagents leading to useful and interesting derivatives have been described. The nucleophilic addition to fullerenes corresponds to the common mechanism observed for electron-deficient olefins. A nucleophile A- initially attacks the double bond and a reactive intermediate C-0A- is generated. This can be stabilized in several ways. The product C60AE results from the...

Helical Carbon Nanotubes hMWNT

It was not long after the discovery of carbon nanotubes before specimens with coiled or helical shapes were observed. These helical nanotubes hMWNT are often found as by-product in the synthesis of multiwalled nanotubes, yet by now a directed preparation has succeeded as well. Their extraordinary shape turns the helical nanotubes into an interesting subject of research as the expected electronic properties like inductive effect under electrical current should enable an application, for example,...

Chemical Vapor Deposition CVD

Like in the preparation of single -walled carbon nanotubes, the chemical vapor deposition of MWNT consists in the generation of small carbon clusters or atoms from precursor compounds. The products precipitate in the shape of different carbon materials with the reaction conditions determining the specific structure of the substance. The simplest CVD method is the thermal decomposition of carbonaceous compounds in a heated quartz tube bearing a substrate that is coated with catalyst particles....