Molecular beam epitaxy growth of molybdenum ditelluride (MoTe2) on graphene/6H-SiC(0001)
: Phase controlled synthesis and characterization

Student thesis: Doc typesDoctor of Sciences

Abstract

The success of graphene has given rise to two-dimensional materials (2D) as a new resource for various applications. For the applications in electronics, materials with semiconducting character are preferred and the lack of band gap in graphene presents a difficulty in its integration. Other 2D materials, with intrinsically semiconducting nature like transition metal dichalcogendies (TMDs) have been researched as an alternative. TMDs exhibit a wide variety of polymorphs, such as 2H and 1T'. The 2H phase is semiconducting while the 1T0 phase is metallic. Among all the semiconducting TMDs, monolayer molybdenum telluride (MoTe2) has the smallest bandgap about 1.1 eV, making it
attractive in post-silicon electronics. Therefore, it is crucial to obtain large area, highly crystalline, epitaxially grown semiconducting 2H-MoTe2 films with layer controllability.
In this thesis, we achieve a successful synthesis of large area and highly crystalline films of 2H-MoTe2 on graphene terminated SiC(0001) by molecular beam epitaxy (MBE). Graphene/SiC is chemically inert and allows unstrained epitaxial growth. We determine the optimum MBE parameters such as the
growth temperatures, flux ratios and post growth annealing conditions. We show that the substrate temperature plays a critical role in the crystalline quality of the synthesized films. By a post-growth anneal in Te environment, we stabilize the 2H phase with fewer defects. By two distinct processes of
one-step and multi-step process, we improvise the 2H phase with good yield and obtain large domains. Based on our results, we propose that the multi-step process to be very efficient for the large area synthesis of high crystalline films with layer controllability. We make a study of the different Moiré
patterns between the monolayer of the deposited film with the substrate. We explain the structure and the intensity modulation of the Moiré patterns with the simulation. Our analysis reveal interesting
surface and electronic properties of semiconducting MoTe2/graphene system. Finally, we make a study of the surface oxidation of MoTe2 films and propose a way to recover oxidized films.
Date of Award30 Jul 2021
Original languageEnglish
Awarding Institution
  • University of Namur
SupervisorRobert Sporken (Supervisor), Luc Henrard (President), Trung Pham Thanh (Jury), Péter Vancsó (Jury), Jean Marc Themlin (Jury) & Frédéric Joucken (Jury)

Keywords

  • molecular beam epitaxy
  • transition metal dichalcogenides
  • molybdenum ditelluride
  • graphene
  • Moiré patterns
  • van der Waals epitaxy

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