Co-pyrolysis of hydrocarbons and SiEt4 for the synthesis of graduated SixC1–x ceramic thin films by chemical vapour deposition

Abstract

The thermal decomposition of hydrocarbons has been investigated under particular conditions in a low-pressure chemical vapour deposition reactor in order to select suitable carbon sources for the preparation of carbon-rich or graduated Si_xC_1–x layers. Growth of pyrolitic carbon thin films (pyro-C) starts at ca. 1050 K and only above 1273 K using C₆H₅Prⁱ and CH₄, respectively. The microstructure of the pyro-C layers is more dependent on the deposition temperature than on the nature of hydrocarbons. Their co-pyrolysis with SiEt₄ used as SiC precursor has been achieved in the temperature range 1050–1250 K. As expected, the film composition does not change significantly at 1173 K using CH₄ as an additional C source. By contrast, the C content of the films deposited by co-pyrolysis of SiEt₄ and C₆H₅Prⁱ increases continuously from 0.48 to 1 by increasing the mole fraction ratio x(C₆H₅Prⁱ)/[x(C₆H₅Prⁱ)+x(SiEt₄)] from 0 to 1. Multilayers and compositional gradient layers can be prepared by discrete or continuous changes of the gas-phase composition, respectively. These films were successfully used as interphase in ceramic–ceramic composite materials to weaken the fibre/matrix bond and to improve their ductility.