Theoretical studies of beta-C3N4 and other crystalline carbon nitride structures indicate that several crystalline phases are metastable, with high bulk modulus values. There are many reports of successful synthesis of some crystalline carbon nitride phases. In spite of questionable data analysis in a significant number of such reports, there is sufficient evidence in the literature to indicate that some nanocrystalline carbon nitride phases have been synthesised. Usually, such crystalline phases are embedded in an amorphous carbon nitride matrix. Amorphous carbon nitride films can be synthesised readily using many different techniques and are dominated by sp(2) carbon bonding, along with strong evidence of carbon-nitrogen bonding. Above a certain deposition temperature, fullerene-like structures can be formed with high hardness and excellent elastic recovery in nanoindentation testing. These thin films display excellent wear performance compared with carbon and hydrogenated carbon films under a wide range of tribological conditions. They are now widely used as protective overcoats in computer disk drive systems. In conclusion, several potential areas for future research in carbon nitride are suggested. (C) 2002 IoM Communications Ltd and ASM International.

This review summarizes our most recent findings in the structure and properties of amorphous and crystalline carbon nitride coatings, synthesized by reactive magnetron sputtering. By careful control of the plasma conditions via proper choice of process parameters such as substrate bias, target power and gas pressure, one can precisely control film structure and properties. With this approach, we were able to produce amorphous carbon nitride films with controlled hardness and surface roughness. In particular, we can synthesize ultrathin (1 nm thick) amorphous carbon nitride films to be sufficiently dense and uniform that they provide adequate corrosion protection for hard disk applications. We demonstrated the strong correlation between ZrN(111) texture and hardness in CNx/ZrN superlattice coatings. Raman spectroscopy and near-edge x-ray absorption show the predominance of sp3-bonded carbon in these superlattice coatings.

Carbon nitride and titanium diboride films were grown using magnetron sputtering. The carbon nitride films have an ultrasmooth surface and exhibit excellent corrosion resistance at film thickness of around 2 nm. Titanium diboride films deposited at ambient temperature are crystalline and textured with hardness exceeding 40 GPa. Additionally, growth of amorphous carbon nitride films by negative carbon ion beam deposition was investigated. The role of bombardment by ionized species in the resulting film properties is discussed.

Results concerning the operation of a new ultrahigh vacuum (UHV) ion-beam assisted deposition system for in situ investigation of ultrahard thin films are reported. A molecular beam epitaxy (MBE) chamber attached to a surface science system (SPEAR) has been redesigned for deposition of cubic-boron nitride thin films. In situ thin film processing capability of the overall system is demonstrated in preliminary studies on deposition of boron nitride films on clean Si (001) substrates, combining thin film growth with electron microscopy and surface characterization, all in situ.