Kinetics of surface segregation in alloys

• Published in: Surface science Vol. 290; no. 3; pp. 345 - 361
• Main Authors: Cserháti, Cs, Bakker, H., Beke, D.L.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 20.06.1993; Amsterdam Elsevier Science; New York, NY
• Subjects: Applied sciences; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Metals. Metallurgy; Physics; Solid surfaces and solid-solid interfaces; Surface structure and topography; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Transition metal Alloys; Metastable state; Surface segregation; BCC crystals; Cobalt Iron Alloys; Antiphase domain; Chemical composition; Kinetics; Binary alloy
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/0039-6028(93)90718-Y

The kinetics of surface segregation in ordering alloys are studied with the help of a multilayer model in slabs of different thicknesses. The time evolution of the concentrations of atomic layers perpendicular to the (100) planes of an AB-type BCC ordering alloy (CoFe) are calculated. As a result of the competition between the surface segregation of A atoms and ordering in the bulk, a metastable configuration with two anti-phase boundaries (APB) inside the slab, with odd numbers of layers, was obtained if we started from an ordered initial state with B atoms on the free surfaces (B-termination). The effect of the temperature was also investigated for a slab with 41 layers and from the calculation of the free energies of the metastable and stable states it was shown that the metastable state can exist below T 1 = 0.95 T c , where T c is the critical temperature of the order-disorder transition in bulk. It was obtained that T 1 decreases with decreasing thickness of the slab, while the difference of free energies of the metastable and stable states slightly increases. The effect of the slab thickness is a typical size effect: the time necessary to reach the steady state decreases with decreasing number of layers.