DYNAMIC PROCESSES OF ALTERED LAYER FORMATION IN CU-PT ALLOYS UNDER ION-BOMBARDMENT

Three different experimental approaches have been developed to study t he dynamic process of subsurface altered layer formation in a Cu-Pt al loy under Ar+ ion bombardment: (1) sputter neutral mass spectrometry b y multiphoton ionization (MPI-SNMS) for the study of preferential sput tering caused by the collision cascade process in the very initial sta ge of sputtering; (2) ion scattering spectroscopy (ISS)-Auger electron spectroscopy (AES) sequential measurements for investigating radiatio n-enhanced Gibbsian segregation in the transient stage of sputtering; (3) an approach based on ISS monitoring by prompt switching of the ion bombardment with (He+ + Ar+) ions to that with He+ ions, for revealin g the cooling effect in radiation-enhanced diffusion in the final stea dy state of sputtering. For this we have developed a specific coevapor ating device for depositing Cu and Pt simultaneously on a substrate at constant deposition rate. The coevaporating device was attached to bo th of the specimen chambers of the Auger microprobe, JAMP-3, and of th e MPI-SNMS apparatus. The results have clearly revealed: (i) ion bomba rdment causes a preferential sputtering of Cu atoms in the very initia l stage of sputtering, (ii) followed by gradual formation of an altere d layer as ion sputtering proceeds in the transient stage, and (iii) f inally the alloy system approaches a steady state where the compositio n profile is controlled by cascade mixing, radiation-enhanced Gibbsian segregation and radiation-enhanced diffusion to satisfy the mass bala nce law. In the steady state the approach (3) has, first, revealed tha t the cooling effect does exist in radiation-enhanced diffusion.