Is surface crystallization in liquid eutectic AuSi surface-induced?

摘要

Recent x-ray measurements have revealed surface crystallization in the liquid eutectic Au0.82Si0.18 alloy accompanied by a pronounced surface-induced layering with a thickness of seven to eight well-defined atomic layers. For the crystalline surface monolayer a stoichiometry of AuSi2 has been determined, implying a strong Si surface enrichment. In this study we have analysed the composition at the interface with vacuum of the solid and liquid eutectic alloy by means of x-ray photoelectron spectroscopy (XPS). Evaluation of the XPS spectra using a homogeneous interface model and an inhomogeneous interface model clearly indicates a strong interfacial enrichment of Si in agreement with the x-ray measurements. In an interfacial layer of 2 nm thickness the average Si concentration is nearly three times larger than that in the bulk. However, the XPS spectra give evidence for a low concentration (similar to 3 at.%) of oxide impurities at the interface-in all probability SiO2-which raises the question of whether surface crystallization in this alloy is surface-induced or driven by SiO2 nucleation centres.