Défense de thèse en sciences physiques - Roshan CASTELINO

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

Jury

Prof. HENRARD Luc (UNamur, département de physique), président
Prof. SPORKEN Robert (UNamur, département de physique), secrétaire
Dr. JOUCKEN Frédéric (Arizona State University, Physics Department), frederic.joucken@uclouvain.be
Prof. THEMLIN Jean-Marc (Aix-Marseille Université, département physique à l’échelle nano), jean-marc.themlin@univ-amu.fr
Dr. VANCSO Peter (Institute of Technical Physics and Materials Science, Budapest), vancso.peter@energia.mta.hu
Dr. PHAM THANH Trung (UNamur, département de physique)

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 1T’ 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). We show that the substrate temperature plays a critical role in the crystalline quality of the synthesized films.

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.

Link

https://medias.unamur.be/lives/live-these-roshan-castelino-30072021/

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