Evaluation of the Surface Tension of Silicon-Gold Binary Liquid Alloy

Abstract

The gold-catalyzed vapor-liquid-solid (VLS) method is widely used for silicon nanowire (Si NW) fabrication. As the VLS process is influenced by the physical properties of the catalytic silicon-gold (Si-Au) droplet, quantifying the surface tension of the liquid alloy is important to achieve better control of the wire growth. Because the experimental measurement of the surface tension is difficult, it is necessary to obtain reasonable estimates from computational models. In this work, we conducted molecular dynamics simulations with a modified embedded-atom potential developed for the Si-Au binary system, and evaluated the surface tension γ based on the Virial stress expression. The dependence of surface tension γ on the Si fraction χ and temperature T is predicted. The entropy of the liquid-vapor interface was extracted from the slope of the γ-T curve. The Si concentration and stress distributions near the surface are also predicted. Our surface tension evaluation enables theoretical predictions of droplet and nanowire shape, and provides physical inputs for continuum phase field models of VLS growth.