The mechanism of destruction of a-C : H films under the action of aggressive liquids

The a-C:H films were deposited on monocrystalline silicon (001) substrates from RF (13.56 MHz) discharge plasma in a capacity-type reactor. The stabil ity of a-C:H films in different aggressive liquids was investigated by the methods of wettability and thermodesorption (TD) using a mass spectrometer to detect particles being desorbed in the temperature range 20-800 degrees C. Comparative analysis of the data on film wettability and TD has allowed us to suggest the mechanism of a-C:H film destruction. The mechanism is bas ed on the catalytic activity of ions in solution, which interact intensivel y with surface carbon atoms. The highest destabilisation of carbon bonds in the film near-surface layer, which causes film destruction to form CO2, is found to occur in contact with an alkali solution. In this case the CO2 io n how intensity is two orders of magnitude higher than that from the initia l film surface. This finding corresponds to the best wettability (wetting a ngle theta = 10-12 degrees) and the highest work of adhesion (W-a = 158.5 m J/m(2)) of alkali solution to a-C:H film surface. The replacement of hydrog en by nitrogen in the film structure increases its chemical stability when contacting with aggressive media. (C) 2000 Elsevier Science S.A. All rights reserved.