Dynamic Structural Evolution of Metal–Metal Bonding Network in Monolayer WS2

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• 作者：Kiran Kumar Amara ; Yifeng Chen ; Yung-Chang Lin ; Rajeev Kumar ; Eiji Okunishi ; Kazu Suenaga ; Su Ying Quek ; Goki Eda
• 刊名：Chemistry of Materials
• 出版年：2016
• 出版时间：April 12, 2016
• 年：2016
• 卷：28
• 期：7
• 页码：2308-2314
• 全文大小：486K
• 年卷期：0
• ISSN：1520-5002

文摘

Layered transition metal dichalcogenides (TMDs) exist in a range of crystal phases with distinct electronic character. Some crystal phases are known to exhibit unique in-plane anisotropy characterized by a periodic distortion of the lattice and a formation of metal–metal bonding network. Here, we report in situ observation of dynamic structural evolution in the one-dimensional zigzag chains of single layer WS₂ induced by electron beam irradiation. Metastable zigzag chains of tungsten atoms are found to undergo reorganization of metal–metal bonds, resulting in emergence of tetramer clusters and zigzag chains with a new orientation. Our first-principles calculations reveal a small (∼0.1 eV per formula unit) activation energy barrier for monolayer WS₂ zigzag chain reorientation and a metastable transition state in the form of tetramer clusters. We further show that local tetramer clusters can be induced and stabilized by local electronic charging effects. The formation of local tetramer clusters indicate that this dynamic structural evolution is not a charge density wave phenomenon; we find instead that these lattice changes are a response to electronic instabilities that weaken the W–S bonds in the zigzag phase. Our findings shed light on the origin of structural instabilities and phases in two-dimensional materials, and constitute a step further toward their potential uses in phase change applications.