Mixing of noble metals in oxides and formation of colloids by ion irradiation

The mixing of noble metals (M) with various oxides under 4.5 MeV ion irradiation and the concurrent process of metal segregation were studied by means of Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). Simulations of the widening of RBS M peaks due to the spheroidization of the M layer, using particles sizes measured in TEM, indicate that the effect is noticeable but does not determine the mean square spread of the M depth distribution. RBS analyses show that recoil implantation is the predominant mechanism of injection of M atoms into the oxide matrix. The spreading is controlled either by the recoil implantation or the radiation-enhanced diffusion of M atoms according to their mobility. In particular this mobility depends on the M mass and on the oxide ionicity.