Synthesis and processing of superhard carbon nitride solids

Abstract

Carbon nitride solids, predicted to exhibit bulk moduli comparable with or exceeding that of diamond, are reviewed for both theoretical and experimental developments. Progress in the theory and preparation of these solids is described detailing the structure, composition, thermodynamic aspects, and physical and mechanical properties. The synthesis and characterisation techniques involved are described from the viewpoint of their potential usefulness. Such issues as assessing the quality of synthesised films by revealing the nature of the chemical bonds between carbon and nitrogen and their chemical composition in each bonding state are discussed. Based on assessment of the experimental work to date, future directions for investigation of both amorphous and crystalline 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 the deposited heterostructures.