Hamburg 2001 – wissenschaftliches Programm

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O: Oberflächenphysik

O 25: Postersitzung (Grenzfl
äche fest-flüssig, Methodisches, Nanostrukturen, Organische Dünnschichten, Rastersondentechniken, reine Oberfl
ächen, Teilchen und Cluster, Zeitaufgelöste Spektroskopie, Sonstiges)

O 25.86: Poster

Mittwoch, 28. März 2001, 15:00–18:00, Foyer zu B

Near surface phase transitions in 2H-NbSe₂ and 2H-TaSe₂ — •B. M. Murphy, M. Traving, J. Stettner, M. Tolan, and W. Press — Institut für Experimentelle und Angewandte Physik, Universität Kiel, D–24118 Kiel

Surface sensitive X-ray diffraction studies have shown, that the phase transitions in solid state materials are explicitly influenced by a spatial boundary (e.g. by a surface or a thin layer). Transition metal dichalcogenides like 2H-TaSe₂ and 2H-NbSe₂ show distinct 2-dimensional properties because of the weak van der Waals bonding between the layers. Therefore, it is interesting to study, if in the case of these layered materials the influence of the surface on the phase transitions is still observable. At low temperatures these crystals form charge density waves (CDWs) accompanied by a periodic lattice distortion. We investigated the phase transitions of 2H-TaSe₂ and 2H-NbSe₂ at T_C^bulk = 122.3 K and T_C^bulk = 33.5 K, respectively. At beamline BW2 (HASYLAB, Hamburg) Grazing Incidence Diffraction (GID) measurements have been performed at different incident angles to get data describing the surface behavior (α_i=0.2^o<α_c) and the bulk behavior (α_i=0.5^o>α_c).