when cigar-shaped, capped tubes of 1- to 2-nanometer diameter, and even extended "nanotubes" of essentially macroscopic lengths, were experimentally discovered. Nanotubes are, in essence, sheets of graphite that have been rolled into tiny tubes. It is predicted that they can be either semiconductors or metals, depending on the angle of the bonding with respect to the tube axis. Nested nanotubes have also been recently observed.

More broadly, the discovery of buckyballs and the carbon variants has stimulated researchers in many other fields to consider a wide range of useful nanostructures that might be built from curved graphite sheets. Researchers are now actively pursuing the growth of continuous carbon nanotubes. When grown in length to many meters, these nanotubes would constitute a fiber of incredible tensile strength. Multifilament cables of such pure carbon nanofibers are expected to be the strongest (and toughest) cables that could ever be constructed of any material—roughly 100 times stronger than a steel cable of the same diameter and 400 times stronger than steel per unit weight. Nanofibers, doped with metal atoms down the hollow inside cavity, are expected to have electrical conductivity at room temperature substantially higher than pure copper and could provide an attractive replacement for use in electrical power transmission lines worldwide. Furthermore, their large thermal conductivity suggests they may replace diamond and copper in many applications requiring heat sinks. AMO science was critical to the genesis of these ideas and will be critical in bringing them to life.

The importance of C60 is extending into research areas beyond those associated with new materials. For example, in biomedical research, recent theoretical and experimental tests have shown that C60 derivatives interact with the active site of HIV-1, removing much of the active area of this deadly virus (Figure 1.4). Thus it is conceivable that this recently discovered particle may offer some help in the worldwide battle against AIDS.

Carbon, already important in biology and organic chemistry, now offers the possibility of new materials, devices, and products with numerous potential applications.



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