Transmission electron microscopy observation of polymorphic epitaxial growth of YSi2-x layer in Al(001)/YSi2-x/Si(001) systems

The structures of compounds in the heteroepitaxial system Al/YSi2-x/Si have been examined by high resolution transmission electron microscopy. YSi2-x grown in two stages by a template method consists of two phases. Hexagonal YSi2-x(1(2) over bar0$) (low-temperature phase) grows on Si(001) when Y is deposited at 330 degrees C and then annealed at 500 degrees C for 10 min. Subsequent deposition of Y at 330 degrees C followed by annealing at 330 degrees C for Ih results in the growth of tetragonal YSi2-x(001) (high-temperature phase) on the hexagonal phase. The growth of Al(001) on YSi2-x is confirmed. The epitaxial relationship Al[100]//tetragonalYSi(2-x)[100]//hexagonalYSi(2-x)[100]//Si[110] is found in this system. It is also revealed that in the formation process of YSi2-x, the tetragonal phase is nucleated first from a supercooled melt in the solid phase and then the hexagonal phase is formed by a polymorphic transformation during annealing at appropriate temperatures for the transition.