Mechanical properties and characterisation of very thin CNx films synthesised by IBAD

Nanoindentation has been used to investigate the mechanical properties of very thin ( < 1 mum) CN, films deposited by IBAD in order to understand the variation of properties with process parameters. The structural features of the films were characterised by EELS, XPS and ERDA. Examining the load-displacement (P-delta) curves in detail revealed a number of film responses such as pure elastic behaviour, densification and elastic-plastic deformation. The film-only hardness was calculated using a recently developed energy based model while the Hertzian contact analysis and laser-acoustic measurements were used to determine the Young's modulus. Generally, the film hardness and modulus exhibit two different regimes depending on the deposition parameters. Films deposited at high temperature contain less nitrogen and have lower hardness and Young's modulus than those deposited at room temperature. All films examined displayed P-delta curves exhibiting unusually large elastic recovery ( similar to 80% or more) during unloading. Because of this, resultant indentation sizes always appear to be very small thus apparently producing very high hardnesses. However, our results clearly establish that the film behaviour is better viewed as that of a 'super-hard rubber' in which a large proportion of the contact load is supported elastically. (C) 2001 Elsevier Science B.V. All rights reserved.