Competition between surface energy and interphase energy in transition region and diameter-dependent orientation of silicon nanowires

A small sandwiched transition region between the Au catalysis droplet and silicon nanowires (SiNWs) is proposed to investigate the diameter-dependent orientation of SiNWs grown by the vapor-liquid-solid (VLS) mechanism. Atomic-scale calculation shows that for a given transition region width, there is always a critical diameter. Below the critical value, surface energy dominates and the <1 1 0> orientation is preferred, whereas at larger diameters, the interphase energy dominates and SiNWs grow along the <1 1 1> direction. The variability of the critical diameter is also included in our model by adjusting the transition region width. The theoretical results are in agreement with those from experiments.