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M: Metallphysik
M 25: Wasserstoff in Metallen I
M 25.1: Fachvortrag
Wednesday, March 28, 2001, 15:15–15:30, S12
Raman spectroscopy on switchable yttrium hydride thin films — •A.-M. Carsteanu, H. Kierey, M. Rode, A. Borgschulte, A. Jacob, and J. Schoenes — Institut für Halbleiterphysik und Optik, Technische Universität Braunschweig, Mendelssohnstrasse 3, D-38106 Braunschweig, www.tu-bs.de/institute/halbleiterphys
The hydrides of yttrium and other rare-earth metals have been the subject of increasing research due to their switchable optical properties. The first order Raman spectra of YH3 and YD3 thin epitaxial films deposited on CaF2 and BaF2 substrates have been studied in the temperature range from 4K to 300K. The switching process was observed by resistivity measurements during loading with hydrogen. Several rather broad lines from YH3 have been found. The linewidth becomes smaller with decreasing temperature and the lines are very distinct and sharp at 4K. Isotopically exchanged samples give a clear indication that YH3 is at the origin of the Raman lines. From polarization resolved measurements together with a Factor Group Analysis and the angular dependence at different inclination angles one can distinguish between the different proposed structures for YH3. The number of experimentally observed A1 phonons is not compatible with a P3c1 structure. Also the appearance of additional lines for 45∘ inclination is not possible in the P3c1 structure. All these investigations point towards a P63cm or P63 structure. Also the comparison of the energies of the lines in the Raman- and IR spectra promotes the picture of a non-centrosymmetric structure like P63cm or P63.