Vacancy ordering structures in epitaxial RESi2−x thin films on (111)Si and (001)Si

The vacancy ordering structures of epitaxial TbSi2−x, ErSi2−x, YSi2−x, and DySi2−x thin films on (001)Si and (111)Si have been investigated by electron diffraction analysis. From a combination of studying planview and cross-sectional transmission electron microscope samples, the 3-dimensional structures of vacancy ordering were determined. The vacancy ordering superstructure of unit cell (a3 a3 2c) was found in epitaxial TbSi2−x, ErSi2−x and YSi2−x thin films on (001)Si samples. However, the vacancy ordering superstructure of unit cell (a3 a3 2c) was found in epitaxial TbSi2−x and DySi2−x thin films on (111)Si samples. The variation in strains induced in these films is suggested to result in the change of the vacancy ordering structure.