[Zurück]

C. Schrank, B. Schwarz, C. Eisenmenger-Sittner, E. Neubauer:
"RECRYSTALLIZATION INDUCED DE-WETTING OF COPPER-COATINGS FROM CARBON SURFACES STUDIED BY AFM AND TEM";
Poster: International Vacuum Congress 16, IVC-16, Venedig, Italien; 28.06.2004 - 02.07.2004.

Sputter deposited Copper (Cu) coatings on plane glassy Carbon (C) substrates serve as a model for the interface between Cu and C-fibers in Cu-C Metal Matrix Composites (MMC's). This interface is of crucial importance for the mechanical and thermal properties of Copper Carbon MMC's.
If the Cu-coating is deposited on a Nitrogen-RF-Plasma treated C-substrate at room temperature (RT) the adhesion of Cu to C is excellent. In a further step the Cu coated C-samples are subjected to a thermal treatment at 800°C under high vacuum conditions for 1 hour to partially mimic the hot pressing step involved in the production of real MMC's. This thermal treatment drastically reduces the adhesion of Cu to C due to de-wetting of the Cu coating from the C substrate. De-wetting can be described as the transition of a continuous coating to single, isolated droplets which is caused by the tendency of the coating to reduce it's surface free energy.
In this work the de-wetting process of Cu from C is studied in detail by Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM). From the AFM investigation of the de-wetting steps of 300 nm thick Cu-coatings it is found that de-wetting is triggered by the recrystallisation of the previously very fine grained Cu-coating. The process of hole-formation in the formerly continuous coating can be quantitatively described by a model of heterogenous de-wetting proposed by Srolovitz et al. (see D. J. Srolovitz, M. G. Goldiner, JOM 47(3) (1995), 31). In this model, grain boundary grooving (GBG) is the main driving force for hole formation.
The preparation of TEM cross sections of 1500 nm thick Cu-coatings by ultramicrotomy showed that GBG is present not only at the film surface but also at the interface between Cu and C. This specific GBG process leads to the formation of voids located at the Cu-C interface which drastically reduce the contact surface between the coating and the substrate and therefore lead to the significant reduction in adhesion which is observed after the thermal treatment.
This work is supported by the Austrian Science Fund (FWF) under grant Nr. P-14534. The TEM-investigations were performed in collaboration with the University Service Centre for Transmission Electron Microscopy (USTEM) of the Vienna University of Technology.