Recent advances in the synthesis and properties of amorphous and crystalline carbon nitride

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Abstract
As a result of the prediction by Liu and Cohen that crystalline β‐C3N4 has mechanical properties similar to diamond, many research groups have attempted to synthesize carbon nitride using various deposition techniques. Most groups succeeded in producing amorphous carbon nitride coatings. These coatings, though softer than diamond, display excellent tribological properties and are now used as protective overcoats for computer hard drive systems. The lack of success to make crystalline coatings suggests that β‐C3N4 is metastable. Using TiN(111) and ZrN(111) as seeding layers (which have similar lattice symmetry and commensurate unit cell dimensions as β‐C3N4(001)), we were able to synthesize fully crystalline carbon nitride composite coatings with hardness in the 50 GPa range, which is in the low end of diamond films.