Characterization of transition metal dichalcogenides using micro-differential reflectance and second harmonic signal generation

Author(s)

Daniel Schmitz Bertini

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin
• Defense date: 2023-10-31

Examining board members

Odilon Divino Damasceno Couto Júnior; Helder Vinícius Avanço Galeti; Ingrid David Barcelos

• Advisor: Christoph Friedrich Deneke; Odilon Divino Damasceno Couto Júnior

Abstract

This work aimed to implement two optical spectroscopy techniques for the study of two-dimensional materials: micro-differential reflectance (micro-RD) and second harmonic generation (SHG). Using the experimental setup of micro-RD, integrated to the micro-photoluminescence (micro-PL) apparatus, and SHG, different samples of mono and multilayers of WSe2 and MoSe2 on substrates of sapphire, quartz, h-BN, and LiNbO3 were characterized at room temperature and 5K. The micro-RD setup was integrated with the micro-PL setup with acoustic modulation, allowing the same region of a sample to be studied using both experimental techniques. micro-RD enables the study of both fundamental optical transitions and transitions associated with excited states observed at higher energies. We also conducted a study to determine the number of layers in TMD (Transition Metal Dichalcogenides) samples using this technique. Using micro-RD, we observed that we could easily identify the number of layers in few-layer samples of WSe2 on substrates such as quartz, sapphire, and LiNbO3. We also determined the Stokes shift using micro-RD and micro-PL together, which can be associated with doping in the fabricated samples. An automated SHG system was also integrated into the acoustic modulation setup. With this system, we determined the relative orientation of different TMD samples with an odd number of layers. We observed that even in LiNbO3, which has a non-negligible SHG signal, the system works quite efficiently in determining the relative orientation of TMDs. With this, we now have a system in our laboratory that can be used for characterizing new samples of TMD heterostructures. We also used the SHG signal curves of monolayers of WSe2 and MoSe2 to assess the presence of mechanical strain in TMD samples (AU)

• FAPESP's process: 22/01839-3 - Growth and optical characterization of transition metal dichalcogenides epitaxial layers
• Grantee: Daniel Schmitz Bertini
• Support Opportunities: Scholarships in Brazil - Master