Plasmon Dispersion in MoS2 by Momentum-Resolved Electron Energy-Loss Spectroscopy
Chien-Ting Wu1*, Jyun-Hong Huang2, Tuo-Hung Hou2, Ming-Wen Chu3
1National Nano Device Laboratories, National Applied Research Laboratories, Hsinchu, Taiwan
2Department of Electronics Engineering and Institute of Electronics, National Chiao Tung University, Hsinchu, Taiwan
3Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
* presenting author:Chien-Ting Wu,
Momentum-resolved electron energy-loss spectroscopy is a well established method to study electronic properties of materials. With this technique, the momentum information of indirect band gaps, interband transitions as well as characteristic dispersion behavior of bulk and surface mode plasmons could be realized.
In this study, we report q-dependent EELS studies in free-standing MoS2 with an improved q resolution. With the fine q resolution and extensive q range, we were able to explore the plasmon dispersion characteristic of 2D collective excitations along the two principal in-plane directions, ΓM and ΓK. It was found to display the square root of the q dispersion characteristic of the collective excitation of the 2D electron systems, and further unveil an in-plane electronic anisotropy. In additions, the E-q map experiments of MoS2 are exhibited. The calculations based on Kroger’s formulae are also compared with the experimental results and good agreements are obtained.

Keywords: electron energy-loss spectroscopy, MoS2, plasmons, E-q map