Ion-beam mixing in Au-Al thin film bilayers

The formation of intermetallic compounds in Au-Al thin film bilayers induced by ion implantation were investigated using 2.0 MeV He backscattering and X-ray diffraction techniques. Kr ions of energy in the 60-240 keV range and fluence in the 1015-1016/cm2 interval were used to bombard targets at LN2 temperature. After irradiation of an Al-Au pair the two compounds Au2Al and AuAl2 are formed. The presence of a thin Au5Al2 layer at the Au-Al interface formed during deposition enhances the compound's growth rate versus ion fluence. The measured rate of intermixing increases linearly with the square root of the ion fluence. In addition, the relative amount of nuclear deposited in the Au and Al layers determines not only the final phase (AuAl2 or Au2Al) but also their growth rate. The results seem to indicate that the process is mainly governed by the supply of one or of the other element. This supply is related to the number of atoms which have received a sufficient energy during the collision. (orig.)