Verma Divya, Kumar Pawan, Mukherjee Sankha, Thakur Deepa, Singh Chandra Veer, Balakrishnan Viswanath
School of Engineering, Indian Institute of Technology, Mandi, Himachal Pradesh 175075, India.
Department of Electrical and System Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.
ACS Appl Mater Interfaces. 2022 Apr 13;14(14):16876-16884. doi: 10.1021/acsami.2c00901. Epub 2022 Mar 30.
The defect engineering of two-dimensional (2D) materials has become a pivotal strategy for tuning the electrical and optical properties of the material. However, the reliable application of these atomically thin materials in practical devices require careful control of structural defects to avoid premature failure. Herein, a systematic investigation is presented to delineate the complex interactions among structural defects, the role of thermal mismatch between WS monolayer and different substrates, and their consequent effect on the fracture behavior of the monolayer. Detailed microscopic and Raman/PL spectroscopic observations enabled a direct correlation between thermal mismatch stress and crack patterns originating from the corner of faceted voids in the WS monolayer. Aberration-corrected STEM-HAADF imaging reveals the tensile strain localization around the faceted void corners. Density functional theory (DFT) simulations on interfacial interaction between the substrate (Silicon and sapphire -AlO) and monolayer WS revealed a binding energy between WS and Si substrate is 20 times higher than that with a sapphire substrate. This increased interfacial interaction in WS and substrate-aided thermal mismatch stress arising due to difference in thermal expansion coefficient to a maximum extent leading to fracture in monolayer WS. Finite element simulations revealed the stress distribution near the void in the WS monolayer, where the maximum stress was concentrated at the void tip.
二维（2D）材料的缺陷工程已成为调节材料电学和光学性质的关键策略。然而，这些原子级薄材料在实际器件中的可靠应用需要仔细控制结构缺陷，以避免过早失效。在此，我们进行了一项系统研究，以描述结构缺陷之间的复杂相互作用、WS单层与不同衬底之间热失配的作用及其对单层断裂行为的影响。详细的微观和拉曼/光致发光光谱观察使热失配应力与源自WS单层中多面空洞角落的裂纹模式之间建立了直接关联。像差校正的扫描透射电子显微镜-高角度环形暗场成像揭示了多面空洞角落周围的拉伸应变局部化。对衬底（硅和蓝宝石-Al₂O₃）与单层WS之间界面相互作用的密度泛函理论（DFT）模拟表明，WS与硅衬底之间的结合能比与蓝宝石衬底之间的结合能高20倍。由于热膨胀系数的差异，WS与衬底之间这种增加的界面相互作用在最大程度上辅助了热失配应力，导致单层WS断裂。有限元模拟揭示了WS单层中空洞附近的应力分布，其中最大应力集中在空洞尖端。
