Origin of Thermal Instability for ZnSe Nanowires and ZnSe/SiO2Nanocables in Air

Abstract

Thermal instability of ZnSe nanowires in air results from the oxidation of ZnSe by O2. As a barrier to slow the diffusion, a SiO2 sheath improves the thermal stability of ZnSe nanowires. But thermal instability of ZnSe/SiO2 nanocables still exists at elevated temperatures, due to the diffusion of Zn2+, Se2−, and O2 under the driving force of concentration gradients inside and outside the SiO2 sheath. For a thin sheath, Zn2+ and Se2− diffuse through the SiO2 sheath to the surface, and meanwhile O2 diffuses inside and oxidizes residual ZnSe in the core. For thick sheath, the longer diffusion length makes Zn2+ and Se2− diffuse completely through the ZnSe−SiO2 interface before O2 diffuses to this interface. Therefore, an approach to enhance the thermal stability of non-oxide semiconductor nanowires as much as possible is to find a suitable sheath, in which the core material and O2 have a low diffusion coefficient.