Preparation and Structural Properties of Tetrahedrally Bonded Amorphous Carbon

Abstract

The most common naturally occurring crystalline forms of carbon are cubic diamond and a-graphite. Graphite is one of the softest known materials whereas diamond is the hardest. Although these are the most common they are by no means the only crystalline forms of carbon. There are at least 5 others which are rarely found in nature but can be produced in the laboratory. These are ß-graphite, lonsdaleite, chaoite, carbon (IV) and most recently fullerenes. Such a wide array of available materials and contrasting properties arises from the versatility of the atomic structure of the carbon atom. It has 6 electrons in total. Two of these lie in the ls core and hence do not contribute to bonding. The other 4 are in the 2s and 2p configuration and can bond in three distinct ways to their neighboring atoms to form a sp³, sp² or sp¹ bond. See figure 1.