Time：25th May 13:30-14：30
Place：Room 318，11th teaching building ，Yuquan campus
Title：The phase transition in transition metal dichalcogenides on metallic substrates
Speaker：Prof. Wenjing Zhang
Abstract: The emergence of two-dimensional transition metal dichalcogenides (2D-TMDs) and their unique polymorphic features such as the semiconducting 1H and quasi-metallic 1T' phases exhibits intriguing optical and electronic properties, which can be used in novel electronic and photonic device applications. With the favorable quasi-metallic nature of 1T’-phase of 2D-TMDs, the 1H to 1T'phase engineering process has been exploited for novel device applications. Here, we report a high-yield 1H-1T'phase transition of monolayer-MoS2on Cu and monolayer-WSe2 on Au after a simple annealing process. A comprehensive study involving Raman, photoluminescence and synchrotron-based photoemission spectroscopies, spectroscopic ellipsometry, and first-principles calculations is performed to elucidate the phase transition process and understand the underlying mechanisms. Moreover, a general trend for the high-yield phase transition process of 2D-TMDs on metallic substrates is derived. While each 2D-TMD possess different intrinsic 1H-1T'energy barriers, the use of an metallic substrate with high chemical reactivity plays a more pivotal role in increasing the 1H-1T'phase transition yield. As demonstrated by the first-principles study, this increased in yield is brought about through the enhancement of the interfacial hybridization by the means of increased interfacial binding energy, larger charge transfer, shorter interfacial spacing and weaker bond strength. This study provides new insights into the fundamental understanding of how phase transition dynamics of 2D-TMDs is mediated by interfacial hybridization, it further opens up the field of 2D-TMD on metallic substrate systems to further inquiry and research, thereby unlocking new possibilities for 2D-TMD-based device applications.
Bio： Wenjing Zhang, graduated from the Department of electronics, Peking University in 2008. 2008-2014,he did postdoctoral research respectively in Nanyang Technological University, Singapore, Taiwan Central Institute, National University of Singapore. In 2014,he became a Professor of Shenzhen University and was slected in " Young overseas high-level talents introduction plan" . Since 2008, he has been devoted to the research of new two-dimensional photoelectric materials and devices. A series of original achievements have been achieved in this field, some of which are leading in the world, and 50 papers have been published in the journals of materials and optoelectronics. The papers have been cited more than 5500 times in famous academic journals such as Science, Nature, Nature Physics, Nature Photonics, Nature Nanotechnology, Physical Review Letters and so on. The average number of quotes is more than 120 times, and the maximum number of references is 1300 times. The representative results are as follows: 1) the controllable preparation method of two-dimensional semiconductor atomic crystal is developed: three representative papers have been cited more than 2200 times, and the preparation method has become the main method for the preparation of two-dimensional semiconductor atomic crystals. 2) the construction of a new optoelectronic device based on the vertical heterojunction of molybdenum disulfide - graphene: a representative paper was cited more than 300 times, and was affirmed by the forward-looking papers published by American scientific experts in Nature News. 3) establishing and improving the metal - semiconductor contact model of atomic size and optimizing the performance based on the two-dimensional semiconductor atomic crystal optoelectronic devices: the three representative papers are currently cited more than 400 times. 4) Expanding the application of Raman spectroscopy in characterizing new optoelectronic devices: a representative paper in the form of research highlight was reported by Nature Physics.
