Bundled silicon nitride nanorings

Bundled nanorings composed of several self-coiled nanowires are synthesized by catalyst-assisted pyrolysis of a polymeric precursor. Microstructural observation reveals that the nanowires have a bilayer structure consisting of a thin single-crystal Si3N4 layer and a thick amorphous layer. The thickness ratio of the two layers is ∼ 1:2, regardless of the nanowire size. The formation of the thick amorphous layer is likely due to the high A1 concentration within the precursor. The self-coiling mechanism is discussed and attributed to the difference in growth rates of the two layers. A phenomena model is proposed to account for the formation of the nanoring structure.