Regensburg 2002 – scientific programme

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SYME: Mechanical Properties of Thin Films

SYME III: HV III

SYME III.1: Invited Talk

Tuesday, March 12, 2002, 15:30–16:00, H 16

In-situ Electron Microscopy Study of Dislocation Processes in Thin Metal Films — •Gerhard Dehm — MPI for Metals Research, Seestr.92, 70174 Stuttgart

Flow stresses of thin metal films (less than 1micron) deposited on rigid substrates are significantly higher than those observed in the corresponding bulk metal. Furthermore, the flow stresses increase with decreasing film thicknesses. This phenomenon has been attributed to geometrical constraints on the films, which alter the energetics of dislocation motion. Fundamental information regarding plasticity mechanisms in thin metal films on substrates can be obtained by using in-situ transmission electron microscopy (TEM). In the present study epitaxial films on Al2O3 substrates and textured films on amorphous SiNx/SiOx coated Si substrates were thermally strained. In-situ TEM experiments revealed that the film-substrate interface influences thin film plasticity. For crystalline-crystalline interfaces the film-substrate interface acted mainly as a dislocation source, and dislocations advancing through the epitaxial metal films frequently deposited dislocation segments near the film-substrate interface. In contrast, for crystalline-amorphous interfaces the film-substrate interface acted as a dislocation sink. The in-situ TEM observations are compared to flow stress measurements of the thin metal films on Al2O3 substrates and amorphous SiNx-SiOx coated Si substrates. The interfacial dislocation mechanisms observed in thin metal films constrained by a substrate are expected to be of similar importance in lamellar and dispersion strengthened alloys.