First-principles Investigation into the Heterostructures and Moir\'e Bilayers of Transition Metal Dichalcogenides (TMDCs)

Layered two-dimensional (2D) materials, particularly MX₂ transition metal dichalcogenides (TMDCs), where M represents Mo or W and X is S, Se, or Te, exhibit unique properties when configured into hetero- and homo-bilayers with diverse stacking arrangements. This study emphasizes the impact of "magic angles" in twisted homobilayers that lead to transformative Moir\'e patterns, crucial for manipulating material properties. Our computational analysis of heterostructures covered 30 combinations from six MX₂ types, revealing that both the materials' choice and stacking significantly affect stability and band gap energy (Eg). Notably, the MoTe₂/WSe₂ heterostructure with a 60^ twist demonstrates a direct Eg, underscoring its potential in novel applications. In homobilayers, both fully relaxed and low-strain scenarios were examined across various stackings and twists. We found that optimal bilayers' Eg is highly dependent on stacking alignment. Particularly, 1T-MoS₂, WS₂, and WSe₂ can exhibit direct or indirect Eg under specific twisted conditions, with 1T-MoS₂ showing a capability to transition between semiconductor and conductor states. Specific "magic angles" at 17. 9^ and 42. 1^ in twisted WS₂ and WSe₂ bilayers form symmetrical Moir\'e patterns, enabling fine-tuning of Eg through angle adjustments and influencing electronic band flatness. Compared to monolayers, these TMDC bilayers display enhanced stability, which can be strategically adjusted. The use of controlled twisted angles in these bilayers emerges as a powerful tool in materials engineering, offering precise control over various electronic properties.