Berlin 2005 – wissenschaftliches Programm
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DS: Dünne Schichten
DS 8: Ionen-Festkörper-Wechselwirkung I
DS 8.2: Vortrag
Samstag, 5. März 2005, 15:30–15:45, TU HS107
Experimental evidence for a glass transition in amorphous silicon — •André Hedler1, Siegfried Klaumünzer2, and Werner Wesch1 — 1Institut für Festkörperphysik, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena — 2Hahn-Meitner-Institut Berlin, Glienicker Str. 100, 14109 Berlin
Silicon is one of the best investigated elements in materials science, but the phase transition between amorphous silicon and liquid silicon is still subject of discussion. Whereas the low-density amorphous phase is a tetrahedrally coordinated semiconductor, the high-coordinated high-density liquid shows metallic behavior. Because of these structural differences the transition has been classified as a first order phase transition. The melting point of amorphous silicon is believed to be at about 1450 K. In contrast to this, recent computer simulations and the experimental observation of pressure-induced amorphization of nanoporous silicon have revived the idea of an underlying liquid-liquid phase transition implying the existence of a low-density liquid and its glass transition to the amorphous solid. Here we demonstrate that during irradiation with high energy heavy ions amorphous silicon deforms plastically in the same way as conventional glasses. This behaviour provides experimental evidence for the existence of the low-density liquid. The glass transition temperature for a timescale of 10 ps is estimated to be about 1000 K. Our results support the idea of liquid polymorphism as a general phenomenon in tetrahedral networks.