Síntese e caracterização de cristais de MoS2 por deposição de vapor químico (CVD) em substratos de quartzo e silício

Abstract

This thesis addresses the synthesis and characterization of two-dimensional molybdenum disulfide (MoS₂) crystals on quartz glass and oxidized silicon (SiO₂/Si) substrates, with potential applications in thermoelectric generation devices. MoS₂ belongs to the family of transition metal dichalcogenides (TMDs) and exhibits unique electronic, optical, and mechanical properties when reduced to a few layers, distinguishing itself from its bulk form. Notably, it undergoes an energy bandgap transition from indirect (1.2 eV) to direct (1.8 eV) in the two-dimensional phase, resulting in strong photoluminescence and significant potential for technological applications. For the synthesis of MoS₂, the Chemical Vapor Deposition (CVD) technique was employed, allowing controlled material deposition through the sublimation of vapor-phase precursors. The substrates were pre-treated with ultraviolet-ozone (UV-O₃), inducing chemical and morphological modifications that enhance atomic adhesion during synthesis. The UV-O₃ chamber and tubular furnace used in the process were designed and built at the IFQ Laboratory of the Federal University of Itajubá. The synthesized crystals were characterized by Optical and Scanning Electron Microscopy, revealing morphologies consistent with the trigonal structure of MoS₂. Raman Spectroscopy analysis confirmed the presence of characteristic vibrational modes of the material, with a frequency difference of approximately 18.5 cm⁻¹ between the E₂g¹ and A₁g modes, indicating the predominant formation of two-dimensional MoS₂. The results demonstrated that the adopted methodology successfully enabled the synthesis of two-dimensional MoS₂ crystals on both studied substrates. Characterization confirmed the expected structure and composition, highlighting the efficiency of the CVD process. The UV-O₃ treatment proved to be a relevant step in substrate preparation, potentially influencing the quality of the deposited material positively.