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The Ordered Structure of FCC Alloy Thin Film Tailored by the Epitaxial Growth Kinetics

Author: ShiLin
Tutor: NiJun
School: Tsinghua University
Course: Physics
Keywords: epitaxial growth kinetics MEM ordered structure FCC alloy
CLC: O484.1
Type: PhD thesis
Year: 2007
Downloads: 243
Quote: 1
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Abstract


The low dimensional ordered structures of alloys have distinct properties, whichattract considerable interest for applications. The epitaxial methods, especially themolecular beam epitaxy, have been extensively used in alloy growth for the purposeof fabricating various ordered film structures. The epitaxial growth is a nonequilibriumgrowth process, which can form some film structures different from the bulk structure.The kinetic feature of growth is one of the controlling factors in the formation of alloystructures. The study on the kinetic feature will help us to understand further the forma-tion of the alloy structures. In this thesis, we study the kinetic features of face-centeredcubic （FCC） alloy film epitaxial growth by the first-principles based on quantum me-chanics and the master equation method （MEM） based on statistics mechanics, and wepropose the kinetic mechanisms to tailor the ordered structures.We develop the MEM to study the kinetics of ordering in FCC multilayer alloysduring the epitaxial growth. The kinetic phase diagrams for the epitaxial multilayer ofan FCC alloy are calculated. We find that there is a kinetic induced oscillatory orderedphase in addition to the equilibrium ordered phase in the kinetic phase diagrams. Thisordering oscillation is caused by the kinetic correlation of different growth processes.In order to simulate the epitaxial growth of real material, we calculate the inter-action energies between atoms, based on the first-principles and the cluster expansionmethod （CEM）. We obtain the interaction energies of CoPt alloy under different latticeconstants. We find that the equilibrium state changes from L10 [001] ordered struc-ture to L10 [100] ordered structure with the decrease of lattice constant parallel to thesubstrate plane.We propose that the ordered structure can be tailored by adjusting the growth tem-perature or the growth rate to control the growth kinetic processes. In the epitaxialgrowth, we find that there is the kinetic anisotropy. We show there is an ordering-orientation transition of alloy films with the change of growth condition due to thiskinetic anisotropy. As an example, we calculate the epitaxial growth of CoPt alloyfilms. With the increase of growth temperature, the ordered structure of CoPt films changes from the L10 [100] ordered structure to the L10 [001] ordered structure at ade-quate growth rate. With the increase of growth rate, the ordered structure of CoPt filmschanges from the L10 [001] ordered structure to the L10 [100] ordered structure at ade-quate growth temperature. These results can be obtained when the equilibrium state isthe L10 [001] ordered structure. The ordering-orientation transitions are more complexwhen the equilibrium state is the L10 [100] ordered structure.By tailoring of the ordered structure, we propose a method to synthesize theordering-orientation surperlattices. Based on the kinetic feature of alloy epitaxialgrowth, we can change the growth rate or the growth temperature periodically to syn-thesize the ordering-orientation surperlattices, whose odering-orientation is changedperiodically while concentration is kept constant.

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CLC: > Mathematical sciences and chemical > Physics > Solid State Physics > Thin Film Physics > Film growth,structure and epitaxy
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