Thickness-dependent ultrafast charge-carrier dynamics and coherent acoustic phonon oscillations in mechanically exfoliated PdSe2 flakes

Chang-Fu Huo; Rui Wen; Xiao-Qing Yan; De-Kang Li; Kai-Xuan Huang; Yizhi Zhu; Qiannan Cui; Chunxiang Xu; Zhi-Bo Liu; Jian-Guo Tian

doi:10.1039/d1cp03202j

Thickness-dependent ultrafast charge-carrier dynamics and coherent acoustic phonon oscillations in mechanically exfoliated PdSe₂ flakes

Phys Chem Chem Phys. 2021 Sep 22;23(36):20666-20674. doi: 10.1039/d1cp03202j.

Authors

Chang-Fu Huo¹, Rui Wen¹, Xiao-Qing Yan¹, De-Kang Li¹, Kai-Xuan Huang¹, Yizhi Zhu², Qiannan Cui², Chunxiang Xu², Zhi-Bo Liu^{1

3

4}, Jian-Guo Tian^{1

3

4}

Affiliations

¹ The Key Laboratory of Weak Light Nonlinear Photonics, Ministry of Education, School of Physics and Teda Applied Physics Institute, Nankai University, Tianjin 300071, China. yanxq01@nankai.edu.cn.
² State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University, Nanjing 210096, China.
³ Renewable Energy Conversion and Storage Center, Nankai University, Tianjin 300071, China.
⁴ The collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China.

PMID: 34515274
DOI: 10.1039/d1cp03202j

Abstract

Recently, palladium diselenide (PdSe₂) has emerged as a promising material with potential applications in electronic and optoelectronic devices due to its intriguing electronic and optical properties. The performance of the device is strongly dependent on the charge-carrier dynamics and the related hot phonon behavior. Here, we investigate the photoexcited-carrier dynamics and coherent acoustic phonon (CAP) oscillations in mechanically exfoliated PdSe₂ flakes with a thickness ranging from 10.6 nm to 54 nm using time-resolved non-degenerate pump-probe transient reflection (TR) spectroscopy. The results imply that the CAP frequency is thickness-dependent. Polarization-resolved transient reflection (PRTR) measurements reveal the isotropic charge-carrier relaxation dynamics and the CAP frequency in the 10.6 nm region. In addition, the deformation potential (DP) mechanism dominates the generation of the CAP. Moreover, a sound velocity of 6.78 × 10³ m s^-1 is extracted from the variation of the oscillation period with the flake thickness and the delay time of the acoustic echo. These results provide insight into the ultrafast optical coherent acoustic phonon and optoelectronic properties of PdSe₂ and may open new possibilities for PdSe₂ applications in THz-frequency mechanical resonators.