Carrier dynamics of nanomaterials probed at the space- and time-limit

• Main Author: Lim, Justin Wei Xiang
• Other Authors: Loh Zhi Heng
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Physics; Ultrafast spectroscopy; Transition metal dichalcogenides; Time-resolved photoemission electron microscopy; Ultrafast carrier dynamics; Carrier-carrier scattering
• Online Access: https://hdl.handle.net/10356/175677
• Institution: Nanyang Technological University

Studies of transition metal dichalcogenides have mostly been focused on the popular semiconducting group VI dichalcogenides with symmetry in the crystal lattice, such as MoS2, MoSe2, WS2 and WSe2. However, there exists a class of less investigated, semiconducting group VII dichalcogenides, such as ReS2, exhibiting anisotropy in its crystal lattice. They demonstrate different stacking orders in their layered form and exhibit optically polarization anisotropic behavior, adding new dimensions into controlling the optical response in the material. In this Final Year Project, we utilize femtosecond time-resolved photoemission electron microscopy with the time resolution of sub-50 fs pulses, ~160 nm spatial resolution and ~180 meV energy resolution to investigate the ultrafast free-carrier dynamics of bulk ReS2. Carrier thermalization is found to occur at early time delays of <1 ps, where two carrier-carrier scattering dimensionalities were observed. The carrier-carrier scattering dimensionality is found to be controlled by the polarization of the excitation pulse, where excitation parallel to the b-axis results in one-dimensional carrier-carrier scattering, and excitation perpendicular to the b-axis results in two-dimensional carrier-carrier scattering. The different carrier-carrier scattering dimensionalities observed demonstrates an additional degree of tunability in anisotropic TMDs which could be utilized in polarization sensitive applications of the material.