title: Bandgap tunability at single-layer molybdenum disulphide grain boundaries.
abstract: Two-dimensional transition metal dichalcogenides have emerged as a new class of semiconductor materials with novel electronic and optical properties of interest to future nanoelectronics technology. Single-layer molybdenum disulphide, which represents a prototype two-dimensional transition metal dichalcogenide, has an electronic bandgap that increases with decreasing layer thickness. Using high-resolution scanning tunnelling microscopy and spectroscopy, we measure the apparent quasiparticle energy gap to be 2.40 ± 0.05 eV for single-layer, 2.10 ± 0.05 eV for bilayer and 1.75 ± 0.05 eV for trilayer molybdenum disulphide, which were directly grown on a graphite substrate by chemical vapour deposition method. More interestingly, we report an unexpected bandgap tunability (as large as 0.85 ± 0.05 eV) with distance from the grain boundary in single-layer molybdenum disulphide, which also depends on the grain misorientation angle. This work opens up new possibilities for flexible electronic and optoelectronic devices with tunable bandgaps that utilize both the control of two-dimensional layer thickness and the grain boundary engineering.
authors: 1] Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore [2] Centre for Advanced 2D Materials and Graphene Research, National University of Singapore, Block S14, Level 6, 6 Science Drive 2, Singapore 117546, Singapore.
authors: Yu Li
authors: YL
authors: Huang
authors: 1] Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore [2] Centre for Advanced 2D Materials and Graphene Research, National University of Singapore, Block S14, Level 6, 6 Science Drive 2, Singapore 117546, Singapore.
authors: Yifeng
authors: Y
authors: Chen
authors: 1] Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore [2] SZU-NUS Collaborative Innovation Center for Optoelectronic Science and Technology, Shenzhen University, Shenzhen 518060, China [3] Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, Shenzhen University, Shenzhen 518060, China.
authors: Wenjing
authors: W
authors: Zhang
authors: 1] Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore [2] Centre for Advanced 2D Materials and Graphene Research, National University of Singapore, Block S14, Level 6, 6 Science Drive 2, Singapore 117546, Singapore.
authors: Su Ying
authors: SY
authors: Quek
authors: Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.
authors: Chang-Hsiao
authors: CH
authors: Chen
authors: 1] Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan [2] Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia.
authors: Lain-Jong
authors: LJ
authors: Li
authors: Department of Electrophysics, National Chiao Tung University, Hsinchu 30010, Taiwan.
authors: Wei-Ting
authors: WT
authors: Hsu
authors: Department of Electrophysics, National Chiao Tung University, Hsinchu 30010, Taiwan.
authors: Wen-Hao
authors: WH
authors: Chang
authors: Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore.
authors: Yu Jie
authors: YJ
authors: Zheng
authors: 1] Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore [2] Centre for Advanced 2D Materials and Graphene Research, National University of Singapore, Block S14, Level 6, 6 Science Drive 2, Singapore 117546, Singapore [3] Department of Chemistry, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore.
authors: Wei
authors: W
authors: Chen
authors: 1] Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore [2] Centre for Advanced 2D Materials and Graphene Research, National University of Singapore, Block S14, Level 6, 6 Science Drive 2, Singapore 117546, Singapore.
authors: Andrew T S
authors: AT
authors: Wee