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Crystalline Surface Phases of the Liquid Au-Si Eutectic Alloy

Oleg G. Shpyrko, Reinhard Streitel, Venkatachalapathy S. K. Balagurusamy, Alexei Yu. Grigoriev, Moshe Deutsch, Benjamin M. Ocko, Mati Meron, Binhua Lin, Peter S. Pershan

cond-mat.mtrl-sciarXiv:cond-mat/0702413

Abstract

A two dimensional crystalline layer is found at the surface of the liquid eutectic Au82Si18 alloy above its melting point TM=359 C. Underlying this crystalline layer we find a layered structure, 6-7 atomic layers thick. This surface layer undergoes a first-order solid-solid phase transition occurring at 371 C. The crystalline phase observed for T>371 C is stable up to at least 430 C. Grazing Incidence X-ray Diffraction data at T>371 C imply lateral order comprising two coexisting phases of different oblique unit cells, in stark contrast with the single phase with a rectangular unit cell found for low-temperature crystalline phase 359 C<T<371 C.

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