HRTEM study of atomic defects in 2D materials and correlation with optical and electrical characterization

Abstract

In this dissertation, an experimental routine is introduced, designed to prepare specific densities of sulfur vacancies in selected 2D materials using High-Resolution Transmission Electron Microscopy (HRTEM). A key contribution of this work is the development of the reverse transfer technique, which enables both optical and electrical characterization of the same sample exposed by the electron beam in HRTEM. This technique allows the transfer of 2D material flakes from TEM grids to a suitable substrate, demonstrating successful transfers for various 2D materials. The dissertation also presents a robust HRTEM analysis of the atomic structure and the creation dynamics of defects in MoS2 and WS2. The research demonstrates that defects can be created even in the middle layer of trilayer MoS2, making electrical tunneling measurements on TEM-generated defects feasible. Finally, the study provides electrical and optical characterization through vertical tunneling measurements and photoluminescence and Raman spectroscopy. The research reports on defect-bound excitons and defect-activated LA(M) Raman modes on samples with TEM-generated defects, reverse-transferred to suitable substrates. In conclusion, this dissertation provides valuable insights into the properties and potential applications of 2D materials, contributing significantly to the field of material science and nanotechnology. It also presents innovative techniques and methodologies for the preparation and analysis of these materials, paving the way for future research and technological advancements.