Rui Xu, Yingzhuo Lun, Lan Meng, Fei Pang, Yuhao Pan, Zhiyue Zheng, Le Lei, Sabir Hussain, Yanjun Li, Yasuhiro Sugawara, Jiawang Hong, Wei Ji & Zhihai Cheng*
Abstract
Strain engineering plays a crucial role in controlling the physical properties of two-dimensional (2D) materials. However, the mechanical behavior of stressed 2D crystals has not been fully understood. In this study, the fracture behavior and accompanying properties of a strained single-crystal monolayer WS2 of submicron scale were investigated using a theoretical–experimental joint study. After thermal strain, the WS2 monolayer was split into different forms by several cracks, with the cause of the crack formation being studied using finite element analysis (FEA). The cracks were initiated from the vertex of the nucleation center, extending along the stronger von Mises stress isolines and terminating at the edges of the monolayers. Within the separate sections, ripple regions were observed, forming several typical nanopatterns. The band gap, frictional, viscosity, and elasticity characteristics of the different strain regions were also investigated. The nanopattern should enable flexibility in the design of more sophisticated devices based on 2D materials.
Haohan Li, Mykola Telychko, Linwei Zhou, Zhi Chen, Xinnan Peng, Wei Ji, Jiong Lu & Kian Ping Loh
Abstract
Formation of a two-dimensional (2D) supramolecular self-assembly and a 2D organometallic framework derived from a brominated N-heterocyclic aromatic molecule (4Br-TAP) on Au(111) and Ag(111) substrates were studied using chemical bond-resolved scanning tunneling microscopy (STM) and noncontact atomic force microscopy (ncAFM) techniques combined with density functional theory (DFT) calculations. The 4Br-TAP-based 2D molecular framework on Au(111) is constructed by diverse Br···Br and Br···N noncovalent interactions, which are resolved with sub-angstrom resolution using combined STM and ncAFM imaging with a CO-functionalized tip and further quantified using DFT calculations. The distortion of molecular backbones, triggered by a highly nonuniform bonding environment, leads to lifting of the degeneracy of the intrinsic resonance structures of tetraazapyrene (TAP) moieties and emergence of two chiral Kekulé-like structures. In contrast, debromination of 4Br-TAP on Ag(111) leads to the formation of an ordered 2D organometallic framework linked by C–Ag–C bonds. Our results underpin the tremendous potential of the tip-functionalized ncAFM technique for microscopic identification of a complex interplay of intermolecular interactions and their associated impact on the molecular resonance structures.
Jun Zhang, Linwei Zhou, Pengcheng Chen, Bingkai Yuan, Zhihai Cheng, Wei Ji & Xiaohui Qiu
Abstract
Catalytic bond cleavage and formation of transient intermediates on metal substrates play an essential role in surface synthesis and heterogeneous catalysis. Previous studies usually focus on the bond-breaking process, whereas the knowledge regarding the construction of dissociative moieties that lead to the final products is limited. Here, we investigate the facet-selective dissociation of dibenzotetrathiafulvalene (DBTTF) molecules on Cu(110) and Cu(100) surfaces using low-temperature scanning tunneling microscopy and first-principles calculations. Atomic resolution images enable the identification of various intermediates and reaction pathways on different facets. The dissociation of DBTTF molecules generated 1,2-BDT–Cu complex chains on Cu(110), while phenyl diradical superstructure islands were observed on Cu(100). The various chemical species found on different Cu facets were explained in the context of their formation energies related to the spatial inhomogeneity of surface electronic states. Our results address the effects of electronic and geometrical diversities on the surface mobility of intermediate products and subsequent on-surface reaction pathways.
