Nanotwinning in silicon nanocrystals produced by ion implantation

Si nanocrystals (Si nc) were formed by the implantation of Si+ into a SiO2 film on (100) Si, followed by high-temperature annealing. The microstructure of the Si nc produced by a high-dose (3 × 1017 cm-2) implantation has been extensively investigated using high-resolution transmission electron microscopy (HRTEM). For most of the Si nc (∼90%) with diameters larger than 6 nm, their configurations are characterized by the existence of nanotwins. The twinning structures include single twins, double twins, and multiple twins. The other planar defects such as stacking faults are also observed in some nanoparticles. However, in the Si nc smaller than 5 nm, no evident microstructural defects are observed. Possible reasons that no evident microstructural defects are found in the smaller Si nc are discussed. The microstructural defects inside the Si nc have a great influence on the optical properties.