The nucleation and growth of intermetallic phases on amorphous carbon layer were investigated by co-deposition of Al and Pt to form a thin film system. The composition of the deposited films was varied in the range of Al1-xPtx with 0 less than or equal to X less than or equal to 0.4. The samples were investigated by transmission electron microscopy techniques. The electron diffraction patterns have been evaluated by the ProcessDiffraction computer program. The formation of Al6Pt, Al5Pt, Al2Pt and Al3Pt2 intermetallic phases have been found in correlation with the variation of the Pt concentration in the vapour beam. When the composition of the vapour beam is different from the composition of existing phases the excess species are segregated to the surface of the forming majority phase. These segregated species form a new phase, which is not necessarily the next neighbour phase in the phase diagram. (C) 2003 Elsevier Science B.V. All rights reserved.