Single detector and coincidence Doppler broadening (CDB) spectroscopy measurements using slow positron beam were carried out to study as-deposited and annealed Ti/Al multilayer films. The changes of the film structure and defects in each layer by heat treatment have been investigated through the analysis of Doppler broadening lineshape variation. The coincidence Doppler broadening measurements revealed that Ti is the dominant diffusion species during the alloying process of Ti/Al by high temperature annealing. These results highlight the potential of slow positron beam in characterizing the vacancy-type defects evolution and mechanism of interlayer diffusion in Ti/Al multilayer film. (c) 2007 Elsevier B.V. All rights reserved.