The temporal evolution of Ga and Ca vacuum deposited onto thin films of tris (8-hydroxy quinoline) aluminum (Alq) was studied with valence and atomic core level photoelectron spectroscopy. It was found that Ga, which exhibits weak reactivity with the Alq diffused into the organic at room temperature. Conversely Ca, a significantly more reactive metal, shows strong interaction with the organic surface. Effects of the initial morphology of the deposited materials on diffusivity will be described. ©1997 American Institute of Physics.