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

Nanoindentation has been used to investigate the mechanical properties of v ery 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-dis placement (P-delta) curves in detail revealed a number of film responses su ch as pure elastic behaviour, densification and elastic-plastic deformation . The film-only hardness was calculated using a recently developed energy b ased model while the Hertzian contact analysis and laser-acoustic measureme nts were used to determine the Young's modulus. Generally, the film hardnes s and modulus exhibit two different regimes depending on the deposition par ameters. Films deposited at high temperature contain less nitrogen and have lower hardness and Young's modulus than those deposited at room temperatur e. All films examined displayed P-delta curves exhibiting unusually large e lastic recovery ( similar to 80% or more) during unloading. Because of this , resultant indentation sizes always appear to be very small thus apparentl y producing very high hardnesses. However, our results clearly establish th at 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.