Crystallization of amorphous silicon during thinhyphen;film gold reaction

摘要

The crystallization ofahyphen;Si inahyphen;Si (50hyphen;nm) and Au (5hyphen;nm) thinhyphen;film bilayers has been investigated during heat treatment in a transmission electron microscope. When crystallization ofahyphen;Si first begins at 130thinsp;deg;C, the Auhyphen;Si alloy (Au and a precursor phase) reflections observed at lower temperatures vanish, and several new reflections from metastable Auhyphen;Si compounds occur. Dendritically growing islands of polyhyphen;Si are observed after heating at 175thinsp;deg;C. If the samples are held at a constant temperature of 175thinsp;deg;C for 10 min, the polyhyphen;Si islands coalesce. The formation of polyhyphen;Si depends on the diffusion of Au intoahyphen;Si and the formation of metastable Auhyphen;Si compounds, which act as transport phases for both Si and Au. After crystallization Au segregates to the front and back surfaces of the polyhyphen;Si film. The result of this work and earlier diffraction investigations are interpreted in terms of superlattices based on a sublattice. A fundamental bodyhyphen;centeredhyphen;cubic structure witha=5.52 Aring; and composition Au4Si is suggested for the Auhyphen;Si compounds.