Berlin 2008 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 47: SYM Hydrogen in Materials: New Developments V
MM 47.4: Vortrag
Freitag, 29. Februar 2008, 11:15–11:35, H 1058
Hydrogen-induced plastic deformation of rare earth metal thin films — •Mathias Getzlaff1 and Astrid Pundt2 — 1Inst. of Applied Physics, University of Düsseldorf, D-40225 Düsseldorf — 2Inst. of Material Physics, University of Göttingen, D-37077 Göttingen
Surface modification of thin Gd films during hydrogen adsorption and absorption has been investigated on the nanometer scale by STM.
The adsorption occurs in two steps. It is initiated by surface imperfections. Starting from these nucleation centers a domain-like spreading is present which is strongly hindered at surface steps.
The measurements have shown that during hydrogen loading two different types of surface pattern develop above a particular concentration: disc-like islands and ramps. These surface patterns can be well described by two plastic deformation processes in the films that lead to glide steps on the film surface: the emission of dislocation loops during hydride precipitation occurs and misfit dislocations near the film-substrate interface. Since plastic deformation leads to stress release we suggest that a lot of thin metal films that are clamped to a substrate relax plastically after reaching a certain hydrogen-induced stress that corresponds to a critical hydrogen concentration. This conclusion is corroborated by the observation that free-standing Gd islands are deformed without structural deformation. Overall, combining the ability of preparing high-quality epitaxial thin films with the detailed analysis of the mechanical properties during hydrogen absorption may lead to a deeper fundamental understanding of hydrogen switchable thin films. It may also improve their industrial applications.