Vertical or Horizontal: Understanding Nanowire Orientation and Growth from Substrates

Abstract

We have established a theoretical model to address quantitatively the temperature-dependent growth of nanowire orientation and growth from substrates upon the vapor–liquid–solid (VLS) process by introducing thermal fluctuations. It was found that there is a critical temperature, depending on the Gibbs free energy of the nanowire nucleus, and that the nanowires with higher critical temperature tend to align horizontally to the substrate. Moreover, nanowires are vertically aligned on the substrate, or their growth direction is angled from the substrate, varying between 90 and 40°, if the critical temperature is lower. The critical temperatures of nanowires can be enormously dissimilar, which accounts for the fact that growth directions can be modulated by temperature. The developed theory explains the findings from a recent set of experiments on the temperature-dependent orientation of nanowires grown by the VLS process. These investigations concluded that thermal fluctuations play a crucial role in the VLS...