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

Abstract

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., Al 65Cu 15Co 20. 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 Al 50Cu 20Co 30 yielded maximum amount of Al 65Cu 15Co 20 quasicrystalline phase, coexisting with ternary τ 3 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.