Irradiation-induced amorphization and growth of dodecagonal phase in an immiscible Co–Cu system

Abstract

Anomalous structural evolution was observed in an equilibrium immiscible Co–Cu system while the Co–Cu multilayers were irradiated by Xenon ions at 77 K. In the as-deposited Co 15Cu 85 multilayers consisting of polycrystalline Co and Cu of fcc structure, 100 keV Xenon ion irradiation to a dose of 7×10 15 Xe +/ cm 2 resulted in amorphization and the formation of a new dodecagonal phase embedded in the amorphous matrix. In another sample with an overall composition of Co 35Cu 65, the same dodecagonal phase was also obtained by 200 keV Xenon ion irradiation within a dose range of 5×10 15–9×10 15 Xe +/ cm 2 and interestingly, the formed dodecagons assembled themselves in a superlattice with an in-plane four-fold rotational symmetry. According to the non-equilibrium characteristics involved in ion irradiation process, the mechanism of the above structural evolution is discussed in terms of the similarity in the atomic configuration between the quasicrystal and amorphous short-range orders as well as the effect of interfacial free energy stored in the Co–Cu multilayers.