Formation of Crystallographically Oriented Metastable Mg1.8Si in Mg Ion-Implanted Si

Metastable hexagonal Mg-Si was synthesized by implanting Mg ion into Si. Single-crystalline Si(111) was irradiated with Mg ions at elevated temperature followed by thermal annealing under vacuum. Microstructural analysis with transmission electron microscopy revealed the formation of precipitates with sizes of several 10 nm in the damaged crystalline Si matrix. Using electron diffraction, the precipitates were identified as Mg1.8Si, and the crystallographic orientation relationship between Mg1.8Si precipitates and Si was determined. The phase stability of Mg1.8Si in the Si matrix is discussed in terms of the internal stress generated during the precipitation process.