SYNTHESIS AND PROCESSING OF SUPERHARD CARBON NITRIDE SOLIDS

Carbon nitride solids, predicted to exhibit bulk moduli comparable wit h or exceeding that of diamond, are reviewed for both theoretical and experimental developments. Progress in the theory and preparation of t hese solids is described detailing the structure, composition, thermod ynamic aspects, and physical and mechanical properties. The synthesis and characterisation techniques involved are described from the viewpo int of their potential usefulness. Such issues as assessing the qualit y of synthesised films by revealing the nature of the chemical bonds b etween carbon and nitrogen and their chemical composition in each bond ing state are discussed. Based on assessment of the experimental work to date, future directions for investigation of both amorphous and cry stalline carbon nitrides are suggested. Some lattice matched compounds as suitable intermediate layers to promote the epitaxy of metastable C3N4 have been proposed and superlattice geometries with these lattice matched compounds are suggested to enhance further the hardness of th e deposited heterostructures. (C) 1997 The Institute of Materials and ASM International.