In recent years, two-dimensional materials have been widely studied and studied for their excellent electrical, optical and mechanical properties. Thanks to the two-dimensional material layer structure and the weak interlayer van der Waals interaction, different two-dimensional materials can be like each other like LEGO bricks. Combine to form a variety of two-dimensional material heterojunctions. Just as LEGO bricks have infinite construction methods, two-dimensional materials can also combine two-dimensional material heterojunctions with different properties, which provides for device applications and many basic physical phenomena research. An excellent material system. In addition, by adjusting the heterojunction stack structure of the two-dimensional material, the performance of the two-dimensional material heterojunction can be further changed, and even many novel physical phenomena are generated. Among them, the two-dimensional material heterojunction As an important means, stack corner regulation has attracted extensive attention in the field of two-dimensional materials research. There have been many interesting heterojunction stack corner regulation phenomena, such as zero-turn graphene/hexagonal boron nitride heterojunction. Quantum transport properties, graphene/hexagonal boron nitride/graphene heterojunction resonant tunneling under corner control, corner molybdenum diselenide/tele selenide layer The formation of exciton, as well as the transition of the Mott insulator and the superconductivity in the double-angle graphene. Therefore, it is of great significance to study the influence of stacking angle on the heterojunction properties of two-dimensional materials.
Recently, Liao Mengzhou, Ph.D. student of Zhang Guangyu Research Group, Key Laboratory of Nanophysics and Devices, Institute of Physics, Chinese Academy of Sciences/Beijing National Laboratory for Condensed Matter Physics, collaborated with Wu Zewen, Ph.D. student of Yao Yugui Research Group, Beijing Institute of Technology, combined with scanning probe technology and first principles The vertical electrical behavior of a single layer of molybdenum disulfide/graphene heterojunction under the control of stacking angle is studied. The experimental results provide important information for understanding the influence of stacking angle on heterojunction performance.
In-situ manipulation and measurement by atomic force microscopy can continuously control the monolayer of molybdenum disulfide epitaxially grown on graphene to form a heterojunction with adjustable stack angle, and measure the vertical conductance of the heterojunction in situ. The vertical conduction behavior of the molybdenum disulfide/graphene heterojunction strongly depends on the stacking angle of the heterojunction, and its vertical resistance increases monotonically with the stacking angle from 0 to 30 degrees. The vertical resistance of the 30 degree stacking corner heterojunction is approximately It is 5 times of the 0 degree stacking angle. The first principle calculation shows that the vertical resistance change of the molybdenum disulfide/graphene heterojunction under different stacking angles is caused by the tunneling coefficient of the tunneling current through the molybdenum sulfide layer at different corners. Different, that is, the tunneling coefficient gradually decreases from 0 degrees to 30 degrees. The different tunneling coefficients are caused by the different distribution of tunneling currents in the K-space of the molybdenum disulfide layer under different stacking corners, which ultimately affects The size of the tunneling current.
Since the graphene/molybdenum disulfide heterojunction has good potential for optoelectronic and gas sensing applications, graphene electrodes are widely used to reduce the contact resistance of the transition metal chalcogenide. Therefore, this study is to adjust molybdenum disulfide / Graphene heterojunction performance provides guidance, and provides a new idea for the use of graphene as a two-dimensional transition metal chalcogenide contact electrode to reduce contact resistance. Electron and optoelectronics for two-dimensional transition metal chalcogenides Device applications are of great significance. Related work is published in Nature Communications 9, 4068, doi: 10.1038/s41467-018-06555-w (2018).
The above work has been approved by the National Key Research and Development Program (Grant No. 2016YFA0300904), the Chinese Academy of Sciences Frontier Scientific Research Key Project (Grant No. QYZDB-SSW-SLH004), the Chinese Academy of Sciences Pilot B Project (Grant Nos. XDPB06, XDB07010100), National Natural Science Foundation of China (Grant Nos. 51572289, 61734001, 11574029, 11574361), the Ministry of Science and Technology (Grants No. 2014CB920903) and the Chinese Academy of Sciences Youth Innovation Promotion Association (Grants No. 2018013) and other funding.
Figure 1. Atomic force microscope rotating molybdenum disulfide/graphene heterojunction. a, schematic. b-f, different angles of molybdenum disulfide/graphene heterojunction.
Figure 2. Stacking angle control of molybdenum disulfide/graphene heterojunction electrical behavior. a, Conductive atomic force microscopy. b, resistance distribution of different stacking angle molybdenum disulfide/graphene heterojunction. c, d, 0 degrees and 30 degree stacking angle molybdenum disulfide / graphene heterojunction tunneling coefficient thermal distribution diagram. e, calculated tunneling coefficient with stacking angle change.
