Transformation of silicon nanowires to nanocoils by annealing in reducing atmosphere

Silicon nanocoils were synthesized by annealing silicon nanowires with an outer oxide layer in reducing atmosphere. The high resolution transmission electron microscopy revealed that the reduction rate of the oxide layer was non-uniform; more precisely the cross-section of the interface of SiOx/Si was not straight but sinusoidal along the axial direction of nanowires. As a result, if the oxide layer was thicker, the diameter of the core silicon was smaller and vice versa. This non-uniformity would produce alternating tensile and compressive stresses, which were believed to cause the nanowires to get coiled.

► Transformation of silicon nanowires to silicon nanocoils.
► Migration of SiOx/Si interface by a diffusion-controlled process.
► Shape transformation caused by alternating tensile and compressive stresses in nanoscale.