Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

2 Publications
Defect studies of hydrogen-loaded thin Nb films
Cizek, J.; Prochazka, I.; Brauer, G.; Anwand, W.; Mücklich, A.; Kirchheim, R.; Pundt, A.; Bähtz, C.; Knapp, M.;
Hydrogen interaction with defects in thin niobium (Nb) films was investigated using slow positron implantation spectroscopy (SPIS) combined with X-ray diffraction (XRD) and transmission electron microscopy (TEM). Thin Nb films on Si substrates were prepared using cathode beam sputtering at room temperature. Initially, the microstructure of the virgin (hydrogen-free) films was characterized. Subsequently, the films were step-by-step electrochemically charged with hydrogen and the evolution of the microstructure with increasing hydrogen concentration was monitored. Hydrogen loading leads to a significant lattice expansion which was measured by XRD. Contrary to free-standing bulk metals, thin films are highly anisotropic. The in-plane expansion is prevented because the films are clamped on the elastically hard substrate. On the other hand, the out-of-plane
expansion is substantially higher than in the bulk samples. Moreover, an enhanced hydrogen solubility in the a-phase was found in nanocrystalline Nb films. It was found that most of positrons in the films are trapped at open-volume defects at grain boundaries (GBs). These defects represent trapping sites also for hydrogen atoms. Hydrogen trapping at vacancy-like defects like GBs leads to a local increase of the electron density and is reflected by a pronounced decrease of the S parameter in the hydrogen-loaded samples. In addition, it was found that new defects are introduced at higher concentrations of hydrogen due to the formation of NbH (b-phase) particles.
  • Lecture (Conference)
    10th International Workshop on Slow Positron Beam Techniques for Solids and Surfaces (SLOPOS-10), 19.-25.03.2005, Doha, Qatar
  • Applied Surface Science 252(2006), 3237-3244


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Publ.-Id: 8216