Unveiling the electronic dispersions in layered MoS₂ by electron energy loss spectroscopy

Electronic dispersions of free-standing MoS₂ layers have been investigated by momentum-resolved electron energy-loss spectroscopy 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. Here, we report the q-dependent EELS analysis on the free-standing layered MoS₂ thin films from long-wavelength to large-momentum transfer. Also, the E-q map experiments of MoS₂ are exhibited. 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. Furthermore, the STEM-EELS studies show that the predominant excitations at ~8.5, ~23 and ~12 eV arise from the respective resonances of bulk and surface plasmons in aloof mode. Calculations elucidating the q-resolved EELS analysis are also discussed.