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Li , Peize

University of British Columbia

The hexagonal, or Kagome 1:1 FeGe phase, has yet to be successfully realized in large-scale thin-film form. In this study, we investigated various methods to stabilize the Kagome phase on c-plane (0001) sapphire substrates. Using the co-deposition method, even with treated substrates featuring terrace structures, the films became polycrystalline at lower growth temperatures (200-300 °C). As temperatures increased to 500-550 °C, an iron-rich β-FexGe (1.33<x<2) phase emerged, causing significant phase segregation. At 600 °C, the film transitioned into a 3D, discontinuous morphology. For the recrystallization method, we observed well-crystallized films upon heating from 100 to 550 °C, but the β-phase remained dominant. To reduce lattice mismatch, we introduced an Fe (110) buffer layer, achieving high-quality Fe (110) layers on untreated Al₂O₃ (0001) substrates at 400 °C. RHEED simulations showed that the (110) tetragonal plane was distorted into two hexagonal structures, with additional features suggesting another phase, likely the Fe (111) phase, although its simulations couldn’t fully account for these features. Ge was also deposited in equal proportions (1:1 ratio) on 7 nm Fe buffers across various temperatures. However, even at temperatures as low as 300 °C, interdiffusion occurred, where the buffer layer reacted with the Ge, resulting in the formation of the β-phase. Additionally, when Ge was deposited on much thinner 1.4 nm Fe buffers, it altered the buffer’s morphology from a 2D form to a multi-faceted 3D structure. Interestingly, neither the Ge (110) nor the Kagome FeGe (001) simulations were sufficient to fully capture the extra RHEED features that appeared. This study, therefore, outlines the various approaches attempted and notable challenges faced in realizing single-phase Kagome FeGe thin films, establishing a crucial groundwork for future investigations.

Text

2024-10-24

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/89481

Physics

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/