Study of solid state reactions in Nb/Al multilayer thin films

Solid state reactions of sputter-deposited Nb/Al multilayer thin films, with periodicities in the range 10–333 nm, have been studied by differential scanning calorimetry. The first phase to form upon annealing the films in NbAl₃. Constant-heating-rate calorimetric measurements show the presence of two peaks for the formation of this phase, while isothermal scans reveal that the first peak is associated with a nucleation and growth type transformation. The formation of NbAl₃ is thus interpreted as a two-stage process of nucleation and growth to coalescence (first peak) followed by growth until the consumption of one or both reactants (second peak).We thank NSF for support through DMR-9308651, K. Coffey, S. Vivekanand and B. Gadicharla for assistance and TA Instruments for the donation of a 1600°C furnace.