Berlin 2005 – wissenschaftliches Programm

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O: Oberflächenphysik

O 27: Phasenüberg
änge

O 27.1: Vortrag

Samstag, 5. März 2005, 15:00–15:15, TU EB107

Surface freezing and surface phase transition studied on the liquid eutectic AuSi surface — •Reinhard Streitel, Alexei Grigoriev, Oleg G. Shpyrko, and Peter S. Pershan — Division of Applied Sciences and Department of Physics, Harvard University, Cambridge, MA 02138

We present x-ray investigations on the liquid surface of the eutectic AuSi alloy. Reflectivity and GID (grazing incidence diffraction) measurements indicate surface freezing well above the bulk melting temperature, T_m (bulk) = 636 K. A reversible surface phase transition occurs at about T = 645 K. Measurements performed on other metal or alloy (eutectic) surfaces did not show a similar behaviour to date. In comparison to other metals and alloys, AuSi shows a temperature dependent anomalous behaviour of the specular reflectivity in a range of q_z = 1.0 − 2.5 Å. Solid like surface structures on liquids were studied on different alloys before [1]. Surface free energy and entropy play a key role in surface freezing effects [2]. Our measurements were performed at the APS (Advanced Photon Source at Argonne National Lab, Chicago, USA). [1] Two-dimensional freezing in the liquid-vapor interface of dilute Pb:Ga alloy - B. Yang, S.A. Rice et al. [2] Wetting prewetting and surface freezing transitions in fluid Ga-based alloys: a surface light scattering study - W. Freyland et al.