| Author: | Tsang, Chi Shing Ben |
| Title: | Synthesis of ferroelectric two dimensional materials and its heterostructure |
| Advisors: | Zhao, Jiong (AP) |
| Degree: | M.Phil. |
| Year: | 2024 |
| Subject: | Two-dimensional materials Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Applied Physics |
| Pages: | xii, 73 pages : color illustrations |
| Language: | English |
| Abstract: | This thesis presents a study on the growth methods and latest research of three important two-dimensional materials: In2Se3, WS2, and MoS2, with a focus on their phase controllability and heterostructure synthesis mechanisms. The study covers chemical vapor deposition (CVD) methods for the growth of different crystal phases of two-dimensional In2Se3 materials. Key aspects investigated include: (1) studying the mechanism for growing large-area In2Se3 during the growth process; (2) achieving phase modulation of In2Se3 through direct and indirect methods to create ferroelectric hybrid heterostructures with great potential in electronic devices; (3) synthesizing thin films of single-layer WS2 and MoS2 separately using molten salt assistance, analysing the influence of NaCl on film growth, and focusing on the growth of WS2 to examine the growth conditions at different temperature. The study also explores the influence of growth processes on the interfaces and provides important insights for the investigation of nanoscale hybrid interfaces. Initially, we prepared few-layer In2Se3 using chemical vapor deposition on 2D mica substrates and other templates. By adjusting the duration, sources amount, substrate distance, precursor. We obtained different morphologies and phases of In2Se3, with varying growth pathways. The morphological evolution from triangular flakes to layer-dependent shapes was observed through changes in conditions, which were confirmed using Raman spectroscopy to identify the phase transition. We concluded that the growth mechanism depends on the substrate. Furthermore, we systematically investigated the influence of precursor variation on domain size and surface coverage. By optimizing the growth conditions, we successfully grew β' In2Se3 and α In2Se3 thin films to gain a deeper understanding of the nanophase diagram of In2Se3, we further observed the dynamic phase transition of In2Se3 using optical polarized microscopy, identifying the in-situ evolution from β'-In2Se3 to α-In2Se3 and elucidating the fundamental reasons for this phase transition. This led to the creation of ferroelectric hybrid heterostructures. Our research focuses on the synthesis and analysis of two-dimensional materials such as In2Se3, MoS2, and WS2, which are poised to revolutionize semiconductor technologies as alternatives to silicon. Ferroelectric capabilities of In2Se3, and their electron mobility, are main reasons these materials were chosen for research. We investigate the chemical vapor deposition (CVD) methods to control the phase and growth of In2Se3, aiming to create ferroelectric hybrid phase heterostructures. Our investigation also extends to the effects of growth conditions on WS2 and MoS2, and the creation of WS2-MoS2 single-layer lateral heterostructures. Through this work, we have observed the dynamic phase transition of In2Se3 and uncovered the growth mechanisms dependent on substrate choice. The study confronts the challenges of synthesizing heterostructures with controllable interface and provides valuable insights into interfaces control and next-generation electronic devices. |
| Rights: | All rights reserved |
| Access: | open access |
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