Intermetallic growth and properties in Bi–Sn–Au thin film structure deposited in high vacuum

Abstract

Structure and phase growth mechanism of vacuum deposited Au/Sn/Bi thin films have been studied by X-ray diffraction (XRD) method, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). It is found that the crystallites of Au–Sn intermetallic compounds are randomly distributed in Bi-rich matrix that forms a top-capping layer. The average sizes of AuSn 2 and AuSn 4 crystallites are 756 and 667 Å, respectively. The lattice constants of AuSn 4 in the capping layer are determined to be a=6.3694, b=6.4092 and c=11.4785 Å by Cohen's analytical extrapolation method. The capping layer of Au–Sn intermetallic grains in Bi-rich matrix covers most surface area, thus minimizing the exposure of inner Sn atoms to air and effectively prevents oxidation of the resulting thin film structure.