Interfacial reaction-dominated full oxidation of 5 nm diameter silicon nanowires

While almost all Si nanostructures, including Si nanowires (SiNWs), Si nanocrystals, and Si nanotrench-like structures on a supra- or sub-10 nm scale exhibit self-limiting oxidative behavior, herein we report full oxidation of SiNWs 5 nm in diameter. We investigated the oxidative behavior of SiNWs with diameters of 5 nm and compared our findings with those for SiNWs with diameters of 30 nm. Single-crystalline SiNWs 5 and 30 nm in diameter were grown by a chemical vapor deposition (CVD) process using Ti as a catalyst. The SiNWs were then oxidized at 600-1000 °C for 30 min to 240 min in O₂. The thicknesses of the resulting oxide layers were determined by transmission electron microscopy (TEM). As expected, the SiNWs 30 nm in underwent self-limiting oxidation that was parabolic in nature. However, under the same conditions, the SiNWs 5 nm in diameter underwent full oxidation that was linear in nature. Atomic-scale molecular dynamic simulations revealed that the compressive stress in the oxide layer, which is generated owing to the increase in the volume of the oxide formed, decreased in the case of the SiNWs 5 nm in diameter. It is likely that this decrease in the compressive stress results in a lowering of the energy barrier for the diffusion of oxygen into the oxide layer, leading to the full oxidation of the SiNWs 5 nm in diameter. It is also responsible for the oxidation in the case of SiNWs 5 nm in diameter being interfacial reaction-dominated as opposed to the diffusion dominated-oxidation typical for SiNWs.