Is stress necessary to stabilise sp bonding in diamond - like carbon ? 3

The role of compressive stress in producing sp bonding in diamond-like carbon is of interest both technologically and 3 scientifically. Stress limits the maximum thickness of adherent films, and it is desired to produce much thicker films for protective coatings and for making micro-electromechanical systems. Stress is important theoretically, because it is often linked to the deposition process. A strong correlation between macroscopic stress and sp fraction in diamond-like carbons has been noted, 3 particularly for tetrahedral amorphous carbon (ta-C). However, a survey of data shows that a given stress produces films with sp contents between 20 and 85%, while for a given sp content, stresses between 2 and 19 GPa have been found. We propose 3 3 that the main cause of stress is ion bombardment, and that a low energy of only 20 eVyion is needed to produce films with an sp content over 70%. We discuss the various models linking stress and the sp fraction in ta-C. The role of densification vs. 3 3 compressive stress in stabilising sp bonding is also discussed. 2002 Elsevier Science B.V. All rights reserved. 3