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Simulation à l'échelle atomique de la croissance de couches d'oxydes de métaux à la surface d'un substrat monocristallin

Abstract : Numerical simulation of the homoepitaxial growth of magnesium oxide thin films has been performed. We have built a complete and realistic growth model taking into account numerous elementary phenomena. We have also studied the influence of these phenomena on the morphology and the thickness of the obtained layers. Surface diffusion has been emphasized: diffusion of both molecules (MgO) and vacancies (Mg and O). The Schottky defect at both the flat MgO{100} surface and the <100> monatomic-step edge has been investigated by Molecular Dynamics simulation. The calculated formation enthalpy increases monotonically as a function of the distance between the anion and cation vacancies, on the flat or stepped MgO{100} surface as well as in the bulk. The most stable configuration of the Schottky defect is the divacancy at the step edge. The migration mechanism has been elucidated and an intermediate state has been identified. The associated activation enthalpies have been determined in the 700 K-1100 K temperature range. Both magnesium and oxygen vacancies at the surface are very mobile and can play a role during the crystal growth. A Kinetic Monte Carlo (KMC) code has been developed. It relies on the results of the study of the Schottky defect and therefore the growth model gathers both vacancy and molecule diffusion. This allows to obtain results not accessible by other approaches. Indeed, the KMC is efficient when fast events, as diffusion, and slow events, as molecular deposition, coexist. This code has been used to simulate the homoepitaxial growth of MgO{100}. We have emphasized the contribution of each type of diffusion and the role of each mechanism on the quality of the layers. We have brought to light that, to obtain smooth surfaces, all the diffusion mechanisms must be taken into account. We have shown that vacancy diffusion play an important role in the growth of MgO layers. The simultaneous inclusion of both molecule and vacancy diffusion provides thin films of best quality. The growth operates layer-by-layer, in agreement with experimental data. The value of the roughness of 0.4 ± 0.1 nm in the 700 K-1100 K temperature range is compatible with the experimental results of Chambers et al..
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Contributor : Ekaterina Antoshchenkova <>
Submitted on : Wednesday, December 8, 2010 - 3:58:52 PM
Last modification on : Friday, July 31, 2020 - 9:24:06 AM
Long-term archiving on: : Thursday, March 10, 2011 - 12:14:38 PM

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Ekaterina Antoshchenkova. Simulation à l'échelle atomique de la croissance de couches d'oxydes de métaux à la surface d'un substrat monocristallin. Science des matériaux [cond-mat.mtrl-sci]. Ecole Polytechnique X, 2010. Français. ⟨pastel-00544653⟩

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