The moving species during ion beam mixing of Si/Ni and Si/Pt bilayers were investigated at temperatures between liquid‐nitrogen temperature (LN2) and 180 °C using imbedded markers and Rutherford backscattering. For Si/Ni samples irradiated with Ar ions, the flux ratio of Si to Ni decreased from 1.6 to 0.2 as the substrate temperature increased from LN2to 180 °C. Over this range of substrate temperatures, the individual amount of Si atoms transported was found to remain unchanged; whereas the transport flux of Ni atoms was observed to increase. Similar temperature dependence of the flux ratio was found for the Si/Pt system. The experimental results indicate that the substantial Si motion is due to the temperature‐independent part of ion mixing which is associated with collision cascades. The Ni motion is characteristic of radiation‐enhanced diffusion which is substrate temperature dependent.