A growth mechanism for 1D nanocrystals: Pseudoscrew packing of polyhedral growth units

Here we report a formation mechanism for 1D nanocrystals. Numerous growth configurations of alpha-Si3N4 nanobelts formed by chemical vapor deposition have been examined by high-resolution transmission electron microscopy. We explicitly resolve that it is polyhedral clusters rather than individual atoms that are building blocks for the crystal growth. Packing of polyhedrons takes place in a pseudoscrew style, which immediately forms a wirelike seed. The packing pattern hence the growth direction could vary much, which is mainly dominated by kinematical elements at high temperatures, i.e. the length of packing vectors, the packing probability, and the seed structure. A low supersaturation of the source materials is found to restrict the number of packing routes, hence the low dimensionality and nanometer scale of the formed crystals. Finally, we show that the formation mechanism suggested here could also be successfully applied to the 1D growth of Si nanowires.