THE discovery1 of buckminsterfullerene (C60) and its production in macroscopic quantities2 has stimulated a great deal of research. More recently, attention has turned towards other curved graphitic networks, such as the giant fullerenes (Cn, n > 100)3,4 and carbon nanotubes5–8. A general mechanism has been proposed9 in which the graphitic sheets bend in an attempt to eliminate the highly energetic dangling bonds present at the edge of the growing structure. Here, I report the response of carbon soot particles and tubular graphitic structures to intense electron-beam irradiation in a high-resolution electron microscope; such conditions resemble a high-temperature regime, permitting a degree of structural fluidity. With increased irradiation, there is a gradual reorganization of the initial material into quasi-spherical particles composed of concentric graphitic shells. This lends weight to the nucleation scheme proposed9 for fullerenes, and moreover, suggests that planar graphite may not be the most stable allotrope of carbon in systems of limited size.

Curling and closure of graphitic networks under electron-beam irradiation

Nanochemistry: Synthesis in diminishing dimensions

The idea1 that fullerenes might be able to encapsulate atoms and molecules has been verified by the successful synthesis of a range of endohedral fullerenes, in which metallic or non-metallic species are trapped inside the carbon cage2,3,4,5,6,7,8,9,10,11,12,13. Metal-containing endohedral fullerenes have attracted particular interest as they might exhibit unusual material properties associated with charge transfer from the metal to the carbon shell. However, current synthesis methods have typical yields of less than 0.5%, and produce multiple endohedral fullerene isomers, which makes it difficult to perform detailed studies of their properties. Here we show that the introduction of small amounts of nitrogen into an electric-arc reactor allows for the efficient production of a new family of stable endohedral fullerenes encapsulating trimetallic nitride clusters, ErxSc3-xN@C80 (x = 0–3). This ‘trimetallic nitride template’ process generates milligram quantities of product containing 3–5% Sc3N@C80, which allows us to isolate the material and determine its crystal structure, and its optical and electronic properties. We find that the Sc3N moiety is encapsulated in a highly symmetric, icosahedral C80 cage, which is stabilized as a result of charge transfer between the nitride cluster and the fullerene cage. We expect that our method will provide access to a range of small-bandgap fullerene materials, whose electronic properties can be tuned by encapsulating nitride clusters containing different metals and metal mixtures.

Small-bandgap endohedral metallofullerenes in high yield and purity

Since their first detection and bulk production, the fullerenes have
gained a primary role on the scientific scene, reaching their climax when
the 1996 Nobel Prize for Chemistry was awarded to Kroto, Curl and Smalley
for their seminal discovery. The unique physical and chemical properties
of these new forms of carbon led many scientists to predict several
technological applications. This created a heavy disappointment when it
was clear that fullerene-based materials would not soon be ready for the
market. However, the fullerenes have so far delighted several dozens of
researchers who found that C
 60
 and its relatives undergo a
variety of chemical reactions. In most cases, the new derivatives retain
the main properties of the original fullerene, and it is now not unlikely
that some functionalized fullerenes may find useful applications in the
field of materials science and technology. In this Article we summarize
the basic principles of the organic chemistry of fullerenes, together with
a description of the physicochemical properties that have made these
carbon cages popular in materials science, and review the most recent
achievements in the functionalization of fullerenes aimed at the
production of new molecular materials.

[60]Fullerene chemistry for materials science applications

Encapsulating atoms or molecules inside fullerene cages could give rise to a myriad of novel molecules and materials. The existence of such species is now strongly supported by a growing body of experimental evidence. Fullerene& ndash;metal complexes generally thought to be endohedral are being produced and purified in milligram quantities, and their structure and properties are beginning to be explored

Atoms in carbon cages: the structure and properties of endohedral fullerenes

Fullerenes with a single lanthanum atom trapped on the inside of the carbon cage were produced by laser vaporization of a lanthanum oxide/graphite composite rod in a flow of argon gas at 1200 °C. When sublimed with C_(60) and C_(70), they formed 
an air-stable film containing principally LaC_(60), LaC_(70), LaC_(74), and LaC_(82). When dissolved in toluene and exposed to air, 
LaC_(82) was found to be uniquely stable. Evidence was also obtained for coalescence reactions between these fullerenes at
high temperatures to form larger cages with as many as three lanthanum atoms inside. Indications have also been obtained 
for the successful production of KC_(60), C_(59)B, and KC_(59)B where the boron has substituted for a carbon in the soccerball cage. 
The use of the @ symbol is advocated for specifying such complex fullerenes as (K@C_(59)B).

J. Michael Alford

Papers

Fullerenes with metals inside