Revisiting the Epitaxial Growth Mechanism of 2D TMDC Single Crystals

• Published in: Advanced materials (Weinheim) Vol. 36; no. 51; pp. e2404923 - n/a
• Main Authors: Li, Chenyang, Zheng, Fangyuan, Min, Jiacheng, Yang, Ni, Chang, Yu‐Ming, Liu, Haomin, Zhang, Yuxiang, Yang, Pengfei, Yu, Qinze, Li, Yu, Luo, Zhengtang, Aljarb, Areej, Shih, Kaimin, Huang, Jing‐Kai, Li, Lain‐Jong, Wan, Yi
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.12.2024; John Wiley and Sons Inc
• Subjects: chemical vapor deposition; Crystal growth; Epitaxial growth; Evaporation rate; Molybdenum disulfide; Nucleation; orientation control; Production methods; Sapphire; sapphire substrate; Single crystals; Sulfur; surface reconstruction; Transition metal compounds; Two dimensional materials; orientation control; molybdenum disulfide; surface reconstruction; sapphire substrate; chemical vapor deposition
• ISSN: 0935-9648; 1521-4095; 1521-4095
• DOI: 10.1002/adma.202404923

Epitaxial growth of 2D transition metal dichalcogenides (TMDCs) on sapphire substrates has been recognized as a pivotal method for producing wafer‐scale single‐crystal films. Both step‐edges and symmetry of substrate surfaces have been proposed as controlling factors. However, the underlying fundamental still remains elusive. In this work, through the molybdenum disulfide (MoS2) growth on C/M sapphire, it is demonstrated that controlling the sulfur evaporation rate is crucial for dictating the switch between atomic‐edge guided epitaxy and van der Waals epitaxy. Low‐concentration sulfur condition preserves O/Al‐terminated step edges, fostering atomic‐edge epitaxy, while high‐concentration sulfur leads to S‐terminated edges, preferring van der Waals epitaxy. These experiments reveal that on a 2 in. wafer, the van der Waals epitaxy mechanism achieves better control in MoS2 alignment (≈99%) compared to the step edge mechanism (<85%). These findings shed light on the nuanced role of atomic‐level thermodynamics in controlling nucleation modes of TMDCs, thereby providing a pathway for the precise fabrication of single‐crystal 2D materials on a wafer scale. This study uncovers the pivotal role of sulfur evaporation rates in directing the growth modes of MoS2 on sapphire. Low sulfur levels preserve O/Al‐terminated step edges, fostering atomic‐edge epitaxy, while high sulfur levels favor S‐terminated edges, promoting van der Waals epitaxy. The findings highlight that van der Waals epitaxy achieves superior MoS2 alignment (≈99%) on a 2 in. wafer, offering new insights into precise 2D material fabrication.