Transient SHG Imaging on Ultrafast Carrier Dynamics of MoS2 Nanosheets |
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| Authors: | Houk Jang Krishna P Dhakal Kyung‐Il Joo Won Seok Yun Sachin M Shinde Xiang Chen Soon Moon Jeong Suk Woo Lee Zonghoon Lee JaeDong Lee Jong‐Hyun Ahn Hyunmin Kim |
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| Affiliation: | 1. School of Electrical and Electronic Engineering, Yonsei University, Seoul, Republic of Korea;2. School of Electronics and Engineering, Kyungpook National University, Daegu, Republic of Korea;3. Department of Emerging Materials Science, DGIST, Daegu, Republic of Korea;4. Smart Textile Convergence Research Group, DGIST, Daegu, Republic of Korea;5. School of Materials Science and Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, Republic of Korea;6. Companion Diagnostics and Medical Technology Research Group, DGIST, Daegu, Republic of Korea |
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| Abstract: | Understanding the collaborative behaviors of the excitons and phonons that result from light–matter interactions is important for interpreting and optimizing the underlying fundamental physics at work in devices made from atomically thin materials. In this study, the generation of exciton‐coupled phonon vibration from molybdenum disulfide (MoS2) nanosheets in a pre‐excitonic resonance condition is reported. A strong rise‐to‐decay profile for the transient second‐harmonic generation (TSHG) of the probe pulse is achieved by applying substantial (20%) beam polarization normal to the nanosheet plane, and tuning the wavelength of the pump beam to the absorption of the A‐exciton. The time‐dependent TSHG signals clearly exhibit acoustic phonon generation at vibration modes below 10 cm?1 (close to the Γ point) after the photoinduced energy is transferred from exciton to phonon in a nonradiative fashion. Interestingly, by observing the TSHG signal oscillation period from MoS2 samples of varying thicknesses, the speed of the supersonic waves generated in the out‐of‐plane direction (Mach 8.6) is generated. Additionally, TSHG microscopy reveals critical information about the phase and amplitude of the acoustic phonons from different edge chiralities (armchair and zigzag) of the MoS2 monolayers. This suggests that the technique could be used more broadly to study ultrafast physics and chemistry in low‐dimensional materials and their hybrids with ultrahigh fidelity. |
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| Keywords: | excitons molybdenum disulfide photoinduced acoustic phonons transient second‐harmonic generation microscopy ultrafast carrier dynamics |
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