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-degrees-C; the MoSi2 films evolved first from an amorphous to a hexagonal structure and then to a tetragonal structure. Films annealed below 800-degrees-C yielded predominantly needle-like, hexagonal MoSi2 crystallites with a layered microstructure. Partial phase transformation of the MoSi2 from hexagonal to tetragonal structures occurred in the films annealed at 800-degrees-C. In addition, the tetragonal Mo5Si3 phase also emerged during the structural evolution. Annealing of the films at temperatures above 900-degrees-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 crystalline materials made by reaction sintering and hot pressing.