Abstract
We address the general question of segregation in deep layers of bimetallic alloys and crystal preparation by heat treatment. A new analysis of LEED I(V) spectra collected on an originally Pt25Co75(110) surface reveals that: (1) LEED is very sensitive to the bulk concentration and lattice parameter; (2) the bulk was enriched with Pt to form a Pt35Co65(110) alloy. The results obtained for the segregated surface layers differ very little from those assuming a 25% Pt substrate: the concentration in the five top layers are respectively 1, 99, 0, 55, 0% Pt. The first interlayer spacing is strongly reduced (−16%) with respect to the bulk value, the second one is expanded by about 10% and the third one is almost bulklike (−1.9%). For this bulk composition, no metastable state corresponding to a Pt-rich top layer is observed although the predictions from TBIM and EAM left this possibility as an open question.
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