Heating and EELS experiments of CuAl reactive multilayers

The microstructure and phase stability of a CuAl-on-sapphire thin film material is examined using in-situ and ex-situ heating experiments and TEM, SAD, HREM, and EELS as analysis technique. An in-situ heating sequence has revealed formation and decomposition of the metastable tetragonal θ-alloy phase CuAl₂ at two consecutive reaction temperatures. Pockets of unreacted Al remain at the interface to the substrate. The epitaxial orientation relationship of the θ <=> α-Al₂O₃ interface is examined by HREM, while composition mapping across the metal-alloy-oxide regions is demonstrated using plasmon (low-loss) spectrum imaging and EDX mapping. A 2nd derivative technique is shown to be powerful for enhancing phase changes which exhibit similar plasmon resonance energies.