Thermal oxidation and facet-formation mechanisms of Si nanowires

Abstract

Silicon nanowires were grown along the [111] direction on Si(001) by the vapor-liquid-solid mechanism using 1 nm Au as a catalyst. They were subsequently oxidized at 900 °C for 60 min, 120 min and 180 min, which lead to the formation of a circular shell of amorphous SiO2 surrounding the Si core defined by primary (202), (220) (022) and secondary (422) crystal facets that form a polygon with nine sides having a lower symmetry compared to the hexagonal shape of the Si nanowires before oxidation. We explain the facet-formation mechanism by the oxidation of alternate vertices of the original hexagon, which leads to the appearance of higher index crystallographic planes tangential to a circle corresponding to the energetically favorable core geometry. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.