title: Gap States at Low-Angle Grain Boundaries in Monolayer Tungsten Diselenide.
abstract: Two-dimensional (2D) transition metal dichalcogenides (TMDs) have revealed many novel properties of interest to future device applications. In particular, the presence of grain boundaries (GBs) can significantly influence the material properties of 2D TMDs. However, direct characterization of the electronic properties of the GB defects at the atomic scale remains extremely challenging. In this study, we employ scanning tunneling microscopy and spectroscopy to investigate the atomic and electronic structure of low-angle GBs of monolayer tungsten diselenide (WSe2) with misorientation angles of 3-6°. Butterfly features are observed along the GBs, with the periodicity depending on the misorientation angle. Density functional theory calculations show that these butterfly features correspond to gap states that arise in tetragonal dislocation cores and extend to distorted six-membered rings around the dislocation core. Understanding the nature of GB defects and their influence on transport and other device properties highlights the importance of defect engineering in future 2D device fabrication.
authors.affiliation: Institute of Materials Research & Engineering (IMRE), A*STAR (Agency for Science, Technology and Research) , 2 Fusionopolis Way, Innovis, Singapore 138634, Singapore.|Department of Physics, National University of Singapore , 2 Science Drive 3, Singapore 117551, Singapore.
authors.forename: Yu Li
authors.initials: YL
authors.lastname: Huang
authors.affiliation: SZU-NUS Collaborative Innovation Center for Optoelectronic Science & Technology, Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, Shenzhen University , Shenzhen 518060, China.|Department of Physics, National University of Singapore , 2 Science Drive 3, Singapore 117551, Singapore.
authors.forename: Zijing
authors.initials: Z
authors.lastname: Ding
authors.affiliation: SZU-NUS Collaborative Innovation Center for Optoelectronic Science & Technology, Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, Shenzhen University , Shenzhen 518060, China.
authors.forename: Wenjing
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Department of Electrophysics, National Chiao Tung University , Hsinchu 300, Taiwan.
authors.forename: Yung-Huang
authors.initials: YH
authors.lastname: Chang
authors.affiliation: Physical Sciences and Engineering, King Abdullah University of Science and Technology , Thuwal 23955-6900, Saudi Arabia.
authors.forename: Yumeng
authors.initials: Y
authors.lastname: Shi
authors.affiliation: Physical Sciences and Engineering, King Abdullah University of Science and Technology , Thuwal 23955-6900, Saudi Arabia.
authors.forename: Lain-Jong
authors.initials: LJ
authors.lastname: Li
authors.affiliation: Institute of Materials Research & Engineering (IMRE), A*STAR (Agency for Science, Technology and Research) , 2 Fusionopolis Way, Innovis, Singapore 138634, Singapore.|Department of Physics, National University of Singapore , 2 Science Drive 3, Singapore 117551, Singapore.
authors.forename: Zhibo
authors.initials: Z
authors.lastname: Song
authors.affiliation: Department of Physics, National University of Singapore , 2 Science Drive 3, Singapore 117551, Singapore.
authors.forename: Yu Jie
authors.initials: YJ
authors.lastname: Zheng
authors.affiliation: Institute of Materials Research & Engineering (IMRE), A*STAR (Agency for Science, Technology and Research) , 2 Fusionopolis Way, Innovis, Singapore 138634, Singapore.
authors.forename: Dongzhi
authors.initials: D
authors.lastname: Chi
authors.affiliation: Department of Physics, National University of Singapore , 2 Science Drive 3, Singapore 117551, Singapore.|Centre for Advanced 2D Materials, National University of Singapore , Block S14, Level 6, 6 Science Drive 2, Singapore 117546, Singapore.
authors.forename: Su Ying
authors.initials: SY
authors.lastname: Quek
authors.affiliation: Department of Physics, National University of Singapore , 2 Science Drive 3, Singapore 117551, Singapore.|Centre for Advanced 2D Materials, National University of Singapore , Block S14, Level 6, 6 Science Drive 2, Singapore 117546, Singapore.
authors.forename: Andrew T S
authors.initials: AT
authors.lastname: Wee
keywords: STM/STS; dislocation core; first-principles calculations; gap states; low-angle grain boundaries; monolayer WSe2