New Frontiers in Nanocarbons

Abstract

Carbon is an extraordinary element. Its ability to covalently bond with different orbital hybridizations leads to a uniquely rich array of molecular structures that form the vast subject of organic chemistry. Approximately 20 million organic compounds containing carbon and other elements have been characterized, and it is estimated that than more than 90% of all recognized chemical compounds include carbon. By contrast, for millennia only two known substances were composed exclusively of carbon atoms: the elemental allotropes graphite and diamond. This situation changed dramatically in 1985 with the discovery of a new molecular allotrope, the soccer-ball shaped cage molecule C60, also known as Buckminsterfullerene. The discovery of C60 marked the dawn of carbon nanostructure research. In this field the focus is on all-carbon materials whose properties are determined by their specific covalent bonding geometries and the resulting well defined nanoscale structures. Activity in nanocarbon research grew explosively after the 1991 report of a method for making bulk quantities of fullerenes, and two years later a Fullerenes Group was formed within The Electrochemical Society to serve this new research community. With dimensions of approximately 1 nm, C60 and related larger fullerenes such as C70, C76, C84, etc. are studied using the experimental methods and concepts of chemistry. The scientific literature currently contains approximately 28,000 papers dealing with fullerenes. A second category of carbon nanostructure emerged in the early 1990s: nanotubes. Like fullerenes, these ordered cage structures are composed entirely of 5and 6-membered covalently bonded carbon rings, but nanotubes are highly elongated and contain 5-membered rings only at their caps. Carbon nanotubes also exist in far more structural varieties than fullerenes. With their large aspect ratios and crystalline order along the tube axis, nanotubes must be studied from an interdisciplinary viewpoint that combines concepts from chemistry and condensed matter physics. Carbon nanotubes display remarkable properties that have attracted great interest among basic and applied researchers working in chemistry, physics, materials science, chemical engineering, electrical engineering, and biomedicine. More than 85,000 papers have been published to date on carbon nanotubes. In 2004, a technique was demonstrated for removing and studying single atomic layers of carbon from graphite. These graphene sheets represent a third category of carbon nanostructures, with particularly unusual electrical properties arising from the semi-metallic pielectron band structure. As is true for nanotubes, the network of covalent carbon–carbon bonds linking the entire structure also gives graphene very high strength and suggests novel mechanical New Frontiers in Nanocarbons