Dresden 2006 – wissenschaftliches Programm
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MM: Metall- und Materialphysik
MM 15: Hydrogen in Metals II
MM 15.3: Vortrag
Dienstag, 28. März 2006, 12:15–12:30, IFW D
Optical characterisation of MBE grown neodymiumhydride films — •S. Weber, H. Schröter, and J. Schoenes — Institut für Physik der Kondensierten Materie, Mendelssohnstr. 3, D-38106 Braunschweig
Many rare earth metals have attracted attention because of their metal-insulator transition during hydrogen loading. Neodymium takes a special place among these as in addition to the opening of a large gap a transition to a ferromagnetic state has been reported.
Thin films of Nd have been grown onto CaF2 and Si-substrates using the MBE technique. In order to prevent corrosion in ambient air and to allow hydrogenation of the samples a protective layer of palladium is mandatory. A Nb-bufferlayer is used to prevent interdiffusion between the Pd-layer and the Nd-film which strongly deteriorates the quality of the samples. Temperature dependend measurements on hydrogenated samples have been performed using a FT-IR-spectrometer in the energy range of 5meV to 1eV. The spectra show 5 phonon modes which can be assigned unambiguously to hydrogen vibrations by comparison with deuterium loaded samples. The transmission spectra of the samples which are multiple layer systems can be simulated using a thin film model. Subsequently, the optical properties of NdHx can be determined. The modelling parameters indicate an expansion of the films by a factor of about 2 during hydrogenation which was confirmed by AFM measurements. Furthermore, the optical band gap was measured by UV/Vis-spectrometry.