Ion irradiation induced solid-state amorphous reaction in Ni/Ti multilayers

Abstract

The effects of Ar ion irradiation on interfacial reactions induced in Ni/Ti multilayers were investigated. Structures consisting of 10 alternate Ni (∼26nm) and Ti (∼20nm) layers of a total thickness ∼230nm were deposited by ion sputtering on Si (100) wafers. Argon irradiations were done at 180keV, to the doses of 1–6×1016ions/cm2, the samples being held at room temperature. The projected implanted ion range is 86±36nm, maximum energy loss is closer to the surface, and maximum displacements per atom (dpa) from 47 to 284 for Ni and 26 to 156 for Ti. Characterizations of samples were performed by transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS). It is shown that ion irradiation induced a progressed intermixing in the mostly affected zone already for the lowest dose, the thickness of the mix increasing linearly with the irradiation dose. The mixed phase is fully amorphous, starting with a higher concentration of Ni (which is the diffusing species) from the initial stages, and saturating at Ni:Ti∼66:34. A thick amorphous layer (∼127nm) formed towards the surface region of the structure for the irradiation dose of 4×1016ions/cm2 remains stable with increasing the dose to 6×1016ions/cm2, which introduces up to 6–7at.% of Ar within the mix. The results are discussed in light of the existing models. They can be interesting for introducing a selective and controlled solid-state reaction and towards further studies of ion irradiation stability of amorphous Ni–Ti phase.