Controllable Amorphization and Nanocrystallization in Metallic Thin Films
J.P. Chu, S.F. Wang and M.J. O'Keefe
National Taiwan Ocean University, TW
Keywords: nanocrystallization, solid-state amorphization, metallic Film
We present a direct experimental evidence for the first time that the controllable amorphization and nanocrystallization during annealing of a metastable film could serve as a precursor for exciting new nano materials. Unlike other metallic glassy materials that exhibit devitrification during annealing, our sputter deposited film with good glass-forming ability is transformed into various nano-scale and amorphous structures due to annealing process. Upon low-temperature annealing, a metastable crystalline phase that is formed due to the non-equilibrium sputtering re-dissolves. The new interesting discovery is that the metastable phase in the form of nanocrystalline is further transformed into another metastable phase in the amorphous state, instead of a crystalline state in the supercooled liquid region, with a subsequent crystallization at higher temperatures. The measured film properties (hardness and electrical resistivity) are in good agreement with those derived from the microstructure/crystal structure evolution. Such a structural development provides the opportunity to adjust the structure/property relationships necessary to tailor specific optical, electrical, and mechanical properties. The exceptional amorphization behavior can be rationalized as a consequence of the low free energy of amorphous phases, with combined effects of thermal and interfacial energies between the nanocrystalline and amorphous phases.
Nanotech 2004 Conference Technical Program Abstract