Segregation and phase separation in thin films |
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| Affiliation: | 1. School of Materials Science and Engineering, Central South University, Changsha 410083, PR China;2. Key Laboratory of Nonferrous Metal Materials Science and Engineering, Ministry of Education, Central South University, Changsha 410083, PR China;3. Shanghai Key Laboratory for R&D and Application of Metallic Functional Materials, School of Materials Science & Engineering, Tongji University, Shanghai 201804, PR China;4. Institute of Mechanical Engineering, École polytechnique fédérale de Lausanne, 1015 Lausanne, Switzerland;5. State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Micro-system and Information Technology, Chinese Academy of Sciences, Shanghai 200050, PR China;1. College of Materials, Shanghai Dianji University, Shanghai 201306, China;2. Materials Genome Institute, Shanghai University, Shanghai 200444, China |
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| Abstract: | Surface segregation and phase separation in binary AB systems have been calculated in a slab consisting of atomic planes perpendicular to the free surfaces. For strongly segregating systems, if the average concentration lies in the two phase region of the binary phase diagram, a phase separation from the surfaces develops and two layers of the A-rich phase cover the A-poor central phase in the slab (lamellar structure). Furthermore, there is an enrichment (segregation) of A atoms in the near surface layers of the upper phase. For weakly segregating systems there exists a critical concentration Ch. If T > Th (Th is the temperature on the miscibility gap at Ch), a similar phase separation and segregation has been observed as above. However, for T < Th, two different phases can be in equilibrium in a columnar structure. The concentrations in their central layers, if the slab is thick enough, correspond to the compositions of the miscibility gap at the given temperature. At the same time, there is a strong segregation of A atoms in the A-poor phase, while, due to the stronger separation tendency, the minority B atoms will ‘separate’ at the surface, leading to a desegregation of A atoms in the A-rich phase. |
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