We present an amorphous phase growth model in the Al-Pt thin film system prepared by high-temperature successive deposition (HTSD) under various experimental conditions. Our theory is based on detailed TEM, XTEM and SAED investigations. The model contains a brief explanation of the quasi two-dimensional phase formation on the sample surface during Pt deposition and deals with the diffusional Al transport in the newly developed Al-Pt phases. Theoretical calculations, according to the experimental results, prove the existence of a critical thickness (L C1 ) of the amorphous phase. Related phenomena of intermetallic phase nucleation (Al 3 Pt 2 ) and amorphous⇒ polycrystalline phase transition are also treated. Additionally, the diffusional limitation of the growth of coexisting amorphous—intermetallic phases could be explained and characterised by the second critical thickness (L C2 ). It will be shown also that various thin film structures, e.g. thick (250 nm) pure a-Al 2 Pt surface coatings, can be tailored by using HTSD and different parameter ranges.