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.
Bibliographical noteFunding Information:
Dr. S. M. Jeong Smart Textile Convergence Research Group DGIST Daegu 42988, Republic of Korea S. W. Lee, Prof. Z. Lee School of Materials Science and Engineering Ulsan National Institute of Science and Technology (UNIST) Ulsan 44919, Republic of Korea Dr. H. Kim Companion Diagnostics and Medical Technology Research Group DGIST Daegu 42988, Republic of Korea E-mail: email@example.com
This work was supported by the National Research Foundation of Korea (2015R1A3A2066337) and the basic research programs (2018010032, 17-BT-01, 17-BT-02 and 17-BD-06) through the Daegu Gyeong-buk Institute of Science and Technology (DGIST) funded by the Ministry of Science and ICT of Korea.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Mechanics of Materials
- Mechanical Engineering