Ordered Pt3–Co Alloy Studied in the Field-Ion Microscope

Atomically resolved field-ion microscope images of the {111} planes of ordered Pt3–Co confirm unambiguously our hypothesis of the invisibility of the Co atom species in Pt–Co alloys. From the known lattice structure, L12, the composition of {110} and {100} planes of ordered Pt3–Co are expected to alternate in subsequent layers between pure Pt layers and equiatomic Pt and Co layers. This is confirmed by direct observation during controlled layer-by-layer field evaporation. Antiphase domains show up clearly only when the domain boundary passes through a {110} or {100} plane, but tracing the boundary through the matrix is difficult. No sharp boundary between the ordered and the disordered phase has been observed in the partially ordered state of the alloy.