Lateral Conversion TMD synthesis: investigating sub-20 nm features, Material Quality and Optical Device Design

The research presented in this master’s thesis delves into the synthesis and characterization of transition metal dichalcogenides (TMDs), with a particular emphasis on WS2, renowned for its exceptional properties among TMDs. The primary objective of this study was to investigate the reduction of TMD features down to 20 nm utilizing a bottom-up lithographic approach employing block copolymers to create the desired features and a lateral conversion growth mechanism to convert a uniformly deposited metal oxide layer to the desired TMD. To analyze the resulting material, a transfer method onto TEM grids was developed. Scanning transmission electron microscopy (STEM) and Raman spectroscopy were used for initial TMD characterization and to optimize the transfer technique. Further microstructural analysis was made possible using high-resolution transmission electron microscopy (HRTEM). The results gained from this analysis provided valuable information about the structure and properties of the synthesized WS2, and gave insight into the synthetic parameters of the conversion process. Building on this work, it has been investigated the design performance of an optical device using the lateral conversion method. Finite-difference time-domain (FDTD) simulations were used to develop a model of a distributed Bragg reflector (DBR) based on W S2. DBR structures were then fabricated and compared with silicon nitride (SiN) for perfor- mance evaluation. The fabrication of the designed optical device took place in a controlled environment within a cleanroom, examining different approaches to treat the substrates. A systematic study on the dynamics of the conversion technique was conducted to ultimately assess the optimal growth conditions. To gauge the effectiveness of the device, thorough characterization was carried out through white light measurements. Looking ahead, the prospects of this research encompass optimizing the synthesis methods of such a structure, and deeply understanding the dynamics of the reactions and the subsequent changes produced in the morphology of the material. An interesting application would involve the generation of Bloch Surface Waves (BSW) on top of the dielectric stack, whose design is investigated at the end of the dissertation. The design and fabrication of an optical device using this synthetic method will establish a foundation for potential future applications in advanced optoelectronic systems.