Microstructural investigation on the grain refinement occurring in Cu-doped Ni-Ti thin films

The mechanism of grain refinement in Cu-doped Ni-Ti thin films has been investigated by transmission electron microscopy. Sputter-deposited (Ni,Cu)-rich Ni-Ti-Cu thin films exhibited a columnar structure consisting of grains whose lateral size decreased with increasing Cu content. Cu-rich grain boundary segregation was found to become prominent in films containing higher Cu contents. This segregation was attributed to a non-polymorphic crystallization process which lowered the grain growth rate as the Cu content in the films increased.