Ion-irradiation induced phase transformation in Al2O3 thin film

In order to crystallize the amorphous Al2O3 film, mass-separated ion beam was irradiated on it. The most effective ions for the transformation was investigated. Amorphous Al2O3 thin films on Fe substrate prepared by ion beam sputtering were irradiated with one of several ions, under the conditions of accelerating voltage: 180 kV, flux: 1.5 x 1014 ions/cm2·s, irradiation time: 4200 s, at 458 K. X-ray diffraction examination showed that the transformation from the amorphous phase to the γ-crystal occurred after B, O, Al, Ar ion irradiations. This happened effectively in the sequence Ar < B < Al < O. On the other hand, in the case of He, Ti, Zr, Xe ion irradiations, no transformation was observed. These phenomena were considered on the basis of not the residual stress but rather the frequency of thermal spikes and displacement spikes and the amount of displacement atoms, which produced by the interaction between ions and substrate atoms. In addition, the energy transferred from the ion to the target atom was thought to be partially responsible for the result. (author)