Regensburg 2007 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 20: Poster session

MM 20.37: Poster

Tuesday, March 27, 2007, 14:45–18:00, Poster C

Preparation and optical characterisation of rare earth hydride films — •Helge Schröter, Stefan Weber, and Joachim Schoenes — Inst. für Physik der Kondensierten Materie, Medelssohnstraße 3 38106 Braunschweig, Germany

It is well known that rare earth metals like yttrium or europium show a metal insulator transition, if they are exposed to a hydrogen atmosphere. Yttrium changes from a reflective metal to a very weakly transparent metal (YH2) and finally to a transparent insulator (YH3). Europium also undergoes a metal to insulator transition, in contrast to yttrium-hydride it additionally undergoes a transition from antiferromagnetism to ferromagnetism. For an understanding of the mechanism driving this metal-insulator transition, the precise measurement of the optical properties is mandatory. Therefore the change of the optical properties of the samples connected with the metal insulator transition, was examined by spectroscopic ellipsometry which allows a direct measurement of the dielectric function. Because of the reactivity of the pure rare earth metals it is difficult to grow stable films. We have used two methods to prepare hydride-films: (I) growth of in-situ hydrogenated films by pulsed laser deposition in a hydrogen atmosphere. By variation of the hydrogen pressure thereby, it is possible to grow layers with different hydrogen concentrations. (II) growth of pure rare earth metal films by molecular beam epitaxy and subsequent evaporation of a protective Pd cap-layer . These films have been hydrogenated ex-situ in an hydrogen-cell which is directly inserted into the ellipsometer.