Formation of quasicrystalline and vacancy ordered phases in vapour deposited thin films of Al–Cu–Co alloys

Thin films of Al–Cu–Co alloys were grown by thermal vapour deposition technique by varying the composition of the target material. The films were characterized by scanning and transmission electron microscopes together with EDX and X-ray diffraction techniques. It was observed that quasicrystalline decagonal phase does not form in thin film when the composition of the target material is close to that of quasicrystalline phase, i.e., Al65Cu15Co20. The deposited film of lower thickness (<200 nm) was always found to contain amorphous phase which transforms mainly to crystalline phases. By several trials of changing the composition of the target material it was found that target alloy composition close to Al50Cu20Co30 yielded maximum amount of Al65Cu15Co20 quasicrystalline phase, coexisting with ternary τ3 phase in the film of thickness 1000–2000 nm. The composition variation between the target alloy and the deposited film was explained based on differential deposition rate due to the significant differences in partial vapour pressure among the constituent elements.