 Research FieldUltrafast Imaging Lab @ USTC 1. Ultrafast Microscopy Understanding charge, spin and energy migration in low-dimensional materials are critical in designing high efficient optoelectronics and quantum communation devices. Here, we develop and employ an ultrafast pump-probe microscopy with high temporal (~ 100 fs) and spatial resolutions (~ 100 nm) to directly visualize charge, spin and energy flow in time and space domains, shedding new light on learning the nature of charge transport and energy conversion mechanism. 2. Imaging Charge Carriers Transport in Low-Dimensional Solar Energy Conversion Systems We spatially and temporally resolved exciton population distribution in two-dimension semiconductors using ultrafast microscopy and reveal how intrinsic (exciton-phonon scattering) and extrinsic factors (surface impurities and defects) affect exciton transport properties. (Long Yuan et al, The Journal of Physical Chemistry Letters, 2017.)
3. Ultrafast Charge and Energy Transfer in Two-Dimensional Heterostructures We use ultrafast transient absorption microscopy to elucidate the effect of interlayer coupling on charge transfer dynamics in WS2-graphene heterostructures. Furthermore, we show evidences of interlayer charge transfer transitions and hot carrier injection could lead to enhanced carrier generation well below the bandgap of WS2 (Long Yuan et al, Science Advances, 2018. ).
4. Interlayer Exciton Recombination and Transport in 2D Heterostructures We investigate interlayer exciton dynamics and transport in WS2–WSe2 heterobilayers in time, space and momentum domains using transient absorption microscopy and show that the exciton motion is modulated by the interplay between twist-angle-dependent moiré potentials and strong exciton–exciton interactions. Furthermore, we show exciton-population dynamics are controlled by the twist-angle-dependent energy difference between the K–Q and K–K excitons. Our study indicates a promising way to use 2D Moire excitons for quantum information applications (Long Yuan et al, Nature Materials, 2020.).
5. Non-Equibilum Exciton Mott Transition in 2D Lateral Heterojunctions Our ultrafast imaging measurements present evidences of a first-order exciton phase transition from insulated exciton phase to electron-hole plasma phase at 2D lateral interface. The nature of electron-hole plasma propagates with a velocity as high as 3.2×10^6 cm*s^(-1) over micrometer distances. Our results paves a new path to design 2D lateral heterojunctions for high-speed electronic applications (ArXiv:2111.07887, 2021).
Selected Publications: 1. Long Yuan et al. Manipulation of Exciton Dynamics in Single-Layer WSe2 Using a Toroidal Dielectric Metasurface, Nano Letters, 2021, 21, 23, 9930–9938. 2. Long Yuan et al. Twist-Angle-Dependent Interlayer Exciton Diffusion in WS2-WSe2 Heterobilayers, Nature Materials, 2020, 19, 617-623. 3. Long Yuan et al. Photocarrier Generation from Interlayer Charge-Transfer Transitions in WS2-Graphene Heterostructures, Science Advances,2018, 4, e1700324. 4. Tong Zhu#, Long Yuan# et al. Highly Mobile Charge-Transfer Excitons in Two-Dimensional Tetracene-WS2 Heterostructures, Science Advances,2018, 4, eaao3104. (#co-first author) 5. Long Yuan et al. Exciton Dynamics, Transport, and Annihilation in Atomically Thin 2D Semiconductor, Journal of Physical Chemistry Letters, 2017, 8, 3371–3379 6. Long Yuan et al. Exciton Dynamics and Annihilation in WS2 2D Semiconductor, Nanoscale, 2015, 7, 7402-7408. Join Us! Undergraduate Students We welcome undergraduate students who are interested in our research to visit our lab and join us for their undergraduate research projects. Graduate Students We are seeking graduate students who are strongly self-motivated and interested in ultrafast microscopy to join in our group. Postdoctoral Research Associates We have multiple postdoc position openings for candidates with background of ultrafast spectroscopy, 2D materials and other related areas. Please send your CV to lyuan565@ustc.edu.cn if you are interested in these positions. |
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