Long-term termination of carbon layers synthesized using RF PACVD method onto metal substrates

The work presented here concerns changes of surface properties of carbon layers synthesized on metal substrates using RF PACVD method. Investigated layers were deposited from methane plasma onto Ti6Al7Nb alloy substrates. Manufactured DLC type layers showed good adhesion to the substrate and their thickness was about 200 nm. The experiment was based on observation of the contact angle of substrate surfaces over time. That effect was investigated for layers kept in atmosphere of air, oxygen, nitrogen and hydrogen. It was observed for all sample contact angles changed with different dynamics. Directly after the deposition process layers presented strong hydrophilic properties which over time were gradually changing into hydrophobic state. That effect was independent of the atmosphere where the samples were stored. Samples were observed during the period of 100 days. During that time the contact angle changed from 0 to 120° and more. The effect observed proves that a strongly reactive surface in carbon layer synthesized in RF plasma was manufactured. To explain this effect additional surface tests and measurements were conducted, including AFM and XPS.

► Thin amorphous hydrogenated carbon layers were deposited onTi6Al7Nb titanium alloy.
► Different gases were used for long time termination of the carbon surface.
► Over the 100 day period the contact angle of surface was studied.
► The change in the contact angle from several degrees to 120° in time was observed.
► The atmosphere of termination had no observable influence on wettability.