Phase transformation and mechanical properties of thin MoSi₂ films produced by sputter deposition

Thin molybdenum disilicide (MoSi₂) films have been produced by sputter deposition. As-deposited films exhibited an amorphous structure. Crystallization of the films was studied at temperatures ranging from 300 to 900°C; the MoSi₂ films evolved first from an amorphous to a hexagonal structure and then to a tetragonal structure. Films annealed below 800 °C yielded predominantly needle-like, hexagonal MoSi₂ crystallites with a layered microstructure. Partial phase transformation of the MoSi₂ from hexagonal to tetragonal structures occured in the films annealed at 800°C. In addition, the tetragonal Mo₅Si₃ phase also emerged during the structural evolution. Annealing of the films at temperatures above 900°C gave rise to the formation of the thermodynamically stable, tetragonal MoSi₂ with an equiaxed granular morphology. The origin of the concurrent formation of tetragonal Mo₅Si₃ during the phase transformation from hexagonal MoSi₂ to tetragonal MoSi₂ is discussed. The mechanical properties, such as hardness and Young's modulus, of the sputter-deposited (amorphous) films were measured by nanoindentation. Comparisons are made between these properties and those of the bulk crysrtalline materials made by reaction sintering and hot pressing. © 1992.