IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Friday Sessions
       Session SS1-FrM

Paper SS1-FrM5
Surface Freezing in Binary Metallic Melts

Friday, November 2, 2001, 9:40 am, Room 120

Session: Dynamics of Metal Surfaces
Presenter: A. Turchanin, University of Karlsruhe, Germany
Authors: A. Turchanin, University of Karlsruhe, Germany
W. Freyland, University of Karlsruhe, Germany
D. Nattland, University of Karlsruhe, Germany
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We report on a new phenomena of surface freezing, whereby an ordered solid film forms on top of the bulk liquid at temperatures above the bulk crystallisation. Recently this phenomenon has been observed in dilute Ga-Pb@footnote 1@ and Ga-Bi@footnote 2@ liquid alloys. Here we present new results on the investigation of surface freezing in the entire composition range of the Ga-Bi system. Second Harmonic Generation and Plasma Generation methods were applied to distinguish between the solid and liquid states of the alloy surfaces as a function of temperature and composition. The surface freezing was detected for all investigated alloys with composition between the eutectic (x(Bi)=0.0022, T(eut)=29.48°C) and monotectic point (x(Bi)=0.085, T(mono)=222 °C). On cooling of such alloys a Bi-rich solid-like film forms on top of the bulk liquid phase at temperatures well above the liquidus line. This film disappears on heating at higher temperatures, which characterizes this transition as a first-order phase transition. The maximum difference between the liquidus temperature and the temperature of the surface freezing transition was detected for the eutectic alloy (T(tr)-T(eut)=20 K). The lines of surface freezing and respective melting merge with the liquidus line approaching the monotectic point. The thickness of the forming Bi-rich solid-like films estimated from our measurements lies in the ranges from 0.5-1 nm to 100 nm. We have indications that it has a tendency to increase approaching the monotectic point. The relation of the surface freezing and wetting transitions occurring in Ga-Bi will be discussed. The surface freezing in Ga-Bi system will be compared with the two-dimensional freezing in dilute Ga-Pb alloy detected by x-ray reflectivity and grazing incidence diffraction methods.@footnote 1@ @FootnoteText@ @footnote 1@B. Yang, D. Gidalevitz, D. Li, Z. Huang, S.A. Rice, Proc. Nat. Acad. Svi USA, 96 (1999) 13009 @footnote 2@A. Turchanin, D. Nattland, W. Freyland, Chem. Phys. Lett. 337 (2001) 5.