The Oxidation Characteristics of Silicon Nanowires Grown with an Au Catalyst

In this study, we investigated the thermal oxidation of silicon nanowires (SiNWs) grown via the vapor–liquid–solid (VLS) method with an Au catalyst. We systematically analyzed the oxidation mechanism of the SiNWs in both the radial and axial directions and mapped the behavior of the Au atoms on the sidewall and at top of the wire as a function of oxidation time. After thermal oxidation at a temperature of 900 ℃, two kinds of oxidation behavior in SiNWs were observed: one was conventional radial oxidation and the other was axial oxidation. In particular, the axial oxidation rate at the Si/Au interface increased dramatically compared with the radial oxidation rate, which can be explained by the reaction between the Si atoms precipitated from the Au tip and the O₂ gas injected in the area surrounding the Au tip. Additionally, we observed that the oxidation rate in the axial direction was inversely proportional to the wire diameter, which is related to the SiO₂ surrounding the Si wire. Moreover, the Au shape changed with respect to the wire diameter, suggesting that both the stress in the Au–Si alloy and the SiO₂ shell thickness of the wire critically affect the growth of SiO₂ on Au.