Heat treatment of thin carbon films and the effect on residual stress, modulus, thermal expansion and microstructure

Thin carbon films are used to hermetically seal and improve the performance of devices exposed to extreme conditions. Such films, which are deposited by chemical vapor deposition, develop residual thermal stresses due to a mismatch in the coefficient of thermal expansion between the film and substrate. Residual stresses reduce the adhesion of the film, and are a common cause of coating failure. This work investigates heat treatment as a potential technique to reduce residual stresses in thin carbon films. The magnitude of the residual stress has been challenging to measure due to the associated size scales and mechanical properties. In this study, experimental measurements of mechanical properties and residual stresses in thin carbon films are performed using nanoindentation and Raman spectroscopy. The results relate surface residual stresses to film thickness and heat treatment temperature. The approach presented in this study is a nondestructive and non-intrusive method for measuring residual surface stress and properties in thin films, and is ideal for small or curved-surface specimens such as optical fibers and other photonic devices.