Structural engineering of non-layered 2D materials

• Main Author: Yang, Jiefu
• Other Authors: Liu Zheng
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Engineering; 2D materials; Structural engineering; Phase engineering; Chemical vapor deposition
• Online Access: https://hdl.handle.net/10356/174638
• Institution: Nanyang Technological University

This thesis investigates advanced materials, specifically delving into the realm of non-layered two-dimensional (2D) materials and their potential for structural engineering. Innovative methodologies are employed to gain fresh insights into material synthesis, structural modification, and properties tunings. The ensuing chapters reveal groundbreaking discoveries, which collectively redefine our understanding of the intricate interplay between structural nuances and material properties within non-layered 2D materials. In the first project, structure-selective growth of nonlayered 2D chromium (III) chalcogenides has been realized, covering Cr2S3, Cr2Se3, and Cr2Te3. Guided by a mica substrate template, the chapter demonstrates van der Waals epitaxy (vdWe) growth leading to controlled synthesis of Cr2X3 belonging to the same space group, P-31c. Taking advantage of an on-chip microelectronic device, the hydrogen evolution reaction (HER) activities of Cr2X3 with similar thicknesses are compared. Therefore, insights on the sole impact of chalcogen types on electrocatalytic catalytic and electrical conductivities in 2D TMCs have been elucidated. In the second project, the viability of alloying non-layered 2D transition metal oxides by meticulously controlling precursor elements within a CVD process was demonstrated. Similarly, the template-assisted technique using F-mica is also employed to facilitate the vdWe growth of metal oxide nanosheets and alloyed metal oxide nanosheets. Moreover, the enhanced oxygen evolution reaction attributed to the concerted effort of the Co-Fe bimetallic site has been illustrated, emphasizing the importance of alloying in electrocatalytic activities tunning. In the last project, phase-selective synthesis of both layered and nonlayered chromium tellurides (CrxTey) has been achieved through precise manipulation of CVD synthesis parameters such as temperature and precursor compositions. The impact of thermodynamical stability at various temperatures and precursor environments has been qualitatively discussed based on experimental observation and previous literature. The major structural differences between as-grown CrTe, Cr2Te3, and CrTe2 nanosheets, Cr intercalants, have been highlighted with an articulation of the introduced strain and noncollinearity on the materials’ intrinsic magnetic properties.